2À ratios exhibited a strong dependence on the MS concentration with systematically higher ratios at higher MS concentrations, a peculiarity which is also evident in a firn core drilled at this site.

NO, NOy (total reactive nitrogen oxides), gaseous HNO3, and particulate nitrate (p‐NO3−) were measured at Neumayer Station from February 1999 to January 2000. In addition, during February 1999, the NOy component species peroxyacetyl nitrate (PAN) and methyl, ethyl, i‐propyl, and n‐propyl nitrates were determined. We found a mean NOy mixing ratio of 46 ± 29 pptv, with significantly higher values between February and end of May (58 ± 35 pptv). Between February and November, the (HNO3 + p‐NO3−)/NOy ratio was extremely low (around 0.22) and in contrast to NOy the seasonality of p‐NO3− and HNO3 showed a distinct maximum in November and December, leading to a (HNO3 + p‐NO3−)/NOy ratio of 0.66. Trajectory analyses and radioisotope measurements (7Be, 10Be, 210Pb, and 222Rn) indicated that the upper troposphere or stratosphere was the main source region of the observed NOy with a negligible contribution of ground‐level sources at northward continents. Frequent maxima of NOy mixing ratios up to 100 pptv are generally associated with air mass transport from the free troposphere of continental Antarctica, while air masses with the lowest NOy mixing ratios were typically advected from the marine boundary layer.

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