Patterns and Processes in Aerosol Bulk Deposition: Insights from a
9-year Study of 7Be, 210Pb, Sulfate and Major/Trace Elements
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.