Measurement-based modeling of bromine chemistry at the Dead Sea boundary layer ? Part 2: The influence of NO₂ on bromine chemistry at mid-latitude areas

Abstract

International audienceUnderstanding the interaction between anthropogenic air pollution and Reactive Halogen Species (RHS) activity has had only limited support of direct field measurements, due to the fact that past field measurements of RHS have been mainly performed in Polar Regions. The present paper investigates the interaction between NO2 and Reactive Bromine Species (RBS) activity by model simulations based on extensive field measurements performed in the Dead Sea area, as described in a companion paper (Tas et al., 2006). The Dead Sea is an excellent natural laboratory for this investigation since elevated concentrations of BrO (up to more than 150 pptv) are frequently observed, while the average levels of NO2 are around several ppb. The results of the present study show that under the chemical mechanisms that occur at the Dead Sea, higher levels of NO2 lead to higher daily average concentrations of BrOX, as a result of an increase in the rate of the heterogeneous decomposition of BrONO2 that in turn causes an increase in the rate of the "Bromine Explosion" mechanism. The present study has shown that the influence of NO2 on BrOX production clearly reflects an enhancement of RBS activity caused by anthropogenic activity. However, above a certain threshold level of NO2 (daily average mixing ratios of 0.2 ppbv during RBS activity), the daily average concentrations of BrOX decrease for a further increase in the NO2 concentrations