Spatiotemporal Characteristics of Tropospheric and Surface NO2 from Sentinel-5 Precursor (S5P) and in-situ Observations in Taiwan

        Sentinel-5 Precursor (S5P) is a new generation environmental satellite, and provides trace gases concentrations along with cloud and aerosol information for global coverage. In this study, we focus on a regional scale nitrogen oxide (NO_x) which is not only mainly air pollutant but also the precursors of secondary aerosol and ozone. However, the atmospheric NOx is primary in the form of Nitrogen dioxide (NO₂). To understand the chemical properties and air pollution of NO₂ from S5P in Taiwan, this study accesses the tropospheric NO₂ which is retrieved from the TROPOMI onboard S5P, in conjunction with in-situ surface NO₂ concentration observation from Environmental Protection Administration (EPA) of Taiwan. The temporal period is from June 2018 to May 2019, and surface observation is collocated with daily revisit of S5P spatiotemporally. The data are analyzed in 15 sub-regions of Taiwan for the relationship between tropospheric vertical column and surface concentration of NO₂.

        The preliminary results reveal high correlation between surface NO₂ and tropospheric NO₂ in North Taiwan (Taipei/New Taipei City/Keelung), Yunlin, Tainan and Kaohsiung. Relative low correlation in Yilan, Hualian because of broad area with less ground-based stations. On the other hand, in order to avoid the impact of short-term factors, monthly mean concentration of NO₂ is applied for further statistics. The results indicate high relationship in most of counties, except Hsinchu and Taitung. This suggests that the tendency of surface NO₂ is similar to the tropospheric NO₂ in most of countries in Taiwan in the monthly scale. Therefore, in order to monitor and analysis of NO₂ concentration, spaceborne TROPOMI on S5P might be an alternative choice for conducting related research in Taiwan.