Potential significance of photoexcited NO2 on global air quality with the NMMB/BSC chemical transport model

Abstract

Atmospheric chemists have recently focused on the relevance of the NO2* + H2O → OH + HONO reaction to local air quality. This chemistry has been considered not relevant for the troposphere from known reaction rates until nowadays. New experiments suggested a rate constant of 1.7 × 10−13 cm3 molecule−1 s−1, which is an order of magnitude faster than the previously estimated upper limit of 1.2 × 10−14 cm3 molecule−1 s−1, determined by Crowley and Carl (1997). Using the new global model, NMMB/BSC Chemical Transport Model (NMMB/BSC-CTM), simulations are presented that assess the potential significance of this chemistry on global air quality. Results show that if the NO2* chemistry is considered following the upper limit kinetics recommended by Crowley and Carl (1997), it produces an enhancement of ozone surface concentrations of 4–6 ppbv in rural areas and 6–15 ppbv in urban locations, reaching a maximum enhancement of 30 ppbv in eastern Asia. Moreover, NO2 enhancements are minor (xemissions are present; however, differences are small in most parts of the globe