Aerosol Populations, Processes, and Ages in Bulk Deposition: Insights From a 9-Year Study of Be-7, Pb-210, Sulfate, and Major/Trace Elements

We report fallout radionuclide (FRN) and major/trace element (MTE) contributions to bulk atmospheric deposition in Hanover, NH, USA (43.7022 degrees N, 72.2896 degrees W). Deposition of Be-7, Pb-210, and SO4 covary [R-2 > 0.4, n = 461] but are discriminated by production sources, depositional mechanisms, meteorological controls, MTE associations, and seasonal biases. Be-7 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 Be-7 affinity for biogenic aerosols. Pb-210 is dominated by dry + washout deposition (54% of total) and convective storms (+107% o.m), 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 Pb-210 (-14%, -4% per year) suggest co-scavenging by PbSO4. Be-7:Pb-210 ratios increase asymptotically with precipitation through the dry-washout-rainout transition and recharge of Be-7. At the global scale, Be-7:Pb-210 increases with precipitation for North American/European sites due to recharge of Be-7 in midlatitude storm belts [R-2 = 0.64, n = 31]. Conversely, Be-7:Pb-210 is independent of precipitation for Southeast/East Asian sites where Be-7 recharge is low [R-2 = 0.01, n = 40]. Globally, Be-7:Pb-210 ratios in dry deposition reflect resuspended aerosols with mean age of ca. 200 days, contributing <5% of Pb-210 deposition. Different aerosol populations contributing to FRN deposition across spatial and temporal scales should emerge as a focus in terrestrial Be-7, Pb-210, and Be-10 tracer applications.