Abstract
Abstract. In this second part of a series of articles dedicated to a detailed analysis of bromine chemistry in the atmosphere we address one (out of two) dominant natural sources of reactive bromine. The two main source categories are the release of bromine from sea salt and the decomposition of bromocarbons by photolysis and reaction with OH. Here, we focus on C1-bromocarbons. We show that the atmospheric chemistry general circulation model ECHAM5/MESSy realistically simulates their emission, transport and decomposition from the boundary layer up to the mesosphere. We included oceanic emission fluxes of the short-lived bromocarbons CH2Br2, CH2ClBr, CHClBr2, CHCl2Br, CHBr3 and of CH3Br. The vertical profiles and the surface mixing ratios of the bromocarbons are in general agreement with the (few available) observations, especially in view of the limited information available and the consequent coarseness of the emission fields. For CHBr3, CHCl2Br and CHClBr2 photolysis is the most important degradation process in the troposphere. In contrast to this, tropospheric CH2Br2, CH3Br and CH2ClBr are more efficiently decomposed by reaction with OH. In the free troposphere approximately 40% of the C1-bromocarbons decompose by reaction with OH. Our results indicate that bromoform contributes substantial amounts of reactive bromine to the lower stratosphere and thus should not be neglected in stratospheric simulations.
Highlights
The abundance of bromine in the troposphere and the importance of individual bromine sources to atmospheric halogen chemistry is highly uncertain
In this second part of a series of articles dedicated to a detailed analysis of bromine chemistry in the atmosphere we address one dominant natural sources of reactive bromine
We show that the atmospheric chemistry general circulation model ECHAM5/MESSy realistically simulates their emission, transport and decomposition from the boundary layer up to the mesosphere
Summary
The abundance of bromine in the troposphere and the importance of individual bromine sources to atmospheric halogen chemistry is highly uncertain. In the present study about atmospheric bromine, the focus is on C1-bromocarbons (further denoted as bromocarbons) Their emission fluxes, the transport and the main regions and processes of degradation are investigated here. The most comprehensive model studies of bromocarbons far have been performed by Warwick et al (2006a,b) who applied the Chemistry Transport Model (CTM) pTOMCAT to simulate atmospheric bromoform (CHBr3) and other short-lived bromocarbons (Table 1 lists all abbreviations). They concluded that global source estimates using the previously used top-down approach were too low and suggested a global emission flux of about 400– 600 Gg(CHBr3)/yr.
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