Dry and Wet Deposition of Nitrogen Emitted in Buenos Aires City to Waters of de la Plata River

摘要

Dry and wet deposition of atmospheric nitrogen species (NO_2 and HNO_3) coming from nitrogen oxides emissions in Buenos Aires city to surface waters of de la Plata River were estimated. Atmospheric dispersion models DAUMOD-RD (v.2) and CALPUFF were applied to area and point sources, respectively. These models were run considering 1 year of hourly meteorological data. Emission information included a typical diurnal variation of area source emissions. Annual atmospheric nitrogen (N-NO_2+N-HNO_3) deposition to 1,763 km_2 of the river was 35,600 kg-N year~(-1). Dry deposition processes accounted for 89% of this value. The small contribution of wet deposition was a consequence of the very few cases (5%) of rain events during offshore wind conditions. Monthly dry deposition to 1,763 km of the river varied from 1,628 kg-N month ' in February to 3,799 kg-N month ' in December, following the monthly occurrence of offshore winds. Monthly wet deposition varied from 1 kg-N month~(-1) in June to 1,162 kg-N month~(-1) in February. These results came from the combination of favorable conditions for formation of HNO3 and the occurrence of precipitation during offshore wind situations. Spatial distribution of annual atmospheric N deposition showed a strong coastal gradient. Deposition values reached a maximum of 137.1 kg-N km~(-2) year~(-1) near the shoreline, which was reduced to the half at 4 km from the coast.