Chemical Apportionment of Size-Segregated Atmospheric Particles during the Burning and Wet Seasons in the Brazilian Amazon O. L. Mayol-Bracero (1,2); M. O. Andreae (2); T. W. Andreae (2), P. Artaxo (3), W. Elbert (2), G. Frank (2), S. González (1), A. Hoffer (2), W. Maenhaut (4), L. Soto (1), I. Trebs (2) (1) Institute for Tropical Ecosystem Studies, University of Puerto Rico, San Juan, Puerto Rico, USA, (2) Max Planck Institute for Chemistry, Department of Biogeochemistry, Mainz, Germany (3) Institute of Physics, University of São Paulo, Brazil, (4) Institute for Nuclear Sciences, University of Gent, Belgium For further information please contact, Dr. Olga L. Mayol-Bracero Tel Ext 3430 Fax: We gratefully acknowledge Pascal Guyon for his collaboration with the EGA analyses. This project was funded by EPSCoR program, University of PR and the Max Planck Society. I. IntroductionII. Sampling and Analysis A Dekati low-pressure impactor (DLPI) with 14 stages was used to collect particles with diameters in the range of 0.03 to 10 μm. This sampler was mounted on a tower at 7m height from the ground (Figure 2). Samples were collected on 25-mm aluminum foils. The mass collected on the substrates was determined by gravimetric analyses. Evolved gas analyses (EGA) were performed on quartz filters before and after water extraction to determine the mass concentrations of aerosol total carbon (TC), total hydrogen (TH), elemental carbon (EC) and organic carbon (OC). Ion chromatography was used for the determination of water-soluble ions such as Na +, NH 4 +, K +, Mg 2+, Ca 2+, Cl , NO 3 , and SO 4 2 . Preliminary results presented here include (1) size-resolved mass concentrations of TC and the water-soluble ions and (2) the contribution of these species to the total aerosol burden during a burning and a wet season case. Results presented here exclude the filter stage and the 1 st stage due to technical problems. Biomass burning is a significant source of fine particulate matter to the regional and global atmosphere (Crutzen and Andreae, 1990). The majority of the biomass burning occurs in the tropics with the Amazonia region being one of the major sources of aerosols to the global atmospheric budget (Andreae and Crutzen, 1997). Atmospheric fine particles emitted in biomass burning, composed mostly of organic material, can perturb the atmospheric radiation balance, and thus the climate, in a similar way to anthropogenic sulfate aerosols. This is in part due to their ability to act as efficient cloud condensation nuclei (CCN) (Warner and Twomey, 1967). These smoke particles increase the number of CCN reducing the cloud droplet size and, therefore, modifying rainfall location and intensity. To have a better understanding of these processes, information is needed on the chemical and physical properties of these aerosols. Figure 1. Aerial view of the sampling site, Fazenda Nossa Senhora. As part of the project Smoke Aerosols, Clouds, Rainfall and Climate: Aerosols from Biomass Burning Perturb Global and Regional Climate (LBA-SMOCC), size- resolved chemical characterization was performed on aerosol samples collected in a pasture site in the Brazilian Amazon during the period that includes the burning season and the beginning of the wet season (September-November 2002). Samples were collected at Fazenda Nossa Senhora (10°45’ S, 62°22’ W), in the city of Ouro Preto D’Oeste, in the state of Rondonia, Brazil (Figure 1). This place was deforested 20 years ago. The main combustion sources in this region are the burning of wood, pasture, and waste. Figure 2. Closer view to the sampling site showing the tower and the DLPI impactor (amplified picture). Online instruments measuring physical, chemical, and optical properties of aerosols (e.g., particle concentration, scattering, absorption, CCN number) and trace gases (e.g., CO, O 3, NO x ) were used in the project and supported our measurements. Most of these instruments were inside the house shown in this picture. III. Results Figure 3. Size distribution of mass and chemical species taken by the DLPI. Sample collected during the dry season (daytime), Oct 3, 2002, 8:30 – 17:30. Sampling time was 540 min. IV. Summary and Conclusion Dry Season Wet Season Figure 4. Size distribution of mass and chemical species taken by the DLPI. Sample collected during the beginning of the wet season (daytime), Oct 30 – Nov 1, Sampling time was 1464 min. The scale is different than in the dry season. No TC results are available for this sample. Figure 5. Pie diagrams showing aerosol water-soluble ionic species for the dry season sample. a) total ionic composition, b) fine fraction (D p 1 μm). TC concentration was 66% of the total mass and about 19% of the mass was not identified (residual mass). Figure 6. Pie diagrams showing aerosol water-soluble ionic species for the wet season sample. a) total ionic composition, b) fine fraction (D p 1 μm). TC was not determined here, therefore, residual mass (including TC) constitutes ca. 94% of the total mass. Gravimetric mass μg m -3 Fine μg m -3 Coarse μg m -3 Gravimetric mass μg m -3 Fine μg m -3 Coarse μg m -3 V. References Crutzen, P.J. and Andreae, M.O., Science, 250, , Andreae, M.O. and Crutzen, P.J., Science, 276, , Warner, J. and Twomey, S., J. Appl. Meteorol., 24, , Artaxo et al., J. Geophys. Res.-Atmos., 103, , Guyon et al., J. Geophys. Res.-Atmos., in press, Here we present preliminary results of size-resolved chemical composition for particles emitted during the burning and the beginning of the wet seasons in the Amazon Basin. The concentration of particles emitted to the atmosphere was significantly higher during the burning period and started to decrease as the wet season started (Figures 3-6). Size distributions (Fig 3-4) show that the fine mode consists mainly of TC, SO 4 =, NO 3 -, NH 4 + and K +. During the dry season, the predominant source of this material is the burning of biomass. The coarse fraction is mainly TC (not shown in Fig 4), Cl -, Na +, Mg 2+, Ca 2+, K +, and NO 3 -. Some of these are important constituents of plants and therefore are emitted into the air when plants are burnt, but most of them originate from the emission of primary biogenic material and soil dust (Na +, Ca 2+, Mg 2+, K +, Cl - ). These last two sources predominate during the wet season. Aerosol NO 3 - concentrations depend on the relative abundances of NH 4 + and SO 4 =, therefore the differences between the dry and wet seasons. For more information about the sources of these aerosols see Artaxo et al and Guyon et al Presently, we are finishing the evaluation of the data/samples collected, with emphasis on the carbonaceous fraction (TC, EC, OC and TH). This will give us a complete picture and better understanding of the size-resolved chemical composition of the aerosol collected. With this information, along with the rest of the results generated during this project, we expect to have a better understanding about how smoke particles increase the number of CCN reducing the cloud droplet size and, modifying rainfall location and intensity.