Studies were performed to characterize the physical nature of the air-ice interface, and to clarify its role in processes that occur there. A glancing-angle Raman probe was developed to monitor hydrogen bonding at atmospheric interfaces; we saw enhanced hydrogen-bonding on ice compared to on water. Using glancing-angle laser-induced fluorescence (LIF), we determined that small acids and bases dissociated to similar extents at air-water and air-ice interfaces, but aromatic compounds were less well solvated at air-ice interfaces, resulting in self-association even at low surface coverages. We measured uptake kinetics of organic compounds using LIF and Raman spectroscopy. The uptake kinetics can be adequately fit by a single-exponential growth equation, but in order to properly describe the self-association of aromatics observed at the air-ice interface, equations accounting for self-association should be incorporated into the uptake model. A simple model was developed for naphthalene which included terms for self-association; good fits to the observed growth of intensity from monomeric and self-associated naphthalene were obtained. Direct photolysis of aromatics was faster at air-ice interfaces than in bulk ice or aqueous solution. While red shifts in the absorption spectra of benzene and naphthalene at air-ice interfaces could explain their enhanced reactivity there, the enhanced anthracene photolysis kinetics on ice are likely due to enhanced absorption cross sections or photolysis quantum yields, or to a different photolysis mechanism there. Oxidation rates of aromatics by photo-formed hydroxyl radicals are suppressed at air-ice interfaces, but not in bulk ice. Similarly, gas-phase OH reacts rapidly with aromatics at air-water interfaces, but no reaction is observed at air-ice interfaces. Conversely, the reactivity of ozone toward phenanthrene is enhanced there. This is not due to temperature effects or to enhanced partitioning of ozone to ice. Ozonation of bromide is also more rapid at air-ice interfaces than at air-water interfaces at environmentally relevant bromide concentrations. This enhancement could be due to exclusion of bromide to the air-ice interface during freezing. The rapid reactions of ozone with bromide and phenanthrene at air-ice interfaces suggest that both reactions could be atmospherically important.

Remote sensing of atmospheric gases improves our understanding of the state and evolution of the Earth’s environment. At the beginning of the thesis, the basic principles for the retrieval of concentrations of atmospheric gases from spectra are presented with a focus on ground-based observations. An overview of the characteristic features of different platforms, viewing geometries, measurement sites, and Fourier Transform Spectrometers (FTSs) used in the measurements are provided. The thesis covers four main projects. The first study of the global distribution of atmospheric phosgene was carried out using a total of 5614 measured profiles from the satellite-borne Atmospheric Chemistry Experiment FTS (ACE-FTS) spanning the period February 2004 through May 2006. The phosgene concentrations display a zonally symmetric pattern with the maximum concentration located approximately over the equator, at about 25 km in altitude, and the concentrations decrease towards the poles. A layer of enhanced concentration of phosgene spans the lower stratosphere at all latitudes, with volume mixing ratios of 20-60 pptv. The reasons for the formation of the phosgene distribution pattern are explained by the insolation, lifetime of phosgene and the Brewer-Dobson circulation. The ACE observations show lower phosgene concentrations in the stratosphere than were obtained from previous observations in the 1980s and 1990s due to a significant decrease in source species. The Portable Atmospheric Research Interferometric Spectrometer for the Infrared (PARIS-IR) is a copy of the ACE-FTS that was designed for ground-based and balloon-borne measurements. The first balloon flight was part of the Middle Atmosphere Nitrogen TRend Assessment (MANTRA) 2004 balloon payload. Some useful engineering information was obtained on the thermal performance of the instrument during the flight. As part of the MANTRA program, a ground-based inter-instrument comparison campaign was conducted with the objective of assessing instrument performance, and evaluating data processing routines and retrieval codes. PARIS-IR provides similar quality results for stratospheric species as does the University of Toronto FTS. An advanced study was carried out for the Carbon Cycle science by Fourier Transform Spectroscopy (CC-FTS) mission, which is a proposed future satellite mission to obtain a better understanding of the sources and sinks of greenhouse gases in the Earth’s atmosphere by monitoring total and partial columns of CO2, CH4, N2O, and CO in