Browsing by Subject "Cloud Condensation Nuclei"
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Item Isolation of ambient aerosols of known critical supersaturation: the differential critical supersaturation separator (DSCS)(Texas A&M University, 2007-09-17) Osborn, Robert JohnA field-deployable instrument has been developed that isolates from an ambient aerosol population only those particles that have critical supersaturations, Sc, within a narrow, user-specified, range. This Differential Critical Supersaturation Separator (DScS) is designed to supply one or more particle size and/or composition analyzers to permit the direct examination of the factors that influence the activation properties of ambient aerosols. The DScS consists of two coupled parallel plate continuous flow thermal gradient diffusion cloud chambers housed within a single enclosure. Descriptions of instrument operation, construction and calibration data collected, when pure ammonium sulfate aerosols were injected into the DScS for operation at 0.15%< Sc<0.175%, 0.30%< Sc<0.35%, and 0.60% < Sc<0.70%, are included. Following instrument development, the DScS was deployed during March 2006 for the Megacities Impact on Regional And Global Environment (MIRAGE) field campaign in Mexico City, Mexico. Throughout the MIRAGE field campaign a Differential Mobility Analyzer/Tandem Differential Mobility Analyzer (DMA/TDMA) system measured aerosol size distributions and size-resolved hygroscopicity of DScS separated aerosol. The dry diameter (Dp*) of particles sampled in the TDMA system as well as the known Sc prescribed in the DScS were combined in a modified version of K????hler Theory to make predictions of particle hygroscopicity. These predictions frequently overestimated the measurements. Further analysis of DScS separated aerosols compares the known particle Sc to a predicted particle Sc, providing insight into particle activation efficiency. Overall, the sampled aerosol exhibited properties that indicate they were more efficient at activation than K????hler Theory would predict.Item Nucleation and Growth of Atmospheric Nanoparticles at Molecular Scale(2014-04-14) Xu, WenAtmospheric aerosols are fine liquid droplets or solid particles of various chemical compositions suspended in the air. They influence the Earth radiation budget, impact cloud formation, cause or enhance diseases on humans, and change photochemical chemistry and partitioning of trace gas species. Atmospheric aerosols are classified into two categories, primary and secondary, on the basis of their formation mechanisms. Although a large portion of atmospheric aerosols is secondary, the mechanisms for secondary aerosol formation remain highly uncertain, preventing the development of physically based representations of their formation in atmospheric models. So far it is known that secondary aerosol formation consists two consecutive steps, nucleation to form critical nucleus and subsequent growth of freshly nucleated nanoparticles. Unfortunately, our current knowledge of these two steps is very limited. In the current study, the dicarboxylic acids (organic acid) assisted nucleation is investigated both experimentally and theoretically. First, nucleation and partitioning theories are presented as the theoretical framework for data analysis and explanation. Subsequently, quantum chemistry calculations are performed to evaluate the hydrogen bonding strength of dicarboxylic acids with common atmospheric nucleation precursors, including sulfuric acid, water, ammonia, and amines. Then, succinic acid (dicarboxylic acid) assisted nucleation experiment is carried out to assess the nucleation enhancement ability of dicarboxylic acids. Next, the growth contributions from epoxides vapors are determined using a combination of Nano-tandem differential mobility analyzer (n-TDMA) and thermo desorption ion drift chemical ionization mass spectrometer (TD-ID- CIMS). Finally, the hygroscopicity and CCN properties of atmospheric polymers are characterized. Our results show that dicarboxylic acids bind strongly with sulfuric acid and enhance nucleation rate by 5-13 times with a concentration of 1 ppb. Dicarboxylic acids also react with amines under hydration to form non-volatile aminium carboxylate ion pairs, which contribute to nanoparticles growth. The n-TDMA and TD-ID-CIMS results show that epoxides contribute to freshly nucleated nanoparticle (sulfuric acid nanoparticles) growth through forming non-volatile organosulfates and oligomers, which subsequently changes the cloud-forming properties of aerosols.Item The Evolution of the Physicochemical Properties of Aerosols in the Atmosphere(2011-02-22) Tomlinson, JasonA Differential Mobility Analyzer/Tandem Differential Mobility Analyzer (DMA/TDMA) system was used to measure simultaneously the size distribution and hygroscopicity of the ambient aerosol population. The system was operated aboard the National Center for Atmospheric Research/National Science Foundation (NCAR/NSF) C-130 during the 2006 Megacity Initiative: Local and Global Research Observations (MILAGRO) field campaign followed by the 2006 Intercontinental Chemical Transport Experiment ? Phase B (INTEX-B) field campaign. The research flights for the MILAGRO campaign were conducted within the Mexico City basin and the region to the northeast within the pollution plume. The aerosol within the basin is dominated by organics with an average measured kappa value of 0.21 /- 0.18, 0.13 /- 0.09, 0.09 /- 0.06, 0.14 /- 0.07, and 0.17 /- 0.04 for dry particle diameters of 0.025, 0.050, 0.100, 0.200, and 0.300 mu m, respectively. As the aerosols are transported away from the Mexico City Basin, secondary organic aerosol formation through oxidation and condensation of sulfate on the aerosols surface rapidly increases the solubility of the aerosol. The most pronounced change occurs for a 0.100 mu m diameter aerosol where, after 6 hours of transport, the average kappa value increased by a factor of 3 to a kappa?of 0.29 /- 0.13. The rapid increase in solubility increases the fraction of the aerosol size distribution that could be activated within a cloud. The research flights for the INTEX-B field campaign investigated the evolution of the physicochemical properties of the Asian aerosol plume after 3 to 7 days of transport. The Asian aerosol within the free troposphere exhibited a bimodal growth distribution roughly 50 percent of the time. The more soluble mode of the growth distribution contributed between 67-80 percent of the overall growth distribution and had an average kappa?between 0.40 and 0.53 for dry particle diameters of 0.025, 0.050, 0.100, and 0.300 mu m. The secondary mode was insoluble with an average kappa?between 0.01 and 0.05 for all dry particle diameters. Cloud condensation nuclei closure was attained at a supersaturation of 0.2 percent for all particles within the free troposphere by either assuming a pure ammonium bisulfate composition or a binary composition of ammonium bisulfate and an insoluble organic.