Secondary organic aerosol yields of 12-carbon alkanes

Abstract

Secondary organic aerosol (SOA) yields were measured for cyclododecane, hexylcyclohexane, n-dodecane, and 2-methylundecane under high-NOx conditions, in which alkyl proxy radicals (RO2) react primarily with NO, and under low-NOx conditions, in which RO2 reacts primarily with HO2. Experiments were run until 95-100% of the initial alkane had reacted. Particle wall loss was evaluated as two limiting cases using a new approach that requires only suspended particle number-size distribution data and accounts for size-dependent particle wall losses and condensation. SOA yield differed by a factor of 2 between the two limiting cases, but the same trends among alkane precursors were observed for both limiting cases. Vapor-phase wall losses were addressed through a modeling study and increased SOA yield uncertainty by approximately 30 %. SOA yields were highest from cyclododecane under both NOx conditions. SOA yields ranged from 3.3 % (dodecane, low-NOx conditions) to 160 % (cyclododecane, high-NOx conditions). Under high-NOx conditions, SOA yields increased from 2-methylundecane < dodecane similar to hexylcyclohexane < cyclododecane, consistent with previous studies. Under low-NOx conditions, SOA yields increased from 2-methylundecane similar to dodecane < hexylcyclohexane < cyclododecane. The presence of cyclization in the parent alkane structure increased SOA yields, whereas the presence of branch points decreased SOA yields due to increased vapor-phase fragmentation. Vapor-phase fragmentation was found to be more prevalent under high-NOx conditions than under low-NOx conditions. For different initial mixing ratios of the same alkane and same NOx conditions, SOA yield did not correlate with SOA mass throughout SOA growth, suggesting kinetically limited SOA growth for these systems

Influence of vapor wall loss in laboratory chambers on yields of secondary organic aerosol

“…The determined optimal k w values are consistent with theoretical estimates (SI Appendix, Vapor Wall Loss and Fig. S4) and some observations (11), but larger than some previous observations in the Caltech chamber (18), most likely reflecting the limited time resolution of those observations, which might not have allowed for separation of filling and mixing of the chamber from wall loss, but potentially also reflecting differences between chemical systems.…”

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

“…Nonetheless, the known products formed from the photooxidation of these hydrocarbons may provide some insight into the inflammatory responses observed. While there are no prior studies involving pentadecane oxidation products, it is expected that the oxidation products will be similar to those reported in the oxidation of dodecane (i.e., same functionalities with a longer carbon chain; Loza et al, 2014). It is therefore likely that pentadecane oxidation products resemble long chain fatty acids and could potentially insert into the cell membrane (Loza et al, 2014), as previous studies have shown that fatty acids can feasibly insert into the cell membrane bilayer (Khmelinskaia et al, 2014;Cerezo et al, 2011).…”

“…While there are no prior studies involving pentadecane oxidation products, it is expected that the oxidation products will be similar to those reported in the oxidation of dodecane (i.e., same functionalities with a longer carbon chain; Loza et al, 2014). It is therefore likely that pentadecane oxidation products resemble long chain fatty acids and could potentially insert into the cell membrane (Loza et al, 2014), as previous studies have shown that fatty acids can feasibly insert into the cell membrane bilayer (Khmelinskaia et al, 2014;Cerezo et al, 2011). This insertion could potentially affect membrane fluidity, which is known to affect cell function substantially although the specific effect depends strongly on the particular modification and cell type of interest (Baritaki et al, 2007;Spector and Yorek, 1985).…”

“…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.…”

The Caltech Photooxidation Flow Tube reactor: design, fluid dynamics and characterization

“…The CPOT has been constructed as a complement to the Caltech 24 m 3 batch chambers (Bates et al, , 2016Schilling et al, 2015;Hodas et al, 2015;Loza et al, 2013Loza et al, , 2014McVay et al, 2014McVay et al, , 2016Nguyen et al, 2014Nguyen et al, , 2015Schwantes et al, 2015;Yee et al, 2013;Zhang et al, 2014; in carrying out studies of SOA formation resulting from the oxidation of volatile organic compounds (VOCs) by oxidants OH, O 3 and NO 3 over timescales not accessible in a batch chamber. Due to its steady-state operation, the CPOT also affords the capability to collect sufficient quantities of SOA generated in the reactor for comprehensive composition determination by offline mass spectrometry.…”