BERYLLIUM-7 AND PB-210 IN THE WESTERN-HEMISPHERE ARCTIC ATMOSPHERE - OBSERVATIONS FROM 3 RECENT AIRCRAFT-BASED SAMPLING PROGRAMS

Concentrations of the natural radionuclides Be-7 and Pb-210 were determined in aerosol samples collected in the western hemisphere Arctic during the recent NOAA Arctic Gas and Aerosol Sampling Program (AGASP 3) and NASA Global Tropospheric Experiment/Arctic Boundary Layer Expeditions (GTE/ABLE 3A and ABLE 3B) missions. Beryllium 7 showed a free tropospheric concentration maximum between 4 and 5 km in the summer of 1990. Previous Be-7 data obtained in the late 1950s and early 1960s also indicated a similar vertical distribution of Be-7 near 70-degrees-N. Injection of stratospheric air through tropopause folds associated with the Arctic jet near 70-degrees-N appears to explain the presence of a layer of air near 4-5 km in the high Arctic free troposphere with elevated Be-7 concentrations. The vertical distribution of Pb-210 showed a distinct difference between the high-Arctic and sub-Arctic in the summer of 1988. At latitudes greater than 65-degrees-N Pb-210 concentrations at 3-6 km were elevated compared to those below 1 km. The reverse of this trend was observed near 60-degrees-N. These same vertical distributions were also apparent in aerosol SO42-, determined in separate aerosol samples collected on the same flights (Talbot et al., this issue). The results for Pb-210 suggest that some of the difference between the summer troposphere in the high- and sub-Arctic is also due to enhanced stratosphere-troposphere exchange in the vicinity of the Arctic jet. These observations, and other findings from ABLE 3A presented in this issue, suggest that for some species the stratosphere may be a principal source influencing their distribution in the Arctic summer troposphere. For example, intrusions of stratospheric air constitute the dominant source term for tropospheric budgets of Be-7 and ozone, and may be important in the Pb-210, SO42-, and NO(y) budgets. Further investigation, including determination of detailed Be-7 and Pb-210 distributions, is needed to quantify the stratospheric impact on the chemistry of the Arctic troposphere during the summer.