Aging of secondary organic aerosol from α-pinene ozonolysis: Roles of hydroxyl and nitrate radicals

Abstract

Secondary organic aerosol (SOA) may undergo aging processes once formed in the atmosphere, thereby altering the physicochemical and toxic properties of aerosol. This study discusses SOA aging of a major biogenic volatile organic compound (VOC; alpha-pinene) after it initially forms SOA. Aging of the alpha-pinene ozonolysis system by OH (through NO or H2O2 injection), NO3 (through N2O5 injection), and photolysis is observed. Although the reaction rate appears to be only sufficient to achieve semivolatile oxygenated organic aerosol (SV-OOA) level of oxygenation on a 1-day scale, it is important that SOA aging be considered in ambient air quality models. Aging in this study is attributed to further oxidation of gas-phase oxidation products of alpha-pinene ozonolysis.

Relating hygroscopicity and optical properties to chemical composition and structure of secondary organic aerosol particles generated from the ozonolysis of α-pinene

“…In particular, temperature and reaction timescales are critical parameters which can significantly affect the chemical composition of SOA (Warren et al, 2009;Shilling et al, 2008;Chhabra et al, 2010). Qi et al (2012) did not provide any uncertainty in their AMS measurements, but taking into account the uncertainties of ±30 % given by Aiken et al (2007), their O : Cs are in agreement with our values.…”

“…The bulk O : C retrieved in our study are in agreement with Shilling et al (2008), , Reinhardt et al (2007) and Tolocka et al (2006). Values at the beginning of the reaction are, however, higher than those obtained by Aiken et al (2007) and Qi et al (2012) who used AMS to retrieve the O : C. Limited information is given by Aiken et al (2007) about their experimental conditions. In particular, temperature and reaction timescales are critical parameters which can significantly affect the chemical composition of SOA (Warren et al, 2009;Shilling et al, 2008;Chhabra et al, 2010).…”

Secondary organic aerosol production from pinanediol, a semi-volatile surrogate for first-generation oxidation products of monoterpenes

“…However, ongoing oxidation must eventually fragment products and drive down the SOA mass because the end state of organic oxidation is CO 2 formation Chacon-Madrid et al, 2012;Donahue et al, 2013). There is considerable evidence that the ongoing oxidation chemistry can increase SOA mass and oxidation state, both from smog-chamber experiments (Donahue et al, 2012a;Henry and Donahue, 2012;Qi et al, 2012) and also from flow tubes that simulate many days of oxidation using intense UV radiation to drive photochemistry (Lambe et al, 2011;Wong et al, 2011;Cubison et al, 2011). The flow-tube results also confirm that oxidation will eventually cause mass loss via fragmentation .…”

Multi-generation chemical aging of <i>α</i>-pinene ozonolysis products by reactions with OH

“…Uncertainties such as "ripening" during which SOA volatility evolves but its mass remains constant, UV photolysis and heterogeneous OH uptake can further complicate the aging process. Qi et al (2012) also explored aging of the α-pinene ozonolysis system through smog chamber experiments using HOOH as an OH source and studied the UV photolysis effect. They observed a 7.5 % increase in the SOA volume concentration and an increase of 0.03 in the O : C after aging.…”