Thesis (Ph. D.)--University of Chicago, Dept. of the Geophysical Sciences, August 1999. / Includes bibliographical references. Also available on the Internet.

A 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 Köhler 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 Köhler Theory would predict.

The extinction of solar radiation by atmospheric aerosols influences the Ultraviolet (UV) flux at the surface, which in turn has implications on both human and environmental health. In this study we present measurements of aerosol optical depth ( and #964;a) in the UV at Boulder, Colorado and Atlanta, Georgia using direct measurements of solar UV radiation. The wavelength dependence of and #964;a and the single scattering albedo ( and #969;o) are determined from the measured values of and #964;a. Daily averages of and #964;a range between 0.09 and 0.52 at Boulder and between 0.23 and 2.09 for Atlanta between the wavelengths of 332 and 340 nm. The average ngstrm exponent ( and #945;) is 0.83 at Boulder and 1.43 in Atlanta. Results clearly show that aerosols have a significant effect on the UV Index. Day-to-day changes in the UV index during the one month measurement period in Atlanta range between 2-3 UV Index units at solar noon. It is estimated that when changes in and #964;a and and #969;o occur simultaneously, the UV Index can change up to 6 units from one day to the next at solar noon in the Atlanta area. The single scattering albedo ( and #969;o) was estimated to range between 0.8 and 0.99 for Atlanta. The results suggest an increasing trend in and #969;o with increases in and #964;a. In addition, a new synthetic current UV Index is developed which expands to nearly 10,000 cities the number of current UV Index reports that can be distributed to the public in the United States. Right now, current UV Index values are limited to specific UV measuring sites, constrained by the difficulties of maintaining accurate calibration within the network of UV instruments. The distribution of UV Index values to more cities will increase the publics awareness of the harmful effects of the sun. This new UV Index can be accessed through The Weather Channel website.

Starting in March of 1999, the ASACA study has measured PM2.5 mass and composition using 24-hr integrated and continuous measurement techniques. The ASACA network has one rural (Fort Yargo) and three urban (Fort McPherson, South Dekalb, and Tucker) monitoring sites located in the metropolitan Atlanta area. Supplementary data from the SEARCH and STN monitoring networks is also used where applicable. Yearly-averaged TEOM measurements recorded violations of the annual PM2.5 NAAQS (>15 μg/m3) every year of the study, and the daily NAAQS (>65 μg/m3) was exceeded on five separate occasions. Seven-year PM2.5 averages for the sites ranged from 18.8 – 19.8 μg/m3. PCMs were employed to collect PM2.5 composition data, detect spatial variations of PM species, and compare results with the continuous mass measurements. From 2004 – 2005, approximately 28% of the mass was OC, 24% was sulfate, 10% was ammonium, 6% was nitrate, and 3% was EC. Lesser ions contribute less than 3% to the total PM2.5 mass. Spatial variation of the major species was minimal, especially for species formed from secondary processes. South Dekalb did exhibit elevated levels of EC compared to the other sites, most likely due to its proximity to an interstate heavily used by diesel vehicles. PCM averages were found to be less than the averaged TEOM data due to the presence of unidentified matter (UM). Depending on the season, UM can contribute as little as 5% and as much as 50+% of the total mass. Secondary organic aerosol (SOA) concentrations from 2004 – 2005 were predicted using the EC-tracer method. Peak SOA occurs in mid-summer, and winter concentrations are significant due to biomass burning increasing the estimated OC/EC ratios. PCM, TEOM, and aethalometer data was also subjected to seasonal, day-of-the-week, and diurnal temporal variations. Active photochemistry plays an important role, as most species exhibit higher concentrations during summer months. The lone exception was nitrate, whose peak occurs in winter. Daily-averaged PM2.5 concentrations tend to peak late in the work-week and reach their low point on Sundays. Morning and afternoon rush-hour spikes in one-hour averaged PM2.5 are visible most days.

This study explored different chemical characterization methods of agricultural and urban airborne particulate matter. Three different field campaigns are discussed. For the agricultural aerosols, measurement of the chemical composition of size-resolved agricultural aerosols collected from a ground site at the nominally downwind and upwind edge of a feedlot in West Texas were reported. High volume cascade impactor samplers were used for the collection of the particles, and two major analytical methods were applied to characterize different components of the aerosols, ion chromatography (IC ) was used to measure ionic composition with the main targets being ammonium (NH4 ), nitrate (NO3 -), and sulfate (SO4 2-), direct thermal desorption gas chromatography-mass spectrometry/flame ionization detection (GC-MS/FID) methodology was used to identify and quantify organic compounds in the aerosol particles. For the urban aerosols, I report the measurement of mass, and the chemical composition of size-resolved aerosols collected from two different locations in Houston, analyzed by the thermal desorption GC-MS/FID method. The investigation of single particle composition using RM is reported as well: RM and chemical mapping techniques have been applied for the qualitative analysis of components in the samples of air particulate matter collected in downtown Houston.

A 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 Köhler 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 Köhler Theory would predict.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Oceanography." Includes bibliographical references (p. 116-133).

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Environmental Sciences." Includes bibliographical references.

Thesis (Ph. D.)--University of Canterbury, 2009. / Typescript (photocopy). "May 2009." Includes bibliographical references (p. 10/1-10/9). Also available via the World Wide Web.

Thesis (M.S.)--Naval Postgraduate School, 2002. / Thesis advisor(s): Philip A. Durkee, Douglas L. Westphal. Includes bibliographical references (p. 81-82). Also available online.