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No description available.

We have developed novel experiments aimed at understanding whether and how quickly organic aerosols (OA) mix using single-particle mass spectrometry, as different treatments of mixing in regional models significantly affect predicted mass and composition. First, we designed experiments that separate OA formation chemistry from thermodynamics to test whether two populations of particles equilibrate with eachother through the gas phase on experimental timescales. Single-particle mass spectrometry measurements from the aerosol mass spectrometer (AMS) allowed us to quantify the extent of mixing that had occurred. We calibrated this technique using pure-component aerosols with known vapor pressure and phase state, the results of which agreed with a condensation-evaporation model. We then applied these techniques to three atmospherically-relevant situations to determine that: 1) anthropogenic secondary OA (aSOA) does not mix with a surrogate for hydrophobic primary OA (POA), 2) biogenic SOA (bSOA) does not mix with hydophobic POA, and 3) bSOA shows significant mixing with aSOA. The sum of these experiments show that these complex interactions can be measured for atmospherically important systems, a first step towards quantifying activity coefficients for complex OA mixtures. We also investigated mixing within individual particles, using mixed-particles of squalane (a surrogate for hydrophobic POA) and SOA from ↵+pinene + O3 that we determined to contain two separate phases. In these experiments, after formation of the mixed-particles, we perturbed smog chamber with a heat ramp. These data revealed that squalane is able to quickly evaporate from the mixed-particles, and that almost all of the SOA is comprised of material lower in volatility than squalane (a low-volatility constituent of pump oil). For this latter “comparative volatility analysis,” we had to correct for the highly variable collection efficiency (CE) of the mixed particles to correctly calculate the mass fraction of SOA remaining. One of the larger implications of this work is highly dependent on the particle morphology, which we were not able to determine definitively: if indeed the particles are coreshell with squalane inside a thick layer of SOA, our results show that diffusivity within SOA is not ultra-low. Lastly, we present work that furthers our understanding of single-particle CE in the AMS, a quantity especially important for experiments where particle phase is dynamic or there are two separate populations of particles. We report the particle CE of SOA, ammonium sulfate, ammonium nitrate, and squalane. We also determine that half of SOA particles that give meaningful signal, do so at a time later than would be predicted based on their optically-measured flight time through the instrument. We present convincing evidence that the nature of this delay is due to particles ricocheting around the ionization region of the instrument before vaporizing on an auxillary surface near the the vaporizer. This process affects how much mass signal comes from a particle, the particle mass spectrum, and the bulk mass distribution derived from particle time-of-flight mode. Our results also show that while there is no size dependence to CE for SOA, particles that have passed through a thermodenuder have lower CE, implicating oxidation state and/or volatility as a controller of particle bounce.

A novel method was developed for producing high-resolution (∼ 11km) maps of surface NO2 concentrations by combining satellite retrieved NO2 columns from OMI with in situ measurements made by permanent monitoring networks. Field data from the BAQS-met field campaign in the Windsor area during 2007 was used to validate this method and explore the uncertainties and biases in the inferred values. Good correlation with the network of passive monitors was found (R = 0.69). Interference of NOz in traditional NO2 measurements was found to be small (0.9 ppb) when considered for 24-hr averages. The inference method was extended to qualitatively analyze long-term trends in Windsor. Comparison against a land-use regression model in Toronto showed similar overall trends, but the downtown core was underestimated considerably by the OMI-inferred map. While the presented inference method can simplify and increase the utility of OMI NO2 data, limitations remain as to the spatial and temporal resolution achievable.

A novel method was developed for producing high-resolution (∼ 11km) maps of surface NO2 concentrations by combining satellite retrieved NO2 columns from OMI with in situ measurements made by permanent monitoring networks. Field data from the BAQS-met field campaign in the Windsor area during 2007 was used to validate this method and explore the uncertainties and biases in the inferred values. Good correlation with the network of passive monitors was found (R = 0.69). Interference of NOz in traditional NO2 measurements was found to be small (0.9 ppb) when considered for 24-hr averages. The inference method was extended to qualitatively analyze long-term trends in Windsor. Comparison against a land-use regression model in Toronto showed similar overall trends, but the downtown core was underestimated considerably by the OMI-inferred map. While the presented inference method can simplify and increase the utility of OMI NO2 data, limitations remain as to the spatial and temporal resolution achievable.

No description available.

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Includes bibliographical references. Issued in print and online. Available via ProQuest Digital Dissertations.

Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2005. / Russell, Armistead G., Committee Chair ; Chameides, William L., Committee Member ; Wang, Yuhang, Committee Member ; Noonan, Douglas, Committee Member ; Chang, Michael E., Committee Member. Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 10, 2010). Includes bibliographical references. Also issued in print.