Laboratory reaction chamber experiments will be undertaken for the comprehensive characterization of the conditions for fast uptake of glyoxal on ammonium sulfate aerosol, identification of the reaction products formed within the aerosol under conditions of fast uptake, and determination of whether gas-phase or aerosol phase reaction products primarily contribute to secondary organic aerosol (SOA) yields. Whereas analogous laboratory studies on bulk samples have been previously undertaken, the work proposed here is exploratory in that it is one of the first to investigate with molecular detail and mechanistically the pathways in which a small high-volatility compound is taken up by aerosol and processed to form high-molecular weight, low-volatility compounds. The results will not only provide information critical to modeling SOA formation from glyoxal, specifically, but also have the potential to lend fresh perspective on general questions about SOA formation and aging.
This exploratory research is related to factors affecting climate change (aerosol radiative forcing) and human health (respirable particles), which affect society at large. The research will engage students in teaching and learning as part of a multi-disciplinary group gathering the type of expansive dataset necessary to capture the complexity of atmospheric chemical processes. The students will have the opportunity to analyze their own data in the context of broader datasets and to draw conclusions concerning both the scientific and societal implications of their work.
Aerosols influence climate and have a direct impact on human health and the biosphere. Organic aerosol corresponds to an important fraction of ambient aerosol. In addition to being directly emitted, organic aerosol is also produced in the atmosphere via oxidation of volatile organic compounds (VOCs) emitted from anthropogenic and biogenic sources. This type of organic aerosol is referred to as secondary organic aerosol (SOA). Models of SOA formation often have difficulty reproducing SOA concentrations from observations. Much of the recent effort within the atmospheric chemistry community has focused on improving our understanding of SOA formation. One pathway of SOA formation that has recently been proposed involves the gas-to-particle partitioning of small VOC oxidation products, in particular glyoxal. Laboratory studies of glyoxal uptake onto existing (seed) aerosol under dark and photochemical conditions (presence and absence of sunlight and oxidants, respectively) can provide insight into the underlying mechanisms of this potentially important process and generate new questions for the next stage of research into SOA formation and growth. The work under this NSF grant investigated photochemical and dark uptake of glyoxal onto aqueous ammonium sulfate seed aerosol. In conjunction with previous work, this study suggests that the uptake rate and mechanism are sensitive to the detailed nature of the seed aerosol, in particular the possible presence of coatings. These results suggest that an improved understanding of the nature of coatings on ambient aerosol are needed to estimate the importance of the fast photochemical uptake of glyoxal and its contribution to ambient SOA mass loading. The project also investigated the effect of sulfate, a common aerosol constituent that often derives from anthropogenic sources, on the partitioning of glyoxal between the gas- and condensed-phase. Experiments revealed that sulfate exhibits an ion-specific enhancement on the hydration of glyoxal, which may help explain the enhanced partitioning coefficient of glyoxal in sulfate-containing solutions observed in previous work. The work has implications for the role of glyoxal in the atmosphere, especially for models of the contribution of glyoxal to SOA formation, and potentially for predictions of the behavior of other similar molecules in the atmosphere. These findings may also have broader implications for SOA formation and growth studies at high relative humidity, i.e. in the presence of aqueous aerosol.
