Isoprene NO3 Oxidation Products from the
RO2 + HO2 Pathway

Schwantes, Rebecca H.; Teng, Alexander
P.; Nguyen, Tran B.; Coggon, Matthew M.; Crounse, John D.; M. St. Clair, Jason; Zhang, Xuan; Schilling, Katherine
A.; Seinfeld, John H.; Wennberg, Paul O.

doi:10.1021/acs.jpca.5b06355.s001

jp5b06355_si_001.pdf (2.03 MB)

Isoprene NO₃ Oxidation Products from the RO₂ + HO₂ Pathway

journal contribution

posted on 2015-10-08, 00:00 authored by Rebecca H. Schwantes, Alexander P. Teng, Tran B. Nguyen, Matthew M. Coggon, John D. Crounse, Jason M. St. Clair, Xuan Zhang, Katherine A. Schilling, John H. Seinfeld, Paul O. Wennberg

We describe the products of the reaction of the hydroperoxy radical (HO₂) with the alkylperoxy radical formed following addition of the nitrate radical (NO₃) and O₂ to isoprene. NO₃ adds preferentially to the C₁ position of isoprene (>6 times more favorably than addition to C₄), followed by the addition of O₂ to produce a suite of nitrooxy alkylperoxy radicals (RO₂). At an RO₂ lifetime of ∼30 s, δ-nitrooxy and β-nitrooxy alkylperoxy radicals are present in similar amounts. Gas-phase product yields from the RO₂ + HO₂ pathway are identified as 0.75–0.78 isoprene nitrooxy hydroperoxide (INP), 0.22 methyl vinyl ketone (MVK) + formaldehyde (CH₂O) + hydroxyl radical (OH) + nitrogen dioxide (NO₂), and 0–0.03 methacrolein (MACR) + CH₂O + OH + NO₂. We further examined the photochemistry of INP and identified propanone nitrate (PROPNN) and isoprene nitrooxy hydroxyepoxide (INHE) as the main products. INHE undergoes similar heterogeneous chemistry as isoprene dihydroxy epoxide (IEPOX), likely contributing to atmospheric secondary organic aerosol formation.