A scheme for representing aromatic secondary organic aerosols in chemical transport models: Application to source attribution of organic aerosols over South Korea during the KORUS-AQ campaign

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.