Abstract
Abstract. Isoprene oxidation by nitrate radical (NO3) is a potentially important source of secondary organic aerosol (SOA). It is suggested that the second or later-generation products are the more substantial contributors to SOA. However, there are few studies investigating the multi-generation chemistry of isoprene-NO3 reaction, and information about the volatility of different isoprene nitrates, which is essential to evaluate their potential to form SOA and determine their atmospheric fate, is rare. In this work, we studied the reaction between isoprene and NO3 in the SAPHIR chamber (Jülich) under near-atmospheric conditions. Various oxidation products were measured by a high-resolution time-of-flight chemical ionization mass spectrometer using Br− as the reagent ion. Most of the products detected are organic nitrates, and they are grouped into monomers (C4 and C5 products) and dimers (C10 products) with 1–3 nitrate groups according to their chemical composition. Most of the observed products match expected termination products observed in previous studies, but some compounds such as monomers and dimers with three nitrogen atoms were rarely reported in the literature as gas-phase products from isoprene oxidation by NO3. Possible formation mechanisms for these compounds are proposed. The multi-generation chemistry of isoprene and NO3 is characterized by taking advantage of the time behavior of different products. In addition, the vapor pressures of diverse isoprene nitrates are calculated by different parametrization methods. An estimation of the vapor pressure is also derived from their condensation behavior. According to our results, isoprene monomers belong to intermediate-volatility or semi-volatile organic compounds and thus have little effect on SOA formation. In contrast, the dimers are expected to have low or extremely low volatility, indicating that they are potentially substantial contributors to SOA. However, the monomers constitute 80 % of the total explained signals on average, while the dimers contribute less than 2 %, suggesting that the contribution of isoprene NO3 oxidation to SOA by condensation should be low under atmospheric conditions. We expect a SOA mass yield of about 5 % from the wall-loss- and dilution-corrected mass concentrations, assuming that all of the isoprene dimers in the low- or extremely low-volatility organic compound (LVOC or ELVOC) range will condense completely.
Highlights
Atmospheric submicron aerosols have an adverse effect on air quality, human health, and climate (Jimenez et al, 2009; Pöschl, 2005)
We present the results of chamber experiments on isoprene oxidation by NO3 under near-atmospheric conditions, where NO3 was produced in situ by O3 reaction with NO2
Considering the fact that the existing GC methods tend to underestimate saturation vapor pressures of the highly functionalized organic molecules due to their limited capability to deal with intramolecular interactions, and the consistent results of two experimentally derived methods, we suggest that the experimental method might be a good choice to determine the volatility of highly oxidized compounds accurately
Summary
Atmospheric submicron aerosols have an adverse effect on air quality, human health, and climate (Jimenez et al, 2009; Pöschl, 2005). Due to its high abundance, as well as its high reactivity with atmospheric oxidants, isoprene plays a significant role in tropospheric chemistry, and its chemistry affects the global aerosol burden and distribution (Carlton et al, 2009; Fry et al, 2018; Ng et al, 2008, 2017; Surratt et al, 2010), its SOA yield is much lower than those of monoterpenes and sesquiterpenes (Friedman and Farmer, 2018; Kim et al, 2015; Marais et al, 2016; McFiggans, et al, 2019; Mutzel et al, 2016; Ng et al, 2007, 2008; Surratt et al, 2010; Thornton et al, 2020). It is essential to fully characterize the potential of isoprene to form condensable products and its contribution to SOA formation (Carlton et al, 2009)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
