Sorption Behavior and Aerosol–Particulate Transitions of ⁷Be, ¹⁰Be, and ²¹⁰Pb: A Basis for Fallout Radionuclide Chronometry

Abstract

We investigated the partitioning of 7Be, 10Be, and 210Pb aerosols between operationally dissolved and >0.5 μm particulate fractions in wet and dry atmospheric deposition. Bulk deposition in situ-log­(K D ) averaged 4.27 ± 0.46 for 7Be and 4.79 ± 0.59 for 210Pb (±SD, n = 163), with corresponding activity-fractions particulate (f P) = 24 and 48%. K D was inversely correlated with particulate mass concentration (p C ), a particle concentration effect (p.c.e.) that indicates that dissolved 7Be and 210Pb are bound to submicron colloids. Experimental desorption-K D was higher than in situ by a factor of 20 for 7Be and 4 for 210Pb (n = 27), indicating that FRN sorption to particulates was irreversible. 7Be:10Be ratios confirmed that colloidal and particulate fractions were geochemically distinct, with corresponding ages of 120 ± 30 and 260 ± 45 days, respectively [mean ± SE, n = 9, p = 0.011]. Fractions particulate f Be7, f Be10, and f Pb210 each increased with 7Be:10Be bulk age, a particle-age effect (p.a.e). In multiple regression, f Be7 was best predicted by N, Mn, Al, and Ni [R 2 = 0.75, p < 0.0001], whereas f Pb relied on N, S, Fe, and Mn [R 2 = 0.69, p < 0.0001]. Despite differences in magnitude and controls on partitioning, the ratio f Be :f Pb converged to 1 with p C in the range of 10–100 mg L–1. Given sufficient solid surfaces, irreversible sorption and p.a.e. form a basis for 7Be:210Pb chronometry of aerosol biogeochemical cycling.

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

“…Regressions and shaded confidence intervals are shown by region: NAE, 7 Be: 210 Pb = 4.5(±1.6) + 0.095(±0.013)· p D ; SAE, 7 Be: 210 Pb = 5.4(±0.7) + 0.002(±0.004)· p D ; SAE‐j, 7 Be: 210 Pb = 3.7(±4.6) + 0.012(±0.028)· p D . For sites with multi‐year records, 1‐sigma confidence ellipses and linear fits display interannual variation (none significant at p < 0.05): (a) Malaga ( n = 11, Dueñas et al., 2017); (b) Monaco ( n = 13, Pham et al., 2013); (c) Hanover ( n = 9; Landis et al., 2021); (d) Shanghai ( n = 7, Du et al., 2015); (e) Rokkasho ( n = 5, Akata et al., 2008); (f) Tatsunokuchi ( n = 12, Yamamoto et al., 2006); (g) Taipei ( n = 17, H. I. Lee et al., 2015).…”

“…We can similarly estimate the age of recycled aerosols using 7 Be: 210 Pb ratios, provided these assumptions (Landis et al., 2014): that the aerosols have an initial 7 Be: 210 Pb ratio equal to that of flux‐weighted precipitation (=10.8, see also Landis et al., 2021), that FRNs accumulate in aerosols at constant rate and are lost only through radioactive decay (open‐system model), and that that there is no fractionation between the FRNs. In this case, the dry‐deposited particles have a mean time in atmospheric transport, deposition, and resuspension of about 180 days (Figure 4).…”

“…These are described in detail by Landis et al. (2021). Upon retrieval, these collectors were weighed to measure p D .…”

“…Collectors were of identical polyethylene construction, trace-metal clean, with open area = 650 cm 2 , volume = 20 L, and surface area index = 5.2 (total interior surface to projected ground surface areas). The "A" collector was acidified following collection to recover total FRN deposition and the "B" collector was not acidified to allow speciation analyses of FRNs (described by Landis et al [2021]). Collectors were placed at a height of 40 cm on a stable aluminum base above the natural lawn to prevent toppling or rainwater splash from exposed soil.…”

“…G Kim et al (1999),. G Kim et al (2000),Laguionie et al (2014),Lal et al (1979),Landis et al (2021),. H. I Lee et al (2015),.…”