Session information

[E] Poster

A (Atmospheric and Hydrospheric Sciences )

»A-AS Atmospheric Sciences, Meteorology & Atmospheric Environment

[A-AS07] Atmospheric Chemistry

convener:Naoko Saitoh(Center for Environmental Remote Sensing), Tomoki Nakayama(Graduate School of Fisheries and Environmental Sciences, Nagasaki University), Sakae Toyoda(Department of Chemical Science and Engineering, Tokyo Institute of Technology), Risa Uchida(Japan Automobile Research Institute)

This session provides a forum for the presentation of the broad spectrum of tropospheric and stratospheric chemistry, including various research topics (e.g., dynamical processes, air quality and climate), approaches (modeling, field measurements, remote sensing, and laboratory studies), and species (gas and aerosol). This session also provides an opportunity for discussing possible future collaboration with other research fields relevant to atmospheric chemistry.

[AAS07-P01] Top-down estimation of terrestrial CO2 flux in Northern Eurasia

*Tomoko Shirai1, Misa Ishizawa2, Motoki Sasakawa1, Akihiko Ito1, Toshinobu Machida1, Shamil Maksyutov1 (1.National Institute for Environmental Studies, 2.Environment and Climate Change Canada)

Keywords:CO2, carbon flux, inverse modeling, greenhouse gas, Siberia, climate change

We present a multi-year trend of terrestrial CO2 flux from northern Eurasia, estimated by atmospheric inversion using a coupled model GELCA (Global Eulerian-Lagrangian Coupled Atmospheric model). Global monthly CO2 flux distributions were estimated for the period 2002-2015 for 42 land and 22 ocean regions using the Observation Package data products (ObsPack GLOBALVIEWplus) which includes data from various types of atmospheric CO2 direct measurements provided by large numbers of laboratories in the world. In this study, we added 9 tower observations from JR-STATION (Japan-Russia Siberian Tall Tower Inland Observation Network) to better constrain the area of interest.

In order to examine the impact of additional observational constraints in Siberia, we compared the inversion results with and without JR-STATION data. For the entire period, estimated global land fluxes agreed well with each other regardless of JR-STATION data. At regional scales, estimated fluxes showed significant difference mostly in Siberia and northeastern Europe. When focusing on the mean seasonal variations, summer uptake increased in western Siberia and northeastern Europe whereas it decreased in northeastern Siberia by adding JR-STATION data.

In terms of the long-term trend, the terrestrial sink was increasing both in Siberia and in Europe. Terrestrial CO2 fluxes estimated for Siberia using JR-STATION data is -0.88 ±0.55 GtCyr-1 and -1.36 ±0.42 GtCyr-1 over the period 2002-2009 and 2010-2015, respectively. Those for Europe is -0.19 ±0.43 GtCyr-1 and -0.42 ±0.30 GtCyr-1, respectively. The increasing trend of the carbon sink in northern boreal areas can be explained by the combination of warming climate and the fertilization effect . Time series of these fluxes also reflect the effect of ENSO and extreme weather conditions. The interpretation of the multi-year variation of estimated fluxes in northern Eurasia will be presented.

[AAS07-P02] Recent stagnation of CH4 emission growth from East Asia based on the analysis of synoptic variations of atmospheric CH4 and CO2 observed at Hateruma Island

*Yasunori Tohjima1, Jiye Zeng1, Akihiko Ito1, Naveen Chandra2, Yosuke Niwa1, Hitoshi Mukai1, Tomoko Shirai1, Motoki Sasakawa1, Prabir Patra2, Toshinobu Machida1 (1.National Institute for Environmental Studies, 2.Japan Agency for Marine-Earth Science and Technology)

Keywords:atmospheric CH4, atmoshperic CO2, synoptic variation

Atmospheric mixing ratios of greenhouse gases including CO2 and CH4 have been monitored at Hateruma Island, Japan (HAT; lat. 24.1°N, long. 123.8°E) for more than 20 years by the National Institute of Environmental Studies (NIES). The observed CO2 and CH4 show secular increasing trends and seasonal variations, typical of a regional background sites, and consist of synoptic variations (ΔCO2 and ΔCH4) with duration ranging from several hours to several days. These synoptic variations were contain signals arising from the regional emissions from the continental East Asia, especially China, and were observed more often during late fall to early spring because of the suppression of the continental emissions signal during the East Asian monsoon in summer. Since the observed ΔCO2 and ΔCH4 in wintertime generally showed fairly good correlations, the variation ratio (ΔCH4/ΔCO2 ratio) can be used to constrain the regional emission ratio. In previous study (Tohjima et al., 2014), based on the fact that the fossil fuel CO2 emissions were relatively well determined, we obtained the increasing rate of the CH4 emission from China (about 1 Tg-CH4 yr-2) in 2000s from the comparison of theΔCH4/ΔCO2 ratios between the observation and simulation. In this study, we revisited the temporal change in ΔCH4/ΔCO2 ratio at HAT and investigate the recent change in the CH4 emissions from China. The observed ΔCH4/ΔCO2 ratio showed decrease for the entire period (1997-2019) from about 13 ppb/ppm to 8 ppb/ppm while its decreasing rate showed a gradual slowdown and appeared to reach bottom after 2010. Such change in the decreasing rate is mostly attributed to the slowdown of the increase in the fossil fuel CO2 emissions from China. We calculated ΔCO2 and ΔCH4 by using a Lagrangian Particle Dispersion Model (LPDM) and several CH4 and CO2 flux maps based on bottom-up and top-down approaches. Then we scaled the CH4 emissions from China so as to match the calculated ΔCH4/ΔCO2 ratio with the observation. The results suggested that the linear increasing trend of the CH4 emissions from China for 2010s is significantly reduced in comparison with that for the 2000s.

[AAS07-P03] Spatio-temporal variations of atmospheric methane concentrations over Japan: Data analysis of governmental monitoring and TROPOMI satellite from air pollution research viewpoint

*Yugo Kanaya1 (1.Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology)

Keywords:Atmospheric environment, climate change, methane, cluster analysis, seasonal patterns, source analysis

As being an important greenhouse gas as well as a short-lived climate forcer, sources of atmospheric methane need to be understood well toward effective mitigation of climate change. Our best practice is to build bottom-up emission inventories by compiling available socio-economic data and emission-relevant information to optimize control measures; however, the uncertainty in the inventories is large and thus independent information is required for their evaluation and improvement. Ground-based and satellite observations will serve for the purpose. In this study, we analyzed long-term methane measurement data contained in the governmental monitoring to elucidate features of spatio-temporal variations. Here, the measured methane concentration levels are generally only used to be subtracted from the total hydrocarbon concentrations to yield non-methane hydrocarbon levels, important to ozone chemistry - and thus the data set has seldom been analyzed. Among the available data at several hundreds of sites during FY2009-2016, data at 39 non-roadside sites were selected, where annual average concentrations ranked within top 20 at least once. The data during 6-9 LT were monthly averaged and their normalized seasonal patterns were analyzed. From cluster analysis, three distinct patterns were found: First pattern was with large increases in summer/autumn. Two sites (Toasa in Hokkaido and Narashino-Saginuma in Chiba) with very high monthly-averaged concentrations (>2.5 ppm) were categorized to this cluster, where very strong local emissions were suspected. Second pattern was with wintertime increases, to which 20 sites normally within Tokyo/Osaka metropolitan areas were categorized. The pattern was understood as general air pollution behavior in terms of dilution/diffusion, suggesting influence from urban sources. The third pattern was with summertime increases, particularly during June-August. The categorized 17 sites are mostly from rural regions and emissions from rice paddy fields were implied. We will show more results on correlations with wind and other pollutants (e.g., NOx, CO). Features from TROPOMI satellite observations of methane over Japan are also to be discussed together with the analysis of the ground-based observations.

[AAS07-P04] Variations of surface ocean pCO2 and air-sea CO2 fluxes in the Western Pacific Ocean

*Wataru Konarita1, Shinji Morimoto1, Shuji Aoki1 (1.Center for Atmospheric and Oceanic Studies, Graduate School of Science, Tohoku University)

Keywords:co2 partial pressure, Pacific, ENSO

Temporal and spatial variations of CO2 partial pressure in surface sea water (pCO2,sea) observed in the western Pacific were analyzed in terms of physics and chemistry of the ocean and the CO2 fluxes between the atmosphere and ocean were also evaluatedand the CO2 flux between the atmosphere and ocean . The pCO2,sea has been observed continuously on-board a cargo ship “Trans Future 5” on her round-trip between Japan and Australia. Systematic observations for the atmospheric pCO2 (pCO2,air) were have been also conducted in the western Pacific by a grab-sampling method using container ships sailing almost similar route.

In the equatorial region, interannual variabilities of pCO2,sea were clearly observed, and were highly correlated with the El Niño Southern Ocsillation (ENSO). Higher pCO2,sea observed in 2008 and 2012, coincident with La Nina, could be caused by transport of high salinity, low temperature and high dissolved inorganic carbon water upwelled off the coast of Peru to the observation line at the western Pacific Ocean. When large and strong El Nino occurred from 2015 to 2016, significant increase of pCO2,sea was observed between 25°N and 25°S. The pCO2,sea increase could be associated with remarkable decrease of the precipitation observed in the western Pacific region.

The CO2 flux between the atmosphere and the ocean was calculated by using the air-sea pCO2 difference in pCO2 (DpCO2) between the atmosphere and the surface ocean, sea surface temperature and wind speed at 10m height. In the western Pacific Ocean, the largest CO2 absorption was found at 20°S (−13.0 gC m-2 yr-1), and the net CO2 outgassing at equatorial area (1.2 gC m-2 yr-1) were found.

The increase in pCO2,sea associated with the strong El Niño event in 2015 and 2016 may have caused a decrease in the oceanic CO2 absorption throughout the western Pacific.

