Rapid Aqueous-Phase Photooxidation of Dimers in the α-Pinene Secondary Organic Aerosol

Chemical complexity significantly hinders our understanding of the formation and evolution of secondary organic aerosol (SOA), which is known to have impacts on air quality and global climate. Dimeric substances present in SOA comprise a major fraction of extremely low-volatile organic compounds that are especially poorly characterized. Using online mass spectrometry, we have investigated the aqueous phase OH oxidation of dimers present in the water-soluble fraction of SOA arising from ozonolysis of alpha-pinene. This study highlights very rapid OH oxidation of dimeric compounds. In particular, using pinonic acid as a reference compound, we obtained second-order rate constants for the loss of 12 dimers, with an average value of (1.3 +/- 0.5) X 10(9) M-1 s(-1) at room temperature. For the first time, this study demonstrates that rapid loss of dimeric compounds will occur in cloudwater and potentially also in aqueous aerosols.