Background characteristics of atmospheric sulfur hexafluoride concentrations at Zhongshan Station, Antarctica

Abstract

Sulfur hexafluoride (SF6) is one kind of highly stable anthropogenic greenhouse gas with a global warming potential (GWP) of 2.35×104 over a 100-year time horizon. SF6 emissions are targeted for reduction under the Kyoto Protocol. Therefore it is important for the research about global change to observe atmospheric SF6 background concentrations. Here, we present the patterns for the seasonal and annual variations of atmospheric SF6 concentrations at Zhongshan Station, east Antarctica from February 2008 to January 2013. The prevailing wind direction at the observation site was from the east with the frequency of 92.0%. The average SF6 concentration was about 6.89 pptv under east wind, lower than that under west wind (7.16 pptv). More frequent west wind occurred in autumn and thus average SF6 concentration was higher in autumn than other seasons, indicating that the airflow from western sea area contained higher SF6 concentration than the airflow from east Antarctic continent. On the whole, SF6 concentrations showed an insignificant change under different wind speeds and directions, indicating that the influence of wind and local pollution could be ignored. Our results could represent the background concentrations for atmospheric SF6 at Zhongshan Station. The SF6 concentrations ranged from 6.01 to 7.80 pptv with the average of 6.90±0.40 pptv from February 2008 to January 2013. Annual SF6 concentrations in the atmosphere steadily increased at the rate of 0.28 pptv a - 1, and the increasing magnitudes were very close to each other per year during the period of 2008–2012, similar to the results from other global observation sites, indicating that annual SF6 emission amount could be almost stable each year. No evident periodical changes in SF6 concentrations were observed during the five years. The seasonal SF6 concentration did not show insignificant variation in spring and summer, but an evident decrease in its level occurred in autumn, and then it rose back to normal level in winter. Combined our data with those from other nine observation sites, atmospheric SF6 concentrations showed an evident gradient change with the latitudes at the global scale, and its concentrations in the Northern Hemisphere were 0.3–0.4 pptv higher than those in the Southern Hemisphere because the main emission sources for atmospheric SF6 concentrated in the Northern Hemisphere. The primary source for atmospheric SF6 is industrial emissions in the Northern Hemisphere, whereas its main source is the SF6 southward transportation in the Southern Hemisphere. Our results prove that atmospheric SF6 concentration is continuously growing and its industrial emission control needs to be strengthened. Antarctica is less affected by human activities on the globe, which makes it an ideal area to observe SF6 background concentrations. Our data in the present study will guide industry in optimizing and controlling the SF6 emissions. The SF6 sources and its transportation pathways will be further studied at Zhongshan Station in the future.