[AAS07-P05] In-situ and continuous observation of atmospheric N2O and CO concentrations at Syowa Station, Antarctica.

*Shogo Akai1, Shinji Morimoto1, Wei Li1, Daisuke Goto2, Shuji Aoki1 (1.Graduate School of Science, Tohoku University, 2.National Institute of Polar Research)

Keywords:Global Warming, Atmosphere, Antarctica, Syowa, N2O, CO

Nitrous oxide (N2O) is one of the most important anthropogenic greenhouse gases and its infrared absorption efficiency is 200 times more than that of carbon dioxide (CO2). In addition, since N2O catalytically decomposes stratospheric ozone (O3), N2O is concerned to be a major factor for the destruction of the stratospheric ozone after the concentrations of atmospheric chlorofluorocarbons decreases in near future. Carbon monoxide (CO) is not considered as greenhouse gas generally, but atmospheric CO is closely related to the atmospheric CH4 concentration through OH radicals, which are important reactant both with CH4 and CO. Furthermore, CO is also a useful tracer for biomass burning and has an important role in the atmospheric chemistry. Therefore, it is important to reveal the temporal and spatial variations the atmospheric N2O and CO concentration and to understand the cause of their variations quantitatively.

In this study, we developed a new continuous observation system for atmospheric N2O and CO concentrations based on an OA-ICOS (Off-Axis Integrated Cavity Output Spectroscopy) laser spectrometer (Los Gatos Research, model N2O/CO r23) (Fig.1). Repeatability for the analysis of N2O and CO concentrations by the system is estimated to be 0.14 ppb and 0.09 ppb (one standard deviation), respectively. The system was installed at Syowa Station, Antarctica, and continuous observation started in January 2019.

Figure 2 shows the temporal variations of the N2O and CO concentrations observed by our system at Syowa Station since January, 2019. As shown in the figure, characteristic variations of N2O and CO are found in each season. In the austral summer, in-phase and out-of-phase fluctuations of N2O and CO were observed several times. These fluctuations could be caused by the transport of high N2O and CO air mass affected by outgassing from the Southern Ocean and downward transport of stratospheric air into Syowa Station. In austoral spring, high CO event was captured at Syowa Station. It had been affected by serious biomass burning in Amazon and Australia.

In this presentation, we will introduce the observation system, thus developed, and show the temporal variations in the N2O and CO concentration observed at Syowa Station in more detail.

[AAS07-P06] Seasonal variations in the atmospheric Ar/N2 ratio observed at ground-based stations in Japan and Antarctica and its application to an evaluation of the air-sea heat flux

*Shigeyuki Ishidoya1, Kentaro Ishijima2, Satoshi Sugawara3, Yosuke Niwa4, Yasunori Tohjima4, Daisuke Goto5, Kazuhiro Tsuboi2, Shohei Murayama1, Nobuyuki Aoki1, Takashi Maki2, Taichu Y Tanaka2, Takashi Nakamura6 (1.National Instutite of Advanced Industrial Science and Technology (AIST), 2.Meteorological Research Institute, 3.Miyagi University of Education, 4.National Institute for Environmental Studies, 5.National Institute of Polar Research, 6.Japan Meteorological Agency)

Keywords:Atmospheric Ar/N2 ratio, air-sea heat flux, seasonal cycle, atmospheric transport model

Variations of the atmospheric Ar/N2 ratio at the ground surface are driven principally by air-sea Ar and N2 fluxes due to changes in solubility in seawater (e.g. Keeling et al., 2004). Recently, we expanded our model study for the gravitational separation to Ar/N2 ratio, and found that temporal variations of gravitational separation in the middle atmosphere could also modify the long-term trend of the surface Ar/N2 ratio (Ishidoya et al., in preparation). Therefore, the surface Ar/N2 ratio is a unique tracer of the spatiotemporally-integrated air-sea heat flux and the circulation in the middle atmosphere. We have continued systematic observations of the Ar/N2 ratio by using a mass spectrometer at Cape Ochiishi (43°N, 146°E), Tsukuba (36°N, 140°E), Takayama (36°N, 137°E), Hateruma Island (24°N, 124°E) and Minamitorishima (24°N, 154°E), Japan and Syowa station (69°S, 40°E), Antarctica since 2012. Clear seasonal Ar/N2 ratio cycles with summertime maxima have been observed at the middle to high latitudinal stations, and the peak-to-peak amplitudes of the average seasonal cycles at Ochiishi, Tsukuba, Hateruma and Syowa were found to be 21, 11, 5 and 32 per meg, respectively. To evaluate the seasonal air-sea heat flux based on seasonal cycles of Ar/N2 ratio in the atmosphere, we carried out simulations of the Ar/N2 ratio using an atmospheric transport model (GSAM-TM) that incorporated the Ar (N2) flux derived from an equation of the relationship between the air-sea Ar (N2) flux and the air-sea heat flux (Keeling et al., 1993; Weiss, 1970). We use the air-sea heat flux components, which mainly drive spatiotemporal variations of the air-sea Ar (N2) fluxes, and sea surface temperature (SST) from the ERA5 (Hersbach et al., 2019). Thus simulated seasonal cycles of Ar/N2 ratio agreed well with those observed. On the other hand, the amplitudes of the seasonal cycles of Ar/N2 ratio simulated by using the TransCom seasonal air-sea N2 flux (Garcia and Keeling, 2001), widely used in the simulation of the atmospheric O2/N2 ratio and based on the past ECMWF seasonal air-sea heat flux, underestimate the observed seasonal cycles significantly. These facts suggest that the air-sea heat fluxes and SST from the ERA5 is reasonable to reproduce the atmospheric Ar/N2 variations on the seasonal time scale.


We thank staff of Global Environmental Forum (GEF), the Science Program of the Japan Antarctic Research Expedition (JARE) and Japan Meteorological Agency (JMA) for their works to collect the air samples at Hateruma and Ochiishi stations (GEF), Syowa station (JARE) and Minamitorishima (JMA), respectively. This study was partly supported by the JSPS KAKENHI Grant Number 15H02814 and 18K01129, and the Global Environment Research Coordination System from the Ministry of the Environment.


Garcia, H. & Keeling, R.: On the global oxygen anomaly and air-sea flux. J. Geophys. Res. 106 (C12), 31155-31166, 2001.
Hersbach et al., Global reanalysis: goodbye ERA-Interim, hello ERA5, ECMWF Newsletter No. 159-Spring 2019, 17-24, 2019.
Ishidoya et al., Secular change of the atmospheric Ar/N2 ratio and its implications for ocean heat uptake and Brewer-Dobson circulation, in preparation.
Keeling, R. F. et al., What atmospheric oxygen measurements can tell us about the global carbon cycle, Global Biogeochem. Cycles, 7, 37-67, 1993.
Keeling, R. F. et al., Measurement of changes in atmospheric Ar/N2 ratio using a rapid-switching, single-capillary mass spectrometer system, Tellus B, 56, 322–338, 2004.
Weiss, R. F., The solubility of nitrogen, oxygen and argon in water and seawater, Deep-Sea Res., 17, 721-735, 1970.

[AAS07-P07] Development of a new ISEE Chemical Lagrangian Model to elucidate the atmospheric composition changes in the mesosphere

*Tomoo Nagahama1, Shingo Nakanishi2, Fujita Ken2, Tac Nakajima1, Akira Mizuno1 (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.Graduate School of Science, Nagoya University)

Keywords:Chemical Lagrangian model, Mesospheric composition, Trajectory analysis

Chemical composition in the mesosphere fluctuates significantly due to factors such as temperature, solar UV radiation and energetic particle precipitation from the space. In order to elucidate these mechanisms and evaluate their impacts, we have newly developed a chemical Lagrangian model that can handle from the troposphere to the mesosphere (e.g. Nakanishi et al., JpGU meeting, 2019). In the model, the trajectory of the particle box is calculated by a Lagrangian particle dispersion model which works with meteorological input data, and the chemical reactions in the particle box are also calculated by using a box model simultaneously. As the Lagrangian particle dispersion model, we used the FLEXible PARTicle (FLEXPART) model, which is extended so that the MERRA-2 reanalysis data can be used as input. As a result, we can calculate the trajectory up to an altitude of about 80 km from the surface. The position of the particle box is calculated every 15 minutes. As a box chemistry model, neutral molecule reactions consisting of 156 chemical reactions involving 58 chemical species and ion reactions of 263 reactions involving 77 species are calculated, respectively, using chemical reaction calculation software Kinetic Preprocessor (KPP). The concentration of each molecule in the box is calculated every 10 and 0.1 seconds, respectively. To validate the model calculations, 324 airmass boxes were released from the point at the altitude of 70 km in the polar and mid-latitude regions, and the two-day change in the concentration of ozone and ozone related substances was calculated. As a result, the diurnal variation of mesospheric ozone was qualitatively reproduced, although the value was about half of the value observed with Aura/MLS. In addition, we find that the difference in the ozone concentration in the Arctic region depends on the temperature on the transport route of the airmass. In the presentation, we will report on the details of the developed model, the characteristics of the time variation of the substances in the mesosphere as well as the results of comparison with observations.

