NASA - National Aeronautics and Space Administration

We present a new volatility basis set (VBS) representation of aromatic secondary organic aerosol (SOA) for atmospheric chemistry models by fitting a statistical oxidation model with aerosol microphysics (SOM-TOMAS) to results from laboratory chamber experiments. The resulting SOM-VBS scheme also including previous work on SOA formation from semi- and intermediate volatile organic compounds (S/ IVOCs) is implemented in the GEOS-Chem chemical transport model and applied to simulation of observations from the Korea-United States Air Quality Study (KORUS-AQ) field campaign over South Korea in May–June 2016. Our SOM-VBS scheme can simulate the KORUS-AQ organic aerosol (OA) observations from aircraft and surface sites better than the default schemes used in GEOS-Chem including for vertical profiles, diurnal cycle, and partitioning between hydrocarbon-like OA and oxidized OA. Our results confirm the important contributions of oxidized primary OA and aromatic SOA found in previous analyses of the KORUS-AQ data and further show a large contribution from S/IVOCs. Model source attribution of OA in surface air over South Korea indicates one third from domestic anthropogenic emissions, with a large contribution from toluene and xylenes, one third from external anthropogenic emissions, and one third from natural emissions. Plain Language Summary We have created a new way of understanding how air pollution is formed. We did this by looking at how certain chemicals change when they are exposed to oxygen in the air. We used a computer model of lab experiments to see how these chemicals would react in the atmosphere. The new method is called SOM-VBS. We used this method to study a type of air pollution called secondary organic aerosol that comes from the reaction of oxygen in the air with emissions from both natural and human activities. We found that the new method was able to explain the observations from a field campaign in South Korea better than previous methods. This new understanding can help us figure out where the pollution is coming from. We also found that one third of the pollution comes from human activities in South Korea, one third comes from human activities outside of South Korea, and one third comes from natural sources like plants and wildfires.