Relationships between Pb and ²¹⁰Pb in aerosol and precipitation at a Semiremote Site in northern Wisconsin

Abstract

Measurements of A1, Pb, 21øpb, and 21øpo in precipitation and aerosol were used to estimate wet and dry components of the atmospheric flux at a semiremote site in northern Wisconsin. Wet deposition was primarily responsible for removing airborne Pb, 21øpb, and 2•øpo, while dry deposition was also important for A1. Although Pb and 2•øpb both exhibited a wet/total ratio of about 0.8, precipitation washout ratios for Pb and 2•øpb suggested that 2•øpb was washed from the atmosphere with greater efficiency than was Pb. This phenomenon was also illustrated by comparing the weighted mean annual specific activity in precipitation (976 pCi 21øpb mg -• Pb) and in aerosol (476 pCi 21øpb mg -• Pb) at this site between June 1979 and June 1980. By consideration of the apparent differential precipitation washout of Pb and 2•øpb, a reasonable estimate of the atmospheric flux of Pb was obtained by using the mean Pb/2• øPb ratio in aerosol and the 21Opb flux. The atmospheric flux to northern Wisconsin was estimated to be 0.8 #g crn -2 yr -• for Pb and 0.70 pCi cm -2 yr -• for 2•øpb. INTRODUCTION Despite convincing evidence that the atmosphere is the principal source of lead to the oceans [Duce et al., 1976; Patterson et al., 1976; Schaule and Patterson, 1981; Settle and Patterson, 1982] and many freshwater lakes [Winchester and Nifon•?, 1971; Gatz, 1975; Eisenreich, 1980; Talbot, 1981], surprisingly few data have been reported on wet and dry deposition of Pb and the naturally occurring radionuclide 2'øpb (t,/z = 22.3 years) to surface waters. In most cases the atmospheric fluxes of Pb and •"øPb have been inferred from their accumulation rates in sediments. Although this sometimes provides an adequate time-averaged record of lead deposition for chronological and historical input purposes, the specific aspects of the atmospheric input are not revealed. Furthermore, sedimentation regimes and postdepositional processes may redistribute the lead, making such natural repositories unreliable indicators of the actual lead flux. It is therefore highly desirable to conduct atmospheric sampling to estimate atmospheric input to the system. In conjunction with our studies of lead transport within lake systems (R. W. Talbot and A. W. Andren, unpublished manuscript, 1982), it was also of particular interest to us to explore the relationships between Pb and 2•øpb in both precipitation and aerosol over a period of 1 year. These measurements have been used to assess the relative contributions of wet and dry fallout to the total atmospheric deposition of Pb and 2 • Opb ' The specific activity (picocuries of 2• Opb per milligram of Pb) and the ratios Pb/A1 and 2•øPb/A1 have been employed to evaluate the potential for using 2•øpb as a natural geochemical tracer of Pb at sites removed from direct urban influence. SAMPLE COLLECTION Atmospheric sampling was conducted at a site within the Northern Highlands State Forest of north central Wisconsin (Vilas County). The site (46ø3'N, 89ø39'W) is about 80 km southeast of Lake Superior and 190 km west of the no...

Depositional characteristics of 7Be and 210Pb in southeastern Michigan

“…The washout ratios for 7 Be and 210 Pb varied between 210–2097, (mean: 948) and 55–2244, (mean: 637), respectively (Table 8). These values can be compared to the values in other places: mean value of 780 for 210 Pb in the Northern Wisconsin, Talbot and Andren [1983]; 370 and 215, for 7 Be and 210 Pb, respectively, Todd et al [1989] for the Southeastern Virginia coast ; 144 for 7 Be at Thessaloniki, Greece (40°38′N; 22°58′E [ Papastefanou and Ioannidou , 1991]); and 30 for 210 Pb, for the Western North Atlantic, Hussain et al [1998].…”

“…The possibility of differential washout of 7 Be and 210 Pb always exist and cannot be ruled out from our data. Talbot and Andren [1983] have shown that 210 Pb was removed from the atmosphere with greater efficiency than was stable Pb and attributed this difference to the source function of these species. In the case of atmospheric 210 Pb, most of it is derived from the decay of 222 Rn that reaches some heights in the atmosphere before its decay while most of the stable Pb was derived from gaseous emission sources and confined to limited vertical distances above the Earth's surface.…”

Po-210 and Pb-210 as atmospheric tracers and global atmospheric Pb-210 fallout: a Review

“…However, if another air mass is intruding from an adjacent area and the precipitation is derived from that air mass, then, this value could result in considerable error. The average washout ratios based on 210 Pb is reported to vary between 30e2500 (mean: 780, Northern Wisconsin, Talbot and Andren, 1983;215 Southeastern Virginia, Todd et al, 1989; 30 for the Western North Atlantic, Hussain et al, 1998;637 for Detroit, Michigan, McNeary and Baskaran, 2003;1908for southeastern Spain, Dueñas et al, 2005. There is only one set of data exist for the washout ratio based on 210 Po.…”

“…Concentrations of 210 Po in surface air vary widely, ranging from 0.01 to 0.26 mBq m À3 (Moore et al, 1973;Talbot and Andren, 1983;McNeary and Baskaran, 2007). Kim et al (2005) reported excess 210 Po in Seoul (S. Korea) and attributed this excess to anthropogenic sources associated with burning and incineration processes.…”

“…It has been shown that there is a very strong correlation between airborne concentrations of Al and total suspended particulate matter (collected using Whatman 41) when the ground is not covered with snow (e.g., Talbot and Andren, 1983). A major portion of these dusts are derived from dust storms in sub-tropical highs at latitudes near 30 where most of the deserts occur.…”