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Accurate measurements of the trace nitrogenous atmospheric species amines (NR3) and nitrous acid (HONO) are essential to understanding their chemistry and potential influence on new particle formation and oxidation capacity in the atmospheric boundary-layer, respectively. Ambient Ion Monitor – Ion Chromatography (AIM-IC) methods developed in this work have provided quantitative online observations of atmospheric amines in the gaseous and condensed phases with detection limits of pptv and ng m-3 at hourly time resolution. Size-resolved particle observations demonstrated maximum amine mass loadings in 320 – 560 nm particles, and an increase in importance relative to ammonium for the smallest particles measured (56 – 180 nm). In particular, the size-resolved samples analysed in this work indicate that bulk aerosol measurements may not be appropriate for modelling the atmospheric processes that govern the incorporation of amines and ammonia in to atmospheric particles. Measurements of HONO made during the two intensive field campaigns (NACHTT, CalNex) and a lab study provided a new perspective on the interactions of this trace compound with ground surfaces. Integrated atmospheric column measurements of HONO and NO2 during NACHTT provided clear evidence that the ground surface dominates HONO production and loss at night. Simultaneous measurements of the gas and particle phases made by the AIM-IC system during CalNex demonstrated the potential for reactive uptake of HONO on mineral dust/soil as a nocturnal sink. Similarly, the potential for nitrite salts to react with strong acids, displacing HONO during the day was suggested by this dataset. Lab study results showed that HONO is taken up irreversibly on carbonate salts and real soil extracts. Relative humidity-dependent reactive uptake coefficients were derived. Subsequent release of HONO by displacement reactions with HNO3 and HCl was also confirmed. Together, these field and lab studies have produced a new picture of HONO surface interactions by providing i) a more explicit description of a nocturnal sink of HONO that could act as a surface reservoir and ii) a new mechanism for daytime HONO formation that does not require NO2.

Accurate measurements of the trace nitrogenous atmospheric species amines (NR3) and nitrous acid (HONO) are essential to understanding their chemistry and potential influence on new particle formation and oxidation capacity in the atmospheric boundary-layer, respectively. Ambient Ion Monitor – Ion Chromatography (AIM-IC) methods developed in this work have provided quantitative online observations of atmospheric amines in the gaseous and condensed phases with detection limits of pptv and ng m-3 at hourly time resolution. Size-resolved particle observations demonstrated maximum amine mass loadings in 320 – 560 nm particles, and an increase in importance relative to ammonium for the smallest particles measured (56 – 180 nm). In particular, the size-resolved samples analysed in this work indicate that bulk aerosol measurements may not be appropriate for modelling the atmospheric processes that govern the incorporation of amines and ammonia in to atmospheric particles. Measurements of HONO made during the two intensive field campaigns (NACHTT, CalNex) and a lab study provided a new perspective on the interactions of this trace compound with ground surfaces. Integrated atmospheric column measurements of HONO and NO2 during NACHTT provided clear evidence that the ground surface dominates HONO production and loss at night. Simultaneous measurements of the gas and particle phases made by the AIM-IC system during CalNex demonstrated the potential for reactive uptake of HONO on mineral dust/soil as a nocturnal sink. Similarly, the potential for nitrite salts to react with strong acids, displacing HONO during the day was suggested by this dataset. Lab study results showed that HONO is taken up irreversibly on carbonate salts and real soil extracts. Relative humidity-dependent reactive uptake coefficients were derived. Subsequent release of HONO by displacement reactions with HNO3 and HCl was also confirmed. Together, these field and lab studies have produced a new picture of HONO surface interactions by providing i) a more explicit description of a nocturnal sink of HONO that could act as a surface reservoir and ii) a new mechanism for daytime HONO formation that does not require NO2.

<p> This research investigates the kinetics of the hydroxyl radical (OH)-initiated oxidation of several volatile organic compounds (VOCs) including ethanol, 3-methylfuran, and methyl ethyl ketone (2-butanone). Oxidation by OH is the dominant loss process for many biogenic and anthropogenic VOCs, making ambient concentrations of OH and the rate constants of OH + VOC reactions useful for determining the lifetime of various VOCs in the atmosphere. The rate constants of OH + VOC reactions are important for improving the accuracy of input parameters used in urban and regional air quality models which can be used to inform the development of air quality control strategies. The absolute rate constants for the reaction of OH with ethanol, 3- methylfuran, and methyl ethyl ketone (2-butanone) and, in some cases, their deuterated isotopomers have been measured as a function of pressure and temperature using discharge-flow techniques coupled with laser-induced fluorescence detection of OH. Theoretical studies of the potential energy surface for the various pathways in the OH + ethanol and OH + methyl ethyl ketone (2-butanone) reactions indicate a mechanism involving hydrogen-abstraction through a hydrogen-bonded pre-reactive complex. The experimental measurements of the rate constants and the kinetic isotope effect have been used in conjunction with the results of the theoretical studies to improve our understanding of the kinetics of these reactions.</p>

