Uncovering the Missing Organic Aerosols
Secondary organic aerosols (SOA) constitute a major fraction of submicrometer atmospheric particulate matter. Quantitative simulation of SOAs within air-quality and climate models—and their resulting impacts—depends on the translation of SOA formation observed in laboratory chambers into robust parameterizations. Accumulating worldwide data indicate that model SOA predictions are substantially lower than ambient observations. Although possible explanations for this mismatch have been advanced, none has addressed the laboratory chamber data. Losses of particles to chamber walls are routinely accounted for, but little evaluation has been conducted of the effects on SOA formation of losses of semivolatile vapors to chamber walls. In a recent study, U.S. Department of Energy-funded investigators experimentally demonstrate that such vapor losses can lead to substantially underestimated SOA formation, by as much as 4 factors. Accounting for such losses has the clear potential to bring model predictions and observations of organic aerosol levels into much closer agreement.
Zhang, X., C. D. Cappa, S. Jathar, R. C. McVay, J. J. Ensberg, M. J. Kleeman, and J. H. Seinfeld. 2014. “Influence of Vapor Wall-Loss in Laboratory Chambers on Yields of Secondary Organic Aerosol,” Proceedings of the National Academy of Sciences (USA), DOI:10.1073/pnas.1404727111.