Model Analysis of Secondary Organic Aerosol Formation by Glyoxal in Laboratory Studies: The Case for Photoenhanced Chemistry

Abstract

The reactive uptake of glyoxal by atmospheric aerosols is believed to be a significant source of secondary organic aerosol (SOA). Several recent laboratory studies have been performed with the goal of characterizing this process, but questions remain regarding the effects of photochemistry on SOA growth. We applied GAMMA (McNeill et al. Environ. Sci. Technol. 2012, 46, 8075-8081), a photochemical box model with coupled gas-phase and detailed aqueous aerosol-phase chemistry, to simulate aerosol chamber studies of SOA formation by the uptake of glyoxal by wet aerosol under dark and irradiated conditions (Kroll et al. J. Geophys. Res. 2005, 110 (D23), 1-10; Volkamer et al. Atmos. Chem. Phys. 2009, 9, 1907-1928; Galloway et al. Atmos. Chem. Phys. 2009, 9, 3331- 306 3345 and Geophys. Res. Lett. 2011, 38, L17811). We find close agreement between simulated SOA growth and the results of experiments conducted under dark conditions using values of the effective Henry's Law constant of 1.3-5.5 × 10(7) M atm(-1). While irradiated conditions led to the production of some organic acids, organosulfates, and other oxidation products via well-established photochemical mechanisms, these additional product species contribute negligible aerosol mass compared to the dark uptake of glyoxal. Simulated results for irradiated experiments therefore fell short of the reported SOA mass yield by up to 92%. This suggests a significant light-dependent SOA formation mechanism that is not currently accounted for by known bulk photochemistry, consistent with recent laboratory observations of SOA production via photosensitizer chemistry.

simpleGAMMA v1.0 – a reduced model of secondary organic aerosol formation in the aqueous aerosol phase (aaSOA)

“…The role of UV light in aaSOA formation by glyoxal is unresolved (Galloway et al, 2009(Galloway et al, , 2011Volkamer et al, 2009;Kampf et al, 2013). A recent data analysis study using GAMMA (Sumner et al, 2014) suggested a possible role for photo-enhanced chemistry in aaSOA formation by glyoxal involving organic photosensitizers such as fulvic acid (Monge et al, 2012). This chemistry can be represented in simpleGAMMA by including irreversible glyoxal uptake with γ ∼ 10 −3 during sunlit hours, consistent with Fu et al (2008), who based their representation on the experiments of Liggio et al (2005), and with Waxman et al (2013).…”

“…The aqueous-phase species tracked in simpleGAMMA are IEPOX, glyoxal, 2-methyltetrol, and IEPOX organosulfate. Mass transfer between the gas and Sumner et al (2014) aerosol phases only occurs for IEPOX and glyoxal. The effective Henry's law constants (H * ) and accommodation coefficients used to describe uptake for these species are given in Table 1.…”

“…GAMMA represents aaSOA (SOA formation in aerosol water formation in terms of aqueous uptake followed by aqueous-phase reaction (Schwartz, 1986). GAMMA includes IEPOX chemistry following Eddingsaas et al (2010) and uses effective Henry's law constant, H * , constrained by aerosol chamber studies (Sumner et al, 2014) to describe glyoxal uptake and dark reactions, as well as detailed photochemical organosulfate formation and brown carbon formation from glyoxal, methylglyoxal, and acetaldehyde (Woo et al, 2013). For more information regarding other specific mechanisms included in GAMMA, as well as rate constants for these reactions and other physical parameters, the reader is referred to McNeill et al (2012) (including the Supplement) and Woo et al (2013).…”

On-road vehicle emissions of glyoxal and methylglyoxal from tunnel tests in urban Guangzhou, China

“…Although the direct emission of glyoxal and methylglyoxal from vehicle exhausts seemed much smaller when compared to that of toluene, they would also contribute substantially to SOA due to their higher SOA formation potentials (Liggio et al, 2005;Warneck, 2005;Yu et al, 2005). The SOA yields of glyoxal and methylglyoxal were 0.56e1.20 and 0.66e0.95, respectively, against that of 0.3 for toluene (Ng et al, 2007;Lim et al, 2013;Sumner et al, 2014), so SOA formed from vehicle-emitted glyoxal and methylglyoxal altogether could reach 25.3e49.5% of SOA formed from vehicle emitted toluene.…”

Aqueous-phase mechanism for secondary organic aerosol formation from isoprene: application to the southeast United States and co-benefit of SO<sub>2</sub> emission controls

“…Glyoxal forms SOA with higher yields during the day than at night due to OH aqueousphase chemistry (Tan et al, 2009;Volkamer et al, 2009;Sumner et al, 2014). We use a daytime γ of 2.9 × 10 −3 for glyoxal from Liggio et al (2005) and a nighttime γ of 5 × 10 −6 (Waxman et al, 2013;Sumner et al, 2014).…”