[A-AS07] Atmospheric Chemistry

[AAS07-02] Characterization of CO₂ emission sources in urban areas using Oxidative Ratio (OR)

*Yutaka Arai¹, Qiduo Hu¹, Ryoichi Imasu¹, Shigeyuki Ishidoya², Hiroaki Kondo², Hirofumi Sugawara³ (1.Atmosphere and Ocean Research Institute, The University of Tokyo, 2.National Institute of Advanced Industrial Science and Technology, 3.Earth and Ocean Science, National Defense Academy of Japan)

Keywords:CO2, O2, Oxidative Ratio, Urban area, CO2 emission sources, Atmospheric transport model

The exchange ratio of O₂ and CO₂ associated with fossil fuel consumption and biological activity, Oxidative Ratio (OR), is defined as the ratio of changes in atmospheric O₂ concentration and CO₂ concentration (ΔO₂, ΔCO₂), OR = -ΔO₂/ΔCO₂. In this study, we attempt to analyze the characteristics of CO₂ emission sources in urban areas by comparing the observed OR values and model calculated values. Continuous measurement of CO₂ and O₂ concentrations has been conducted in Tokyo (Yoyogi) since March 2016 using a magnetic O₂ analyzer (POM-6E, Air Liquide) and NDIR (Li-820, LI-COR). Air sampling heights are 52 m and 37 m from ground, and raw data were averaged for 10 minutes. On the other hand, CO₂ and O₂ concentrations have been measuring at an Ibaraki (Tsukuba) site with a mass spectrometer (Thermo Scientific Delta-V) since February 2012. Air sampling is performed on the roof of the experimental building at a height of 8 m from the ground. This time, we analyzed the data from 2016 to 2018 within the above period. Numerical calculation of CO₂ concentration was performed with a spatial resolution of 2 km using the regional transport model AIST mesoscale model, AIST-MM. CO₂ emission inventory data is based on EAGrid2000-Japan, scaled using data from the NIES GHG Inventory Office, and applied to the target year. Calculations are performed for each of the emission sources of “Thermal power plants”, “Vehicles”, “Plants” and “Other anthropogenic sources”, and each unique OR value weighted by the calculated atmospheric CO₂ concentration is summed to get the model-calculated OR value. At this time, the OR value of "Vehicles (OR=1.44)" and "Plants (OR=1.10)" is fixed, and we assume that "Thermal power plant" include three possible fuels; coal (OR=1.17), oil (OR=1.44), and natural gas(OR=1.95), and “Other anthropogenic sources” include two possible fuels: liquefied petroleum gas (OR=1.44) and natural gas (OR=1.95). As a result, there are six possible combinations of OR values for the fuels of “Thermal power plants” and “Other anthropogenic sources”, and the fuel combination that was actually used can be inferred through the comparison between the model-calculated OR value and the observed OR value. Since the OR values actually analyzed fluctuate greatly on a daily basis, monthly average values were obtained, and by finding the model-calculated OR of which seasonal variation curve is closest to that of observed OR we can infer the best combination of the fuels for both “Thermal power plants” and “Other anthropogenic sources”. As a result, at both the Yoyogi and Tsukuba sites, the observations and models tended to match relatively well when petroleum was assumed to be the main fuel for "Thermal power plants". On the other hand, for "Other anthropogenic sources", it was estimated that natural gas was the main fuel for Yoyogi and liquefied petroleum gas for Tsukuba. This result is consistent with the statistical data that natural gas is mainly used for domestic use in Tokyo, while propane gas is used in Tsukuba. However, it has been confirmed that there are differences in these results due to wind direction dependence and atmospheric stability, and there is a possibility that they are affected by coal-fired power plants and steel mills that use coal. In the future, we would like to conduct a detailed analysis that also considers weather conditions.