[AAS07-P08] Analysis of the mesospheric ozone enhancement event in the Arctic winter with a new ISEE Chemical Lagrangian Model

*Fujita Ken1, Tomoo Nagahama2, Shingo Nakanishi1 (1.Graduate School of Science, Nagoya University, 2.Institute for Space-Earth Environmental Research, Nagoya University)

Keywords:Chemical Lagrangian model, Mesosphere, Composition change

Mesospheric chemical composition largely varies caused by environmental changes from the earth inside and outside. Environmental changes are, for example, temperature changes, solar UV, a large event of energetic particle precipitation. To understand the atmospheric composition changes caused by natural phenomena, we have installed millimeter-wave spectrometers in Rikubetsu (Japan), Syowastation (Antarctic), Atacama (Chile), Rio Gallegos (Argentine), and Tromso (Norway), and have been observing atmospheric minor molecules such as ozone, NOx, HOx, and ozone-depleting substances in the stratosphere and mesosphere. In addition to these observations, we need to analyze model simulation results to understand the impact of these changes on the global. For this purpose, ISEE has developed a new chemical transport model which is a combination of two models, FLEXPART and KPP. FLEXPART is a Lagrangian transport and dispersion model that is extended so that the MERRA2 reanalysis data can be used as input. Also, a chemical reaction software KPP (Kinetic Preprocessor) can calculate chemical changes simultaneously with the transport model. In order to validate the model calculation results, we compared the model output with mesospheric ozone dataset measured with JEM-SMILES from December 2009 to January 2010. During this period, a sudden increase in the ozone concentration (1 to 5 ppmv) in the Arctic mesosphere occurred. The analysis of the trajectories and ozone distribution in the mesosphere revealed that the ozone increase over Alaska region was caused by the effect of the air mass passing through the low temperature region. On other hand, the air mass passing through a region where the temperature was high contains with low ozone concentration. Therefore, it was found that the ozone concentration in the mesosphere depends on the temperature on the transport route. In this presentation, we will present the results of the comparison between the simulation and the JEM-SMILES dataset as well as the analysis results of the event which mesospheric ozone suddenly increases in the Arctic winter in 2009/2010 season.

[AAS07-P09] Short-term variations of HCl and HF trends observed with FTIR at Tsukuba

*Isao Murata1, Yoshihiro Tomikawa2,3, Isamu Morino4, Hideaki Nakajima4, Hideharu Akiyoshi4 (1.Graduate School of Environmental Studies, Tohoku University, 2.National Institute of Polar Research, 3.The Graduate University for Advanced Studies, SOKENDAI , 4.National Institute for Environmental Studies)

Keywords:FTIR, Ozone depletion, Chlorine compounds

HCl is a main chlorine reservoir species in the stratosphere. The amount of HCl is a good indicator of the potential for ozone depletion. Observed total column of HCl was decreasing in the 2000s after CFC regulations were introduced but showed increase from 2007 to 2011. Mahieu et al. [2014] investigated that this increase is due to interannual dynamical variability in the northern stratosphere from Fourier Transform Infrared spectrometer (FTIR) observations at 8 sites including Tsukuba and 3D-chemical transport model simulations.
In this study we extended the analysis of HCl total column observed with FTIR at Tsukuba to 2018 and HF total column was also anlyzed. HF is a good tracer of atmospheric transport. The temporal variation of HCl and HF total columns showed decrease again from 2011 to 2014 then increase from 2015 to 2018. Mass stream function was calculated from ERA-Interim meteorological data to confirm that these temporal variations are also due to stratospheric circulation change. The difference of the mass stream function between the average of 2003 - 2006 and the average of 2007 - 2010 shows negative values in the northern lower stratosphere. This means the deceleration of circulation and it is consistent with the result of Mahieu et al. [2014]. The difference between the average of 2007 - 2010 and the average of 2011 - 2014 shows positive values in the northern lower stratosphere that means the acceleration of circulation. These changes correspond to the HCl and HF temporal variation. Thus we confirm that the temporal variation of HCl and HF is basically due to stratospheric circulation change.
The situation is somewhat different for the period after 2015. The difference of mass stream function between the average of 2011 - 2014 and the average of 2015 - 2018 shows negative values in the northern lower stratosphere again and this is also consistent with the increase of HCl and HF total columns after 2015. However, MIROC3.2 Chemistry-Climate Model (CCM) results show that the decrease rates of HCl and HF became lower but continue to decrease after 2015. This means that the circulation change after 2015 isn't enough to explain the trend reversal and there are some possibility that the emission change in CFC-11 affects the increase of HCl and HF after 2015.

[AAS07-P11] Impact of HFCs on stratospheric ozone and temperature as simulated by chemistry-climate models

*Hideharu Akiyoshi1, Eric Dupuy1, Yousuke Yamashita2,1 (1.National Institute for Environmental Studies, 2.Japan Agency for Marine-Earth Science and Technology)

Keywords:HFC, ozone, chemistry-climate model, stratosphere, temperature

Hydrofluorocarbons (HFCs) are anthropogenic compounds used as substitutes for ozone-depleting substances (ODSs). While they do not chemically interact with ozone (O3), as greenhouse gases (GHGs) they substantially affect stratospheric temperature and circulation patterns, thus indirectly influencing O3 concentrations. Steps have been taken to curb production of HFCs (Kigali Amendment to the Montreal Protocol, 2016). Assuming global compliance, HFC emissions should, therefore, reach their peak around 2040. Until then, however, their atmospheric abundance will keep increasing [1]. We present ensemble model simulations designed to assess the response of O3, temperature and atmospheric circulation to increasing levels of HFCs. We analyze this response for climate conditions of 2095, following the Representative Concentration Pathway (RCP) 2.6 [2]. In this scenario, uncontrolled HFC emissions would induce a radiative forcing comparable to that of carbon dioxide, methane and nitrous oxide combined.

We simulate the effect of varying HFC concentrations in a 2095 climate, using the CCSRNIES-MIROC3.2 and CCSRNIES-MIROC5.0 three-dimensional (3D) chemistry-climate models [3,4]. These models use the same chemical module, but their physical modules are partly different. For each model, three ensemble simulations (“experiments”) are performed with different amounts of HFCs: no HFCs (control run), and two or three times (“2xHFC”, “3xHFC”) the HFC concentrations of Hurwitz et al. (2015) [5]. These correspond to abundance estimates for 2050, in the case of unregulated HFC emissions. Each experiment is an ensemble of 100 independent, year-long simulations. Background atmospheric levels of GHGs follow the RCP2.6 scenario for 2095. Estimated abundances of ODSs assume full compliance with the Montreal Protocol.

For each model version, results for the “2xHFC” and “3xHFC” cases are qualitatively similar. Therefore, we focus our analysis on the “3xHFC” experiment and illustrate ensemble-mean results for total column O3, as well as for latitude/pressure cross-sections of O3, temperature and zonal mean zonal wind.

At tropical and subtropical latitudes, we obtain ozone responses to increasing HFC concentrations which are roughly consistent with those from the zonal-mean two-dimensional (2D) model of Hurwitz et al. (2015) [5]. In addition, at these latitudes, the O3 responses of the MIROC3.2 and MIROC5.0 models are consistent. For O3, this robust response is a decrease around 50 hPa and an increase above and below. The temperature response to HFC increases is a warming of the stratosphere below 20 hPa. The resulting total ozone response is very small, because the positive and negative O3 anomalies cancel each other vertically. When considering the high latitudes, however, the calculated O3 responses are quite different, not only between the 2D model and both 3D MIROC models, but also between MIROC3.2 and MIROC5.0. Such discrepancies in the high-latitude responses may be due to differences of planetary wave activity in the models, and of their interaction with stratospheric HFCs and O3.


[1] WMO, 2018, Project Report No.58.

[2] IPCC, 2014, Climate Change 2014: Synthesis Report.

[3] Morgenstern, O., 2017, Geosci. Model Dev., 10, 639-671.

[4] Akiyoshi, H., 2016, J. Geophys. Res., 121, 1361-1380.

[5] Hurwitz, M., 2015, Geophys. Res. Lett., 42, 8686-8692.

[AAS07-P12] ODS and GHG dependence of total ozone at mid- and high latitudes indicated by multi-ensemble simulations using MIROC3.2 and MIROC5 chemistry-climate models

*Hideharu Akiyoshi1, Masanao Kadowaki2, Yousuke Yamashita3,1, Eric Dupuy1, Toshiharu Nagatomo1 (1.National Institute for Environmental Studies, 2.Japan Atomic Energy Agency, 3.Japan Agency for Marine-Earth Science and Technology)

Keywords:ozone, ODS, GHG, chemistry-climate model, multi-ensemble simulation, polar regions

Total ozone in the Arctic shows large interannual variations. The total ozone amount during Arctic spring is larger when the meridional circulation in the wintertime is stronger, thus when the Arctic polar vortex is weaker, and vice-versa. These variations mask the dependence of ozone concentration on ozone depleting substances (ODSs) and greenhouse gases (GHGs). Therefore, it is difficult to evaluate and isolate the effects of ODS regulations and GHG emissions from natural atmospheric variability, although ODSs and GHGs may influence the interannual variation of the atmosphere.

We conducted multi-ensemble simulations using two chemistry-climate models (CCMs). We considered the variability of interannual ozone variations to be a statistical variance. We investigated the ODS and GHG dependence of total ozone for extreme values of the variance, as well as for the mean of all ensemble members. In these simulations, the ODS and GHG concentrations were fixed at observed or projected values for specific years in the past and future (e.g., for the years 1960, 2000, 2050). Each simulation or experiment is uniquely defined by ODS and GHG levels corresponding to a specific year (for example, observed ODS levels of 1980 and projected GHG levels for 2050). For one experiment, the ozone variability among the ensemble members is then considered to be the interannual variation. We examined the ODS and GHG dependence of total ozone (i.e., as a function of the experiment), based on the minimum value found for each ensemble member at latitudes 45-90°N (‘polar cap’) during Northern spring (March – May). From the single-member minimum values, we then calculated the multi-ensemble mean, the mean for the 5 ensemble members with largest minimum value (hereafter “highest 5 members”), and for the 5 ensemble members with the smallest minima (hereafter “lowest 5 members”). The results show that the ODS and GHG dependence is large for the lowest 5 ensemble members and small for the highest 5 ensemble members. For the lowest 5 members, ozone levels should be smaller in a high-ODS atmosphere and larger in a high-GHG atmosphere. Furthermore, the zonal-mean zonal wind is stronger than for the multi-ensemble mean, while the corresponding polar cap temperature in the lower stratosphere is lower than the mean. This indicates that the Arctic polar vortex is comparatively stronger in the lowest 5 members.

