Diurnal Variation of Aerosol Optical Depth in Korea: A synthesis from AERONET, Satellite, KORUS-AQ observation, and WRF-Chem model

Aerosols play a large role in air quality, climate, and human health. Data from surface monitors, aircrafts, satellites, and chemistry transport models are integral components of atmospheric research. We investigate the diurnal variation of aerosol optical depth (AOD) and single scattering properties at 550 nm using 12 AERONET sites from 1999 to 2017 and an additional 10 sites during the KORUS-AQ field campaign in South Korea, the WRF-Chem model, and the GOCI satellite. AERONET sites are grouped by land classification into coastal urban (4 sites), coastal rural (5 sites), inland urban (7 sites), and inland rural (6 sites). The coastal rural sites show the most similarities amongst one another with virtually zero AOD diurnal variation, while the coastal urban sites show the least similarities. In contrast, the inland rural sites as a whole do not show a consistent AOD diurnal pattern. However, further breaking the inland rural sites by location shows that the eastern, inland rural sites are characterized by virtually zero AOD diurnal variation and lower average values around 0.2, while the western, inland rural sites have distinct diurnal variations and higher average values around 0.4, reflecting the impact of pollutants from upwind regions. Narrowing our focus, we investigate the AOD diurnal variation at 15 of the 22 sites during the KORUS-AQ timeframe and see that the observed diurnal variations departed from their climatological patterns. Additionally, the WRF-Chem model tended to have a high bias in predicting AOD values throughout the campaign, and its AOD diurnal variation differs from the AERONET AOD diurnal variation at most of the sites. AOD from GOCI is also compared with the AERONET AOD diurnal variation. A synthesis on how long of an observational data record is needed to establish a robust characterization of AOD diurnal variation will also be presented.