the near infrared together with the molecular O2 column. To evaluate the spectral regions, resolution, optical components, and spectroscopic parameters required for the mission, ground-based Fourier transform spectra, recorded at Kiruna, Kitt Peak, and Waterloo, were used. Dry air volume mixing ratios of CO2 and CH4 were retrieved from the ground-based observations. A FTS with a spectral resolution of 0.1 cm-1, operating between 2000 and 15000 cm-1, is suggested as the primary instrument for the mission. Further progress in improving the atmospheric retrievals for CO2, CH4 and O2 requires new laboratory measurements to improve the spectroscopic line parameters. Atmospheric observations were made with three FTSs at the Polar Environment Atmospheric Research Laboratory (PEARL) during spring 2006. The vertical column densities of O3, HCl, HNO3, HF, NO2, ClONO2 and NO from PARIS-IR, the Eureka DA8 FTS, and the ACE-FTS show good agreement. Chorine activation and denitrification in the Arctic atmosphere were observed in the extremely cold stratosphere near Eureka, Nunavut, Canada. The observed ozone depletion during the 2006 campaign was attributed to chemical removal.

Remote sensing of atmospheric gases improves our understanding of the state and evolution of the Earth’s environment. At the beginning of the thesis, the basic principles for the retrieval of concentrations of atmospheric gases from spectra are presented with a focus on ground-based observations. An overview of the characteristic features of different platforms, viewing geometries, measurement sites, and Fourier Transform Spectrometers (FTSs) used in the measurements are provided. The thesis covers four main projects. The first study of the global distribution of atmospheric phosgene was carried out using a total of 5614 measured profiles from the satellite-borne Atmospheric Chemistry Experiment FTS (ACE-FTS) spanning the period February 2004 through May 2006. The phosgene concentrations display a zonally symmetric pattern with the maximum concentration located approximately over the equator, at about 25 km in altitude, and the concentrations decrease towards the poles. A layer of enhanced concentration of phosgene spans the lower stratosphere at all latitudes, with volume mixing ratios of 20-60 pptv. The reasons for the formation of the phosgene distribution pattern are explained by the insolation, lifetime of phosgene and the Brewer-Dobson circulation. The ACE observations show lower phosgene concentrations in the stratosphere than were obtained from previous observations in the 1980s and 1990s due to a significant decrease in source species. The Portable Atmospheric Research Interferometric Spectrometer for the Infrared (PARIS-IR) is a copy of the ACE-FTS that was designed for ground-based and balloon-borne measurements. The first balloon flight was part of the Middle Atmosphere Nitrogen TRend Assessment (MANTRA) 2004 balloon payload. Some useful engineering information was obtained on the thermal performance of the instrument during the flight. As part of the MANTRA program, a ground-based inter-instrument comparison campaign was conducted with the objective of assessing instrument performance, and evaluating data processing routines and retrieval codes. PARIS-IR provides similar quality results for stratospheric species as does the University of Toronto FTS. An advanced study was carried out for the Carbon Cycle science by Fourier Transform Spectroscopy (CC-FTS) mission, which is a proposed future satellite mission to obtain a better understanding of the sources and sinks of greenhouse gases in the Earth’s atmosphere by monitoring total and partial columns of CO2, CH4, N2O, and CO in the near infrared together with the molecular O2 column. To evaluate the spectral regions, resolution, optical components, and spectroscopic parameters required for the mission, ground-based Fourier transform spectra, recorded at Kiruna, Kitt Peak, and Waterloo, were used. Dry air volume mixing ratios of CO2 and CH4 were retrieved from the ground-based observations. A FTS with a spectral resolution of 0.1 cm-1, operating between 2000 and 15000 cm-1, is suggested as the primary instrument for the mission. Further progress in improving the atmospheric retrievals for CO2, CH4 and O2 requires new laboratory measurements to improve the spectroscopic line parameters. Atmospheric observations were made with three FTSs at the Polar Environment Atmospheric Research Laboratory (PEARL) during spring 2006. The vertical column densities of O3, HCl, HNO3, HF, NO2, ClONO2 and NO from PARIS-IR, the Eureka DA8 FTS, and the ACE-FTS show good agreement. Chorine activation and denitrification in the Arctic atmosphere were observed in the extremely cold stratosphere near Eureka, Nunavut, Canada. The observed ozone depletion during the 2006 campaign was attributed to chemical removal.

