Investigating possible causes of the observed diurnal variability in Antarctic NOy

The occurence of a diurnal variability in measured total oxidised nitrogen (NO y ) was observed at Neumayer, Antarctica, (70°39′S, 8°15′W) during a recent summer measurement campaign. Minima and maxima occurred in the early morning/early evening respectively, with the amplitude of the cycle around 40% of the daily mean NO y values. Given that this campaign was the first to attempt NO y measurements on the Antarctic continent, it is not presently clear whether this is an Antarctic‐wide phenomenon, or local to Neumayer. A similar cycle was observed for HNO 3 , although HNO 3 concentrations and fluctuations are too small to account for all of the NO y variability. In this paper we investigate possible mechanisms that might cause such diurnal signals, focussing on the influence of local meteorology and also of the snow‐pack. Exchange processes at the air/snow interface appear to dominate the observed NO y variability, although an influence from the changing surface inversion strength exists. These findings have important implications in understanding and hence correctly interpreting ice core nitrate data.