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 (o17 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 210 Pb 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. 7 Be 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: longterm records of 7 Be, 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 B30% of the nonsea-salt sulfate. Various possible explanations for the low values of R (¼ 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. r 2004 Elsevier Ltd. All rights reserved.