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Trends in the oxidation and relative volatility of chamber-generated secondary organic aerosol
Citation:
Docherty, K., E. Corse, M. Jaoui, J. Offenberg, Tad Kleindienst, J. Krug, T. Riedel, AND M. Lewandowski. Trends in the oxidation and relative volatility of chamber-generated secondary organic aerosol. AEROSOL SCIENCE AND TECHNOLOGY. Taylor & Francis, Inc., Philadelphia, PA, 52(9):992-1004, (2018). https://doi.org/10.1080/02786826.2018.1500014
Impact/Purpose:
Atmospheric particulate matter impacts global climate and visibility through its ability to absorb and scatter radiation and increases both morbidity and mortality in susceptible populations [Pope and Dockery, 2006]. The role of particles in these processes is influenced by both particle size and chemical composition, with many of these effects being correlated with fine particles (PMf, defined as particles having an aerodynamic diameter, da, <2.5 μm or <1 μm). While effective PMf control strategies rely on complete characterization of the sources, composition, and formation mechanisms of ambient aerosol, significant gaps remain with respect to aerosol composition and formation mechanisms. PMf is a complex mixture comprised of organic and inorganic species either directly emitted from combustion sources or formed through chemical reactions with trace contributions from wind-blown fugitive dust and crustal materials. Sources and production of individual species comprising the inorganic fraction are relatively well characterized. The organic aerosol (OA) fraction which contributes the bulk of PMf mass on a global scale [Zhang et al., 2007] remains poorly characterized.
Description:
The relationship between the oxidation state and relative volatility of secondary organic aerosol (SOA) from the oxidation of a wide range of hydrocarbons is investigated using a fast-stepping, scanning thermodenuder interfaced with a high-resolution time-of-flight aerosol mass spectrometer (AMS). SOA oxidation state varied widely across the investigated range of parent hydrocarbons but was relatively stable for replicate experiments using a single hydrocarbon precursor. On average, unit mass resolution indicators of SOA oxidation (e.g., AMS f43 and f44) are consistent with previously reported values. Linear regression of H:C vs. O:C obtained from parameterization of f43 and f44 and elemental analysis of high-resolution spectra in Van Krevelen space both yield a slope of ∼−0.5 across different SOA types. A similar slope was obtained for a distinct subset of toluene/NOx reactions in which the integrated oxidant exposure was varied to alter oxidation. The relative volatility of different SOA types displays similar variability and is strongly correlated with SOA oxidation state (C). On average, relatively low oxidation and volatility were observed for aliphatic alkene (including terpenes) and n-alkane SOA while the opposite is true for mono- and polycyclic aromatic hydrocarbon SOA. Effective enthalpy for total chamber aerosol obtained from volatility differential mobility analysis is also highly correlated with C indicating a primary role for oxidation levels in determining the volatility of chamber SOA. Effective enthalpies for chamber SOA are substantially lower than those of neat organic standards but are on the order of those obtained for partially oligomerized glyoxal and methyl glyoxal.
URLs/Downloads:
DOI: Trends in the oxidation and relative volatility of chamber-generated secondary organic aerosol