Variation, Patterns & Sources of Air Pollution: A Study of Ambient PM2.5 in Wisconsin

Air quality is a high priority research area of the United States Environmental Protection Agency (EPA) and research on the changing spatiotemporal patterns of PM2.5 is part of the EPA's current focus. The EPA is looking for studies on the relationship between long-term exposure to PM2.5 and cardiovascular health in order to to reduce the uncertainty of the concentration---response relationships, especially at low ambient concentration of PM2.5. A comprehensive analysis of a large volume of available PM2.5 data collected at four different regions in Wisconsin was performed to study the spatialtemporal variations, the patterns of the variations and the changes in patterns of ambient PM2.5. A systematic approach was established in the study that enables utilizing the broadely available PM2.5 data for future health research.;Spatial and temporal variations of the characteristics and the changes of the discovered patterns of ambient PM2.5 and the aerosol acidity of PM2.5 were studied using statistical and graphical software. The changes in the concentrations of ambient sulfate, nitrate and OC highlight the need for changing PM2.5 reduction strategies. A change in the ambient aerosol acidity trend was observed around 2009 and 2010. P value analysis indicated both the downward and upward trends were not insignificant. A further study to determine if there is a permanent increasing trend is recommended. An ascending trend of aerosol acidity was discovered during winter episodes in Milwaukee from 2002 to 2009, which also needs additional study.;A thermodynamic principle-based method was developed using the deliquescent relative humidity (DRH) as a criterion to determine if the inorganic ions in PM2.5 were in aqueous phase. If the relative humidity (RH) on the sampling day was higher than the DRH of the aerosol system, the inorganic ions were in aqueous phase and were selected for modeling. The Extended Aerosol Inorganic Model (EAIM) was used to estimate the in-situ acidity. The calculated in-situ acidity has reasonable correlation with other aerosol acidity indexes used in the study.;Pattern changes in ambient PM2.5 were observed. The periods when trends change direction provide valuable opportunities to study the underlying causes of the changes.