SOA formation from naphthalene, 1-methylnaphthalene, and 2-methylnaphthalene photooxidation

Abstract

h i g h l i g h t sHigh SOA yields from 2-ring PAH photooxidation were found. Fractal-like and solid SOA was observed for the methylnaphthalene isomers during high NO x photooxidation. A m/z 104 peak was observed as a marker of phthalic acid from PAH photoxidation by HR-ToF-AMS analysis. a r t i c l e i n f o b s t r a c tThe SOA yield and chemical characteristics of SOA formation from naphthalene and two methyl substituted naphthalenes, 1-methylnaphthalene and 2-methylnaphthalene, were studied for high NO x , low NO x , and ultra-low NO x conditions. The SOA yields are high compared to previous studies for all three PAHs precursors: 1-methylnaphthalene > 2-methylnaphthalene~naphthalene for all atmospheric conditions studied. The SOA yields range from 0.03 to 0.60 for naphthalene, 0.21e1.52 for 1-methylnaphthalene, and 0.34e0.55 for 2-methylnaphthalene under high NO x with HONO (initial PAH:NO ratio ¼ 0.03e0.17) conditions. The SOA yield ranges from 0.04 to 0.31 for naphthalene, 0.14e0.72 for 1-methylnaphthalene, and 0.06e0.49 for 2-methylnaphthalene under low NO x (initial PAH:NO ratio ¼ 0.54e2.20) conditions. SOA yields were substantially greater than 1.0 under H 2 O 2 (ultra low NO x ) and low NO x þ H 2 O 2 conditions for all three PAH precursors. The system reactivity influenced by OH radicals, NO x levels, initial PAH/NO ratios, NO 2 /NO ratios, and all impacted the SOA formation from the PAH precursors. Fractal-like SOA is observed for the methylnaphthalene isomers during high NO x photooxidation experiments, implying that researchers studying SOA formation from this precursor must carefully account for particle shape or effective density. A m/z 104 (C 7 H 4 O þ ,104.026) peak, consistent with SOA products phthalic acid from earlier studies, was observed as a potential marker of PAH oxidation during HR-ToF-AMS analysis.

Gas- and particle-phase products from the photooxidation of acenaphthene and acenaphthylene by OH radicals

“…Indeed, Shakya and Griffin (2010) proposed yields in the range of 0.08e0.16, while Chan et al (2009) determined yields to be 0.19e0.74. As discussed by Chen et al (2016), differences of SOA yields could be attributed to different chamber conditions such as light intensity, NO x levels, OH radicals, and organic mass loading. In the case of aromatic chemistry, it has been shown that photolysis processes play a major role in the loss of carbonyl products (Wang et al, 2006;Clifford et al, 2011).…”

“…Although PAHs are potentially carcinogenic and mutagenic (Atkinson and Arey, 1994) some of their oxidation products present a larger toxicity than their parent hydrocarbons (Lin et al, 2005). Gas-phase products can partition to the particle phase and participate in SOA formation Kautzman et al, 2010;Shakya and Griffin, 2010;Kleindienst et al, 2012;Riva et al, 2015aRiva et al, , 2016Chen et al, 2016). A few studies have previously reported the importance of naphthalene gas phase photooxidation in SOA formation Kleindienst et al, 2012).…”

Secondary organic aerosol from atmospheric photooxidation of indole

“…The yield is higher than that for SOA formed from another bicyclic aromatic compound, naphthalene, which has a reported yield range of 0.04-0.73 under low-NO x conditions (Chan et al, 2009;Chen et al, 2016). The high yield suggests that the major fraction of indole oxidation products ends up in the particle phase at the concentrations used in this work.…”

“…The amount of the collected SOA material on each filter was estimated from SMPS data assuming 100 % collection efficiency by the filters and SOA material density of 1.4 g cm −3 . The density of indole SOA is unknown, but the adopted value of 1.4 g cm −3 is similar to the reported range of densities of 1.47-1.55 g cm −3 for SOA prepared from another bicyclic aromatic compound, naphthalene (Chan et al, 2009;Chen et al, 2016). In addition, densities of known indole oxidation products, for example isatin (1.47 g cm −3 ), anthranilic acid (1.40 g cm −3 ), indigo dye (1.20 g cm −3 ), isatoic anhydride (1.52 g cm −3 ), and 3-oxindole (1.20 g cm −3 ), range from 1.2 to 1.5 g cm −3 , suggesting that 1.4 g cm −3 should be a reasonable guess for indole SOA.…”

“…Henry's law constants are calculated according to the group contribution method of Suzuki et al (1992). Several studies have used the UCI-CIT model to investigate SOA formation, dynamics, reactivity, and partitioning phase preference in the SoCAB (Carreras-Sospedra et al, 2005;Chang et al, 2010;Cohan et al, 2013;Dawson et al, 2016;Griffin et al, 2002b;Vutukuru et al, 2006). For a more detailed description of recent model developments incorporated into the UCI-CIT model and its SOA modules, the reader is referred to Dawson et al (2016).…”