Sources and formation pathways of organic aerosol in a subtropical metropolis during summer

According to the simulations, biogenic sources contributed to 60% and 72% of total OA production at the NTU (urban) and HL (rural) sites. The simulated fractions of SOA in total OA were 67% and 79% near the surface of NTU and HL, respectively, and these fractions increased with height and reach over 90% at the 1-km altitude. Estimated from the simulation results, aqueous-phase dicarbonyl uptake was responsible of 51% of OA production in the urban area, while the primary emissions, reversible partitioning of semi-volatile oxidation products, oligomerization of semi-volatile SOA in the particulate phase and acid-enhanced oxidation contributed to 33%, 10%, 5% and 1% respectively; in the rural area, the percentages were 59%, 21%, 13%, 7% and 1%, respectively. Meteorological factors, including large-scale wind direction, local circulation and planetary boundary layer height, all have strong influences on the source contributions and diurnal variations of OA concentration.