The dependence of total ozone between 45-90°S in September – November (Southern spring) was also investigated. We found much smaller GHG dependence and much larger ODS dependence than for the Northern Hemisphere. The differences in the ODS and GHG dependence were much smaller among the multi-ensemble mean, the highest 5 members, and the lowest 5 members. This is consistent with much smaller interannual variations in the Southern Hemisphere and, hence, more influence of atmospheric chemistry on the ozone variations.

We conducted these analyses for MIROC3.2-CCM and MIROC5-CCM and compared the results of the two models. The difference in the ODS and GHG dependence of total ozone between these two models is consistent with their transport properties.

[AAS07-P13] A modeling study on the roles of cloud distribution in global tropospheric chemistry: detailed evaluation of clouds in a chemistry climate model (MIROC-CHASER)

*Ryoki Matsuda1, Kengo Sudo1,2 (1.Graduate School of Environmental Studies, Nagoya University , 2.Japan Marine-Earth Science and Technology)

Keywords:Cloud, Chemistry-transport model, Ozone, OH radical

Chemical reactions in the atmosphere directly affect the formation and loss of ozone, methane, nitrogen oxides, sulfur oxides, and aerosols, and have a great influence on the atmospheric environment and climate change. Since these reactions are driven by photodissociation of ozone and related species caused by ultraviolet radiation, they can be largely modulated by the distribution of clouds. This study quantitatively investigates the photolytic impacts of clouds on atmospheric chemistry by using a global chemical transport model (chemical climate model, CHASER), observational (satellite and aircraft) data, and reanalysis data.
For cloud fields, CHASER reproduced generally well the global distribution of total cloud amount as observed in the satellite (ISCCP D2) and reanalysis data (JRA-55). This model, however, tends to underestimate low-level clouds in the tropics with an overestimate in the high latitudes. Further verification for the other cloud parameters like optical thickness and radiative forcing is now in progress and will be discussed in the presentation.
Our sensitivity experiments with respect to the impacts of clouds on photolytic processes show that clouds reduce OH radical concentrations by 10-20% near the surface and increase by 10-20% in the upper troposphere, basically as a result of scattering and reflection of UV radiation by low-middle level clouds. Our simulations also suggest that the global mean OH concentration, proxy of the oxidizing capacity of the atmosphere, increases by about 14% due to clouds. Also, tropospheric ozone (O3) concentrations decreaced by about 3% near the surface and increased by about 4% in the upper troposphere reflecting changes in NOx concentration. These clouds' impacts on the atmospheric chemistry were verified by using aircraft observation data (NASA ATom-1, 2, 3). The result shows that the observed OH and O3 concentrations are reproduced more accurately when clouds are properly considered in the model.
These results indicate that clouds have significant influences on the global atmospheric chemistry (especially on the OH concentration field). Since OH determines the concentrations of chemical species such as methane, carbon monoxide (CO), fluorocarbons (CFCs), etc. which are important for climate and stratospheric ozone, this study suggests that the variation and trends in the clouds can largely affect the chemical species, which may give an additional influence on climate and atmospheric environment.

[AAS07-P14] Impacts of tropospheric bromine and iodine on global tropospheric ozone: a modeling study using CHASER

*Takashi Sekiya1, Yugo Kanaya1, Kengo Sudo2,1, Fumikazu Taketani1, Maki Noguchi Aita1, Akitomo Yamamoto1, Yoko Iwamoto3, Katsuhiro Kawamoto4 (1.Japan Agency for Marine-Earth Science and Technology, 2.Graduate School of Environmental Studies, Nagoya University, 3.Graduate School of Integrated Sciences for Life, Hiroshima University, 4.Graduate School of Maritime Sciences, Kobe University)

Keywords:Tropospheric ozone, Halogen, Chemical transport model

Bromine and iodine catalytic cycles are recognized as additional and important sinks of tropospheric ozone, though most of global climate transport models do not consider processes relevant to tropospheric bromine and iodine compounds (Young et al., 2018). A few global models have been used to evaluate impacts of tropospheric bromine and iodine on global tropospheric ozone (e.g., Saiz-Lopez et al., 2014; Sherwen et al., 2016), while large uncertainties in emission model process representation and emission estimation still remain. We newly implement iodine chemistry process, short-lived halocarbon emission, and ozone-mediated inorganic iodine release from the ocean (Chang et al., 2004; Carpenter et al., 2013) in the CHASER chemical transport model (Sudo et al., 2002; Sekiya et al., 2018) and evaluated impacts of tropospheric bromine and iodine on global tropospheric ozone. Incorporating these processes reduced surface ozone concentration by 20% on the annual and global average over the ocean. The model which incorporates these processes showed better agreements with ship-borne in-situ observations on the R/V Mirai and Hakuho-maru (Kanaya et al., 2019) during 2014-2018 (mean bias = 0.04 ppbv, r = 0.82) than the standard model (mean bias = 2.36 ppbv, r = 0.73). We evaluated impacts of tropospheric bromine on global tropospheric ozone loss using different three oceanic emission estimates of short-lived brominated halocarbons (CHBr3, CH2Br2, CH2BrCl, CHBr2Cl, and CHBrCl2): a bottom-up estimate based on SeaWIFS satellite observations of chlorophyll-a (Ordóñez et al., 2012), a bottom-up estimate for CHBr3 and CH2Br2 using ship-borne observations (Ziska et al., 2013), and a top-down estimate for CHBr3, CH2Br2, CHBr2Cl, and CHBrCl2 derived from the ATOM aircraft-campaign observations (Wofsy et al., 2018) using the Bayesian inversion technique. When using these three emissions, the global tropospheric ozone loss owing to bromine were estimated to be 284, 72, and 211 Tg O3/yr, respectively, which suggested that bromine-catalyzed loss highly depends on short-lived halocarbon emissions. For tropospheric iodine sources, oceanic iodine release (as HOI and I2) triggered by heterogeneous ozone loss at the sea surface was dominant over iodinated halocarbons (CH3I, CH2ICl, CH2IBr, and CH2I2). The global tropospheric ozone loss owing to atmospheric iodine chemistry was estimated to be 643 Tg O3/yr, which was comparable to the values reported by previous studies. Furthermore, model results suggested that the initial heterogeneous ozone loss at the sea surface (192 Tg O3/yr) was an important sink of global tropospheric ozone which has not been evaluated explicitly in the previous studies. These results demonstrated the importance of the processes related to tropospheric bromine and iodine on global tropospheric ozone. In future studies, it is necessary to get a better understanding of tropospheric bromine and iodine compounds’ emission processes and to reduce their uncertainties.

[AAS07-P15] The weekday/weekend ozone differences induced by the emissions change in Guangzhou megacity of China

*Yu Zou1 (1.Institute of Tropical and Marine Meteorology, CMA,Guangzhou,China)

Keywords:Emissions change, Weekday/ weekend ozone, Guangzhou

Guangzhou, one of China’s megacities, is beset with frequent occurrence of atmospheric photochemistry events in summer and autumn. In this study, weekday/weekend mixing ratios of ozone (O3) and the O3 precursors of non-methane hydrocarbons (NMHCs) and nitrogen oxides (NOx) were recorded at Guangzhou Panyu Atmospheric Composition (GPACS), a comprehensive site in Guangzhou, during the summer (June, July, and August) and autumn (September, October and November) of 2011. In both summer and autumn, weekday/weekend O3 differences in the morning and at midday largely depend on how much the O3 precursors are affected by anthropogenic emissions. In the mornings (6:00–9:00 LT), pollutants (i.e. NOx and NMHCs) were more strongly influenced by vehicular emissions in autumn than in summer. In autumn, O3 titration and lower NOx on weekends in NMHCs-limited regimes lead to more rapid O3 production, which resulted in the O3 weekend effect during autumn morning. No O3 weekend effect occurred on summer mornings because O3 formation was in a NOx-limited regime, although O3 titration still existed. At midday (10:00–16:00 LT), the increase of biogenic NMHCs emissions reversed the sensitivity of O3 production from NMHCs-to NOx-sensitive. The weekday/weekend diurnal pattern of vehicular sources was the same at midday, more intense other human industrial activities in autumn not only gave rise to the higher mixing ratios of high-reactive anthropogenic NMHCs (e.g. aromatics) on weekdays, but also could affected the temperature in the city, leading to higher isoprene mixing ratio on weekdays. All these factors are likely to contribute to the O3 weekday effect in autumn. Meanwhile no weekday O3 effect occurred in summer due to the low-intensity industrial anthropogenic activities. Our results show that high-reactive NMHCs and NOx control can be effective for reducing peak O3 mixing ratios in Guangzhou. Further investigation based on numerical models is required to reach more robust conclusions.

[AAS07-P16] A Study on the Optimization of 3D Expressions for the Analysis of Local Scale Meteorological and Air Quality Information

*Woosik Jung1, Gunwoo Kim1 (1.INJE University, Department of Atmospheric Environment Information Engineering, Gimhae, Republic of Korea)

Keywords:Air Quality information, 3D expression, Local scale

In the last 10 years (2007 ~ 2016), 162 people have been killed and about 6.3 trillion won in property damage in Korea alone, the report showed. This is due to the increase of severe weather on the local scale as climate change progresses due to global warming. This study developed the 3D expression system specialized for the local scale. We used one of the commercial engines, Unreal Engine 4 and C++ language, to express meteorological and air quality information in 3D. As input data, the result of WRF and CMAQ modeling were used. Using high-resolution DEM data, 3D terrain was created, and wind vector field was implemented to indicate wind. And we have implemented isolines that indicate temperature and precipitation. In addition, by studying a new expression method to represent the wind, we implemented a stream vector and stream line, which is a vector and streamline moving along the wind flow. And the 3D volume rendering method using Raymarching algorithm is applied to express 3D data, cloud and air pollutant density.

