Reactive quenching of electronically excited NO 2 ∗ and NO 3 ∗ by H 2 O as potential sources of atmospheric HO x radicals

Pulsed laser excitation of NO 2 (532–647 nm) or NO 3 (623–662 nm) in the presence of H 2 O was used to initiate the gas-phase reaction NO2∗+H2O → products (Reaction R5) and NO3∗+H2O → products (Reaction R12). No evidence for OH production in Reactions (R5) or (R12) was observed and upper limits for OH production of k5b/k5<1×10-5 and k12b/k12<0.03 were assigned. The upper limit for k 5 b ∕ k 5 renders this reaction insignificant as a source of OH in the atmosphere and extends the studies (Crowley and Carl, 1997; Carr et al., 2009; Amedro et al., 2011) which demonstrate that the previously reported large OH yield by Li et al. (2008) was erroneous. The upper limit obtained for k 12 b ∕ k 12 indicates that non-reactive energy transfer is the dominant mechanism for Reaction (R12), though generation of small but significant amounts of atmospheric HO x and HONO cannot be ruled out. In the course of this work, rate coefficients for overall removal of NO3∗ by N 2 (Reaction R10) and by H 2 O (Reaction R12) were determined: k10=(2.1±0.1)×10-11 cm 3 molecule −1 s −1 and k12=(1.6±0.3)×10-10 cm 3 molecule −1 s −1 . Our value of k 12 is more than a factor of 4 smaller than the single previously reported value.

Abstract licence: CC BY

38 more references, whose wording the paper’s licence keeps private.

A person counts once a day per paper. We keep no cookie and no address: a reader is a hash that changes every day. Any month under five reads shows no number.