Air pollution greatly affects both the environment and human health. According to the World Health Organization, there are an estimated 800,000 premature deaths every year from lung cancer, cardiovascular and respiratory diseases caused by outdoor air pollution. For the last several decades, developed nations such as the United States of America have been studying the extent of the existing pollution, its sources and affects, and designing reduction strategies. Simultaneously, urbanization and industrialization are compounding the problem of urban air pollution in developing countries. The Denver Aerosol Sources and Health (DASH) Study was a six-year epidemiological study that examined speciated fine particulate matter (PM_2.5), sources, and correlations with health effects. The sampling was conducted at one centrally-located site in Denver, and questions were raised as to the applicability of the findings to the Denver area as a whole. The first project goal of this dissertation was to determine the spatial variation and chemical speciation of PM _2.5 in Denver. This involved setting up three additional sampling locations throughout the Denver metropolitan area, and monitoring PM_2.5 over the course of one year. Organic and inorganic analyses were conducted to determine the spatially diverse composition of PM_2.5 at each of the sites and find correlations in concentration levels over time. The second project goal of this dissertation was to find correlations of personal exposure to PM_2.5 in the urban office environment with outdoor air measurements in Xi’an, China. This research was supported by the National Science Foundation’s East Asia and Pacific Summer Institutes program during summer 2009, and was the first of its kind ever to be conducted in China.