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Patterns and Processes in Aerosol Bulk Deposition: Insights from a 9-year Study of 7Be, 210Pb, Sulfate and Major/Trace Elements
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  • Joshua David Landis,
  • Xiahong Feng,
  • James M. Kaste,
  • Carl Renshaw
Joshua David Landis
Dartmouth College

Corresponding Author:[email protected]

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Xiahong Feng
Dartmouth College
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James M. Kaste
College of William and Mary
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Carl Renshaw
Dartmouth College
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Abstract

We report fallout radionuclide (FRN) and major/trace element (MTE) contributions to bulk atmospheric deposition in Hanover, NH USA (43.7022° N, 72.2896° W). Deposition of 7Be, 210Pb and SO4 covary [R2>0.4, n=461] but are discriminated by production sources, depositional mechanisms, meteorological controls, MTE associations, and seasonal biases. 7Be is dominated by rainout (78% of total deposition), recharged by long-range transport (+23% over mean, o.m.), influenced by stratosphere-troposphere-exchange (+9% o.m.) and solar activity (-2% per doubling of sunspot count). Correlation with particulate nitrogen (+9% per doubling of N) indicates 7Be affinity for biogenic aerosols. 210Pb is dominated by dry+washout deposition (54% of total) and convective storms (+107% o.m), is depleted in marine moisture sources (-133% o.m.), correlated with S (+9% per doubling of S) and biased to autumn with Mn, Hg, and V (+7% o.m.). Coincident long-term declines in S and 210Pb (-14%, -4% per year) suggest co-scavenging by PbSO4. 7Be:210Pb ratios increase asymptotically with precipitation through the dry-washout-rainout transition and recharge of 7Be. At the global scale, 7Be:210Pb increases with precipitation for North American/European sites due to recharge of 7Be in mid-latitude storm belts [R2=0.64, n=31]. Conversely, 7Be:210Pb is independent of precipitation for Southeast/East Asian sites where 7Be recharge is low [R2=0.01, n=40]. Globally, 7Be:210Pb ratios in dry deposition reflect resuspended aerosols with mean age of ca. 200 days, contributing <5% of 210Pb deposition. Different aerosol populations contributing to FRN deposition across spatial and temporal scales should emerge as a focus in terrestrial 7Be, 210Pb and 10Be tracer applications.