Abstract
Abstract. The formation of organic nitrates and secondary organic aerosol (SOA) were monitored during the NO3 + limonene reaction in the atmosphere simulation chamber SAPHIR at Research Center Jülich. The 24-h run began in a purged, dry, particle-free chamber and comprised two injections of limonene and oxidants, such that the first experiment measured SOA yield in the absence of seed aerosol, and the second experiment yields in the presence of 10 μg m−3 seed organic aerosol. After each injection, two separate increases in aerosol mass were observed, corresponding to sequential oxidation of the two limonene double bonds. Analysis of the measured NO3, limonene, product nitrate concentrations, and aerosol properties provides mechanistic insight and constrains rate constants, branching ratios and vapor pressures of the products. The organic nitrate yield from NO3 + limonene is ≈30%. The SOA mass yield was observed to be 25–40%. The first injection is reproduced by a kinetic model. PMF analysis of the aerosol composition suggests that much of the aerosol mass results from combined oxidation by both O3 and NO3, e.g., oxidation of NO3 + limonene products by O3. Further, later aerosol nitrate mass seems to derive from heterogeneous uptake of NO3 onto unreacted aerosol alkene.
Highlights
Biogenic volatile organic compounds (BVOCs) make up a large fraction of gas-phase organic compounds emitted to the atmosphere: on a global scale, vegetation emissions of VOCs are an order of magnitude greater than those from
If NO3-initiated aerosol formation from biogenic VOCs is a significant contribution to organic aerosol loading in the atmosphere, this would provide a potential resolution to a paradox noted in the secondary organic aerosol (SOA) literature: 14C measurements show the carbon in organic aerosol to be primarily modern, which is characteristic of natural emissions, from urban (≈50%) to remote areas (80–100%) (Schichtel et al, 2008)
NO2 was measured by laser-induced fluorescence (LIF) and total peroxynitrates ( PNs), total alkyl and multifunctional nitrates ( ANs), and nitric acid (HNO3) were determined using thermal dissociation to NO2 in heated quartz ovens held at different temperatures (“NO2-TD-LIF”) (Thornton et al, 2000; Day et al, 2002)
Summary
Biogenic volatile organic compounds (BVOCs) make up a large fraction of gas-phase organic compounds emitted to the atmosphere: on a global scale, vegetation emissions of VOCs are an order of magnitude greater than those from. NO3 produced BVOC SOA resolves the paradox by requiring both an anthropogenic oxidant “trigger” and biogenic VOC to form aerosol (Hoyle et al, 2011) This mechanism of SOA formation is expected to be most significant in forested areas downwind of urban centers or power plants, where NOx is high and biogenic VOCs are abundant (Pye et al, 2010). Limonene is of interest as a representative BVOC both due to its high emission rate among monoterpenes (Sakulyanontvittaya et al, 2008) and its possession of two double bonds These two reactive sites for oxidation give limonene a rapid and direct route to the types of lowvapor pressure oxidized products that are likely to form secondary organic aerosol. We report chamber measurements and kinetic modeling of gas- and aerosol-phase chemistry during SOA formation initiated by the NO3 + limonene reaction under excess oxidants
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