Long-term measurements of light alkanes and acetylene in the Antarctic troposphere

Abstract

Between 1982 and 1989, biweekly whole air samples were collected at the German Antarctic station “Georg von Neumayer”. In addition, a smaller number of samples were taken in 1988 and 1989 at Scott Base, the New Zealand Antarctic station. These samples were analyzed for several light hydrocarbons and halocarbons. For the light alkanes and acetylene, the average results from the two stations which are located at opposite coasts of Antarctica agree. The annual mean values for ethane, propane, n-butane, i-pentane and acetylene are 380 ± 8 ppt, 84 ± 4 ppt, 50 ± 4 ppt, 15 ± 2 ppt, and 17 ± 1 ppt, respectively. The mixing ratios of ethane, propane, and i-pentane show a seasonal cycle with a peak in August, a minimum in February and an average maximum to minimum variation of 40%-50%. Acetylene also shows a maximum around August, but its seasonal variation is higher by a factor of three. For ethane, propane and acetylene, the measurements indicate that during the last few years, the average mixing ratios in austral winter have slightly increased. A possible explanation of this secular trend is the increase of biomass burning in the Southern Hemisphere. This is also consistent with the assumption that part of the seasonal variation found for ethane, propane and acetylene reflects the seasonal dependence of biomass burning.