Abstract
Abstract. Secondary organic aerosol (SOA) was formed in an environmental reaction chamber from the ozonolysis of β-caryophyllene (β-C) at low concentrations (5 ppb or 20 ppb). Experimental parameters were varied to characterize the effects of hydroxyl radicals, light and the presence of lower molecular weight terpene precursor (isoprene) for β-C SOA formation and cloud condensation nuclei (CCN) characteristics. Changes in β-C SOA chemicophysical properties (e.g., density, volatility, oxidation state) were explored with online techniques to improve our predictive understanding of β-C CCN activity. In the absence of OH scavenger, light intensity had negligible impacts on SOA oxidation state and CCN activity. In contrast, when OH reaction was effectively suppressed (> 11 ppm scavenger), SOA showed a much lower CCN activity and slightly less oxygenated state consistent with previously reported values. Though there is significant oxidized material present (O / C > 0.25), no linear correlation existed between the mass ratio ion fragment 44 in the bulk organic mass (f44) and O / C for the β-C-O3 system. No direct correlations were observed with other aerosol bulk ion fragment fraction (fx) and κ as well. A mixture of β-C and lower molecular weight terpenes (isoprene) consumed more ozone and formed SOA with distinct characteristics dependent on isoprene amounts. The addition of isoprene also improved the CCN predictive capabilities with bulk aerosol chemical information. The β-C SOA CCN activity reported here is much higher than previous studies (κ < 0.1) that use higher precursor concentration in smaller environmental chambers; similar results were only achieved with significant use of OH scavenger. Results show that aerosol formed from a mixture of low and high molecular weight terpene ozonolysis can be hygroscopic and can contribute to the global biogenic SOA CCN budget.
Highlights
Secondary organic aerosol (SOA) is an important contributor to atmospheric particulate mass (Seinfeld and Pankow, 2003)
Β-C-O3 reaction was examined in regards to influences of OH scavenger, lights and another prominent biogenic volatile organic compounds (VOCs), isoprene
Results indicated that β-C-OH reaction in the β-C-O3 system promoted formation of highly oxidized and volatile aerosol
Summary
Secondary organic aerosol (SOA) is an important contributor to atmospheric particulate mass (Seinfeld and Pankow, 2003). Goldstein and Galbally (2007) estimated SOA production of 510–910 Tg C yr−1 from 1300 Tg C yr−1, roughly a 50 % yield, from volatile organic compounds (VOCs). Biogenic volatile organic compounds (BVOC) may contribute to half of the global organic carbon (Hallquist et al, 2009) and isoprene, monoterpernes and sesquiterpenes dominate BVOC emissions (Guenther et al, 1999, 2000; Kanakidou et al, 2005). Terpenes are atmospherically abundant and reactive, as reflected by ephemeral chemical lifetimes (∼ several minutes, Goldan et al, 1993; Guenther et al, 1995; Neeb et al, 1997). Sesquiterpenes may have a similar large potential for SOA formation as monoterpenes; their contribution to global SOA formation may be as high as 9 % (Donahue et al, 2005; Griffin et al, 1999; Dekermenjian et al, 1999; Bonn and Moortgat, 2003)
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