Abstract
Abstract. Atmospheric organic nitrate (ON) is thought to play a crucial role in the formation potential of ozone and aerosol, which are the leading air pollutants of concern across the world. Limited fundamental knowledge and understanding of the life cycles of ON currently hinder the ability to quantitatively assess its impacts on the formation of these pollutants. Although hydrolysis is currently considered an important loss mechanism of ON based on prior field measurement studies, this process for atmospherically relevant ON has not been well constrained by fundamental laboratory studies. In this comprehensive study, we investigated the chemical composition and hydrolysis process of particulate ON (pON) formed from the oxidation of α-pinene and β-pinene by hydroxyl (OH⚫) and nitrate radicals (NO3⚫). For pON that undergoes hydrolysis, the hydrolysis lifetime is determined to be no more than 30 min for all systems explored. This is significantly shorter than those reported in previous chamber studies (i.e., 3–6 h) but is consistent with the reported lifetime from bulk solution measurement studies (i.e., 0.02–8.8 h). The discrepancy appears to stem from the choice of proxy used to estimate the hydrolysis lifetime. The measured hydrolyzable fractions of pON (FH) in the α-pinene + OH⚫, β-pinene + OH⚫, α-pinene + NO3⚫, and β-pinene + NO3⚫ systems are 23 %–32 %, 27 %–34 %, 9 %–17 %, and 9 %–15 %, respectively. While a very low FH for the NO3⚫ oxidation system is expected based on prior studies, FH for the OH⚫ oxidation system is surprisingly lower than predicted in past studies. Overall, the hydrolysis lifetime as well as FH obtained in this study serve as experimentally constrained parameters that are required in regional and global chemical transport models to accurately evaluate the impacts of ON on nitrogen budget and formation of ozone and aerosol.
Highlights
The oxidation of biogenic volatile organic compounds (BVOCs) by trate radicals(iOs3a),mhayjdorrosxoyulrcraedoicf aslesco(OndHarq)y, and niorganic aerosol (SOA) globally (Kanakidou et al, 2005; Goldstein and Galbally, 2007; Spracklen et al, 2011)
Concerning the chemical composition of SOA from each system, a more distinct difference is observed between different oxidation conditions (i.e., OH q vs. NO3 q oxidation) than between different precursor VOC
A comparison of the ambient mass spectra with those obtained in this study reveals that average ambient particulate ON (pON) resembles daytime pON more than nighttime pON (Fig. S2). pON from daytime experiments has a distribution of masses centered around C10H13,15,17NO7, which is consistent with the ambient measurement data
Summary
The oxidation of biogenic volatile organic compounds (BVOCs) by trate radicals (oNzoOn3eq)(iOs3a),mhayjdorrosxoyulrcraedoicf aslesco(OndHarq)y, and niorganic aerosol (SOA) globally (Kanakidou et al, 2005; Goldstein and Galbally, 2007; Spracklen et al, 2011). Results from ambient field measurements have revealed the ubiquitous presence of particulate ON (pON), where it contributes to a large fraction of submicron organic aerosol at different sites worldwide (Fry et al, 2013; Xu et al, 2015b; Liu et al, 2012; Rollins et al, 2012, 2013; Lee et al, 2016; Kiendler-Scharr et al, 2016; Ng et al, 2017) These findings highlight the importance to understand the formation and fates of ON to accurately evaluate its roles in NOx recycling, O3 formation, and SOA formation. This comprehensive chamber study opnaththweayhsydorfolmysoinsootefrppOenNesparonddupceerdoxfryomradviacrailo(uRs Oo2xiq)daftaitoens provides the fundamental data to better constrain the role of hydrolysis in modulating pON concentrations and lifetimes in the atmosphere; their potential as a NOx loss pathway; and their impacts on overall nitrogen budget, O3 formation, and SOA formation
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