Comment on acp-2022-636

Abstract

Secondary organic aerosols (SOA) play a key role in climate change and public health. However, the oxidation state and volatility of SOA are still not well understood. Here, we investigated the highly oxygenated organic molecules (HOMs) in SOA formed from ozonolysis of β-pinene and limonene. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to characterize HOMs, and a scanning mobility particle sizer (SMPS) was used to measure the concentration and size distribution of SOA particles. The abundance of HOMs in limonene SOA was 5–13 % higher than in β-pinene SOA (3–13 %) exhibiting different trends with increasing ozone concentrations. β-pinene oxidation-derived HOMs prefer to stabilize at high ozone concentration, accompanied by substantial formation of ultra-low-volatility organic compounds (ULVOCs). Limonene-oxidation-derived HOMs prefer to stabilize at moderate ozone concentrations, with semi-, low-, and extremely low-volatility organic compounds (SVOCs, LOVCs, and ELVOCs) play a major role. Combined experimental evidence and theoretical analysis indicate that oxygen-increasing-based peroxy radical chemistry is a plausible mechanism for the formation of compounds with 10 carbon atoms. Our findings show that HOMs and low volatile species in β-pinene and limonene SOA are largely different. The ozone concentration-driven SOA formation and evolution mechanism of monoterpenes is suggested to be considered in future climate or exposure risk models, which may enable more accurate air quality prediction and management.