Resolving Ambient Organic Aerosol Formation and Aging Pathways with Simultaneous Molecular Composition and Volatility Observations

Abstract

Organic aerosol (OA) constitutes a significant fraction of atmospheric fine particle mass. However, the precursors and chemical processes responsible for a majority of OA are rarely conclusively identified. We use online observations of hundreds of simultaneously measured molecular components obtained from 15 laboratory OA formation experiments with constraints on their effective saturation vapor concentrations to attribute the volatile organic compound (VOC) precursors and subsequent chemical pathways giving rise to the vast majority of OA mass measured in two forested regions. We find that precursors and chemical pathways regulating OA composition and volatility are dynamic over hours to days, with their variations driven by coupled interactions between multiple oxidants. The extent of physical and photochemical aging, and its modulation by NO x , was key to a uniquely comprehensive combined composition−volatility description of OA. Our findings thus provide some of the most complete mechanistic-level guidance to the development of OA descriptions in air quality and earth system models.

Impact of NO<sub><i>x</i></sub> on secondary organic aerosol (SOA) formation from <i>α</i>-pinene and <i>β</i>-pinene photooxidation: the role of highly oxygenated organic nitrates

“…We determined OrgNO 3 by the AMS as a diagnostic for ONs in the particulate phase. The OrgNO 3 mass fractions ranged from 0 % (no NO x addition) to 2.7 %, which is within the range 0.6 %-8 % of most literature data but at the lower end (Nozière et al, 1999;Rollins et al, 2010;Xu et al, 2015b;Berkemeier et al, 2016;B. H. Lee et al, 2016;Zhao et al, 2018 (Zhao et al, 2018).…”

“…There are some studies with respect to the SOA content of ON formed by photooxidation (Berkemeier et al, 2016;B. H. Lee et al, 2016;Nozière et al, 1999;Rollins et al, 2010;Takeuchi and Ng, 2019;Xu et al, 2015b;Zhao et al, 2018) wherein in most cases mass fraction of ONs of the total SOA mass is reported.…”

“…We suggest that the RH may be the key to bring this study and the results by Zhao et al (2018) in agreement, although we cannot provide further experimental proof. However, there are several studies implying that ONs undergo hydrolysis in the condensed phase (Bean and Hildebrandt Ruiz, 2016;Boyd et al, 2015;Browne et al, 2013;Day et al, 2010;Fisher et al, 2016;Jacobs et al, 2014;B. H. Lee et al, 2016;Liu et al, 2012;Rindelaub et al, 2016Rindelaub et al, , 2015.…”

The Aarhus Chamber Campaign on Highly Oxygenated Organic Molecules and Aerosols (ACCHA): particle formation, organic acids, and dimer esters from <i>α</i>-pinene ozonolysis at different temperatures

“…The boreal forests are considered abundant sources of α-pinene, with varying but sizeable emissions occurring all year round (Hakola et al, 2003(Hakola et al, , 2009Noe et al, 2012). In addition, Lee et al (2020) and Zhang et al (2018) show that monoterpeneoriginated SOA are the largest sources of particulate matter in the southeastern US. For this reason, the oxidation of αpinene and subsequent formation of SOA is expected to occur at conditions with a wide range of VOC concentrations and atmospheric temperatures.…”

“…Furthermore, Pathak et al (2007) observed that α-pinene SOA yields showed a weak dependence on temperature in the 15 to 40 • C range, implying that the negative temperature dependence of the partitioning is counteracted by a positive dependence of the chemical reaction mechanism. Multiple studies report on new particle formation arising from the oxidation of α-pinene and suggest the formation of so-called extremely low volatility organic compounds (ELVOC; Donahue et al, 2012b) capable of gas-toparticle conversion (Bonn and Moorgat, 2002;Lee and Kamens, 2005;Gao et al, 2010;Tolocka et al, 2006;Claeys et al, 2009;Ehn et al, 2014;Metzger et al, 2010;Kirkby et al, 2016;Bianchi et al, 2019). Although the chemical composition of α-pinene SOA has been extensively studied, uncertainty still remains regarding the chemical structure and functional groups of the compounds responsible for nucleation.…”