Investigating possible causes of the observed diurnal variability in Antarctic NOy

The occurence of a diurnal variability in measured total oxidised nitrogen (NOy) was observed at Neumayer, Antarctica, (70 degrees 39'8, 8 degrees 15'W) during a recent summer measurement campaign. Minima and maxims occurred in the early morning/early evening respectively, with the amplitude of the cycle around 40% of the daily mean NOy values. Given that this campaign was the first to attempt NOy 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 HNO3, although HNO3 concentrations and fluctuations are too small to account for all of the NOy 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 snowpack. Exchange processes at the air/snow interface appear to dominate the observed NOy 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.