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In the lower troposphere over the Arctic Ocean, ozone is often destroyed in spring by chemical chain reactions involving the reactive bromine species Br and BrO. The role of surface snow in generating reactive bromine has been suspected, but many details of the processes not understood. Using unique data such as BrO concentrations from instruments on buoys, Burd et al. (2017) observed that the snowmelt onset date often coincides with the end of the reactive bromine season. They proposed that the decrease in snow-specific surface area and/or the occurrence of liquid water in snow induced by melting dramatically slows the rate of surface reactions generating bromine, indicating that the physical state of the snow is critical for bromine generation. Their suggestion is discussed, and a method to test it using novel instrumentation recently available is proposed.

Plain Language Summary In the lower troposphere over the Arctic Ocean, ozone is often destroyed in spring by chemical reactions involving bromine compounds, whose atmospheric concentrations increased as ozone was destroyed. It has long been suspected that some of these reactions were taking place on snow surfaces, but this had never been proven. Using unique data from instruments on buoys, Burd et al. (2017) observed that the snowmelt onset date often coincides with the end of the high bromine season. They proposed that changes in snow surface properties induced by melting dramatically slow the rate of surface reactions involving bromine, indicating that the physical state of the snow is critical for reactions leading to ozone destruction. Their suggestion is discussed, and a method to test it using novel instrumentation recently available is proposed.