Effects of NO x and SO 2 on the secondary organic aerosol formation from photooxidation of α-pinene and limonene

Zhao, Defeng; Schmitt, Sebastian H.; Wang, Mingjin; Acir, Ismail-Hakki; Tillmann, Ralf; Tan, Zhaofeng; Novelli, Anna; Fuchs, Hendrik; Pullinen, Iida; Wegener, Robert; Rohrer, Franz; Wildt, Jürgen; Kiendler-Scharr, Astrid; Wahner, Andreas; Mentel, Thomas F.

Anthropogenic emissions such as NOinline-formulax and SOinline-formula2 influence the biogenic secondary organic aerosol (SOA) formation, but detailed mechanisms and effects are still elusive. We studied the effects of NOinline-formulax and SOinline-formula2 on the SOA formation from the photooxidation of inline-formulaα-pinene and limonene at ambient relevant NOinline-formulax and SOinline-formula2 concentrations (NOinline-formulax: < 1to 20 ppb, SOinline-formula2: < 0.05 to 15 ppb). In these experiments, monoterpene oxidation was dominated by OH oxidation. We found that SOinline-formula2 induced nucleation and enhanced SOA mass formation. NOinline-formulax strongly suppressed not only new particle formation but also SOA mass yield. However, in the presence of SOinline-formula2 which induced a high number concentration of particles after oxidation to Hinline-formula2SOinline-formula4, the suppression of the mass yield of SOA by NOinline-formulax was completely or partly compensated for. This indicates that the suppression of SOA yield by NOinline-formulax was largely due to the suppressed new particle formation, leading to a lack of particle surface for the organics to condense on and thus a significant influence of vapor wall loss on SOA mass yield. By compensating for the suppressing effect on nucleation of NOinline-formulax, SOinline-formula2 also compensated for the suppressing effect on SOA yield. Aerosol mass spectrometer data show that increasing NOinline-formulax enhanced nitrate formation. The majority of the nitrate was organic nitrate (57–77 %), even in low-NOinline-formulax conditions (< inline-formula∼ 1 ppb). Organic nitrate contributed 7–26 % of total organics assuming a molecular weight of 200 g molinline-formula−1. SOA from inline-formulaα-pinene photooxidation at high NOinline-formulax had a generally lower hydrogen to carbon ratio (H inline-formula∕ C), compared to low NOinline-formulax. The NOinline-formulax dependence of the chemical composition can be attributed to the NOinline-formulax dependence of the branching ratio of the ROinline-formula2 loss reactions, leading to a lower fraction of organic hydroperoxides and higher fractions of organic nitrates at high NOinline-formulax. While NOinline-formulax suppressed new particle formation and SOA mass formation, SOinline-formula2 can compensate for such effects, and the combining effect of SOinline-formula2 and NOinline-formulax may have an important influence on SOA formation affected by interactions of biogenic volatile organic compounds (VOCs) with anthropogenic emissions.

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Zhao, Defeng / Schmitt, Sebastian H. / Wang, Mingjin / et al: Effects of NOx and SO2 on the secondary organic aerosol formation from photooxidation of α-pinene and limonene. 2018. Copernicus Publications.

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