ISCAT 2000: Major Ions and Trace Elements in Aerosols from the South Pole

As part of the ISCAT-2000 Program (Investigation of Sulfur Chemistry in the Antarctic Troposphere), bulk, high-volume, aerosol samples were collected at the South Pole Clean Air Facility and analyzed for major ions (nitrate, sulfate, methanesulfonate, and sodium) by ion chromatography and for trace elements by inductively-coupled plasma mass spectrometry (ICP-MS). A second set of bulk high-volume samples was collected for studies of radionuclides (²¹⁰Pb, ²¹⁰Po, and ⁷Be). The two sets of samples were collected using the same samplers as in the prior ISCAT 1998 campaign. Comparisons of data from the two campaigns show that the ⁷Be activities were generally comparable for ISCAT-1998 and 2000, and they were also similar to long-term record produced by the Environmental Measurements Laboratory, Department of Energy (EML/DOE). The ²¹⁰Pb activities were more than 50% higher in 2000 than in 1998 and towards the high end of long-term EML/DOE record, suggesting relatively strong continental influences during ISCAT 2000 (November 2000 to January 2001. Nitrate concentrations (arithmetic mean, x = 150 ng m^-3) were approximately four-times higher in ISCAT 2000 compared with the earlier study. In contrast, the concentrations of sodium (x < 33 ng m^-3), sulfate (x= 97 ng m-^-3), and methanesulfonate (MSA, x = 4.1 ng m^-3) all were lower in ISCAT 2000 compared with 1998. The MSA to nss-sulfate (the sulfate in excess of that which can be attributed to sea salt) ratios were similar in the two campaigns and comparable to the ratios observed in Antarctic ice cores. A positive nss-sulfate intercept seen in a scatterplot of these data suggests the existence of background, non-biogenic, non-sea salt sulfate. Most of the forty-two elements that can readily be determined by the ICP-MS method were below detection limits in the majority of the aerosol samples. The notable exception was mercury, which was present in concentrations from < 0.1 to approximately 1 ng m^-3. These values of particulate Hg are comparable to or slightly higher than those observed in recent studies in the Arctic, and they are much higher than generally found in more temperate regions. While the cause for the high particulate Hg concentrations has not been determined, it is likely that the oxidation of gas-phase Hg is involved.