Atmospheric chemistry results from the ANTCI 2005 Antarctic plateau airborne study

One of the major goals of the 2005 Antarctic Tropospheric Chemistry Investigation (ANTCI) was to bridge the information gap between current knowledge of South Pole (SP) chemistry and that of the plateau. The former has been extensively studied, but its geographical position on the edge of the plateau makes extrapolating these findings across the plateau problematic. The airborne observations reported here demonstrate that, as at SP, elevated levels of nitric oxide (NO) are a common summertime feature of the plateau. As in earlier studies, planetary boundary layer (PBL) variations were a contributing factor leading to NO fluctuations. Thus, extensive use was made of in situ measurements and models to characterize PBL depths along each flight path and over broader areas of the plateau. Consistent with earlier SP studies that revealed photolysis of nitrate in surface snow as the source of NO_x, large vertical gradients in NO were observed over most plateau areas sampled. Similar gradients were also found for the nitrogen species HNO₃ and HO₂NO₂ and for O₃. Thus, a common meteorological-chemical feature found was shallow PBLs associated with nitrogen species concentrations that exceeded free tropospheric levels. Collectively, these new results greatly extend the geographical sampling footprint defined by earlier SP studies. In particular, they suggest that previous assessments of the plateau as simply a chemical depository need updating. Although the evidence supporting this position comes in many forms, the fact that net photochemical production of ozone occurs during summer months over extensive areas of the plateau is pivotal.