Comparison of Rainwater composition at two sites in Amazonia for dry and wet seasons Comparison of Rainwater composition at two sites in Amazonia for dry and wet seasons Theotonio Pauliquevis 1, Paulo Artaxo 1, Luciene L. Lara 2, Norbert. Miekeley 3, Eduardo T. Fernandes 1. [1] Instituto de Física, Universidade de São Paulo, Rua do Matão, Travessa R, 187, São Paulo, SP, CEP , Brazil. 2 Isotopic Ecology Lab - CENA/USP, Universidade de São Paulo, Av. Centenario, 303, CEP , Piracicaba, SP, Brazil, 3 Departamento de Química, Pontifícia Universidade Católica do Rio de Janeiro, Rio de Janeiro, Brazil, 1) Introduction In this work, rainwater samples from two sites in Amazonia were collected as part of the LBA Experiment. The first site, Rondonia, is located in the western part of Amazonia, and is a heavily disturbed site with significant land use changes. The rainwater sampling was performed from February 1999 to May 1999, only during the wet season. The second sampling site, named Balbina is located in Central Amazonia, about 150 Km North of Manaus. In Balbina, rainwater sampling was performed from April 1998 to May 1999, and is a pristine region, relatively free from biomass burning impacts, representative of natural Amazonian conditions. Samples were analyzed by Ion Chromatography for major cations and anions, and for about 50 trace elements by Induced Coupled Plasma – Mass Spectrometry (ICP- MS). 3) Results and discussion of data Table 1 presents the Volume Weighted Means (VWM) values for the Balbina and Rondonia sites and the comparison of these values with other sites in Central Amazonia. Graphics I and II show the correlation between Na+ and Cl - for both sites. For Balbina, the angular coefficient is 1.07, very close to the Cl/Na ratio in seawater (=1.16). In the graphics III and IV we compare the Na+ results of IC with ICP. Given that IC measures only the soluble fraction and the ICP-MS measures the total amount, its possible to observe a good agreement for Balbina and a not significant correlation for Rondonia, suggesting additional sources of sodium. Graph V: the time series of K, Cl and BC shows a high correlation between K and Cl, but not with black carbon, indicating a natural biogenic source of KCl Graphs I and II: the linear relation between Cl and Na shows the strong presence of marine aerosol at Balbina References M. C. Forti et al, Rainfall composition in two ecosystems in the northeastern Brazilian Amazon (Amapá State);J. Geophys. Res., 105, 28, , 2000 M. C. Forti et al, Química da precipitação e Transprecipitação na Mata Atlântica: uma comparação entre duas áreas constrastantes, unpublished. Williams, M.R., Fischer, T.R.,Melack, J.M., Chemical Composition And Deposition Of Rain In The Central Amazon, Brazil, Atmospheric Environment, 31(2), pp , ) Sampling methods and analytical techniques Samples were collected using Aerochem rainwater wet-only collectors. After collection, the samples were separated in three fractions: to the first, was added Thymol, a biocide, and analyzed by Ionic Chromatography (IC). To the second was added HNO3, and analyzed by the ICP-MS technique, and the third fraction was used to measure pH, still in the field. The samples were not filtered, and were collected by event. The samples were analyzed for principal ions (Cl -, Na +, SO 4 2-, Ca 2+, Mg 2+, K +, NO 3 - ) by IC, and compared to measurements by ICP-MS. Volume Weighted Mean (μM/l) pHH+H+ Cl - NO 3 - SO 4 2- Ca 2+ Mg 2+ Na + K+K+ Williams (Central Amazonia Forti (Northeastern Amazonia) Forti (Atlantic Forest) Balbina (this work) Rondonia (this work) Total deposition (kg ha -1.yr -1) H+H+ Cl - NO 3 - SO 4 2- Ca 2+ Mg 2+ Na + K+K+ Williams Central Amazonia Forti (Northeastern Amazonia) Forti (Atlantic Forest) Balbina (this work) Rondonia (this work) Table 1: Volume weighted mean concentration of rainwater in remote areas of AmazoniaTable 2: Total wet deposition at the same sites of table 1 In graphic V we show for Rondonia, the time series for K, Cl and Na. Its possible to see a correlation between K+ and Cl- concentrations (not present at Balbina), suggesting the existence of KCl, a biomass burning tracer. However, KCl have no correlation with the Black Carbon (BC) concentrations at the same period. It suggests the existence of some natural biogenic source of KCl at Rondônia during the wet season, and not a biomass burning origin. At Table 2, we show the annual deposition of these ions for the several sites. Graphs III and IV: the comparison between IC and ICP-MS shows that Na is not totally soluble in Rondônia. Some unidentified Na source is present Acknowledgments: We acknowledge the support of FAPESP and CNPq/Instituto do Milênio of LBA for this project.