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Title: Comparison of secondary organic aerosol generated from the oxidation of laboratory precursors by hydroxyl radicals, chlorine atoms, and bromine atoms in an oxidation flow reactor
The role of hydroxyl radicals (OH) as a daytime oxidant is well established on a global scale. In specific source regions, such as the marine boundary layer and polluted coastal cities, other daytime oxidants, such as chlorine atoms (Cl) and even bromine atoms (Br), may compete with OH for the oxidation of volatile organic compounds (VOCs) and/or enhance the overall oxidation capacity of the atmosphere. However, the number of studies investigating halogen-initiated secondary organic aerosol (SOA) formation is extremely limited, resulting in large uncertainties in these oxidative aging processes. Here, we characterized the chemical composition and yield of laboratory SOA generated in an oxidation flow reactor (OFR) from the OH and Cl oxidation of n -dodecane ( n -C 12 ) and toluene, and the OH, Cl, and Br oxidation of isoprene and α-pinene. In the OFR, precursors were oxidized using integrated OH, Cl, and Br exposures ranging from 3.1 × 10 10 to 2.3 × 10 12 , 6.1 × 10 9 to 1.3× 10 12 and 3.2 × 10 10 to 9.7 × 10 12 molecules cm −3 s −1 , respectively. Like OH, Cl facilitated multistep SOA oxidative aging over the range of OFR conditions that were more » studied. In contrast, the extent of Br-initiated SOA oxidative aging was limited. SOA elemental ratios and mass yields obtained in the OFR studies were comparable to those obtained from OH and Cl oxidation of the same precursors in environmental chamber studies. Overall, our results suggest that alkane, aromatic, and terpenoid SOA precursors are characterized by distinct OH- and halogen-initiated SOA yields, and that while Cl may enhance the SOA formation potential in regions influenced by biogenic and anthropogenic emissions, Br may have the opposite effect. « less
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Award ID(s):
1934352 1934369
Publication Date:
Journal Name:
Environmental Science: Atmospheres
Page Range or eLocation-ID:
687 to 701
Sponsoring Org:
National Science Foundation
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