Measurements and modeling of reactive nitrogen deposition in southeast Brazil A.G. Allen a, * , C.M.D. Machado b , A.A. Cardoso a a Department of Analytical Chemistry, Institute of Chemistry, State University of São Paulo, CP 355,14800-900 Araraquara, SP, Brazil b Department of Chemistry, Institute of Exact and Earth Sciences, Federal University of Amazonas, Campus Universitário, Coroado I, Manaus, AM, Brazil A new procedure based on NO 2 measurements is used to estimate reactive nitrogen deposition in a developing region experiencing agro-industrial growth. article info Article history: Received 21 October 2010 Received in revised form 27 January 2011 Accepted 1 February 2011 Keywords: Reactive nitrogen Dry deposition Nitric acid Nitrogen dioxide Agriculture abstract Increased reactive nitrogen (N r ) deposition due to expansion of agro-industry was investigated consid- ering 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 w130,000 km 2 in southeast Brazil. Oxidized species were estimated to account for w90% 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. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Under natural conditions, the atmosphere is the main source of essential nutrients, which are transferred to the surface by dry deposition of gases and aerosols, or in rainwater (Avila et al., 1998; Garstang et al., 1998). The relative importance of the dry deposition route is influenced not only by the prevalence of wet or dry meteorological conditions, but also increasingly by anthropogenic pollution of the lower troposphere (Lohse et al., 2009; Lovett, 1994). Reactive nitrogen (N r ) is the only major nutrient present in the atmosphere in both gaseous and particulate forms, whose specia- tion is governed by both primary emissions and secondary reac- tions (Finlayson-Pitts and Pitts, 2000). In rural areas, soil emissions are an important source of nitrogen oxides, but these can be dwarfed by emissions from combustion of fossil fuels, biofuels and biomass. Agro-industry has become the largest single source of ammonia, while over the last century anthropogenic production of N r has increased by a factor of w9, with agricultural cultivation responsible for w30% of the total emission (Erisman et al., 2007; Galloway and Cowling, 2002; Galloway et al., 2004). Increased N r deposition is of concern since greater inputs to natural ecosystems can cause acidification, eutrophication, reduc- tion of species diversity and altered biological productivity (Chen and Driscoll, 2004). In the tropics, outside of large conurbations, increased atmospheric N r concentrations are mainly a result of land-use change, agricultural expansion and installation of new industries (Galloway et al., 2004, 2008; Gruber and Galloway, 2008; Martinelli et al., 1999). With increased deposition, the relative importance of biological nitrogen fixation is reduced in soils and aquatic systems (Fu and Winchester, 1994; Holland et al., 1999; Vitousek et al., 1997), and under these conditions phosphorus or other micronutrients may become limiting, rather than nitrogen (Ahn and James, 2000; Davis, 1994; Hatch et al., 2001). On the other hand, inputs of additional N r from the atmosphere to agricultural systems could be useful, serving to reduce fertilizer costs. Deposition rates depend on the physical and chemical proper- ties of the different N r species, as well as on meteorological conditions and the nature of the receptor surface. The range of dispersal due to atmospheric transport can be up to several thou- sand kilometers, depending on the nitrogen species present (in gaseous, aerosol or dissolved forms) and the efficiencies of the removal processes (Chadwick et al., 1999; Vitousek and Sanford, 1986). It is therefore important to understand the roles of trans- port and reaction, to assist in mapping of deposition. The present work reports on the spatial distribution and dry deposition of atmospheric reactive nitrogen in a developed * Corresponding author. E-mail addresses: andrew@pq.cnpq.br (A.G. Allen), cristinemachado@ufam. edu.br (C.M.D. Machado), cristinemachado@ufam.edu.br (A.A. Cardoso). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol 0269-7491/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2011.02.002 Environmental Pollution 159 (2011) 1190e1197