Photodegradation of Secondary Organic Aerosol Particles as a Source of Small, Oxygenated Volatile Organic Compounds

Abstract

We investigated the photodegradation of secondary organic aerosol (SOA) particles by near-UV radiation and photoproduction of oxygenated volatile organic compounds (OVOCs) from various types of SOA. We used a smog chamber to generate SOA from α-pinene, guaiacol, isoprene, tetradecane, and 1,3,5-trimethylbenzene under high-NOx, low-NOx, or ozone oxidation conditions. The SOA particles were collected on a substrate, and the resulting material was exposed to several mW of near-UV radiation (λ ∼ 300 nm) from a light-emitting diode. Various OVOCs, including acetic acid, formic acid, acetaldehyde, and acetone were observed during photodegradation, and their SOA-mass-normalized fluxes were estimated with a Proton Transfer Reaction Time-of-Flight Mass Spectrometer (PTR-ToF-MS). All the SOA, with the exception of guaiacol SOA, emitted OVOCs upon irradiation. Based on the measured OVOC emission rates, we estimate that SOA particles would lose at least ∼1% of their mass over a 24 h period during summertime conditions in Los Angeles, California. This condensed-phase photochemical process may produce a few Tg/year of gaseous formic acid, the amount comparable to its primary sources. The condensed-phase SOA photodegradation processes could therefore measurably affect the budgets of both particulate and gaseous atmospheric organic compounds on a global scale.

Oxidation of Volatile Organic Compounds as the Major Source of Formic Acid in a Mixed Forest Canopy

“…Other identified primary sources include agriculture (Ngwabie et al, 2008) and combustion of biomass (Chaliyakunnel et al, 2016;Goode et al, 2000) and fossil fuels (Kawamura et al, 1985;Talbot et al, 1988). Heterogeneous sources have also been proposed, including in-cloud formaldehyde oxidation (Jacob, 1986;Lelieveld & Crutzen, 1991), as well as aging of organic aerosol via OH (Vlasenko et al, 2008), O 3 (Eliason et al, 2003;Pan et al, 2009), and photolysis (Malecha & Nizkorodov, 2016;Park et al, 2006). Wet and dry deposition are the predominant HCOOH sinks; together with photochemical loss and a minor contribution from dust uptake, these yield an overall atmospheric lifetime of 2-4 days (Chebbi & Carlier, 1996;Paulot et al, 2011;Stavrakou et al, 2012).…”

Investigating the Tropospheric Chemistry of Acetic Acid Using the Global 3‐D Chemistry Transport Model, STOCHEM‐CRI

“…The photochemical degradation of secondary organic aerosol can be another source of CH 3 COOH in the urban areas (Malecha & Nizkorodov, 2016;Pan et al, 2009;Sareen et al, 2013). Considering the photolysis rate of SOA as J SOA = 4 × 10 À4 .J NO2 (Hodzic et al, 2015) yielding 100% CH 3 COOH, we examined the production of CH 3 COOH from the photodegradation of SOA from the STOCHEM model run (referred to as STOCH-ASOL) and found a negligible amounts of CH 3 COOH production globally (100 kg/year) from this reaction channel.…”

Assessment of carbonaceous aerosols in Shanghai, China – Part 1: long-term evolution, seasonal variations, and meteorological effects

“…Indeed, in contrast to EC, OC is the mixed product of primary emissions and secondary formation, which could vary significantly in different seasons. In summer, for example, strong solar radiation tends to facilitate photochemical reactions and thus enhance the formation of volatile organic compounds (VOCs) to organic aerosols (Tuet et al, 2017;Malecha and Nizkorodov, 2016). Burning of crop residues is also an important source of OC in China (Cheng et al, 2014;Hallquist et al, 2009;Zhang and Cao, 2015), while the burning activities are highly season dependent and mostly concentrated in fall (Chen et al, 2017b).…”