Snow-sourced bromine and its implications for polar tropospheric ozone

X Yang,M Van Roozendael,N Theys,J A Pyle,R A Cox

doi:10.5194/acp-10-7763-2010

Abstract

Abstract. In the last two decades, significant depletion of boundary layer ozone (ozone depletion events, ODEs) has been observed in both Arctic and Antarctic spring. ODEs are attributed to catalytic destruction by bromine radicals (Br plus BrO), especially during bromine explosion events (BEs), when high concentrations of BrO periodically occur. However, neither the exact source of bromine nor the mechanism for sustaining the observed high BrO concentrations is completely understood. Here, by considering the production of sea salt aerosol from snow lying on sea ice during blowing snow events and the subsequent release of bromine, we successfully simulate the BEs using a global chemistry transport model. We find that heterogeneous reactions play an important role in sustaining a high fraction of the total inorganic bromine as BrO. We also find that emissions of bromine associated with blowing snow contribute significantly to BrO at mid-latitudes. Modeled tropospheric BrO columns generally compare well with the tropospheric BrO columns retrieved from the GOME satellite instrument (Global Ozone Monitoring Experiment). The additional blowing snow bromine source, identified here, reduces modeled high latitude lower tropospheric ozone amounts by up to an average 8% in polar spring.

Highlights

Bromine radicals (Br plus BrO) are important atmospheric halogen species which may regulate ozone concentrations in both the stratosphere and troposphere (World Meteorological Organization (WMO), 2003; von Glasow et al, 2004; Salawitch et al, 2005; Yang et al, 2005) and which have significant effects on other tropospheric processes such as the sulfur cycle (von Glasow and Crutzen, 2004; Breider et al, 2009) and mercury oxidation (Holmes et al, 2006; Seigneur and Lohman, 2008)
A recent calculation demonstrates that the sea salt produced in association with blowing snow events could be a significant bromine source (Yang et al, 2008), which is consistent with recent insitu measurements of higher bromide levels in blowing snow in coastal Antarctica (Jones et al, 2009)
Using measurements of the mean column salinity of snow on young Antarctic sea ice (Massom et al, 2001) and a parameterization for sea salt aerosol production in blowing snow events, we have found that the resulting sea salt aerosol production rate can be more than an order of magnitude larger than that from the open ocean (Yang et al, 2008)

Summary

Introduction

Bromine radicals (Br plus BrO) are important atmospheric halogen species which may regulate ozone concentrations in both the stratosphere and troposphere (World Meteorological Organization (WMO), 2003; von Glasow et al, 2004; Salawitch et al, 2005; Yang et al, 2005) and which have significant effects on other tropospheric processes such as the sulfur cycle (von Glasow and Crutzen, 2004; Breider et al, 2009) and mercury oxidation (Holmes et al, 2006; Seigneur and Lohman, 2008). A recent calculation demonstrates that the sea salt produced in association with blowing snow events could be a significant bromine source (Yang et al, 2008), which is consistent with recent insitu measurements of higher bromide levels in blowing snow in coastal Antarctica (Jones et al, 2009). Inclusion of this source in the Arctic has a significant effect on tropospheric BrO and oxidation (through ozone and OH) (Voulgarakis et al, 2009)

Objectives

Methods

Results

Conclusion