Influence of atmospheric processes on the physico-chemical properties of primary particles and their impact on public exposure

Primary sources, especially vehicle emissions, are the dominant contributors of ambient particulate matter (PM) in urban environments. Upon their emissions from primary sources, ambient PM undergoes various atmospheric processes which may alter their physic-chemical and toxicological properties before the exposure to the public. This thesis first investigates the physic-chemical properties of ambient ultrafine aerosols characterized as from primary source in the immediate vicinity of a major freeway in Los Angeles. Then the thesis examines the atmospheric processes (dilution and photochemical oxidation) that dominate the dynamics of primary aerosols following their emission. Atmospheric dilution affects the dynamic behavior of aerosols by affecting the ambient concentration levels of non-labile PM species and also shifting the gas-particle partitioning of the semivolatile PM component. This study discusses the roles of dilution in changing the physico-chemical properties of the ambient aerosols by comparing the normalized fuel-based emission factors of various PM species. This information is complemented with an investigation of secondary aerosol formation from atmospheric photochemical reactions that alters the PM volatility, solubility and chemical properties. Based on the experimental investigation, the thesis reviews the recent findings that link PM semi-volatile components and their redox activity, and also discusses the influence and importance of PM volatility on particle toxicity. Lastly, this thesis discusses possible metrics to regulate PM emissions and establish ambient air quality standards that are pertinent to public health, and suggests future investigations aimed to improve our current understanding of the adverse health effects of public exposure to ambient aerosols.