The abatement of ground-level ozone has been a priority of air pollution policy because of its harmful effects on human health, ecosystems, and climate. The responsiveness of ozone to emissions of its principal precursors, nitrogen oxides (NOx) and volatile organic compounds (VOCs), is known to depend nonlinearly on spatially and temporally variable factors. Given this variability, scientific understanding of ozone formation processes can facilitate the development of sensible control policies. This thesis applies a high-order sensitivity analysis technique, the Decoupled Direct Method in Three Dimensions (HDDM-3D), to examine ozone response to precursor emissions during summertime air pollution episodes in the southeastern United States. HDDM-3D is shown to accurately capture ozone response within an underlying air quality model, even over large ranges of emission perturbations. Nonlinearity of response is quantified, and nonlinear terms are applied to examine how estimates of sensitivity and source attribution respond to uncertainty in an emissions inventory. Ozone production regime is assessed using both HDDM-3D and species indicator ratios and found to be primarily NOx-limited outside urban centers. However, ozone response to region-wide emissions does not necessarily correspond to its sensitivity to local controls, hindering the usefulness of bipartite ozone regime classification. Significant heterogeneity of ozone response to NOx is found even over small spatial scales of emission origin, a potential complication often ignored in atmospheric modeling and emissions trading mechanisms. Atmospheric sensitivity analysis is linked with a comprehensive menu of potential control measures to demonstrate potential integration of scientific and economic considerations for control strategy formulation. Cost-optimized strategies are identified for attainment of federal ozone standards in Macon, Georgia, and for minimizing potential population exposure to unhealthful concentrations of ozone.

In Part 1, we separated surface ozone time series collected from EPA monitoring sites in and around Georgia from 1980-2002 using a Kolmogorov -Zurbenko Filter to assess the influences associated with characteristic timescales to the overall variability of ozone for individual communities. Comparison of time scale variabilities supports that the diurnal and synoptic variation are most influential timescales in small and large urban and rural locations, with the synoptic scale variation decreasing with the increase of urban size. We define boundaries of influence due to a communitys local chemistry and due to transport by utilizing the diurnal and synoptic ozone timescales respectively. We used the synoptic scale to evaluate the boundaries of similarity among sites that share synoptic scale trends due to transport. Results showed two-phased correlation decay with distance from urban centers. We evaluate the diurnal timescale as a means of evaluating the influence of an areas photochemistry, separated from long-range transport mechanisms. We consider isolation of the diurnal timescale extrapolated spatially for a relative sensitivity analysis based on ozone with respect to concentrations of the precursor group NOy. Results show differences base on urban scale and can define photochemical boundaries. In Part 2, a Particle-Into-Liquid Sampler with an anion/cation chromatograph (PILS-IC) was used to evaluate the fine particle desert dust mixed with urban pollution during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia). Three flights in the Yellow Sea boundary layer captured high mineral dust mixed with pollutants from Asian urban centers. Results report on the fine particle ionic compositions and chemical evolution of dust and pollution during those flights. The main component of water-soluble mineral dust was Ca2+ with Mg2+, which existed with significant fractions in the form of carbonates. Nitrate and sulfate measured after transport of nearly half a day, were connected to ammonium or potassium, the rest likely associated with mineral dust. Initial mass accommodation coefficients much less than 0.1 for uptake of SO2 or HNO3 by mineral dust in urban plumes containing fossil fuel and biomass burning emissions could explain the observations. The data suggest a dependence of accommodation coefficient on relative humidity.

