Exploring the factors controlling the long-term trend (1988–2019) of surface organic aerosols in the continental United States by simulations

To understand the driving factors for the long-term surface OA trend, we apply a revised version of the Community Atmosphere Model version 6 with comprehensive tropospheric and stratospheric chemistry representation, considering the heterogeneous formation of isoprene-epoxydiol-derived secondary organic aerosols (SOAIE) and fast photolysis rate of monoterpene-derived secondary organic aerosols (MTSOA) to diagnose the OA evolution in 1988-2019.

Compared to older versions, the revised model better reproduces the climatology, seasonal cycle, and long-term trend of surface OA as evaluated against the Interagency Monitoring of Protected Visual Environments measurements. We find the decrease in EUS summertime OA is likely attributed to the interplay between SOAIE and MTSOA. With anthropogenic emissions reduction, primary organic aerosols (POA) declined, SOAIE decreased along with sulfate, while MTSOA increased along with biogenic emissions driven by a warming climate.