High Summertime Aerosol Loadings Over the Arabian Sea and Their Transport Pathways

Satellite observations show high aerosol loadings over the Arabian Sea in boreal summer, which have great impacts on the Indian monsoon due to absorbing dust aerosols. However, the compositions, origins, transport pathways, and decadal trends of these aerosols have not been well studied. In this study, using multiple satellite retrievals, a back trajectory model, and reanalysis data, we found that (1) aerosol optical depth (AOD) over the Arabian Sea and Arabian Peninsula have a summer peak and dust aerosols dominate the AOD; aerosol reanalysis data tend to considerably underestimate dust AOD compared to satellite data, indicating challenges of extracting dust from total AOD; (2) aerosols over the Arabian Sea are largely transported from South and East Arabian Peninsula by cyclonic winds in the lower troposphere (850 hPa) and from Iran-Afghanistan-Pakistan by anticyclonic winds in the middle troposphere (500 hPa); (3) both case studies and composite analyses show that extremely high aerosol loadings over the Arabian Sea is associated with an abnormally low pressure over the Arabian Sea and the Middle East; and (4) significant positive trends in AOD over the Arabian Peninsula and the Arabian Sea exist during 2000-2011 but disappear during 2000-2016, indicating a strong interdecadal variability of dust activities. This study revealed pathways linking dust emissions in the Middle East to high summertime AOD over the Arabian Sea and identified the atmospheric conditions favorable for dust emissions and transport. Plain Language Summary Tiny particles in air are of great importance in climate system by changing the Earth's radiation balance and clouds. Satellites observe very high concentrations of particles over the Arabian Sea and the Middle East in the boreal summer. This study examined the chemical compositions of these particles over the Arabian Sea and their origins, transport pathways, and long-term changes using multiple satellite products, numerical simulations, and statistical methods. It is found that dust aerosols dominate the particles over the Arabian Sea in the summer. These dust aerosols are lifted from the dry deserts over the Arabian Peninsula to the air and transported to the Arabian Sea under favorable wind patterns. The findings here can benefit future studies on interactions between the Middle East dust particles and regional climate.