Major ions and radionuclides in aerosol particles from the South Pole during ISCAT-2000

As part of ISCAT 2000, bulk, high-volume, aerosol samples were collected at the South Pole (SP) nominally over 24-h intervals, and they were analyzed for major ions, several trace elements, and three naturally occurring radionuclides. The mean concentrations of Na (<17 ng m−3), sulfate (98 ng m−3), and methanesulfonate (MSA, 4.4 ng m−3) all were lower in ISCAT 2000 compared with ISCAT 1998, suggesting weaker marine influences during the latter study. In contrast, the 210Pb activity (0.20 mBq m−3) was more than two-times higher in ISCAT 2000 than in 1998, and nitrate concentrations (150 ng m−3) were approximately four-times higher, suggesting stronger continental influences in the second study. These differences between experiments are consistent with an analysis of meteorological transport and exchange. 7Be activities were generally comparable for ISCAT-1998 and 2000, suggesting that there were, on average, similar upper tropospheric/lower stratospheric influences on surface air during the two experiments: long-term records of 7Be, however, show pronounced annual and lower-frequency cycles. The concentration ratios of MSA to nss-sulfate (R) were similar in the two campaigns, and a regression analysis suggests that a non-biogenic source or sources account for up to 30% of the nonsea-salt sulfate. Various possible explanations for the low values of R (=0.08) relative to other Antarctic sites are discussed, including differences in R due to where the oxidation of DMS takes place (that is, in the marine boundary layer or in the buffer layer/free troposphere), chemical fractionation during transport, and the transport of sulfur compounds from lower latitudes and possibly from Mt. Erebus.