Abstract
Abstract. This is the first article of a series presenting a detailed analysis of bromine chemistry simulated with the atmospheric chemistry general circulation model ECHAM5/MESSy. Release from sea salt is an important bromine source, hence the model explicitly calculates aerosol chemistry and phase partitioning for coarse mode aerosol particles. Many processes including chemical reaction rates are influenced by the particle size distribution, and aerosol associated water strongly affects the aerosol pH. Knowledge of the aerosol pH is important as it determines the aerosol chemistry, e.g., the efficiency of sulphur oxidation and bromine release. Here, we focus on the simulated sea salt aerosol size distribution and the coarse mode aerosol pH. A comparison with available field data shows that the simulated aerosol distributions agree reasonably well within the range of measurements. In spite of the small number of aerosol pH measurements and the uncertainty in its experimental determination, the simulated aerosol pH compares well with the observations. The aerosol pH ranges from alkaline aerosol in areas of strong production down to pH-values of 1 over regions of medium sea salt production and high levels of gas phase acids, mostly polluted regions over the oceans in the Northern Hemisphere.
Highlights
Halogen containing compounds that photochemically decompose in the stratosphere contribute to catalytic ozone destruction
We present first results of a comprehensive atmospheric chemistry general circulation model (AC-GCM) simulation including gas and aerosol phase chemistry
Since this simulation aims at representing bromine chemistry and the largest boundary layer source of bromine is release from aerosol particles, we focus on the aerosol mass, number distributions and the aerosol pH in this first part of a series of articles
Summary
Halogen containing compounds that photochemically decompose in the stratosphere contribute to catalytic ozone destruction. One aim of this work is to compute both column integrated and vertically resolved reactive bromine (e.g. BrO) concentrations that can be directly compared to global satellite measurements (Wagner et al, 2001) The latter will be pursued in a follow-up article, whereas here we focus on the marine boundary layer. We prognostically calculate the chemistry in the aerosol phase, i.e. without equilibrium assumptions using an explicit aqueous phase mechanism for the reactions in the coarse mode aerosol, the heterogeneous reactions on the coarse mode and the phase transitions To our knowledge, this is the first global simulation attempting this in such detail.
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