On Rates and Mechanisms of OH and O₃ Reactions with Isoprene-Derived Hydroxy Nitrates

Abstract

Eight distinct hydroxy nitrates are stable products of the first step in the atmospheric oxidation of isoprene by OH. The subsequent chemical fate of these molecules affects global and regional production of ozone and aerosol as well as the location of nitrogen deposition. We synthesized and purified 3 of the 8 isoprene hydroxy nitrate isomers: (E/Z)-2-methyl-4-nitrooxybut-2-ene-1-ol and 3-methyl-2-nitrooxybut-3-ene-1-ol. Oxidation of these molecules by OH and ozone was studied using both chemical ionization mass spectrometry and thermo-dissociation laser induced fluorescence. The OH reaction rate constants at 300 K measured relative to propene at 745 Torr are (1.1 ± 0.2) × 10–10 cm3 molecule–1 s–1 for both the E and Z isomers and (4.2 ± 0.7) × 10–11 cm3 molecule–1 s–1 for the third isomer. The ozone reaction rate constants for (E/Z)-2-methyl-4-nitrooxybut-2-ene-1-ol are (2.7 ± 0.5) × 10–17 and (2.9 ± 0.5) × 10–17 cm3 molecule–1 s–1, respectively. 3-Methyl-2-nitrooxybut-3-ene-1-ol reacts with ozone very slowly, within the range of (2.5–5) × 10–19 cm3 molecule–1 s–1. Reaction pathways, product yields, and implications for atmospheric chemistry are discussed. A condensed mechanism suitable for use in atmospheric chemistry models is presented.

Rapid deposition of oxidized biogenic compounds to a temperate forest

“…The photooxidation of IEPOX produces C 4 dihydroxy carbonyls (DHC 4 ), C 4 hydroxy dicarbonyls (HDC 4 ), HAC, formic acid, and other products (42,89). In NO-rich environments, the minor route of the OH-initiated reaction of isoprene produces ISOPN, which are subsequently oxidized to HAC, hydroxy nitrates with backbones of MACN and MVKN, and other products (54,90,91). The major route of the NOdominated OH-initiated reaction (not shown) produces carbonyls such as methacrolein, methyl vinyl ketone, and HAC, among other products.…”

“…For unsaturated compounds like ISOPN, deposition may comprise a smaller fraction (<10%) of the daytime sink because its reaction with OH is fast (54). Thus, errors in representation of ISOPN dry deposition will have a much smaller effect on simulated ISOPN surface concentrations.…”

Highly functionalized organic nitrates in the southeast United States: Contribution to secondary organic aerosol and reactive nitrogen budgets

“…The HRToF-CIMS was calibrated for three isomers of isoprene hydroxynitrate (C 5 H 9 NO 4 ) (20). The iodide-adduct ionization is most sensitive to polar organics with hydroxy groups (14), and the dominant ON signal in the particle phase observed during the SOAS was of highly oxygenated compounds.…”

Influence of isoprene chemical mechanism on modelled changes in tropospheric ozone due to climate and land use over the 21st century

“…In CheT2, the overall yield of NO x from ISON was increased, in line with recent measurements (Perring et al, 2009), by increasing the ISON photolysis rate and adding an ISON + OH → NO 2 reaction channel. O 3 initiated degradation of ISON was also added based on the evidence of Lockwood et al (2010) -it should be noted, however, that Lee et al (2014) found that Lockwood et al (2010) substantially overestimated the rate of this reaction. Secondly, CheT2 includes the formation of hydroperoxy-aldehydes (HPALDs) from ISO 2 and subsequent rapid release of OH (Peeters et al, 2009).…”