α-pinene photooxidation under controlled chemical conditions – Part 2: SOA yield and composition in low- and high-NO<sub>x</sub> environments

Abstract

Abstract. The gas-phase oxidation of α-pinene produces a large amount of secondary organic aerosol (SOA) in the atmosphere. A number of carboxylic acids, organosulfates and nitrooxy organosulfates associated with α-pinene have been found in field samples and some are used as tracers of α-pinene oxidation. α-pinene reacts readily with OH and O 3 in the atmosphere followed by reactions with both HO 2 and NO. Due to the large number of potential reaction pathways, it can be difficult to determine what conditions lead to SOA. To better understand the SOA yield and chemical composition from low-and high-NO x OH oxidation of α-pinene, studies were conducted in the Caltech atmospheric chamber under controlled chemical conditions. Experiments used low O 3 concentrations to ensure that OH was the main oxidant and low α-pinene concentrations such that the peroxy radical (RO 2 ) reacted primarily with either HO 2 under low-NO x conditions or NO under high-NO x conditions. SOA yield was suppressed under conditions of high-NO x . SOA yield under high-NO x conditions was greater when ammonium sulfate/sulfuric acid seed particles (highly acidic) were present prior to the onset of growth than when ammonium sulfate seed particles (mildly acidic) were present; this dependence was not observed under low-NO x conditions. When aerosol seed particles were introduced after OH oxidation, allowing for later generation species to be exposed to fresh inorganic seed particles, a number of low-NO x products partitioned to the highly acidic aerosol. This indicates that the effect of seed acidity and SOA yield might be under-estimated in traditional experiments where aerosol seed particles are introduced prior to oxidation. We also identify the presence of a number of carboxylic acids that are used as tracer compounds of α-pinene oxidation in the field as well as the formation of organosulfates and nitrooxy organosulfates. A number of the carboxylic acids were observed under all conditions, however, pinic and pinonic acid were only observed under low-NO x conditions. Evidence is provided for particle-phase sulfate esterification of multi-functional alcohols.

Dithiothreitol activity by particulate oxidizers of SOA produced from photooxidation of hydrocarbons under varied NO<sub><i>x</i></sub> levels

“…As shown in Table 1, the Y values of toluene, TMB, isoprene, and α-pinene SOA ranged from 5 to 15, 6 to 8, 1 to 5, and 14 to 36 %, respectively. Except isoprene SOA, the SOA yields in this study were consistent with those reported in previous studies (Eddingsaas et al, 2012a;Healy et al, 2008;Odum et al, 1996;Sato et al, 2007). Our SOA yields for isoprene SOA were lower than those reported in other studies (Carlton et al, 2009;Xu et al, 2014) because the temperatures in our outdoor experiments were higher than those sourced from indoor chambers.…”

Inflammatory responses to secondary organic aerosols (SOA) generated from biogenic and anthropogenic precursors

“…Indeed, there are several similarities between products formed from the photooxidation of α-pinene and m-xylene. For instance, a large portion of α-pinene and m-xylene oxidation products under both RO 2 + HO 2 and RO 2 + NO pathways are ring-breaking products with a similar carbon chain length (Eddingsaas et al, 2012;Vivanco and Santiago, 2010;Jenkin et al, 2003). As a result of this similarity, products from both SOA systems may interact with the same cellular targets and induce similar cellular pathways, resulting in a similar response regardless of precursor identity and formation condition.…”

“…The selected biogenic precursors include isoprene, the most abundant non-methane hydrocarbon (Guenther et al, 2006); α-pinene, a well-studied monoterpene with emissions on the order of global anthropogenic emissions (Guenther et al, 1993;Piccot et al, 1992); and β-caryophyllene, a representative sesquiterpene. Both monoterpenes and sesquiterpenes have been shown to contribute significantly to ambient aerosol (Eddingsaas et al, 2012;Hoffmann et al, 1997;Tasoglou and Pandis, 2015;Goldstein and Galbally, 2007). Similarly, the anthropogenic precursors include pentadecane, a long-chain alkane; m-xylene, a singlering aromatic; and naphthalene, a polyaromatic.…”

“…These com-pounds are emitted as products of incomplete combustion (Robinson et al, 2007;Jia and Batterman, 2010; and have considerable SOA yields Ng et al, 2007b;Lambe et al, 2011). In addition to precursor identity, the effects of humidity (dry vs. humid) and NO x levels (different predominant peroxy radical, RO 2 , fates; RO 2 + HO 2 vs. RO 2 + NO) on SOA cellular inflammatory responses were investigated, as different formation conditions have been shown to affect aerosol chemical composition and mass loading, which could in turn result in a different cellular response Eddingsaas et al, 2012;Ng et al, 2007a, b;Loza et al, 2014;Chan et al, 2009;Boyd et al, 2015). Finally, correlations between bulk aerosol composition, specifically elemental ratios, and cellular inflammatory responses were investigated to determine whether there is a link between different inflammatory responses and aerosol composition.…”

Elemental composition and clustering behaviour of α-pinene oxidation products for different oxidation conditions

“…In boreal forests, α-pinene is the most abundant monoterpene. It has been extensively studied in laboratory experiments during the past decades due to its large SOA formation potential (Hoppel et al, 2001; Lee and Kamens, 2005;Eddingsaas et al, 2012a). Several oxidation pathways are known (see Fig.…”