Abstract
Abstract. A coupled box model of photochemistry and aerosol microphysics which explicitly accounts for size-dependent chemical properties of the condensed-phase has been developed to simulate the multi-phase chemistry of chlorine, bromine and iodine in the marine boundary layer (MBL). The model contains separate seasalt and non-seasalt modes, each of which may be composed of 1–16 size-bins. By comparison of gaseous and aerosol compositions predicted using different size-resolutions with both fixed and size-dependent aerosol turnover rates, it was found that, for halogen-activation processes, the physical property initialisation of the aerosol-mode has a significant influence on gas-phase chemistry. Failure to adequately represent the appropriate physical properties can lead to substantial errors in gas-phase chemistry. The size-resolution of condensed-phase composition has a less significant influence on gas-phase chemistry.
Highlights
Recent measurements have shown that halogens can play a major role in the destruction of tropospheric ozone – causing up to 50% of the ozone loss in the remote marine boundary layer (MBL) (Read et al, 2008)
The aim of this paper is to investigate the relative importance of size-resolution of both condensed-phase chemistry and aerosol microphysics to the chemistry in the remote
– Where the condensed-phase acts as a chemical source, replicating the size-resolution of chemistry is less important; e.g. greater differences in gas-phase ozone and halogen chemistry between model runs are caused by coarse representations of the physical characteristics of the condensed-phase than by coarsely-resolved condensed-phase chemistry (Sect. 3.2)
Summary
Recent measurements have shown that halogens can play a major role in the destruction of tropospheric ozone – causing up to 50% of the ozone loss in the remote marine boundary layer (MBL) (Read et al, 2008). It has been shown that seasalt particles generated from the sea surface via wind shear are the major source of inorganic halogen species in the MBL (cf Keene et al, 1999; Sander et al, 2003) and size-segregated measurements of aerosols in the MBL have shown that most seasalt aerosol particles have a pH of 3.5–. 4.5, varying across the particle size-range (Keene et al, 2002, 2004). It may be expected that to investigate the causes and impacts of such variations in composition, a sizeresolved aerosol model must be used
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