For the analysis of local scale 3D expression cases, the day when the land and sea breeze was blown off the west coast including Seoul and Incheon was selected. And we analyzed a typhoon case of mesoscale. To show that air quality information can also be analyzed, the density of air pollutants such as fine dust and carbon monoxide was expressed and analyzed in 3D volume rendering. As a result of the case analysis, the modeling results were well reflected and the changes in meteorological and air quality information over time were easily identified. And the 3D volume rendering expression allowed us to analyze the vertical structure and distribution of clouds and air pollutants density in a new perspective.

This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(2017R1D1A3B03036152)

[AAS07-P17] Validation of tropospheric NO2 column density data observed by TROPOMI: Comparison with 4AZ-MAXDOAS

*Hikaru Saito1, Hitoshi Irie1 (1.University of Chiba)

Keywords:Atmosphere, Satellite observation, Nitrogen dioxide

TROPOspheric Monitoring Instrument (TROPOMI) aboard the Sentinel-5 Precursor satellite has an unprecedented fine horizontal resolution of 7 km×3.5 km (at nadir) for tropospheric nitrogen dioxide (NO2) column observations and is expected to improve estimation of emissions, including localized kilometer-scale emissions. However, previous studies reported that underestimation could occur in tropospheric NO2 column data from satellite observations, although its causes are still under discussion. The present study attempts to validate TROPOMI tropospheric NO2 column data to confirm that the underestimate occurs and clarify the causes. For this purpose, we used ground-based 4-different-azimuth-viewing Multi-Axis Differential Optical Absorption Spectroscopy (4AZ-MAXDOAS) installed at Chiba, Japan (35.63ºN, 140.10ºE, 21 m asl). The 4AZ-MAXDOAS observed tropospheric NO2 simultaneously in 4 different azimuth directions, enabling the evaluation of spatial inhomogeneity of NO2, which has been considered to be the major cause of the underestimate. From 4AZ-MAXDOAS data, we found that differences in tropospheric NO2 column data among 4 different azimuth directions reached up to 40%, indicating the existence of significant horizontal spatial inhomogeneity in NO2 around the observation site. Then, we compared 4AZ-MAXDOAS data with coincident TROPOMI data. TROPOMI data showed an underestimation by up to about 50% compared to 4AZ-MAXDOAS data, confirming the underestimate in TROPOMI data. However, the correlation was not clear between the magnitude of the underestimate and the coefficient of variance in 4-azimuth data from 4AZ-MAXDOAS observations. This suggests that the observed underestimate cannot be explained only by the effect of the NO2 spatial inhomogeneity. Instead, the underestimate should be attributed more significantly to the assumption made in the air mass factor calculation.

[AAS07-P18] Chemical composition of atmospheric aerosols over Jakarta megacity

*Masahide Nishihashi1, Hitoshi Mukai1, Yukio Terao1, Shigeru Hashimoto1, Rizaldi Boer2, Muhammad Ardiansyah2, Bregas Budianto2, Adi Rakhman2, Gito Sugih Immanuel2, Rudi Nugroho3, Nawa Suwedi3, Anies Marufatin3, Muhammad Agus Salim3, Dodo Gunawan4, Eka Suharguniyawan4, Asep Firman Ilahi4, Muharam Syam Nugraha4, Ronald Christian Wattimena4, Bayu Feriaji4, Qoriana Maulani4 (1.National Institute for Environmental Studies, 2.IPB University, Indonesia, 3.Agency for the Assessment and Application of Technology (BPPT), Indonesia, 4.Meteorological, Climatological, and Geophysical Agency (BMKG), Indonesia)

Keywords:atmospheric aerosols, PM2.5, chemical composition, urban monitoring, Indonesia

We have implemented a comprehensive observation of air pollutants and greenhouse gases around Jakarta megacity in Indonesia since 2016 to quantify anthropogenic emissions from the city and characterize them in terms of socioeconomic activities in the city.

In addition to the continuous monitoring systems of NOx, SO2, O3, CO, CO2, CH4, and meteorological parameters, we installed three continuous dichotomous aerosol chemical speciation analyzers (ACSA-14, Kimoto) at Bogor (center of Bogor city) in 2016, Cibeureum (mountainous area, background-like site) in 2017, and Serpong (Jakarta suburb) in 2019. The ACSA-14 can automatically measure not only the mass concentrations of PM2.5 and PM10-2.5 and optically measured black carbon (OBC), but also the chemical composition of PM2.5 and PM10-2.5 (nitrate ion (NO3-), sulfate ion (SO42-), water soluble organic compounds (WSOC), ammonium ion (NH4+)), simultaneously. The measurement interval is 3 hours to extend the replacement interval of filter tapes and chemical reagents for the chemical composition analysis of PM2.5 and PM10-2.5.

The averages of PM2.5 from November 2017 to October 2019 are 23.9 μg/m3 at Bogor and 18.3 μg/m3 at Cibeureum. The seasonal averages of PM2.5 observed at Bogor and Cibeureum in the dry season (May to October in 2018/2019) are 34.2 and 28.0 μg/m3, which are 2.4 and 3.2 times higher than those of rainy season (November 2017/2018 to April 2018/2019), respectively. While the long-term trends of PM2.5 observed at Bogor are similar to Cibeureum, the averaged PM2.5 concentrations at Bogor in the dry and rainy seasons are 1.2 and 1.6 times larger than Cibeureum, respectively.

We compared the chemical composition of PM2.5 observed at three sites in February 2020. The amount of SO42- (20.9%) is almost same as WSOC (20.8%) at Bogor. The dominant components at Cibeureum are SO42- (27.4%) and WSOC (13.4%). While the most dominant component at Serpong is WSOC (22%), the percentage of NO3- (13.2%) at Serpong is larger than Bogor (11.8%) and Cibeureum (8.7%). The NO3-/SO42- ratio at Serpong (1.76) is higher than Bogor (0.82) and Cibeureum (0.43). These results suggest that the urban pollution caused by NOx in automobile exhausts is significant at Serpong compared to Bogor and Cibeureum.
In our presentation, we will also present the result of PM10-2.5, OBC, and the other species.

[AAS07-P19] Seasonal Variation of Wet Deposition of Black Carbon in Arctic Alaska

*Tatsuhiro Mori1, Yutaka Kondo2, Sho Ohata3,4, Yongjing Zhao5, Puna Ram Sinha6, Naga Oshima7, Hitoshi MATSUI8, Nobuhiro Moteki9, Makoto Koike9 (1.Tokyo University of Science, 2.National Institute of Polar Research, 3.Institute for Space–Earth Environmental Research, Nagoya University, 4.Institute for Advanced Research, Nagoya University, 5.Air Quality Research Center, University of California-Davis, 6.Department of Earth and Space Sciences, Indian Institute of Space Science and Technology, 7.Meteorological Research Institute, 8.Graduate School of Environmental Studies, Nagoya University, 9.Graduate School of Science, The University of Tokyo)

Keywords:Black carbon, Wet deposition, Arctic, single-particle soot photometer, seasonal variation

Black carbon (BC) aerosol deposited in and onto Arctic snow increases the snow’s absorption of sunlight and accelerates snowmelt. Wet removal of BC from the atmosphere plays a key role in determining its abundance in the Arctic atmosphere and in Arctic snow. However, this process is poorly understood, mainly due to the scarcity of relevant measurements. To reveal characteristic features of the wet deposition of BC, we made highly accurate measurements of mass concentrations of BC in snow and rain (CMBC) and mass concentrations of BC in surface air (MBC) at the Barrow Atmospheric Baseline Observatory, Alaska, from July 2013 to August 2017 and analyzed them along with routinely measured meteorological parameters from Barrow. Monthly mean MBC and CMBC were poorly correlated from midwinter to early spring, when CMBC was close to the annual median while MBC was at its annual peak. Seasonal variations in the altitude distribution of ambient BC concentration may lead to these differences in seasonal variation of MBC and CMBC, as may microphysical processes in mixed phase clouds. About 50% of the annual wet deposition of BC occurred in the three months of summer, associated with high values of total precipitation and BC originating from biomass burning. Size distributions of BC in snow and rain were stable throughout the year, suggesting that the size distribution of BC in the lower troposphere is similarly stable. These observations improve our understanding of the loss processes and hence the BC budget in the Arctic.

[AAS07-P20] Investigation of wet removal rate of black carbon in East Asia: A perspective from airmass pathways

*Yongjoo Choi1, Yugo Kanaya1, Masayuki Takigawa1, Chunmao Zhu1, Seung-Myung Park2, Atsushi Matsuki3, Yasuhiro Sadanaga4, Sang-Woo Kim5, Xiaole PAN6 (1.Japan Agency for Marine-Earth Science and Technology, Japan, 2.National Institute of Environmental Research, Korea, 3.Kanazawa University, Japan, 4.Osaka Prefecture University, Japan, 5.Seoul National University, Korea, 6.Chinese Academy of Sciences, China)

Keywords:Black carbon, Wet scavenging coefficients, FLEXPART, Long-term measurements

Using long-term and harmonized measurements of black carbon (BC) and carbon monoxide (CO) from three representative background sites in East Asia (Baengnyeong and Gosan in South Korea, and Noto in Japan), the regional and seasonal differences in wet removal rates were investigated according to airmass transport pathways and meteorological conditions. To identify the airmass origin and accumulated precipitation along with trajectories (APT), backward trajectories at 500 m during 72 hours were calculated by the Hybrid Single Particle Lagrangian Integrated Trajectory 4 model. The European Center for Medium-Range Weather Forecasts (ECMWF) ERA5 hourly pressure and surface level meteorological data (0.25° × 0.25°) were used as input data to obtain accurate and detailed information of each endpoint of trajectories. The wet removal rates were more efficient in South Korea and Japan among the region and in fall and winter among the season. These differences depending on the regional and seasonal division could be partially explained by the inherent difference in the coating thickness of BC particles, according to the dominant emission sectors. Because the industrial sector (thin coated) is dominant in East and North China, in contrast, the transportation sector (thick coated), mainly emitted from diesel vehicles, has a high portion in South Korea and Japan. By the same token, wet removal rates in winter and summer showed the highest and lowest depending on the dominant emission sectors, such as house heating (thick coated) and industry, respectively. Next, we calculated transport efficiency (TE) from FLEXible PARTicle (FLEXPART) Lagrangian transport model (version 10.4) to investigate the representativeness of wet removal rate of model. Overall median TE from FLEXPART was overestimated compared to measurement, implying underestimation of wet scavenging coefficients. The median of estimated below cloud scavenging coefficients showed slightly overestimation than that calculated from FLEXPART as a factor by 1.7. On the other hand, the median of calculated in-cloud removal coefficients including sub-grid effect was highly underestimated than that of estimation by a factor of 5.1. From the analysis of artificial neuron networks, the convective available potential energy (CAPE), which is well known as an indicator of vertical instability, should be considered in in-cloud scavenging process to improve the better representative regional difference in BC wet scavenging over East Asia.

