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Graham, B, Mayol-Bracero OL, Guyon P, Roberts GC, Decesari S, Facchini MC, Artaxo P, Maenhaut W, Koll P, Andreae MO.  2002.  Water-soluble organic compounds in biomass burning aerosols over Amazonia - 1. Characterization by NMR and GC-MS. Journal of Geophysical Research-Atmospheres. 107   10.1029/2001jd000336   AbstractWebsite

[1] As part of the European contribution to the Large-Scale Atmosphere-Biosphere Experiment in Amazonia (LBA-EUSTACH), aerosols were sampled at representative pasture and primary rainforest sites in Rondonia, Brazil, during the 1999 "burning season" and dry-to-wet season transition (September-October). Water-soluble organic compounds (WSOCs) within the samples were characterized using a combination of H-1 Nuclear Magnetic Resonance (NMR) spectroscopy for chemical functional group analysis, and Gas Chromatography-Mass Spectrometry (GC-MS) for identification and quantification of individual low-molecular-weight compounds. The H-1 NMR analysis indicates that WSOCs are predominantly aliphatic or oxygenated aliphatic compounds (alcohols, carboxylic acids, etc.), with a minor content of aromatic rings carrying carboxylic and phenolic groups. Levoglucosan (1,6-anhydro-beta-D-glucose), a well-known cellulose combustion product, was the most abundant individual compound identified by GC-MS (0.04-6.90 mug m(-3)), accounting for 1-6% of the total carbon (TC) and 2-8% of the water-soluble organic carbon (WSOC). Other anhydrosugars, produced by hemicellulose breakdown, were detected in much smaller amounts, in addition to series of acids, hydroxyacids, oxoacids, and polyalcohols (altogether 2-5% of TC, 3-6% of WSOC). Most correlated well with organic carbon, black carbon, and potassium, indicating biomass burning to be the major source. A series of sugar alcohols (mannitol, arabitol, erythritol) and sugars (glucose, fructose, mannose, galactose, sucrose, trehalose) were identified as part of the natural background aerosol and are probably derived from airborne microbes and other biogenic material. The bulk of the WSOCs (86-91% WSOC) eluded analysis by GC-MS and may be predominantly high-molecular weight in nature.

Guyon, P, Boucher O, Graham B, Beck J, Mayol-Bracero OL, Roberts GC, Maenhaut W, Artaxo P, Andreae MO.  2003.  Refractive index of aerosol particles over the Amazon tropical forest during LBA-EUSTACH 1999. Journal of Aerosol Science. 34:883-907.   10.1016/s0021-8502(03)00052-1   AbstractWebsite

Optical properties of aerosol particles were characterized during two field campaigns at a remote rainforest site in Rond (o) over cap nia, Brazil, as part of the project European Studies on Trace Gases and Atmospheric Chemistry, a contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH). The measurements included background (wet season), biomass burning (dry season), and transition period conditions. Optical measurements of light scattering and absorption were combined with data on number/size distributions in a new iterative method, which retrieves the effective imaginary refractive index of the particles at a wavelength of 545 nm. For ambient relative humidities lower than 80%, background aerosols exhibited an average refractive index of 1.42 - 0.006i. Biomass burning aerosols displayed a much larger imaginary part, with an average refractive index of 1.41 - 0.013i. Other climate-relevant parameters were estimated from Mie calculations. These include single-scattering albedos of 0.93 +/- 0.03 and 0.90 +/- 0.03 (at ambient humidity), asymmetry parameters of 0.63 +/- 0.02 and 0.70 +/- 0.03, and backscatter ratios of 0.12 +/- 0.01 and 0.08 +/- 0.01 for background and biomass burning aerosols, respectively. (C) 2003 Published by Elsevier Ltd.

Guyon, P, Graham B, Beck J, Boucher O, Gerasopoulos E, Mayol-Bracero OL, Roberts GC, Artaxo P, Andreae MO.  2003.  Physical properties and concentration of aerosol particles over the Amazon tropical forest during background and biomass burning conditions. Atmospheric Chemistry and Physics. 3:951-967.   10.5194/acp-3-951-2003   AbstractWebsite

