Seasonal variations of atmospheric trace gases in the high Arctic at 79 degrees N

Since March 1992 the total column abundances of several tropospheric and stratospheric trace gases have been monitored year-round from the Network for Detection of Stratospheric Change station in Ny Alesund, Spitsbergen (78.9 degrees N, 11,9 degrees E). A groundbased Fourier transform infrared (FTIR) spectrometer performed these measurements using the Sun as a light source during the summer, and the Moon during the winter. In situ measurements of C2H2, C2H6, and CCl2F2, made from the top of a nearby mountain, were combined with the FTIR column data to infer additional information about the variation of the volume mixing ratio profiles with altitude and season. The short-lived tropospheric trace gases C2H2, C2H6, and CO exhibit large seasonal variations with a summer minimum, caused by reaction with OH. CH2O shows a second maximum during the summer, caused by its formation by methane oxidation. For the long-lived gases HF, N2O, and CH4 the seasonal cycle is less pronounced and is forced mainly by wintertime stratospheric diabatic descent, which starts in early November and reaches a maximum in March. The total columns of the stratospheric trace gases indicate that the chemical repartitioning of HCl into ClONO2 starts in November, before the widespread production of polar stratospheric clouds. The total columns of the sum of HCl plus ClONO2 suggests that between December and March they are converted into their active counterparts. Photolysis of HNO3 gives rise to its summer minimum, and its winter maximum, with no evidence for a strong winter denitrification.