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

Abstract

Dry and wet deposition of atmospheric nitrogen species (NO2 and HNO3) 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 one year of hourly meteorological data. Emission information included a typical diurnal variation of area source emissions. Annual atmospheric nitrogen (N-NO2 + N-HNO3) deposition to 1763 km2 of the river was 35600 kg-N yr-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 1763 km2 of the river varied from 1628 kg-N month-1 in February to 3799 kg-N month-1 in December, following the monthly occurrence of offshore winds. Monthly wet deposition varied from 1 kg-N month-1 in June to 1162 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 yr-1 near the shoreline, which was reduced to the half at 4 km from the coast.