We investigated the size distribution, scattering and absorption properties of Amazonian aerosols and the optical thickness of the aerosol layer under the pristine background conditions typical of the wet season, as well as during the biomass-burning-influenced dry season. The measurements were made during two campaigns in 1999 as part of the European contribution to the Large-Scale BiosphereAtmosphere Experiment in Amazonia (LBA-EUSTACH). In moving from the wet to the dry season, median particle numbers were observed to increase from values comparable to those of the remote marine boundary layer (similar to400 cm(-3)) to values more commonly associated with urban smog (similar to4000 cm(-3)), due to a massive injection of submicron smoke particles. Aerosol optical depths at 500 nm increased from 0.05 to 0.8 on average, reaching a value of 2 during the dry season. Scattering and absorption coefficients, measured at 550 nm, showed a concomitant increase from average values of 6.8 and 0.4 Mm(-1) to values of 91 and 10 Mm(-1), respectively, corresponding to an estimated decrease in single-scattering albedo from ca. 0.97 to 0.91. The roughly tenfold increase in many of the measured parameters attests to the dramatic effect that extensive seasonal biomass burning (deforestation, pasture cleaning) is having on the composition and properties of aerosols over Amazonia. The potential exists for these changes to impact on regional and global climate through changes to the extinction of solar radiation as well as the alteration of cloud properties.

Guyon, P, Graham B, Roberts GC, Mayol-Bracero OL, Maenhaut W, Artaxo P, Andreae MO.  2003.  In-canopy gradients, composition, sources, and optical properties of aerosol over the Amazon forest. Journal of Geophysical Research-Atmospheres. 108   10.1029/2003jd003465   AbstractWebsite

[1] As part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia-European Studies on Trace Gases and Atmospheric Chemistry (LBA-EUSTACH), size-fractionated aerosol samples were collected at a primary rain forest in the Brazilian Amazon during two field campaigns in April - May and September - October 1999. These two periods encompassed parts of the wet and dry seasons, respectively. Daytime-nighttime-segregated sampling was carried out at three different heights ( above, within, and below canopy level) on a 54-m meteorological tower at the forest site in order to better characterize the aerosol sources. The samples were analyzed for up to 19 trace elements by particle-induced X-ray emission analysis and for carbonaceous components by thermal-optical analysis. Equivalent black carbon (BCe) and gravimetric analyses were also performed. The average mass concentrations for particles < 2 μm diameter were 2.2 and 33.5 μg m(-3) for the wet and the dry seasons, respectively. The elements related to biomass burning and soil dust generally exhibited highest concentrations above the canopy and during daytime, while forest-derived aerosol was more concentrated underneath the canopy and during nighttime. These variations can be largely attributed to daytime convective mixing and the formation of a shallow nocturnal boundary layer, along with the possibility of enhanced nighttime release of biogenic aerosol particles. Mass scattering (α(s)) and mass absorption efficiency (α(a)) data indicate that scattering was dominated by fine aerosol, while fine and coarse aerosol both contributed significantly to absorption during both seasons. The data also suggest that components other than elemental carbon were responsible for a substantial fraction of the absorption.

Guyon, P, Graham B, Roberts GC, Mayol-Bracero OL, Maenhaut W, Artaxo P, Andreae MO.  2004.  Sources of optically active aerosol particles over the Amazon forest. Atmospheric Environment. 38:1039-1051.   10.1016/j.atmosenv.2003.10.051   AbstractWebsite

Size-fractionated ambient aerosol samples were collected at a pasture site and a primary rainforest site in the Brazilian Amazon Basin during two field campaigns (April-May and September-October 1999), as part of the European contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH). The samples were analyzed for up to 19 trace elements by particle-induced X-ray emission analysis (PIXE), for equivalent black carbon (BCe) by a light reflectance technique and for mass concentration by gravimetric analysis. Additionally, we made continuous measurements of absorption and light scattering by aerosol particles. The vertical chemical composition gradients at the forest site have been discussed in a companion article (Journal of Geophysical Research-Atmospheres 108 (1318), 4591 (doi:4510.1029/2003JD003465)). In this article, we present the results of a source identification and quantitative apportionment study of the wet and dry season aerosols, including an apportionment of the measured scattering and absorption properties of the total aerosol in terms of the identified aerosol sources. Source apportionments (obtained from absolute principal component analysis) revealed that the wet and dry season aerosols contained the same three main components, but in different (absolute and relative) amounts: the wet season aerosol consisted mainly of a natural biogenic component, whereas pyrogenic aerosols dominated the dry season aerosol mass. The third component identified was soil dust, which was often internally mixed with the biomass-burning aerosol. All three components contributed significantly to light extinction during both seasons. At the pasture site, up to 47% of the light absorption was attributed to biogenic particles during the wet season, and up to 35% at the tower site during the wet-to-dry transition period. The results from the present study suggest that, in addition to pyrogenic particles, biogenic and soil dust aerosols must be taken into account when modeling the physical and optical properties of aerosols in forested regions such the Amazon Basin. (C) 2003 Published by Elsevier Ltd.