On the Nature of Aerosol Physicochemical Properties and Health Effects in the Southwestern United States

Abstract

Aerosol particles are important components in the Earth's atmosphere. They have been shown to have the following effects: (1) visibility reductions and degrading air quality; (2) negative impact on human health; (3) modification of cloud properties and the spatiotemporal distribution of precipitation; and (4) geochemical cycling of nutrients. It is projected that southern Arizona, which is a semi-arid area, will become drier, which can lead to an enhancement of wildfire and wind-blown dust. These resulting emissions will increase total aerosol particle loading and lead to a new physicochemical signature among the region's aerosol properties. The life cycle of aerosol particles still remains uncertain, which affects our ability to forecast air quality and climate change among other effects associated with particles. The organic fraction of aerosol particles has one of the largest uncertainties in terms of what species it is comprised of and how they are made, which is related to the research described in this dissertation. Another part of this dissertation is advancing knowledge about the interaction between aerosol particles and water vapor using ground measurements and models. The first research topic is that of the role of aqueous secondary organic aerosol (SOA) formation in a semi-arid region. Water-soluble organic carbon (WSOC) and its ratio to organic properties were used as proxies of SOA. Results from ground measurements are presented, which summarized SOA formation results from enhanced moisture in Monsoon season (July-September) and enhanced emissions of biogenic volatile organic compounds (BVOCs) due to rapid plant growth. A second research study was conducted to quantify aerosol and cloud water dimethylamine (DMA) in southern Arizona and by the California coast. The study results include a summary of the DMA size distribution and its ratio to ammonium in the two regions, relationship between PM1.0 DMA and potential influencing factors, and a summary of DMA concentrations in cloud water from the California coastal region. The last part of this study includes a detailed characterization of long-term cloud condensation nuclei (CCN) concentrations at 0.2% supersaturation, aerosol composition, and aerosol size distributions in southern Arizona. The results are used to show diurnal and seasonal patterns and variability. Measured CCN concentrations are compared with modeled values in the form of closure studies. A common thread through all studies presented in this dissertation is the characterization of atmospheric aerosol physicochemical properties in southern Arizona. It is hoped that this dissertation is able to provide an impetus for continuing research on air quality and public health in semi-arid regions such as southern Arizona.