Secondary organic aerosol and organic nitrogen yields from the nitrate radical (NO<sub>3</sub>) oxidation of alpha-pinene from various RO<sub>2</sub> fates

Abstract

Abstract. The reaction of α-pinene with NO3 is an important sink of both α-pinene and NO3 at night in regions with mixed biogenic and anthropogenic emissions; however, there is debate on its importance for secondary organic aerosol (SOA) and reactive nitrogen budgets in the atmosphere. Previous experimental studies have generally observed low or zero SOA formation, often due to excessive [NO3] conditions. Here, we characterize the SOA and organic nitrogen formation from α-pinene + NO3 as a function of nitrooxy peroxy (nRO2) radical fates with HO2, NO, NO3, and RO2 in an atmospheric chamber. We show that SOA yields are not small when the nRO2 fate distribution in the chamber mimics that in the atmosphere, and the formation of pinene nitrooxy hydroperoxide (PNP) and related organonitrates in the ambient atmosphere can be reproduced. Nearly all SOA from α-pinene + NO3 chemistry derives from the nRO2+ RO2 pathway, which alone has an SOA mass yield of 56 (±7) %. Molecular composition analysis shows that particulate nitrates are a large (60 %–70 %) portion of the SOA and that dimer formation is the primary mechanism of SOA production from α-pinene + NO3 under simulated nighttime conditions. Synergistic dimerization between nRO2 and RO2 derived from ozonolysis and OH oxidation also contribute to SOA formation and should be considered in models. We report a 58 (±20) % molar yield of PNP from the nRO2+ HO2 pathway. Applying these laboratory constraints to model simulations of summertime conditions observed in the southeast United States (where 80 % of α-pinene is lost via NO3 oxidation, leading to 20 % nRO2+ RO2 and 45 % nRO2+ HO2), we estimate yields of 11 % SOA and 7 % particulate nitrate by mass and 26 % PNP by mole from α-pinene + NO3 in the ambient atmosphere. These results suggest that α-pinene + NO3 significantly contributes to the SOA budget and likely constitutes a major removal pathway of reactive nitrogen from the nighttime boundary layer in mixed biogenic–anthropogenic areas.

Identification of highly oxygenated organic molecules and their role in aerosol formation in the reaction of limonene with nitrate radical

“…The RO q 2 loss pathway in our study was dominated by the reactions RO q 2 + NO 3 and RO q 2 + RO q 2 , which is relevant for the RO q 2 fate in urban areas and forested areas influenced by an urban plume at nighttime. However, in more pristine forested regions, the RO q 2 fate is mostly determined by RO q 2 + HO 2 and RO q 2 + RO q 2 , as shown by Bates et al (2022) for the example of a Southeast US forest. As NO 3 concentration is generally enhanced with increased anthropogenic emissions, RO q 2 + NO 3 will become more important going from remote to urban areas.…”

“…The reaction of NO 3 with monoterpenes can form secondary organic aerosols (SOAs), which can have a large impact on global climate, air quality, and human health (Hallquist et al, 2009;Shrivastava et al, 2017). Laboratory studies showed that monoterpenes have high SOA yields in the reaction with NO 3 due to the low volatility of oxidation products (Ng et al, 2008;Rollins et al, 2009;Fry et al, 2013Fry et al, , 2014Ayres et al, 2015;Jokinen et al, 2015;Zhou et al, 2015;Boyd et al, 2015;Nah et al, 2016;Boyd et al, 2017;Slade et al, 2017;Claflin and Ziemann, 2018;Bates et al, 2022;Dam et al, 2022). Field studies also showed that nighttime NO 3 -initiated oxidation of monoterpenes contributes significantly to SOA in forested regions influenced by anthropogenic emissions (Pye et al, 2010;Rollins et al, 2012;Fry et al, 2013;Ayres et al, 2015;Zhou et al, 2015;Xu et al, 2015;Lee et al, 2016;Zhang et al, 2018;Chen et al, 2020) and potentially in urban areas due to the extensive usage of so-called volatile chemical products (VCPs) (Nazaroff and Weschler, 2004;McDonald et al, 2018).…”

Modeling Diurnal Variation of SOA Formation via Multiphase Reactions of Biogenic Hydrocarbons

“…Additionally, the recently identified oxidation mechanisms that can yield low volatile products were also integrated with MCM. For example, the Peroxy Radical Autoxidation Mechanism (PRAM) (Roldin et al, 2019) that forms the highly oxygenated organic molecule (HOM) (Molteni et al, 2019) and the accretion reaction to form ROOR from the RO2 (Bates et al, 2022;Zhao et al, 2021) were added. Furthermore, the oxidation 145 process of biogenic HCs by O( 3 P) (Paulson et al, 1992;Alvarado et al, 1998) was included to fulfill the oxidation mechanism in the current regional model.…”

“…4, the NO3-initiated reaction of α-pinene produces a considerable amount of SOA under darkness. The addition of NO3 to the alkene double bond of α-pinene is followed by the addition of an oxygen molecule to form an alkylperoxy radical that can lead to low-volatile peroxide accretion products (ROOR) (Hasan et al, 2021;Bates et al, 2022).…”

“…Figure 4 also shows the SOA potentials at the two different NOx levels for each oxidation path. Overall, the NO3-initiated SOA yield drops in decreasing the NOx level, because the RO2 that forms via the reaction of biogenic HC with NO3 radical followed 280 by the addition of an oxygen molecule can react with HO2 radicals to form organic hydroperoxide, which yields little SOA mass (Bates et al, 2022;Ng et al, 2008). At the low NOx level, the oxidation of HCs with the OH radical tends to form a large amount of SOA mass.…”