Resuspension of Trace Metals in Belgrade Under Conditions of Drastically Reduced Emission Levels

Abstract

Deposition rates of trace metals (Pb, Cu, Zn, Cd) were determined at the MeteorologicalStation in New Belgrade (Hs = 74 m; ϑ = 44°49′N and λ =20°24′E) in the hydrological year 1992/93 (1 November-31 October). The dominantcharacteristics of the observation period were strong drought and drastically reduced pollutantemissions. Traffic and local sources operated at 0-10% of their capacities. Samples of dry and wetprecipitation were taken by an automatic collector at a height of 2 m at weekly intervals. Twopetri polycarbonate dishes of 93.5 mm diameter, facing upward, and one, facing downward, wereused for dry precipitation sampling. Determination in a ‘clean room’ by differential pulse strippingvoltammetry provided the low detection thresholds of 0.1, 1.0, 0.5 and 2.0 ng mL^-1, i.e. themeasurement of minimal dry deposition rates of 0.02, 0.2, 0.1 and 0.4 µg m^-2d-1 for Cd,Pb, Cu and Zn, respectively. The mean annual deposition rates, expressed in µg m^-2d^-1,were found to be as follows: 4.5 (down), 26 (up) and 37 (wet) for Pb, 2.1 (down), 13 (up) and 36(wet) for Cu, and 3.1 (down), 26 (up) and 95 (wet) for Zn. No values above 0.2 µgm^-2d^-1 were found for the Cd dry deposition rate and no Cd concentration higher than 1 ng mL^-1for precipitation with an amount >0.5 mm at the weekly interval was detected. Using theXREDS method with a scanning electron microscope, Si, Al, Fe matrix elements and Mg, Ca, S,K, P, Cu, Zn, W were identified as minor constituents of the single spherical particles and of theagglomerates present. Pb could not be categorized as a minor constituent of the coarse particlessuspended in the air of New Belgrade on the basis of the previous analysis.

Analysis of meteorological data showed road dust transport by outgoing SE-ESE wind fromthe old city of Belgrade (Hs = 100-250 m) as a possible Pb source at the chosen site, which waslocated in a park. A comparative measurement of Pb deposition on linden leaves was carried outin the vegetation period (1 April-31 October) of 1993 and 1994. The Pb distribution on leavesdiffered in the two growing seasons, while the sum of Pb deposition rates on the downward andupward oriented petri dishes remained practically equal. The Pb accumulation on linden leaveswas higher in 1994, first because of an intensive soil supply by rain water. Besides, ‘yellow’ rainwas reported during the night 15/16 April, on 16 and 17 April 1994. A Fe concentration of 2.3µg mL^-1 and a Pb concentration of 312 ng mL^-1 with a total precipitation of 12.6 mmwere found in the weekly wet sample of 13-20 April. Dry deposition rates of 17 and 84 µgm^-2d^-1 for Cd and Pb, respectively, were measured on the upward facing dishes two weeks later(27 April-4 May). The synoptic analysis confirmed the development of the Saharan cyclogenesisand its influence on the Balkan peninsula in the period of 14 to 17 April 1994. In this region theimpact of dustfall originating from the Saharan storm was evident either during wet deposition orthrough resuspension processes.