[AAS07-P21] Light absorption properties of organic aerosols at Fukue Island in 2018 spring

*Chunmao Zhu1, Takuma Miyakawa1, Hitoshi Irie2, Fumikazu Taketani1, Yugo Kanaya1 (1.Japan Agency for Marine-Earth Science and Technology, 2.Chiba University)

Keywords:Brown Carbon Aerosol, Light Absorption, Skyradiometer, Filter Observation

Light-absorbing organic aerosol, also termed as brown carbon (BrC) aerosol, is one of the most understudied aerosol components for its sources and effects on climate change. For a long time, organic aerosols had been deemed to cause cooling on the earth’s surface. Recently model studies indicated that BrC is accounting for ~1/4 of warming effect by carbonaceous aerosols at the tropopause globally. However, observation about the light absorption properties of BrC aerosols, which are fundamental for climate change prediction, is very limited, especially in East Asia. The SKYNET observational data at Fukue Island were used to derive the Absorption Aerosol Optical Depth (AAOD) based on the aerosol optical depth and single scattering albedo. AAOD of BrC and AAESKYNETwere then derived based on the light absorption characteristic differences among BrC, BC and dust. Teflon (PTFE) filter samples were also collected using the Continuous Particulate Monitor with X-ray Fluorescence (PX375, Horiba Inc.). BrC in the filters were extracted using methanol followed by syringe-filtration to remove black carbon and mineral particles. The light absorption coefficient and Absorption Angstrom Exponent (AAEfilter) of BrC were quantified based on measurement of light absorption spectra in the UV-visible light (300–800 nm). The extracts were filtered to remove dusts and black carbon and analyzed for light absorption. We found that AAEfilterwere generally higher than AAESKYNET. Vertical profile of aerosol light absorption properties needs to be further studied in the future.

[AAS07-P22] Can a global chemistry climate model reproduce interannual variabilities and trends of depositions of sulfate, nitrate, and ammonium preserved in the Southeastern Greenland Dome ice core?

*Kengo Sudo1,2, Hinako Shiratsuchi1, Yoshinori Iizuka3 (1.Graduate School of Environmental Studies, Nagoya University, 2.Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 3.Institute of Low Temperature Science, Hokaido University)

Keywords:chemistry climate model, ice core, Arctic, Aerosol deposition, Greenland, Sulfate/Nitrate/Ammonium

Inorganic compounds like sulfur and nitrogen oxides (SOx/NOx) are mainly emitted from fossil fuel combustion or high-temperature air combustion associated with anthropogenic activities. Those components are chemically oxidized in the atmosphere to form sulfate and nitrate which cause air pollution and acid rain. Aerosols like sulfate and nitrate are also involved in the global climate change, inducing negative radiative forcing by scattering solar incident and changing clouds. For accurate evaluation and future projection of global changes in atmospheric environment and climate, it is vital to quantitatively validate a chemistry climate model that simulates global distributions of aerosols including sulfate and nitrate making maximal use of available observations. In this study, we evaluate global simulation by a chemistry climate model (CHASER) using a long-term (60 years) record of aerosol depositions preserved in the High-Accumulation Dome ice core in Southeast Greenland (SE-Dome) and investigate controlling factors of interannual variation and trends in inorganic ions of sulfate (SO42-), nitrate (NO3-), and ammonium (NH4+).

It is found that our model simulation basically well captures both seasonal cycles and interannual variabilities in the flux of each component as seen in the ice core record for 1970s to 2010. The model calculations suggest that the long-term SO42- trend seen in the ice core (-0.15 μmol L-1 d-1) is mostly from SO2 emission changes in the source areas like Europe, U.S. , and Asia over the decades. In contrast, long-term trends for NO3- and NH4+ (-0.06 and 0.01 μmol L-1 d-1, respectively) appear to be affected largely by changes in natural sources and meteorological conditions in addition to the anthropogenic emissions of NOx and NH3.

Interestingly the model simulation replicates the spiky peaks (positive anomalies) in concentrations (particularly for SO42-) recorded in May 1992. The peaks were tentatively attributed to the 1991 eruption of Mt. Pinatubo in the previous studies. Our model simulation, however, nicely reproduces the concentration peaks even without any direct injection from the Mt. Pinatubo to the atmosphere, implying that anomalous changes in meteorological fields (most probably for transport and precipitation) are the dominant factors of the peaks in May 1992. Actually, the model simulation suggests that there were anomalously enhanced transport pathways from Europe and North America toward Greenland and the SE-Dome site for both of SOx, NOx, and NHx.

[AAS07-P23] Evaluation of GCOM-C aerosol products using ground-based sky radiometer observations

*Hossain Mohammed Syedul Hoque1, Hitoshi Irie1, Alessandro Damiani1, Mashiro Momoi1 (1.Center for Environmental Remote Sensing (CEReS), Chiba University)

Aerosol optical thickness (AOT) at 380 and 670 nm retrieved from the Global Change Observation Mission-Climate (GCOM-C) observations from January to September 2019 was evaluated using the ground-based SKYNET sky radiometer measurements at Chiba (35.62° N, 140.10° E), Japan and Phimai (15.18° N, 102.56° E), central Thailand. Chiba and Phimai are urban and rural sites, respectively. AOT retrieved from the sky radiometer observations from were compared with the coincident multi-axis differential optical absorption spectroscopy (MAX-DOAS) AOT values. Under clear sky conditions, both the datasets show excellent agreement. The sky radiometer and GCOM-C AOT values show a good positive correlation (R) ~ 0.90 at 380 nm in both sites. At 670 nm, the R-values were 0.67 and 0.87 for Chiba and Phimai, respectively. Despite the low R-value at 670 nm over Chiba, the temporal variation of AOT was well reproduced by the satellite observations. Over both sites, the agreement between the datasets was mostly within ±0.2. Over Chiba, the higher differences in the AOT values were mostly related to cloud screening in the datasets. The mean bias error (MBE) (GCOM-C – Sky radiometer) for the Chiba site was ~ -0.08 and ~ -0.02 at 380 and 670 nm, respectively, for the coincidence criterion of 0.1° x 0.1°. For the similar coincidence criterion, the MBE values were higher for the observations over the Phimai site. The potential reason was the influence of biomass burning in addition to the cloud influence. The spatial resolution of the satellite coincidence data had a significant impact on the MBE at 380 nm over the Chiba site. Overall, the retrieved AOT values of both datasets were generally consistent indicating the excellent potential of the GCOM-C observations of aerosol properties, especially in the ultra-violet region.

[AAS07-P24] Atmospheric sulfate formation pathways over the past 60 years constrained by a global chemical transport model

*Shohei Hattori1, Becky Alexander2, Sakiko Ishino3, Shuting Zhai2 (1.Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2.Department of Atmospheric Sciences, University of Washington, Seattle WA 98195-1640, USA, 3.National Institute of Polar Research, Research Organization of Information and Systems, Tokyo 190-8518, Japan )

Keywords:Global chemical transport model, Sulfate, Triple oxygen isotopes, Aerosol, Anthropogenic activity

Since the industrial revolution, the increase of sulfur dioxide (SO2) had increased the SO42 load. The period including the 1950s to 1970s had significant SO2 emissions, but these emissions decreased after the 1980s across North America (NA) and Western Europe (WE), reducing atmospheric SO42 burden. However, SO42 aerosols decreased less rapidly than SO2 reduction, suggesting the existence of chemical feedback processes.
In the atmosphere, SO42 is produced from gas-phase SO2 oxidation by hydroxyl radicals (•OH) and oxidation in aqueous-phase (i.e., in clouds). SO2, dissolved in an aqueous-phase, forms S(IV) species (i.e., SO2·H2O, HSO3, and SO32−) that react with hydrogen peroxide (H2O2), ozone (O3), and molecular oxygen (O2) to form SO42. Among these chemical processes, several studies have proposed several mechanisms causing the weakened response of SO42 to SO2 decreases.
To obtain quantitative information in sulfate formation pathways, we simulate global tropospheric sulfate chemistry using the version 12.5.0 of the GEOS-Chem chemical transport model. We performed the model simulations with anthropogenic emissions corresponding to the years 1960, 1973, 1986, 1999, and 2013, to investigate the past changes in atmospheric sulfate formation and its efficiency in response to the changes in anthropogenic emission.
Relative contributions of S(IV)+ O3 and H2O2 were increased between 1973 and 2013 over the Eastern NA (ENA) and WE, and the proportional increases of S(IV) + O3 pathway are consistent with our previous observation of triple oxygen isotopic composition of SO42 in a Greenland ice core. The increase of S(IV) + O3 pathway is best explained by an increase in the cloud water pH over the period, and not by O3 concentration increase.
The promotion of S(IV) + O3 pathway over the period caused higher SO2 conversion efficiency for both summertime and wintertime in ENA and WE. On the basis of the GEOS-Chem model outputs, we found two regional characteristics: (i) gradual increase of SO2 conversion efficiency in WE over the period, and (ii) a small increase of SO2 conversion efficiency in ENA between 1960 and 1999 and an abrupt increase between 1999 and 2013.
In the presentation, we will discuss several implications including perspective for future sulfate formation by the worldwide reduction of SO2 and the important role of acidity (defined as cloud pH) in the atmospheric chemistry.

