Abstract. 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 (NH 3 ), nitric acid (HNO 3 ), nitrous acid (HONO), nitrogen dioxide (NO 2 ), nitric oxide (NO), ozone (O 3 ), aerosol ammonium (NH + 4 ) and aerosol nitrate (NO − 3 ) were measured in real-time, accompanied by simultaneous meteorological measurements. Dry deposition fluxes of NO 2 and HNO 3 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 NH 3 and HONO are estimated by applying a "canopy compensation point model". N dry and wet deposition is dominated by NH 3 and NH + 4 , which is largely the consequence of biomass burning during the dry season. TheCorrespondence to: I. Trebs (ivonne@mpch-mainz.mpg.de) grass surface appeared to have a strong potential for daytime NH 3 emission, owing to high canopy compensation points, which are related to high surface temperatures and to direct NH 3 emissions from cattle excreta. NO 2 also significantly accounted for N dry deposition, whereas HNO 3 , HONO and N-containing aerosol species were only minor contributors. Ignoring NH 3 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 NH 3 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 .
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