Recent field campaigns have measured enhanced levels of NOx (NO+NO2) and HOx precursors (i.e., H2O2, CH2O, and HONO) that can not be accounted for by gas phase chemistry alone. Snowpack emission is now considered a source of these species. Therefore, the photochemistry in the polar boundary layer is now believed to be much more complex than initially thought. Field campaigns to Summit, Greenland in the summer of 2003 and the spring of 2004 have obtained the first measurements of peroxy (HO2+RO2) and hydroxyl (OH) radicals in the Artic boundary layer. Measurements were collected with a chemical ionization mass spectrometer (CIMS). A highly constrained (ie., O3, H2O, CH4, CO, j-values, NO, H2O2,CH2O, and HONO) 0-D steady-state model was employed in order to test our current understanding of photochemistry. HO2+RO2 measurements were in excellent agreement with model predictions for both spring and summer. OH measurements were in good agreement with spring model predictions but were a factor of two greater than summer model predictions. The role of snowpack emission is also addressed in a HOx budget performed on the spring campaign. Measurements of nitric acid (HNO3) and pernitric acid (HO2NO2) were obtained with the CIMS during the Antarctic Tropospheric Chemistry Investigation (ANTCI). The linkage between HOx and NOx chemistry is examined through partitioning of reactive nitrogen between HNO3 and HO2NO2. The possible impact of reactive nitrogen partitioning on nitrate ions (NO3-) at coring sites is also investigated.

This thesis focuses on the characterization of soluble iron in ambient/urban and source emission aerosols, primarily focusing on the sources and atmospheric processes contributing to iron solubility. Multiple techniques, including bulk and single particle measurements, were used to investigate the complex chemistry of iron solubility. A technique was developed and validated (PILS-LWCC), allowing for 12-minute measurements of water-soluble ferrous iron (WS_Fe(II)) in aerosols with a limit of detection of 4.6 ng m-3 and 12% relative uncertainty. The PILS-LWCC was deployed at several urban field sites (Atlanta, GA and Dearborn, MI) and a biomass burning event to determine major sources and atmospheric processes of WS_Fe(II) in aerosols. PILS-LWCC measurements suggest that industrial and biomass burning are sources of WS_Fe(II). In addition, acid-processing mechanisms also appeared to influence WS_Fe(II) concentrations, based on a strong correlation between WS_Fe(II) and SO42- (r2 = 0.76) as well as apparent aerosol acidity (r2 =0.78) during a field campaign in Atlanta, GA. Synchrotron-based techniques, such as X-ray Absorption Near-Edge Structure (XANES) spectroscopy and micro X-ray fluorescence measurements, were also used to identify the chemical composition (redox state and phase) and mixing state (two properties that may influence iron solubility) of source emission and ambient single iron-containing particles. These single particle measurements were used in conjunction with bulk iron solubility to assess the influence of chemical composition and mixing state on iron solubility. Single particle (synchrotron-based) and bulk iron solubility measurements suggested that iron solubility is not primarily driven by chemical composition in source emission and ambient particles. Differences in iron solubility, however, were related to single particle sulfur content in ambient and source emission aerosols, suggesting that similar sources/atmospheric processes control iron solubility in these samples. The relationship between iron solubility and sulfur content corresponded well with bulk ground-based measurements of ambient aerosol using the PILS-LWCC. Combined single particle and bulk online measurements provide compelling evidence that atmospheric acid processing, involving sulfur-containing acids (H2SO4), is an important formation route of soluble iron in ambient urban aerosols. The results of this thesis provide valuable information to further understanding the controls of iron solubility in atmospheric aerosols.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (p. 86-97).

