[1] The aerosol characterization experiment performed within the Large-Scale BiosphereAtmosphere Experiment in Amazonia-Smoke, Aerosols, Clouds, Rainfall and Climate (LBA-SMOCC) field experiment carried out in Rondônia, Brazil, in the period from September to November 2002 provides a unique data set of size-resolved chemical composition of boundary layer aerosol over the Amazon Basin from the intense biomassburning period to the onset of the wet season. Three main periods were clearly distinguished on the basis of the PM 10 concentration trend during the experiment: (1) dry period, with average PM 10 well above 50 mg m À3 ; (2) transition period, during which the 24-hour-averaged PM 10 never exceeded 40 mg m À3 and never dropped below 10 mg m À3 ; (3) and wet period, characterized by 48-hour-averaged concentrations of PM 10 below 12 mg m À3 and sometimes as low as 2 mg m À3 . The trend of PM 10 reflects that of CO concentration and can be directly linked to the decreasing intensity of the biomass-burning activities from September through November, because of the progressive onset of the wet season. Two prominent aerosol modes, in the submicron and supermicron size ranges, were detected throughout the experiment. Dry period size distributions are dominated by the fine mode, while the fine and coarse modes show almost the same concentrations during the wet period. The supermicron fraction of the aerosol is composed mainly of primary particles of crustal or biological origin, whereas submicron particles are produced in high concentrations only during the biomass-burning periods and are mainly composed of organic material, mostly water-soluble, and $10% of soluble inorganic salts, with sulphate as the major anion. Size-resolved average aerosol chemical compositions are reported for the dry, transition, and wet periods. However, significant variations in the aerosol composition and concentrations were observed within each period, which can be classified into two categories: (1) diurnal oscillations, caused by the diurnal cycle of the boundary layer and the different combustion phase active during day (flaming) or night (smouldering); and (2) day-to-day variations, due to alternating phases of relatively wet and dry conditions. In a second part of the study, three subperiods representative of the JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D01201, doi:10

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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 .

. RESUMOEntender os processos naturais que regulam a composição da atmosfera é crítico para que se possa desenvolver uma estratégia de desenvolvimento sustentável na região. As grandes emissões de gases e partículas durante a estação seca provenientes das queimadas alteram profundamente a composição da atmosfera amazônica na maior parte de sua área. As concentrações de partículas de aerossóis e gases traço aumentam por fatores de 2 a 8 em grandes áreas, afetando os mecanismos naturais de uma série de processos atmosféricos na região amazônica. Os mecanismos de formação de nuvens, por exemplo, são profundamente alterados quando a concentração de núcleos de condensação de nuvens (NCN) passa de 200 a 300 NCN/cm³ na estação chuvosa para 5.000-10.000 NCN/centímetro cúbico na estação seca. As gotas de nuvens sofrem uma redução de tamanho de 18 a 25 micrômetros para 5 a 10 micrômetros, diminuindo a eficiência do processo de precipitação e suprimindo a formação de nuvens. A concentração de ozônio, um gás importante para a saúde da floresta amazônica passa de cerca de 12 partes por bilhão em volume (ppb) (concentração típica ao meio do dia na estação chuvosa) para valores em regiões fortemente impactadas por queimadas de até 100 ppb, nível que pode ser fitotóxico para a vegetação. O balanço de radiação é fortemente afetado, com uma perda líquida de até 70% da radiação fotossinteticamente ativa na superfície. PALAVRAS CHAVEPartículas de aerossóis, nuvens, precipitação, química atmosférica, gases traço, ozônio. Atmospheric Chemistry in Amazonia:The forest and the biomass burning emissions controlling the composition of the Amazonian atmosphere. Aerosol particles, clouds, precipitation, atmospheric ABSTRACT The understanding of the natural processes that regulate atmospheric composition in Amazonia is critical to the establishment of a sustainable development strategy in the region. The large emissions of trace gases and aerosols during the dry season, as a result of biomass burning, profoundly change the composition of the atmosphere in most of its area. The concentration of trace gases and aerosols increases by a factor of 2 to 8 over large areas, affecting the natural mechanisms of several key atmospheric processes in the region. Cloud formation mechanisms, for instance, are strongly affected when the concentration of cloud condensation nuclei (CCN) changes from 200-300 CCN/cc in the wet season to 5,000-10,000 CCN/cc in the dry season. The cloud droplet radius is reduced from values of 18 to 25 micrometers in the wet season to 5 to 10 micrometers in the dry season, suppressing cloud formation and the occurrence of precipitation under some conditions. Ozone is a key trace gas for changes in the forest health, with concentrations increasing from 12 parts per billion (ppb), at the wet season, to values as high as 100 ppb (in the dry season in areas strongly affected by biomass burning emissions). At this level, ozone could be damaging the vegetation in regions far from the emissions. The atmospheric radiation balance is ...