[AAS07-P25] High-temporal-resolution elemental characterization of fine-mode aerosols in springtime Asian outflow: Emission and removal characteristics, and comparison with model simulation

*Takuma Miyakawa1, Akinori Ito1, Chunmao Zhu1, Yugo Kanaya1 (1.Japan Agency for Marine-Earth Science and Technology)

Keywords:Elemental composition, Aerosol, PM2.5, Iron

Trace metals in aerosol particles exhibit the various impacts on the ocean biogeochemistry (Mahowald et al., 2018). We conducted the semi-continuous measurements of elemental composition of fine mode (PM2.5) aerosols using an automated X-ray fluorescence analyzer (PX-375, Horiba, Ltd., Asano et al., 2017) in a remote island, Fukue (32.75ºN, 128.68ºE), in Japan in the spring of 2018. Here we report the temporal variations of mass concentrations of geochemically important elements for this period, namely sulfur (S), lead (Pb), copper (Cu), manganese (Mn) and iron (Fe), and their relationships with some tracers, carbon monoxide (CO), black carbon (BC), and calcium (Ca). Positive correlation of Pb and Cu with CO and BC were found during the observation period, indicating the emission sources of these metals share the region where the large CO (and BC) emission sources are located. Further analyses of concentration-weighted trajectories also suggested the similar geographical characteristics of these elements and combustion tracers. We extracted the continental outflow air masses with minimized impacts of the (especially wet) removal during the transport to elucidate the emission ratio of Pb and Cu to CO, which were evaluated, for the first time in Asian outflow, to be 97.8 and 37.4 µg/g, respectively. The wet removal of Pb together with BC was also investigated based on the precipitation along the air mass transport. Impacts of Asian dust and anthropogenic (i.e., combustion) sources on Fe in PM2.5 aerosols were diagnosed by using the measured BC concentration with the emission ratio of iron oxides to BC, and by comparing those simulated by the IMPACT model (Ito et al., 2019). Fraction of combustion-derived Fe for fine mode aerosols was evaluated to be less than 20% on average during the observation period.

Asano et al. (2017), Highly Time-Resolved Atmospheric Observations Using a Continuous Fine Particulate Matter and Element Monitor, Earth Space Chem., 1, 9, 580-590.
Ito A., et al. (2019), Pyrogenic iron: The missing link to high iron solubility in aerosols, Sci. Adv., 5, eaau7671.
Mahowald N. M., et al. (2018), Aerosol trace metal leaching and impacts on marine microorganisms, Nat. Comm., 9:2614.

[AAS07-P26] Comparison of compositional characteristics of aerosol and rainwater samples collected in Nagoya

*Wei Chenran1, Sonia Afsana1, Qingcai Chen2, Dhananjay Kumar Deshmukh3, Kimitaka Kawamura3, Michihiro Mochida1,4 (1.Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan, 2.School of Environmental Science and Engineering, Shaanxi University of Science and Technology, Xi’an, China, 3.Chubu Institute for Advanced Studies, Chubu University, Kasugai, Japan, 4.Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Japan)

Organic aerosol is one of major components of atmospheric aerosol particles. Some volatile organic compounds (VOCs) react in the aqueous-phase of cloud droplets, and after the evaporation of liquid water, they form aerosol, which is called aqueous secondary organic aerosol (aqSOA). Further, organic aerosols may also change to aqSOA through aging in the aqueous phase. Although a number of laboratory experiments and model simulations have explored the mechanism of aqSOA formation, the mechanism in real atmospheric environments is still unclear. To find a clue to understand how aqSOA is formed in could droplets through aqueous-phase reactions, this study compares compositional characteristics of water-soluble components in aerosol and rainwater samples, as a means to compare the components of aerosols before and after the reactions in the real atmosphere.

Aerosol and rainwater samples were collected on campus of Nagoya University in Nagoya, Japan. The organics therein were fractionated into humic-like substances with a neutral nature (HULIS-n), humic-like substances with an acid nature (HULIS-a) and high-polar water-soluble organic matter (HP-WSOM). The optical properties of the samples were measured using a fluorescence spectrophotometer and an ultraviolet-visible spectrophotometer. Fourier transform infrared spectroscopy (FT-IR) was used to compare the chemical structural characteristics of aerosol and rainwater samples.

The analysis of the 3D fluorescence spectra shows that the HULIS-n-to-HULIS-a ratios based on the fluorescence intensity of two spectra regions (excitation wavelength from 240 to 260 nm and emission wavelength from 400 to 460 nm , and excitation wavelength from 320 to 360 nm and emission wavelength from 420 to 460 nm) from aerosol samples were in most cases larger than those of rainwater. A possible explanation is that some of the low-polar fluorescent substances (fluorescent substances in HULIS-n) were decomposed to non-fluorescent substances and that more-polar fluorescent substances (fluorescent substances in HULIS-a) were formed by aqueous-phase reactions. The FT-IR results present that HULIS-n and HULIS-a in aerosol samples show a smaller fraction of carboxyl group but a larger fraction of carbonyl group than those in rainwater samples, implying that the oxidation of carbonyl groups to carboxyl groups occured for HULIS-n and HULIS-a, and/or that aqSOA containing carboxyl group was formed from VOCs. Because the presence of water in the samples for the FT-IR analysis may have influenced on the quantification of functional groups, compositional characteristics of aerosol and rainwater samples should be further compared using other instruments such as an aerosol mass spectrometer.

[AAS07-P27] Formation processes of dimers measured in α-pinene secondary organic aerosol particles

*Kei Sato1, Sathiyamurthi Ramasamy1, Satoshi Inomata1, Shinichi Enami1, Yu Morino1 (1.National Institute for Environmental Studies)

Keywords:Biogenic volatile organic compound, Secondary organic aerosol, Chemical mechanism, Low-volatility organic compound, Smog chamber

Formation of low-volatility compounds such as dimers detected in atmospheric aerosol particles will affect atmospheric organic aerosol level due to the influence from these dimers on volatility and viscosity of particles. In order to study formation mechanisms of dimers detected in forest particles,1) we used liquid chromatograph-mass spectrometry (LCMS) to analyze filter extracts of secondary organic aerosol (SOA) particles generated by chamber experiments on the oxidation of α-pinene. We determined the ratios of dimer to SOA mass for those with molecular weights (MWs) of 344, 358, and 368 as a function of experimental conditions including the oxidant of VOC, initial VOC concentration, the acidity of seed particles, and the temperature of chamber. We used 6 m3 NIES smog chamber and temperature-controllable 0.7 m3 Teflon bag chamber for generation of SOA particles. The dimer/SOA ratios measured for the reactions of O3 with α-pinene were higher than those measured for the reactions of OH and NO3 radicals with α-pinene. Formation of dimers barely occurred during reactions with OH and NO3 radicals although the reactions of OH and NO3 radicals with α-pinene forms carbonyl compounds, which could form dimers through acid catalyzed heterogeneous reactions, and organic peroxy radicals, which could form dimers through gas-phase association reactions. Furthermore, the concentrations of dimers with MWs of 344 and 358 in sample solutions showed linear correlations with the product from multiplication of the concentrations of corresponding monomers. Dimers with MW 358 could be successfully separated with a LC column from the chromatographic peaks of presumed monomers, pinic acid and terpenylic acid; suggesting that signals of dimers with MW 358 are not instrument artifacts and result from stable dimers existing in solution or particle phases. Dimers with MW 358 are likely to be formed through the reactions of Criegee intermediates; however, as formation process for dimer with MW 358 we cannot exclude hydrogen bonding formation2) from monomers formed from the gas-phase reaction with O3. This research has been supported by the Environmental Research and Technology Development Fund from Environmental Restoration and Conservation Agency (grant no.5-1801) and NIES Research Founding Type A.

1) Sato et al., LC/MS analysis of molecular markers present in biogenic secondary organic aerosols collected during year-round observations at a cool-temperature forest, Japan Geoscience Union Meeting 2019, AASO4-22, Chiba, Japan (2019).
2) DePalma et al., Thermodynamics of oligomer formation: implications for secondary organic aerosol formation and reactivity, Phys. Chem. Chem. Phys., 15, 6935-6944 (2013).

[AAS07-P28] Nitric acid gas captured in quasi-liquid layers on ice surfaces

*Ken Nagashima1, Josée Maurais2, Ken-ichiro Murata1, Yoshinori Furukawa1, Patrick Ayotte2, Gen Sazaki1 (1.The Institute of Low Temperature Science, Hokkaido University, 2.Université de Sherbrooke, Québec, Canada)

Keywords:Ice, quasi-liquid layer, nitric acid gas, optical microscopy

Ice crystal surfaces act as “reaction fields” for heterogeneous chemical reactions that involve atmospheric acidic gases, thereby causing serious environmental issues such as the catalytic ozone depletion by hydrogen chloride gas and the generation of nitrogen oxide gases (NOx) from the photolysis of nitric acid/nitrates. These chemical reactions cannot be explained solely by homogeneous processes. In addition, the surfaces of ice crystals near the melting point are covered with thin liquid water layers, called quasi-liquid layers (QLLs), which may play crucial roles in various chemical reactions. In this study, we chose HNO3 as a model atmospheric gas, and directly observed the QLLs on ice basal faces by advanced optical microscopy [1]. Because PHNO3 in the troposphere shows considerable variations (e.g., ranging from ~10-6 Pa in clean air to ~10-2 Pa in polluted urban air [2,3]), the observations in this study were performed under some PHNO3 conditions (0, 10-4 and 10−2 Pa).

