| 1. |
- Rissler, Jenny, et al.
(författare)
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Physical properties of the sub-micrometer aerosol over the Amazon rain forest during the wet-to-dry season transition - comparison of modeled and measured CCN concentrations
- 2004
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Ingår i: Atmospheric Chemistry and Physics. - 1680-7324. ; 4:8, s. 2119-2143
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Tidskriftsartikel (refereegranskat)abstract
- Sub-micrometer atmospheric aerosol particles were studied in the Amazon region, 125 km northeast of Manaus, Brazil (-1degrees55.2'S, 59degrees28.1'W). The measurements were performed during the wet-to-dry transition period, 4-28 July 2001 as part of the LBA (Large-Scale Biosphere Atmosphere Experiment in Amazonia) CLAIRE-2001 (Cooperative LBA Airborne Regional Experiment) experiment. The number size distribution was measured with two parallel differential mobility analyzers, the hygroscopic growth at 90% RH with a Hygroscopic Tandem Mobility Analyzer (H-TDMA) and the concentrations of cloud condensation nuclei (CCN) with a cloud condensation nuclei counter. A model was developed that uses the H-TDMA data to predict the number of soluble molecules or ions in the individual particles and the corresponding minimum particle diameter for activation into a cloud droplet at a certain supersaturation. Integrating the number size distribution above this diameter, CCN concentrations were predicted with a time resolution of 10 min and compared to the measured concentrations. During the study period, three different air masses were identified and compared: clean background, air influenced by aged biomass burning, and moderately polluted air from recent local biomass burning. For the clean period 2001, similar number size distributions and hygroscopic behavior were observed as during the wet season at the same site in 1998, with mostly internally mixed particles of low diameter growth factor (similar to1.3 taken from dry to 90% RH). During the periods influenced by biomass burning the hygroscopic growth changed slightly, but the largest difference was seen in the number size distribution. The CCN model was found to be successful in predicting the measured CCN concentrations, typically within 25%. A sensitivity study showed relatively small dependence on the assumption of which model salt that was used to predict CCN concentrations from H-TDMA data. One strength of using H-TDMA data to predict CCN concentrations is that the model can also take into account soluble organic compounds, insofar as they go into solution at 90% RH. Another advantage is the higher time resolution compared to using size-resolved chemical composition data.
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| 2. |
- Roberts, G C, et al.
(författare)
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Sensitivity of CCN spectra on chemical and physical properties of aerosol: A case study from the Amazon Basin
- 2002
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Ingår i: Journal of Geophysical Research. - 2156-2202. ; 107:D20, s. 8070-8070
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Tidskriftsartikel (refereegranskat)abstract
- Organic material, about half of which is water soluble, constitutes nearly 80% of the wet-season aerosol mass in the Amazon Basin, while soluble inorganic salts (predominantly ammonium bisulfate) represent about 15%. A detailed analysis of number distributions and the size-dependent chemical composition of the aerosol indicates that, in principle, the sulfate fraction could account for most of the cloud condensation nuclei (CCN) activity. Uncertainty about the chemical speciation of the water-soluble organic component precludes a rigorous analysis of its contribution to nucleation activity. Within reasonable assumptions, we can, however, predict a similar contribution of the organic component to CCN activity as that from sulfate. Because of the nonlinear dependence of droplet nucleation behavior on solute amount, the nucleation activity cannot be attributed uniquely to the inorganic or organic fractions. The role of water-soluble organic compounds as surfactants, however, may be significant (especially in the case of biomass-burning aerosol) and more field measurements are needed to quantify their effects on the surface tension of ambient aerosols. The parametric dependence of the CCN spectra on the physical and chemical properties of the aerosol show that the number distribution, soluble content of the aerosol, and surface tension effects all play an important role in determining CCN spectra.
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| 3. |
- Zhou, Jingchuan, et al.
(författare)
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Submicrometer aerosol particle size distribution and hygroscopic growth measured in the Amazon rain forest during the wet season
- 2002
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Ingår i: Journal of Geophysical Research: Atmospheres. - 2169-897X. ; 107:D20
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Tidskriftsartikel (refereegranskat)abstract
- The number-size distribution and hygroscopic growth of submicrometer aerosol particles were measured in central Amazonia during the first Cooperative LBA Airborne Regional Experiment (CLAIRE) wet season experiment in March-April 1998. This was the first time ever that these types of measurements were performed in the Amazon rain forest. A Differential Mobility Particle Sizer (DMPS) was used to measure aerosol number-size distribution with diameters in the range 3-850 nm. The observed total number concentrations were frequently between 300 and 600 cm(-3) with a mean value around 450 cm(-3). Two aerosol particle modes (Aitken and accumulation mode) were always present. The average particle concentrations for those two modes were 239 and 177 cm(-3), with geometric diameters of 68 and 151 nm, respectively. An ultrafine mode had a number concentration and a mean diameter of 92 cm(-3) and 24 nm, respectively, and only occurred at 18% of the time, causing the size distribution to be trimodal instead of bimodal. The hygroscopic growth of aerosol particles was measured in situ with a Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) at six dry particle diameters between 35 and 265 nm. In contrast to the bimodal hygroscopic behavior found in polluted continental environments, the hygroscopic properties of aerosol particles in the Amazon rain forest is essentially unimodal with average diameter growth factors of 1.16-1.32 from dry to 90% relative humidity (RH). Aerosol soluble volume fractions were, in general, between 0.14 and 0.27, estimated by assuming that only ammonium hydrogen sulphate interacted with water vapour.
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