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Abstract. In this analysis a 3.5 years data set of aerosol and precipitation chemistry, obtained in a remote site in Central Amazonia (Balbina, (1 • 55 S, 59 • 29 W, 174 m a.s.l.), about 200 km north of Manaus) is discussed. Aerosols were sampled using stacked filter units (SFU), which separate fine (d < 2.5 µm) and coarse mode (2.5 µm < d < 10.0 µm) aerosol particles. Filters were analyzed for particulate mass (PM), Equivalent Black Carbon (BC E ) and elemental composition by Particle Induced X-Ray Emission (PIXE). Rainwater samples were collected using a wet-only sampler and samples were analyzed for pH and ionic composition, which was determined using ionic chromatography (IC). Natural sources dominated the aerosol mass during the wet season, when it was predominantly of natural biogenic origin mostly in the coarse mode, which comprised up to 81 % of PM 10 . Biogenic aerosol from both primary emissions and secondary organic aerosol dominates the fine mode in the wet season, with very low concentrations (average 2.2 µg m −3 ). Soil dust was responsible for a minor fraction of the aerosol mass (less than 17 %). Sudden increases in the concentration of elements as Al, Ti and Fe were also observed, both in fine and coarse mode (mostly during the April-may months), which we attribute to episodes of Saharan dust transport. During the dry periods, a significant contribution to the fine aerosols loading was observed, due to the large-scale transport of smoke from biomass burning in other portions of the Amazon basin. This contribution is associated with the enhancement of the concentration of S, K, Zn and BC E . Chlorine, which is commonly associated to sea salt and also to biomass burning emissions, presented higher concentration not only during the dry season but also for the April-June months, due to the establishment of more favorable meteorological conditions to the transport of Atlantic air masses to Central Amazonia. The chemical composition of rainwater was similar to those ones observed in other remote sites in tropical forests. The volume-weighted mean (VWM) pH was 4.90. The most important contribution to acidity was from weak organic acids. The organic acidity was predominantly associated with the presence of acetic acid instead of formic acid, which is more often observed in pristine tropical areas. Wet deposition rates for major species did not differ significantly between dry and wet season, except for NH + 4 , citrate and acetate, which had smaller deposition rates during dry season. While biomass burning emissions were clearly identified in the aerosol component, it did not present a clear signature in rainwater. The biogenic component and the long-range transport of sea salt were observed both in aerosols and rainwater composition. The results shown here indicate that in Central Amazonia it is still possible to observe quite pristine atmospheric conditions, relatively free of anthropogenic influences.

While the amount of reactive nitrogen circulating at the global level has increased markedly in the last century, the effects of this increase are largely seen at the regional level due to interacting ecological and socio-economic factors. In contrast with most other regions of the world, Latin America and the Caribbean (LA-Ca) stand out due to the fact that the major input of reactive nitrogen (Nr) still occurs naturally via biological nitrogen fixation (BNF) in natural ecosystems as opposed to anthropogenic inputs of synthetic fertilizer, fossil fuel combustion and cropping with leguminous species. Largely due to economic reasons, the consumption of fertilizer N in the LA-Ca region is still low in comparison with the average consumption of the world. However, the fertilizer N consumption is increasing at a much faster rate than that in developed regions of the world, like Biogeochemistry (2006)

A long-term (2-3 years) measurement of aerosol and precipitation chemistry was carried out in a remote site in Central Amazonia, Balbina, (1 • 55 ′ S, 59 • 29 ′ W, 174 m above sea level), about 200 km north of Manaus city. Aerosols were sampled using stacked filter units (SFU), which separate fine (d<2.5 µm) and coarse mode 5 (2.5 µm