Measurements and modeling of reactive nitrogen deposition in southeast Brazil

摘要

Increased reactive nitrogen (N_r) deposition due to expansion of agro-industry was investigated considering emission sources, atmospheric transport and chemical reactions. Measurements of the main inorganic nitrogen species (NO_2, NH_3, HNO_3, and aerosol nitrate and ammonium) were made over a period of one year at six sites distributed across an area of ～30,000 km~2 in southeast Brazil. Oxidized species were estimated to account for～90% of dry deposited N_r, due to the region's large emissions of nitrogen oxides from biomass burning and road transport. NO_2-N was important closer to urban areas, however overall HNO_3-N represented the largest component of dry deposited N_r. A simple mathematical modeling procedure was developed to enable estimates of total N_r dry deposition to be made from knowledge of NO_2 concentrations. The technique, whose accuracy here ranged from <1% to 29%, provides a useful new tool for the mapping of reactive nitrogen deposition.