Abstract

Abstract. The effect of NO2 on secondary organic aerosol (SOA) formation from ozonolysis of α-pinene, β-pinene, Δ3-carene, and limonene was investigated using a dark flow-through reaction chamber. SOA mass yields were calculated for each monoterpene from ozonolysis with varying NO2 concentrations. Kinetics modeling of the first-generation gas-phase chemistry suggests that differences in observed aerosol yields for different NO2 concentrations are consistent with NO3 formation and subsequent competition between O3 and NO3 to oxidize each monoterpene. α-Pinene was the only monoterpene studied that showed a systematic decrease in both aerosol number concentration and mass concentration with increasing [NO2]. β-Pinene and Δ3-carene produced fewer particles at higher [NO2], but both retained moderate mass yields. Limonene exhibited both higher number concentrations and greater mass concentrations at higher [NO2]. SOA from each experiment was collected and analyzed by HPLC-ESI-MS, enabling comparisons between product distributions for each system. In general, the systems influenced by NO3 oxidation contained more high molecular weight products (MW > 400 amu), suggesting the importance of oligomerization mechanisms in NO3-initiated SOA formation. α-Pinene, which showed anomalously low aerosol mass yields in the presence of NO2, showed no increase in these oligomer peaks, suggesting that lack of oligomer formation is a likely cause of α-pinene's near 0 % yields with NO3. Through direct comparisons of mixed-oxidant systems, this work suggests that NO3 is likely to dominate nighttime oxidation pathways in most regions with both biogenic and anthropogenic influences. Therefore, accurately constraining SOA yields from NO3 oxidation, which vary substantially with the volatile organic compound precursor, is essential in predicting nighttime aerosol production.

Highlights

  • Secondary organic aerosol (SOA) forms in the atmosphere from oxidized volatile organic compounds (VOCs) that are of low enough volatility to be able to partition into the condensed phase

  • These comparisons nicely illustrate the vast diversity of the behavior of each monoterpene with respect to systematically changing oxidant conditions, from O3 dominated to NO3 dominated. α-Pinene exhibits a decrease in both the total number of particles produced (Ntot) and total aerosol volume produced (Vtot) with increasing NO2, consistent with the findings of other studies (Perraud et al, 2012; Presto et al, 2005). β-Pinene and 3-carene both exhibit a similar decrease in Ntot with addition of NO2 as α-pinene, but at early times in the reaction, the addition of NO2 appears to enhance volume growth relative to the O3-only experiment

  • While all three of the monoalkene monoterpenes produce fewer particles at higher [NO2], α-pinene is the only terpene for which the aerosol production seems to be systematically depleted with the addition of NO2. β-Pinene and

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Summary

Introduction

Secondary organic aerosol (SOA) forms in the atmosphere from oxidized volatile organic compounds (VOCs) that are of low enough volatility to be able to partition into the condensed phase. SOA constitutes a large fraction of the total aerosol budget, but it is still poorly constrained in global chemical transport models, which underpredict ambient aerosol concentrations by 1 to 2 orders of magnitude (Heald et al, 2005, 2011). These models use laboratory-derived parameters, but uncertainty in precursors, detailed mechanisms, and mechanistic differences between chamber simulations and the real atmosphere result in the vast discrepancies between models and observations (Kroll and Seinfeld, 2008; Hallquist et al, 2009).

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