Chemical and Optical Properties of SOA from the Oxidation of Volatile Organic Compound Mixtures
YUMENG CUI, Kunpeng Chen, Ying-Hsuan Lin, Roya Bahreini,
University of California, Riverside Abstract Number: 196
Working Group: Aerosol Chemistry
AbstractThe chemical and physical properties of secondary organic aerosols (SOA) have been widely studied by environmental chamber experiments, and the results have been parameterized in atmospheric models to help understand their radiative effects and climate influence. While most chamber studies from the past decades investigated the aerosol formed from a single volatile organic compound (VOC) in batch mode, the potential interactions between reactive intermediates derived from VOC mixtures are not well understood. In this study, we investigated the SOA formed from pure and mixtures of biogenic (longifolene and α-pinene) and anthropogenic (1-methylnaphthalenen and phenol) VOCs using continuous-flow, high-NO
x photooxidation chamber experiments to better mimic ambient conditions. Optical properties, including single scattering albedo (SSA), mass absorption coefficient (MAC) and refractive index (RI) at 375nm, and chemical properties, including the contribution of organonitrate (RONO
2) and nitro-organic (RNO
2) compounds, and the molecular structure of the major chromophores, were explored. Source apportionment models were used to simulate the fractions of particle-phase products from biogenic vs. anthropogenic VOCs. Subsequently, these fractions were combined with the MAC values of pure SOA to predict the MAC of the mixture SOA. Our results show that, in multi-VOCs systems, the scattering biogenic SOA weakened the absorption from aromatic SOA; the discrepancies between the predicted and measured mixture SOA MAC varied among different VOC systems, indicating the potential formation of unique compounds in multi-VOCs experiments. The aerosol mass spectrometer (AMS) results showed the formation of RONO
2 and RNO
2 compounds in all experiments, with the fraction of these nitrogen-containing compounds varying in different systems. Time-integrated aerosol samples collected at the end of the experiments analyzed with offline instruments revealed that RNO
2 compounds are the major light-absorber in the 280-400nm range in both aromatic VOC systems. Overall, this study highlights the importance to consider the presence of multi-VOCs when estimate ambient SOA chemical and optical properties.