| Popis: |
Submicron aerosol deposition to outdoor vegetation was evaluated by measuring vegetation and air concentrations of 212Pb, 214Pb, and 7Be attached to atmospheric aerosols. A biomass-normalized deposition velocity (VD), with units of m3 kg−1 s−1, was used to compare species and isotopes with respect to air-to-vegetation transfer rates. For 212Pb ( t 1 2 = 10·64 h ), higher night-time air concebtrations dominate deposition, while for 214Pb ( t 1 2 = 26·8 min ), deposition measurements over shorter time periods relative to changing atmospheric conditions were possible. Calculated VD values were usually higher for 214Pb, possibly reflecting wind-enhanced deposition during the afternoon period of sampling. Evergreen species, including pines, were not appreciably different from deciduous species. Most striking was the narrow range of results (factor of 6 for 34 212Pb measurements of 20 species). Beryllium-7 ( t 1 2 = 53·3 d ) was used to evaluate time-integrated deposition by sampling vegetation in California near the end of dry summers. Similar deposition rates were found for this isotope. The results of the study indicated that naturally radioactive atmospheric aerosols can be used to understand the dynamics of submicron aerosol deposition to ecosystems. |
