Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 6 2 2006 10.5194/acp-6-447-2006 http://www.atmos-chem-phys.net/6/447/2006/ http://www.atmos-chem-phys.net/6/447/2006/acp-6-447-2006.html http://www.atmos-chem-phys.net/6/447/2006/acp-6-447-2006.pdf 447 469 2006-02-08 Dry and wet deposition of inorganic nitrogen compounds to a tropical pasture site (Rondônia, Brazil) I. Trebs L. L. Lara L. M. M. Zeri L. V. Gatti P. Artaxo R. Dlugi J. Slanina M. O. Andreae F. X. Meixner Max Planck Institute for Chemistry, Biogeochemistry Department, P.O. Box 3060, 55020, Mainz, Germany Centro de Energia Nuclear na Agricultura (CENA), Laboratorio de Ecologia Isotópica, Universidade de São Paulo (USP), Av. Centenario, 303 13400-970, Piracicaba, São Paulo, SP, Brazil Max Planck Institute for Biogeochemistry, Department Biogeochemical Processes, Hans-Knöll-Straße 10, 07745 Jena, Germany Instituto de Pesquisas Energéticas e Nucleares, CQMA, Atmospheric Chemistry Laboratory, Av. Prof. Lineu Prestes, 2242, Cidade Universitaria, CEP 055508-900, São Paulo, SP, Brazil Instituto de Física, Universidade de São Paulo (USP), Rua do Matão, Travessa R, 187, CEP 05508-900, São Paulo, SP, Brazil Working Group Atmospheric Processes (WAP), Gernotstrasse 11, 80804 Munich, Germany Peking University, College of Environmental Sciences, Beijing 100871, China The input of nitrogen (N) to ecosystems has increased dramatically over the past decades. While total (wet + dry) N deposition has been extensively determined in temperate regions, only very few data sets of N wet deposition exist for tropical ecosystems, and moreover, reliable experimental information about N dry deposition in tropical environments is lacking. In this study we estimate dry and wet deposition of inorganic N for a remote pasture site in the Amazon Basin based on in-situ measurements. The measurements covered the late dry (biomass burning) season, a transition period and the onset of the wet season (clean conditions) (12 September to 14 November 2002) and were a part of the LBA-SMOCC (Large-Scale Biosphere-Atmosphere Experiment in Amazonia – Smoke, Aerosols, Clouds, Rainfall, and Climate) 2002 campaign. Ammonia (NH₃), nitric acid (HNO₃), nitrous acid (HONO), nitrogen dioxide (NO₂), nitric oxide (NO), ozone (O₃), aerosol ammonium (NH₄⁺) and aerosol nitrate (NO₃^-) were measured in real-time, accompanied by simultaneous meteorological measurements. Dry deposition fluxes of NO₂ and HNO₃ are inferred using the ''big leaf multiple resistance approach'' and particle deposition fluxes are derived using an established empirical parameterization. Bi-directional surface-atmosphere exchange fluxes of NH₃ and HONO are estimated by applying a ''canopy compensation point model''. N dry and wet deposition is dominated by NH₃ and NH₄⁺, which is largely the consequence of biomass burning during the dry season. The grass surface appeared to have a strong potential for daytime NH₃ emission, owing to high canopy compensation points, which are related to high surface temperatures and to direct NH₃ emissions from cattle excreta. NO₂ also significantly accounted for N dry deposition, whereas HNO₃, HONO and N-containing aerosol species were only minor contributors. Ignoring NH₃ emission from the vegetation surface, the annual net N deposition rate is estimated to be about −11 kgN ha^-1 yr^-1. If on the other hand, surface-atmosphere exchange of NH₃ is considered to be bi-directional, the annual net N budget at the pasture site is estimated to range from −2.15 to −4.25 kgN ha^-1 yr^-1.