Simulating Biogenic Secondary Organic Aerosol During Summertime in China

Abstract

AbstractBiogenic secondary organic aerosol (BSOA) contributes significantly to summertime organic particulate matter. In this study, a simulation of BSOA for summer 2012 over China is performed using the Community Multiscale Air Quality model with an explicit representation of BSOA formation via reactive uptake of isoprene‐derived intermediates, species‐specific parameters for monoterpene‐derived BSOA production, and a multigenerational oxidation scheme. Simulated BSOA tracks the measurements well (normalized mean bias of 1% and r2 of 0.59). Elevated BSOA occurs in the Sichuan Basin and southeastern China (except the coastal areas) where concentrations are mostly within the range of 5–7.5 μg/m3. Nitrate oxidation dominates fresh BSOA originating from monoterpenes. Simulated monoterpene‐formed BSOA increases by a factor of 3–11 with multigenerational oxidation. Isoprene‐formed BSOA shows high concentrations in southwestern China, formed primarily by two methyltetrols (2‐MT) and organosulfates (62%–83%). High concentrations in this region are driven by the abundance of IEPOX and high particle surface area of sulfate‐laden aerosols. NOx emissions influence the formation pathways of isoprene‐formed BSOA, as a high ratio of two‐methylglyceric acid (2‐MG)/2‐MT is found in the North China Plain and part of the Yangtze River Delta Region. The simulated isoprene‐formed BSOA is more strongly correlated with sulfate than with particle water mass concentration or particle acidity, in part because sulfate increases the surface area increasing uptake for heterogeneous reactions. Decreases in isoprene‐formed BSOA were simulated with a pH increase of 2, implying that particle acidity mediates the BSOA formation.