An examination of the atmospheric chemistry of mercury using 210Pb and 7Be.

Abstract

Measurements of Hg (total gas-phase, precipitation-phase andparticulate-phase), aerosol mass, particulate 210Pb and7Be and precipitation 210Pb were made at an atmosphericcollection station located in a near remote area of northcentral Wisconsin,U.S.A. (46°10′N, 89°50′W) during the summers of 1993, 1994and 1995. Total Hg and 210Pb were observed to correlate strongly(slope = 0.06 ± 0.03 ng mBq-1; r 2 =0.72) in rainwater. Mercury to 210Pb ratios in particulate matter(0.03 ± 0.02 ng mBq-1; r 2 = 0.06) wereconsistent with the ratio in rain. Enrichment of the Hg/mass ratio (approx.5–50×) relative to soil and primary pollutant aerosols indicatedthat gas-to-particle conversion had taken place during transport. Comparisonof these results with models for the incorporation of Hg into precipitationindicates that atmospheric particles deliver more Hg to precipitation than canbe explained by the presence of soot. A lack of correlation between totalgas-phase Hg (TGM) and a 7Be/210Pb function suggests novertical concentration gradient within the troposphere, and allows an estimateof TGM residence time of 1.5 ± 0.6 yr be made based on surface airsamples.