Molecular composition and volatility of multi-generation products formed from isoprene oxidation by nitrate radical

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.

Photolytically induced changes in composition and volatility of biogenic secondary organic aerosol from nitrate radical oxidation during night-to-day transition

“…ONs also play an important role in the removal and transport of nitrogen oxides (NO x ), and impact NO x cycling and O 3 formation (Perring et al, 2013). While the lifetime of aerosols in the atmosphere typically spans over multiple day-night cycles, the lifetime of ONs within particles is much shorter (Lee et al, 2016;Zare et al, 2018). Reactions influencing particulate lifetime of ONs include oxidation, hydrolysis (Pye et al, 2015;Takeuchi and Ng, 2019), and photolysis (Müller et al, 2014;Suarez-Bertoa et al, 2012).…”

Impact of ozone and inlet design on the quantification of isoprene-derived organic nitrates by thermal dissociation cavity ring-down spectroscopy (TD-CRDS)

“…This suggests that the ozonolysis of isoprene may play an important role. As the reaction between isoprene and O 3 leads to the formation of OH and additional HO 2 (Zhang et al, 2002;Malkin et al, 2010;Cox et al, 2020), the fraction of RO 2 reacting with HO 2 in this system is enhanced when compared to the experiments in which NO 3 was generated from N 2 O 5 . The major product from the reaction between nitrated δand β-peroxy radicals with HO 2 is hydroperoxides, such as O 2 NOCH 2 C(CH 3 )=CHCH 2 OOH (Schwantes et al, 2015).…”

A Four Carbon Organonitrate as a Significant Product of Secondary Isoprene Chemistry

“…The comprehensive nighttime isoprene chemistry study was conducted in August 2018 in the atmospheric simulation chamber SAPHIR (Section S1 in Supporting Information S1) (Fuchs et al, 2017;Rohrer et al, 2005) at Forschungszentrum Jülich, Germany (Brownwood et al, 2021;Dewald et al, 2020;Vereecken et al, 2021;Wu et al, 2021). One goal of the campaign was to explore different oxidation regimes by applying conditions enhancing the contribution of different reaction pathways (i.e., RO 2 + RO 2 , RO 2 + HO 2 or unimolecular RO 2 ).…”

“…The dominant gas phase nitrated oxidation products from isoprene + NO 3 include compounds like isoprene nitrooxy hydroperoxides (INP) (C 5 H 9 NO 5 ), dihydroxy nitrates (IDHN) (C 5 H 9 NO 5 ), carbonyl nitrates (ICN) (C 5 H 7 NO 4 ), hydroxy nitrates (IHN) (C 5 H 9 NO 4 ), and hydroxy hydroperoxy nitrates (IHPN) (C 5 H 9 NO 6 ), among others (Schwantes et al, 2015;Vereecken et al, 2021;Wennberg et al, 2018;Wu et al, 2021). These compounds have also been observed in the ambient atmosphere (Lee et al, 2016;Schwantes et al, 2015;Xu et al, 2021;Ye et al, 2021).…”