Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-AS Atmospheric Sciences, Meteorology & Atmospheric Environment

[A-AS04] Atmospheric Chemistry

Thu. May 30, 2019 9:00 AM - 10:30 AM 102 (1F)

convener:Tomoki Nakayama(Graduate School of Fisheries and Environmental Sciences, Nagasaki University), Yoko Iwamoto(Graduate School of Biosphere Science, Hiroshima University), Sakae Toyoda(Department of Chemical Science and Engineering, Tokyo Institute of Technology), Nawo Eguchi(Kyushu University), Chairperson:Hisahiro Takashima(福岡大学)

9:15 AM - 9:30 AM

[AAS04-17] Determination of atmospheric NO2 column densities using a Pandora instrument measuring direct-sun spectra at Yokosuka, Japan: Improved validation of TROPOMI satellite observations

*Yugo Kanaya1, Hisahiro Takashima2,1, Masato I. Nodzu3, Takashi Sekiya7, Kazuyuki Miyazaki1, Henk Eskes4, Gaia Pinardi5, Daniel Santana Diaz6, Moritz Müller6, Alexander Cede6 (1.Research and Development Center for Global Change, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2.Fukuoka University, 3.Tokyo Metropolitan University, 4.KNMI, 5.BIRA-IASB, 6.LuftBlick, 7.Japan Agency for Marine-Earth Science and Technology (JAMSTEC))

Keywords:Satellite observations, Validation, Spectroscopy, Air pollution

Satellite observations of NO2, a key atmospheric pollutant, have provided critical information on global distribution of NOx sources and their temporal changes since 1995, and advanced understanding of atmospheric chemistry. A recent remarkable improvement is with their spatial resolution, reaching 7×3.5 km for TROPOMI (Sentinel-5P), launched in 2017. However, there is still a fundamental issue of low bias in the determined tropospheric NO2 column densities (e.g., 25-50% for TROPOMI), when evaluated against ground-based spectroscopic observations. Potential causes would be (1) a-priori vertical profile shapes, (2) co-present aerosols and/or surface albedo, and (3) spatial inhomogeneity of NO2, while (4) uncertainty in the ground-based observations could also be important. At Yokosuka (32.32°N, 139.65°E), located on the south edge of Tokyo-Yokohama metropolitan area, we newly started direct-sun Pandora spectrometer observations in November 2018 and strengthened validation capability, where the scattered-sun MAX-DOAS observations (from a JAMSTEC original instrument) had been solely referenced before. Results during winter 2018/2019 showed TROPOMI (within 0.1° from Yokosuka) had ~40% low bias against MAX-DOAS. The magnitude of difference was similar to the results from longer comparison during Feb-Sep 2018 for TROPOMI and earlier comparisons for OMI (QA4ECV). Pandora (in direct-sun mode) gave values ~24 % less than MAX-DOAS; the cause of difference was likely spatial inhomogeneity, as pollution levels were higher in the northeast for the sight of MAX-DOAS than in south for Pandora. This was consistent with the fact that TROPOMI gave ~18% higher values, when the averaging area was shifted to northeast by 10 km. As such, the importance of factors (3) and (4) was newly evaluated. By considering MAX-DOAS profile shapes in the recalculation of satellite products, we will discuss on factor (1), and the possibility to derive near-surface NO2 concentrations from satellite observations.