Date of Award




Document Type


Degree Name

Doctor of Philosophy (PhD)


Department of Atmospheric and Environmental Sciences

Content Description

1 online resource (viii, 174 pages) : color illustrations.

Dissertation/Thesis Chair

James J Schwab

Committee Members

Robert J Keesee, Christopher Walcek, Fangqun Yu


aerosols, Air pollutant, Air quality regulations, ion balance, organic matter, particulate matter, Air, Atmospheric chemistry, Particulate matter, Atmospheric aerosols

Subject Categories

Atmospheric Sciences | Environmental Sciences | Other Chemistry


Eighteen years of ambient PM2.5 mass and major components are used in this study to harmonize the carbonaceous fraction of PM2.5 data, and to examine long-term trends and seasonal variability changes. The major decreasing trend of PM2.5 mass and major inorganic ions reflects the ambient concentration response to clean air regulations and policies.Although elemental carbon shows a decreasing trend in agreement with most other PM2.5 components, organic carbon shows a different behavior of no-trend to slightly increasing trend in some sites. Organic carbon behavior indicates the growing role of non-combustion sources at the expense of decreasing combustion sources. Seasonal trends are examined; which show significant seasonal differences mainly as more decrease (or increase) during higher concentrations seasons compared to other seasons; and as a decrease in seasonal variability. The annual average range is examined as well, and for most PM2.5 components this range is shrinking. Trend analysis results led to exploration of the relatively slow rates of organic carbon decline compared to inorganic ions, as well as the differences in these rates of decline amongst the inorganics themselves. Potential sources of the different behavior for PM2.5 organic carbon are the increase in wildfires, the increase in vehicular emissions, the migration from the coal fired power plants to natural gas EGUs, and changes in the effective directions of pollutant sources. Also, results indicated that differences in reduction rates of different components affected the inorganic ion-balance, ammonium partitioning, nitrate attribution, regional/rural nature of the sources, and increased the ratio of unaccounted for mass. Potential contributing factors were explored to explain the unaccounted for mass and results indicated that the major contributor to this quantity is organic matter, and that this component is increasing with time. The contribution of nitrate is less clear and convincing, and it seems that the assumption that ammonium nitrate is the only form of nitrate is likely not the best choice. Finally, results of this study can offer a better understanding of both effectiveness of current clean air regulations, and any future regulations, to achieve the goal of a cleaner atmosphere.