From June 2006 to March 2007, the concentrations of water soluble inorganic particulates and their associated precursor gases were semi-continuously measured adjacent to a high traffic street in downtown Toronto, Canada. Measurements underwent extensive quality assurance and control protocols. Seasonal and diurnal variations in HNO3 and NH3 partitioning to NH4NO3 were observed. Long range transported air masses from southwest of Toronto were the predominant source of measured SO4 2- for all seasons. The contributing sources of PM2.5 nitrate mass fluctuated between seasons: pNO3- was predominantly locally derived in the summer and resulted from long range transport in the winter. Comparison between measurements and ISORROPIA thermodynamic model predictions identified model weaknesses and was used to explore the effect of modulating primary gas concentrations on consequent particulate levels. SO2 emissions reductions were the most influential and direct method to reduce overall PM2.5 concentrations; however, limiting ammonia emissions was also another successful strategy.

From June 2006 to March 2007, the concentrations of water soluble inorganic particulates and their associated precursor gases were semi-continuously measured adjacent to a high traffic street in downtown Toronto, Canada. Measurements underwent extensive quality assurance and control protocols. Seasonal and diurnal variations in HNO3 and NH3 partitioning to NH4NO3 were observed. Long range transported air masses from southwest of Toronto were the predominant source of measured SO4 2- for all seasons. The contributing sources of PM2.5 nitrate mass fluctuated between seasons: pNO3- was predominantly locally derived in the summer and resulted from long range transport in the winter. Comparison between measurements and ISORROPIA thermodynamic model predictions identified model weaknesses and was used to explore the effect of modulating primary gas concentrations on consequent particulate levels. SO2 emissions reductions were the most influential and direct method to reduce overall PM2.5 concentrations; however, limiting ammonia emissions was also another successful strategy.

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.

Nano-particle aerosols are one of the major types of air pollutants in the urban indoor and outdoor environments. Therefore, determination of mechanisms of formation, dispersion, evolution, and transformation of combustion aerosols near the major source of this type of air pollution - busy roads and road networks - is one of the most essential and urgent goals. This Thesis addresses this particular direction of research by filling in gaps in the existing physical understanding of aerosol behaviour and evolution. The applicability of the Gaussian plume model to combustion aerosols near busy roads is discussed and used for the numerical analysis of aerosol dispersion. New methods of determination of emission factors from the average fleet on a road and from different types of vehicles are developed. Strong and fast evolution processes in combustion aerosols near busy roads are discovered experimentally, interpreted, modelled, and statistically analysed. A new major mechanism of aerosol evolution based on the intensive thermal fragmentation of nano-particles is proposed, discussed and modelled. A comprehensive interpretation of mutual transformations of particle modes, a strong maximum of the total number concentration at an optimal distance from the road, increase of the proportion of small nano-particles far from the road is suggested. Modelling of the new mechanism is developed on the basis of the theory of turbulent diffusion, kinetic equations, and theory of stochastic evaporation/degradation processes. Several new powerful statistical methods of analysis are developed for comprehensive data analysis in the presence of strong turbulent mixing and stochastic fluctuations of environmental factors and parameters. These methods are based upon the moving average approach, multi-variate and canonical correlation analyses. As a result, an important new physical insight into the relationships/interactions between particle modes, atmospheric parameters and traffic conditions is presented. In particular, a new definition of particle modes as groups of particles with similar diameters, characterised by strong mutual correlations, is introduced. Likely sources of different particle modes near a busy road are identified and investigated. Strong anti-correlations between some of the particle modes are discovered and interpreted using the derived fragmentation theorem. The results obtained in this thesis will be important for accurate prediction of aerosol pollution levels in the outdoor and indoor environments, for the reliable determination of human exposure and impact of transport emissions on the environment on local and possibly global scales. This work will also be important for the development of reliable and scientifically-based national and international standards for nano-particle emissions.