Atmospheric deposition of nitrogen species represents an additional nutrient source to natural environments, and can alter the nitrogen cycle by increasing nutrient levels beyond the requirements of organisms. In Tampa Bay, atmospheric deposition of dissolved inorganic nitrogen species (DIN) has been found to be the second largest nitrogen source, but little is known about dissolved organic nitrogen species (DON). The research goal was to improve the dry and wet deposition estimates by inclusion of the DON contribution. In the atmospheric chemistry field a standard method to measure DON in atmospheric samples has not been agreed upon. This research proposes the use of the ultraviolet (UV)-photolysis method and presents the optimal settings for its application on atmospheric samples. Using a factorial design scheme, experiments on surrogate nitrogen compounds, typically found in the atmosphere, indicated that DON can be xviii measured with no biases if optimal settings are fixed to be solution pH 2 with a 24-hr irradiance period. DIN species (NH4 +, NO2 -, NO3 -) and DON concentrations were determined in fine (PM2.5) and coarse particles (PM10-2.5) as well as in rainwater samples collected at Tampa Bay. The estimates of wet deposition fluxes for NH4 +, NO3 - and DON were 1.40, 3.18 and 0.34 kg-N ha-1yr-1, respectively. Hourly-measured gas concentrations and 24-hr integrated PM10 concentrations were used in conjunction with a below-cloud scavenging model to explain DIN and DON concentration in rainwater samples. Scavenging of aerosol-phase DON contributed only 0.9 ± 0.2% to rainwater DON concentrations, and therefore gas scavenging should be responsible for 99%. These results confirmed the existence of negative biases in the dry and wet deposition fluxes over Tampa Bay. There is increasing interest in simulating wet deposition fluxes, and the proposed below-cloud scavenging model offers a new computational approach to the problem. It integrates the typical gas and particle collection functions and the concept of the deposition-weighted average concentrations. The model uses mass balance to describe the time-dependent cumulative contribution of all droplets in the rain spectrum to the rainwater concentration, giving predictions closer to experimental values and better estimations than those reported in the literature for similar cases.

Understanding future climate requires observations of trace species that can significantly influence the chemical or radiative properties of the atmosphere. The development of optical instruments, utilizing laser-systems as high-resolution light sources, for making in situ observations of trace species from either airborne- or ground-based platforms and results from field campaigns are presented. Glyoxal, the smallest \(\alpha\)-dicarbonyl, is a common product during the oxidation of volatile organic compounds. An instrument using the technique of laser-induced phosphorescence was developed to measure glyoxal at the part per trillion by volume (pptv) level from a tower in a forest canopy. The instrument was deployed as part of the Community Atmosphere-Biosphere INteractions EXperiment. The instrumental limit of detection is 3 pptv with a 1-minute acquisition time. Nearly continuous measurements of glyoxal ranging between 5 – 75 pptv were acquired throughout the campaign and vertical gradients in the forest canopy were found to be driven by elevated temperature. A sensitive instrument using laser-induced fluorescence detection was developed and deployed into remote marine environments to measure iodine monoxide (IO) where the mixing ratio is on the order of 1 – 5 pptv. The challenges and solutions of operating in this environment and results from the field and laboratory are discussed. Laboratory experiments show that IO can be generated from Laminaria digitata, a subtidal kelp species, in the presence of ozone. Observations of the isotopic composition of condensed and vapor water above a large summertime tropical convective system obtained by Hoxotope and ICOS instruments during the TC4 campaign are used to analyze the role of convection in the lower tropical transition layer (TTL). Regions of ice that are characteristic of either convective lofting or in situ condensation are encountered above an active deep tropical convective system. Ice is an important component of water transport models in the TTL, yet its isotopic composition is a relatively unconstrained parameter. The implications from the direct observations of the isotopic composition of ice during convection is explored with respect to transport models of water in the TTL. / Chemistry and Chemical Biology