The multi-seasonal NOy budget in coastal Antarctica and its link with surface snow and ice core nitrate: results from the CHABLIS campaign

Measurements of a suite of individual NOy components were carried out at Halley station in coastal Antarctica as part of the CHABLIS campaign (Chemistry of the Antarctic Boundary Layer and the Interface with Snow). Conincident measurements cover over half a year, from austral winter 2004 through to austral summer 2005. Results show clear dominance of organic NOy compounds (PAN and MeONO2) during the winter months, with low concentrations of inorganic NOy. During summer, concentrations of inorganic NOy compounds are considerably greater, while those of organic compounds, although lower than in winter, are nonetheless significant. The relative concentrations of the alkyl nitrates, as well as their seasonality, are consistent with an oceanic source. Multi-seasonal measurements of surface snow nitrate correlate strongly with inorganic NOy species (especially HNO3) rather than organic. One case study in August suggested that, on that occasion, particulate nitrate was the dominant source of nitrate to the snowpack, but this was not the consistent picture throughout the measurement period. An analysis of NOx production rates showed that emissions of NOx from the snowpack overwhelmingly dominate over gas-phase sources. This result suggests that, for certain periods in the past, the flux of NOx into the Antarctic boundary layer can be calculated from ice core nitrate data.