Irrespective of the presence/absence of the HNO3 gas, the pure-QLLs and HNO3-QLLs appeared with increasing temperature and disappeared with decreasing temperature. The shape of pure-/HNO3-QLLs showed spherical dome and the contact angle of them on the ice basal face was ~1°. The appearance temperatures of the pure-/HNO3-QLLs were not so different (-1.9 and -0.5 to -1.8 °C, respectively). Although the disappearance temperature of pure-QLLs (-2.2 °C) was almost same as the appearance temperature, the disappearance temperature of the HNO3-QLLs (-6.4 °C) was significantly lower than the appearance temperature of them under high-PHNO3 condition (10-2 Pa). The large thermal hysteresis between the appearance and disappearance temperatures suggests that the disappearance mechanisms of the pure-/HNO3-QLLs were different. We found that the HNO3-QLLs are not composed of pure water, but rather of aqueous HNO3 solutions, and also that the HNO3-QLL and the ice crystal were in equilibrium. The evidence and the disappearance mechanism are showed as follows.

The size of the HNO3-QLLs decreased immediately after we started reducing the temperature. We could not observe such changes in the sizes of pure-QLL with temperature in the absence of the HNO3 gas. When we assumed that the mass of HNO3 in the HNO3-QLL was constant during the relatively short observation time period, the volume reduction of the HNO3-QLLs with decreasing temperature meant increasing of HNO3 concentration of the HNO3-QLL. We calculated the volume reductions as a function of temperature by using the HNO3-H2O phase diagram. The calculated volume reductions were in good agreement with the volume reductions determined experimentally.

One of the plausible causes for the disappearance of HNO3-QLLs could be the evaporation of HNO3 from the HNO3-QLLs. We calculated the equilibrium HNO3 partial vapor pressure, Pe(HNO3), of the HNO3-QLLs. As temperature decreases, Pe(HNO3) increases. It is very reasonable to expect that when Pe(HNO3) exceeds PHNO3 in the observation chamber with decreasing temperature, HNO3 evaporates from the HNO3-QLLs, resulting in the disappearance of the HNO3-QLLs.

Recently, we studied the effects of hydrogen chloride gas on the behavior of QLLs (HCl-QLLs) on ice basal faces [4,5]. We found that the HCl-QLLs were also aqueous hydrochloric acid solution, and that the temperature and HCl concentration of the HCl-QLLs were also very close to those of a liquidus line: these results were similar to those found in this study. Therefore, ice crystal surfaces would capture large amount of acidic gas components in the acidic-QLLs.

[1] Nagashima et al. (2020) Crystals 10, 72.

[2] Goldan et al. (1983) Atmos. Environ. 17, 1355.

[3] Hanke et al. (2003) Atmos. Chem. Phys. 3, 417.

[4] Nagashima et al. (2016) Cryst. Growth Des. 16, 2225.

[5] Nagashima et al. (2018) Cryst. Growth Des. 18, 4117.

The details of this study are shown in our paper [1]. We will present this study from other viewpoints in “A-CC39 Glaciology” and "M-IS23: Growth and dissolution of crystal" sessions.

[AAS07-P29] Five-years seasonal variations of nitrogen and triple oxygen isotopic compositions of atmospheric nitrate at Noto Peninsula, Japan

*Kazuki Kamezaki1, Shohei Hattori1, Atsushi Matsuki2, Naohiro Yoshida1,3 (1.Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2.Institute of Nature and Environmental Technology, Kanazawa University, 3.Earth-Life Science Institute)

Keywords:Nitrate, Aerosol, Triple oxygen isotopes, Nitrogen isotope ratio

Anthropogenic nitrogen oxides (NOx) emission from land to the atmosphere have been accelerated in East Asia. By increase of the anthropogenic pollutants in the atmosphere, atmospheric oxidizing capacity can be changed in East Asia. Moreover, the biological cycle can be changed because the atmospheric nitrate deposition is a source of nitrogen. Thus, the understanding of sources and formation pathways of atmospheric nitrate is important.

The nitrogen and triple oxygen isotopic compositions (δ15N and Δ17O = δ17O − 0.52 × δ18O) of atmospheric nitrate can be a tracer of the sources and formation pathways of atmospheric nitrate. The δ15N of atmospheric nitrate can be used to estimate the sources and sinks of atmospheric nitrate. The Δ17O of atmospheric nitrate can be a tracer of the relative importance of mass-independent oxygen-bearing species (e.g. O3, BrO; Δ17O ≠ 0 ‰) and mass-dependent oxygen-bearing species (e.g. OH radical; Δ17O ≈ 0 ‰) during the conversion of NOx to atmospheric HNO3. In this study, we present five-years data of δ15N and Δ17O values in atmospheric nitrate collected at NOTO Ground-based Research Observatory (NOTOGRO) (37.5°N, 137.4°E) located at the north coast of Noto Peninsula, Japan.

The atmospheric nitrate concentrations did not show a clear trend, while the δ15N and Δ17O showed a clear seasonal variation with summer minimum and winter maximum. The trend of Δ17O is caused by the seasonal changes in the O3 / HOx ratios decreasing in summer by ozone destruction and HOX production (e.g. OH, HO2 radicals) via UV irradiance. Although the correlation between δ18O and Δ17O values was observed throughout the year, the slope between δ18O and Δ17O values for coarse particles for the winter-spring period is only different from other seasons and fine particles. We will discuss possible explanations of this different isotope pattern for the winter and spring periods.

[AAS07-P30] Impacts of ship emissions on atmospheric particulate matter and gaseous components over the Seto Inland Sea areas

*Moe Tauchi1, Katsuhiro Kawamoto2, Kazuyo Yamaji1, Ryohei Nakatsubo3, Yoshie Oshita3, Yasuyuki Itano4 (1.Kobe University, 2.Takamatsu Local Meteorological office, 3.Hyogo Prefectural Institute of Environmental Sciences, 4.Osaka City Research Center of Environmental Science)

Keywords:Global Sulphur Cap, Maritime vessel emissions, gaseous pollutants, particulate pollutants, Inland Sea

Our interest issue is to be clear control factors of elevated atmospheric pollutants over the Seto Inland Sea (SIS) and surroundings, where PM2.5 levels are still higher than the other regions in Japan (Nakatsubo et al., 2020). The SIS area is closed and congested with many people live along its coastal zones. Even now, it has been concerned that high sulfur emissions from vessels using heavy fuel oil with relatively high sulfur content effect on air quality.

From 1 January 2020, in such a situation, the sulfur contents in fuel oil used on board ships operating outside emission control areas have been reduced from 3.50% to 0.50% (the sulfur limits). The global sulfur limits will make significantly reductions of sulfur oxides emissions from ships, and that should have major health and environmental benefits for the world, especially for populations living close to ports and coasts. The reduced ship sulfur emissions are expected to affect not only ambient sulfur-containing substance concentrations but also the other atmospheric pollutant components.

To assess the impacts of the fuel sulfur changes on air quality of the SIS areas, we investigated concentrations of SO2 and PM2.5 substances in the atmosphere over both land and sea from March 2017 to March 2020 only for the duration of the research voyage. Automatic sampling data at ambient air pollution monitoring stations facing to SIS were used for analyzing the coastal-landmass pollutants. As regards the marine air mass, SO2 and PM2.5 were sampled over the SIS area on board Training-ship Fukaemaru owned by Kobe University.

From January 1 to March 31 in 2018, percentage of sulfate ion in PM2.5 along the SIS area is about 24.1%. We are carefully watching the atmospheric particulate matter and gaseous components around the SIS after starting the sulfur limits. Continued observation research should contribute for improvement of air quality and formulating environmental policy in the future.

[AAS07-P31] Spatiotemporal variations of NO2 over Fukuoka Japan, observed by multiple MAX-DOAS and 3-D coherent Doppler lidar

*Hironobu Ueki1, Hisahiro Takashima2, Martina Michaela Friedrich3 (1.Fukuoka university graduate school, 2.Fukuoka university, 3.Belgian Institute for Space Aeronomy)

Keywords:NO2, MAX-DOAS, TROPOMI, doppler lidar

To clarify spatiotemporal variations and transport processes in nitrogen dioxide (NO2) over Fukuoka, an urban area in Japan, continuous NO2 profile observations using Multi Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) with high temporal resolution of four minutes have been conducted since October 2018 at three observatories: Yakuin (33.580°N, 130.396°E), Sohara (33.580°N, 130.356°E) and Fukuoka University (33.550°N, 130.364°E).

We first performed case studies at particular days and observed enhanced NO2 contents above the city center on some days. In the case of 29 November 2018, high NO2 concentrations were observed near the ground in the morning (around 7:00–10:30 am). Higher contents of NO2 appeared gradually at higher altitudes over the urban area, and disappeared at around 13:00–14:00 pm. We investigated a three-dimensional (3-D) wind field observed using a 3-D coherent Doppler lidar installed at Fukuoka University. The NO2 variations were consistent with the wind variation: the airmass with high NO2 concentration was transported upward from near the ground over an urban area; it advected southward (landward) because of a sea breeze in the afternoon.

We also validated the tropospheric NO2 vertical column density (VCD) using the Sentinal-5P/TROPospheric Ozone Monitoring Instrument (TROPOMI) satellite with MAX-DOAS observations. Results showed that the satellite data are underestimates, as shown in earlier studies (e.g., Kanaya et al., 2014), but large variations exist from 34% to 154%. These results suggest that underestimation can be attributable not only to the shield effect by aerosols near the ground but also to inhomogeneity and transport processes of the NO2 airmass over urban areas.