LAUSR

Vertical distributions of atmospheric dimethyl sulfide (DMS(g)) were sampled aboard the research aircraft Polar 6 near Lancaster Sound, Nunavut, Canada in July 2014 and on pan-Arctic flights in April 2015 that started from Longyearbyen, Spitzbergen, and passed through Alert and Eureka, Nunavut and Inuvik, Northwest Territories. Larger mean DMS(g) mixing ratios were present during April 2015 (campaign-mean of 116±8 pptv) compared to July 2014 (campaign-mean of 20±6 pptv). Observations in July 2014 indicated a decrease in DMS(g) mixing ratios with altitude up to about 3 km, and the largest mixing ratios were found near the surface above ice-edge and open water, coincident with increased particle concentrations. In contrast, DMS(g) mixing ratios sampled in April 2015 were as high as 100 pptv near 2500 m. The April campaign also exhibited uniform campaign-mean vertical profiles overall although some profiles showed an increase with altitude. GEOS-Chem chemical-transport model simulations indicate that Arctic seawater (north of 66° N) contributes the majority of DMS(g) to the Arctic profiles (>90 %) in July 2014 flight tracks which were below 3000 m. More than 90 % of DMS(g) in April 2015 was from Arctic seawater for measurements below 500 m, but that declined to 60 % for altitudes between 500 m and 3000 m. FLEXPART simulations indicate that for summer 2014, the sampled air mass originated over Baffin Bay and the Canadian Arctic Archipelago. Whereas, for springtime 2015, the air mass sampled on flights near Alert and Eureka originated from Baffin Bay/Canadian Archipelago and from long-range transport (LRT) around the northern tip of Greenland. Our results highlight the role of open water below the flight as the source of DMS(g) during July 2014, and the influence of LRT of DMS(g) from further afield in the Arctic above 2500 m during April 2015.