A kinetic study of the reactions of NO3 with methyl vinyl ketone, methacrolein, acrolein, methyl acrylate and methyl methacrylate

Abstract

Absolute and relative-rate techniques have been used to obtain rate coefficients for the reactions: NO₃+CH₃C(O)CHCH₂→products (1), NO₃+CH₂C(CH₃)CHO→products (2), NO₃+CH₂CHCHO→ products (3), and NO₃+CH₂CHC(O)OCH₃→products (4). The reaction NO₃+CH₂C(CH₃)C(O)OCH₃→ products (5), has been investigated by a relative-rate method only. The rate coefficients obtained by the relative-rate method at T=296±2 K and P=760 Torr are k₁=(4.7±1.7)×10^-16 cm³ molecule^-1 s^-1, k₂=(3.7±1.0)×10^-15 cm³ molecule^-1 s^-1, k₃=(1.1±0.4)×10^-15 cm³ molecule^-1 s^-1, k₄=(1.0±0.6)×10^-16 cm³ molecule^-1 s^-1 and k₅=(3.6±1.3)×10^-15 cm³ molecule^-1 s^-1. The rate coefficients determined by the discharge-flow technique at low pressure (P=1–10 Torr) and at T=293–303 K are k₁=(3.2±0.6)×10^-16 cm³ molecule^-1 s^-1, k₂=(9.6±2.0)×10^-15 cm³ molecule^-1 s^-1, k₃=(8.9±2.8)×10^-15 cm³ molecule^-1 s^-1, k₄=(1.9±0.4)×10^-16 cm³ molecule^-1 s^-1. The discrepancy between the values obtained from the relative-rate technique and the absolute technique are discussed and explained in terms of interference in the absolute study caused by secondary chemistry and fast-reacting impurities. Product studies reveal that methyl glyoxal is a product of reactions (1) and (2) along with peroxymethacryloyl nitrate (MPAN) for reaction (2) in air. A diurnally varying boundary-layer model suggests that reaction (2) is an important loss process for methacrolein and that it can lead to the generation of OH at night.