Abstract
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 NOx, 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.
Highlights
Given that South Pole (SP) studies have shown that the planetary boundary layer (PBL) depth can play a significant role in dictating NOx levels, a major effort was made in this study to characterize the meteorological environment along all aircraft flight paths
The highest concentration found during this segment was when the aircraft penetrated a PBL depth of ∼40 m. (Note that as shown in Figure 3b, the lightest winds (
[49] Based on flight path coverage which involved approximately 8000 km of plateau terrain, we estimate that between the Antarctic Tropospheric Chemistry Investigation (ANTCI) 2003 and the ANTCI 2005 airborne studies, the area sampled was somewhat less than 1% of the plateau
Summary
[2] There has been growing evidence over the last decade that polar regions can display very diverse chemistry during the summer months. [4] emissions of reactive nitrogen in the form of NOx (NO + NO2) have been reported at several polar sites [Beine et al, 2002a, 2002b; Davis et al, 2001, 2004, 2008; Honrath et al, 1999, 2000a, 2000b; Jones et al, 2000; Ridley et al, 2000], nowhere has it resulted in such large‐ scale atmospheric perturbations as seen at SP, Antarctica [Chen et al, 2001, 2004; Crawford et al, 2001; Davis et al, 2001, 2004, 2008; Helmig et al, 2008a, 2008b; Mauldin et al, 2001, 2004; Wang et al, 2008] Representative of these perturbations, during the Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT) studies in 1998 and 2000, NO concentrations ranging from 10 to 600 pptv were observed. Given that SP studies have shown that the planetary boundary layer (PBL) depth can play a significant role in dictating NOx levels, a major effort was made in this study to characterize the meteorological environment along all aircraft flight paths This involved using a combination of aircraft‐generated temperature profiles, satellite data, modeling products, and remote‐site surface observations on the plateau. Spectroradiometric data were recorded for the purpose of evaluating photochemical rate constants during each flight
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