AbstractUnderstanding the NOy budget at high latitudes is important for our knowledge of present day clean air chemistry, and essential for reliable interpretation of existing ice core nitrate data. However, measurements of NOy components at high latitudes have been limited and no measurements have attempted to address the budget of NOy. Here we report on a campaign conducted in the austral summer of 1997 at the German Antarctic research station, Neumayer, with first Antarctic measurements for NOy in addition to light alkyl nitrates, NO, HNO3 and p-NO3-. Inorganic nitrate has generally been assumed to be the dominant component of NOy in Antarctica, although this idea has not previously been tested. However, our results show that for this coastal station, methyl nitrate was present in much higher concentration than inorganic nitrate (median CH3ONO2 = 38 pptv, HNO3 = 5 pptv) . It has been suggested earlier that some alkyl nitrates might have a marine source. If this suggestion is correct, the implication arises that the oceans are supplying an important source of NOy to the Antarctic troposphere, and that their role in determining nitrate concentrations in ice must be considered.