The diurnal variation of pollutant distributions over Asia using observations from the Geostationary Environment Monitoring Spectrometer (GEMS)

Over the last 20 years, low-Earth orbit (LEO) atmospheric composition observations have provided amazing satellite measurements of atmospheric pollutants, mainly at continental-to-global, weekly-to-seasonal scales. The new-generation geostationary (GEO) satellite perspective, with high spatial resolution and hourly measurements, represents a major step forward in capability for understanding how air quality processes change diurnally at the local scale. South Korea's Geostationary Environment Monitoring Spectrometer (GEMS) was launched in February 2020 over Asia and is the first member of the GEO constellation that will eventually include the Tropospheric Emissions: Monitoring Pollution (TEMPO) mission over North America, and Sentinal-4 over Europe. The measurement hourly time resolution is truly the new perspective that the GEO platform provides, and in this presentation, we use a combination of satellite observations from GEMS and chemical transport model simulations to investigate the diurnal variation of pollution over several Asian regions. When considering the GEMS whole-Asia field-of-regard, the most striking impression of the NO2 diurnal variation is of how large it is in magnitude as well as how much the spatial distribution changes hour-by-hour. This questions our understanding of the distributions of reactive species based on the representativeness of once-a-day LEO observations. To help understand daily differences in diurnal patterns at regional and local scales, we use the Multi-Scale Infrastructure for Chemistry and Aerosols (MUSICA-V0). This uses a global modeling framework with regional grid refinement to resolve chemistry at emission and exposure relevant scales. The model shows reasonable agreement with the GEMS data and captures the different diurnal patterns at the different spatial scales and the degree of day-to day variability. The model also allows the drivers of variability due to emissions, meteorology, and photochemistry to be considered separately. The results of this analysis are further compared with the NO2 diurnal variability observed by PANDORA sun spectrometer measurements at polluted and less-polluted Korean and other Asian sites. We investigate spatial scale, including the city-scale within Seoul, at which GEMS captures the differences in diurnal variability between the PANDORAs.