Present-day numerical air quality models are considered essential tools for predicting future air pollutant concentrations and depositions, contributing to the development of new effective strategies for the control and the reduction of pollutant emissions. They simulate concentrations and depositions of pollutants on a wide range of scales (global, national, urban scale) and they are used for identifying critical areas, integrating measurements and achieving a deeper scientific understanding of the physical and chemical processes involving air pollutants in the atmosphere. The use of comprehensive air quality models started in the late 1970s and since then their development has increased rapidly, hand in hand with the rapid increase in computational resources. Today more and more complex and computationally expensive numerical models are available to the scientific community. One of these tools is the Community Multi-Scale Air Quality System (CMAQ), developed in the 1990s by the US Environmental Protection Agency (EPA) and currently widely applied across the world for air pollution studies. This work focuses on the application of CMAQ to the United Kingdom, for estimating concentrations and depositions of acidifying pollutants (NOX, NHX, SOX) on a national scale. The work is divided into seven chapters, the first one describing the main issues related to the emission and dispersion in the atmosphere of acidifying species. It also includes a brief overview of the main international policies signed in the last thirty years in order to reduce the problem of acidification in Europe, as well as a brief description of some models mentioned in this thesis. The second one describes the main features of CMAQ and addresses some issues such as the use of a nesting process for achieving temporally and spatially resolved boundary concentrations, and the implementation of the model on parallel machines, essential for reducing the simulation computing time. It also describes how this study is part of a wider context, which includes the application of CMAQ in the United Kingdom by other users with different scientific purposes (aerosols processes, air quality in the urban area of London, contribution of UK power stations to concentrations and depositions etc.). The third part of the thesis focuses on the application and evaluation over the United Kingdom of the 5th Generation Mesoscale Model MM5, used for providing 3D meteorological input fields to CMAQ. This study was performed assuming that an accurate representation of depositions and concentrations of chemical species cannot be achieved without a good estimate of the meteorological parameters involved in most of the atmospheric processes (transport, photochemistry, aerosol processes, cloud processes etc.). The fourth part of the thesis describes the preliminary implementation of the Sparse Matrix Operational Kernel Emission System (SMOKE) in the United Kingdom. The processor provides input emissions to CMAQ. The use of SMOKE is usually avoided in CMAQ applications of outside America, and CMAQ input emission files are prepared by the application of other software. The reason is that the model requires radical changes for being applied outside Northern and Central America. Some of these changes have been made in this study such as the adaptation of the European emission inventory EMEP and the UK National Inventory NAEI to the modelling system for point and area sources, the introduction of new European emission temporal profiles in substitution of the American ones and the introduction of new geographical references for the spatial allocation of emissions. In the fifth chapter the results of CMAQ application over the UK are discussed. The study focuses on NOX, SO2, NH3 and + 4 NH . Maps of concentration are presented and modelled data are compared to measurements from two different air quality networks in the UK. An analysis of the performance of CMAQ over the UK is also performed. In the final chapter an annual inter-comparison between CMAQ and the Lagrangian transport model FRAME is carried out. Maps of annual wet deposition fluxes of NHX, NOY and SOX for year 1999 are presented. The results of both models are compared to one another and they are also compared to values from the UK official data set CBED. Finally, the last chapter suggests the work that has to be done in the future with CMAQ and it summarizes the conclusions.

<p> We studied the interactions of glyoxylic acid, pyruvic acid and oxalic acid with ammonium and corresponding sodium salts in aqueous solutions simulating a dark and radical free atmospheric aqueous aerosol condition. Cleavage of a carbon-carbon bond in pyruvic acid and glyoxylic acid leading to the decarboxylation was observed in the presence of ammo&not;nium salts but was not observed from oxalic acid. At the beginning of the reaction, the decarboxylation appeared to proceeding slower compare to the later stage of reaction. The empirical rate constants for decarboxylation in the reaction solutions were estimated using a 'quasi-steady state' model: (i) glyoxylic acid and ammonium sulfate was 3.3 (&plusmn; 0.7)&times;10^-8 M^-1 s^-1; (ii) glyoxylic acid and ammonium nitrate was 1.4 (&plusmn; 0.3)&times;10^-8 M^-1 s^-1; (ii) glyoxylic acid and ammonium chloride was 1.9 (&plusmn; 0.2)&times;10^-8 M^-1 s^-1; and (iii) pyruvic acid and ammonium sulfate was 15.8 (&plusmn; 0.4)&times;10^-8 M^-1 s^-1. Negligible CO₂ was observed in the experiments with the corresponding sodium salts indicating the ammonium ion or ammonia is facilitating the carbon-carbon bond cleavage leading to carboxyl fragmentation of the &agr;-oxo carboxylic acids. It was observed that pyruvic acid undergoes decarboxylation at least four times faster than that of glyoxylic acid under similar reaction conditions. This indicates that the structure of the acid plays an important role in the decarboxylation. In the case of pyruvic acid, the reaction is likely faster because of the inhibited hydration of the carbonyl moiety due to the inductive effect of the adjacent methyl group. A tentative set of reaction mechanisms is proposed involving nucleophilic attack by ammonia on the carbonyl carbon leading to fragmentation of the carbon-carbon bond between the carbonyl and carboxyl carbons. Similar carbon-carbon bond cleavage is anticipated for &agr;-dicarbonyl compounds, which are structurally similar to the &agr;-oxo carboxylic acids. In the absence of photolysis and under limited availability of OH radicals, the decay of pyruvic acid can be dominated by the reaction with ammonium sulfate and can be an order of magnitude higher than the loss via reaction with the OH radical. Under similar conditions the reactions with ammonium salts are likely be a major sink for &agr;-oxo carboxylic acids in the atmospheric aqueous phase.</p>

Thesis (Ph. D.)--McMaster University (Canada), 1989. / Source: Dissertation Abstracts International, Volume: 62-13, Section: A, page: 0000.

Thesis (Ph.D.)--York University, 2006. Graduate Programme in Earth and Space Science. / Typescript. Includes bibliographical references (leaves 271-296). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR19790

Thesis (Ph. D.)--University of Nevada, Reno, 2007. / "December, 2007." Includes bibliographical references. Online version available on the World Wide Web.

Thesis (M.S.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 73-76).