Abstract
Abstract. Ozone depletion events (ODEs) in the polar boundary layer have been observed frequently during springtime. They are related to events of boundary layer enhancement of bromine. Consequently, increased amounts of boundary layer volume mixing ratio (VMR) and vertical column densities (VCDs) of BrO have been observed by in situ observation, ground-based as well as airborne remote sensing, and from satellites. These so-called bromine explosion (BE) events have been discussed serving as a source of tropospheric BrO at high latitudes, which has been underestimated in global models so far. We have implemented a treatment of bromine release and recycling on sea-ice- and snow-covered surfaces in the global chemistry–climate model EMAC (ECHAM/MESSy Atmospheric Chemistry) based on the scheme of Toyota et al. (2011). In this scheme, dry deposition fluxes of HBr, HOBr, and BrNO3 over ice- and snow-covered surfaces are recycled into Br2 fluxes. In addition, dry deposition of O3, dependent on temperature and sunlight, triggers a Br2 release from surfaces associated with first-year sea ice. Many aspects of observed bromine enhancements and associated episodes of near-complete depletion of boundary layer ozone, both in the Arctic and in the Antarctic, are reproduced by this relatively simple approach. We present first results from our global model studies extending over a full annual cycle, including comparisons with Global Ozone Monitoring Experiment (GOME) satellite BrO VCDs and surface ozone observations.
Highlights
Events of near-complete depletion of polar boundary layer ozone are observed frequently during springtime over both hemispheres (Oltmans, 1981; Barrie et al, 1988; Bottenheim et al, 1986, 2002, 2009)
We have implemented a bromine release mechanism from sea-ice- and snow-covered land surfaces based on the parameterization suggested by Toyota et al (2011) in the global chemistry–climate model ECHAM/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC)
The resulting spatial patterns of bromine monoxide (BrO) total vertical column densities (VCDs) are in good agreement with BrO VCD retrieval of the Global Ozone Monitoring Experiment (GOME) satellite instrument
Summary
Events of near-complete depletion of polar boundary layer ozone are observed frequently during springtime over both hemispheres (Oltmans, 1981; Barrie et al, 1988; Bottenheim et al, 1986, 2002, 2009). ODEs predominantly occur over the marginal sea ice zone but sometimes over inland ice- and snowcovered regions (e.g., Richter et al, 1998) In addition to their impact on boundary layer ozone, BE events may play an important role in mercury deposition and corresponding environmental impacts (Lindberg et al, 2002; Stephens et al, 2012; Toyota et al, 2014b, a). Pratt et al (2013) have found that snow on sea ice has to be taken into consideration as source of bromine and snow on land surfaces may contribute In addition to these natural sources, anthropogenic NOx emissions enhance reactive bromine species in the polar boundary layer (Custard et al, 2015). Unlike Toyota et al (2011), we do not focus on Arctic springtime only but investigate the applicability of the mechanism on a full annual cycle and in both hemispheres
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