- Atmospheric fine particulate matter (PM2.5) has been linked to the death of 7 million people per year around the planet. The organic portion of PM2.5 is responsible for increases in oxidative stress, inflammation, mutation and carcinogenesis. Anthropogenic activity releases more organic material into the atmosphere, and has increased the amount of PM2.5 which contains organic aerosol including polycyclic aromatic hydrocarbons (PAHs) in the atmosphere. PAHs are ubiquitous environmental contaminants emitted to the atmosphere through incomplete combustion, which traverse the planet in PM2.5. Protected in PM2.5 by glassy organic aerosol coatings, PAHs undergo long-range atmospheric transport.
Recent studies have shown that PAHs increase the viscosity and atmospheric lifetimes of secondary organic aerosol (SOA) particles formed naturally in the atmosphere, but have not shown the chemical speciation responsible for these trends. This dissertation measured PAH oxidation products formed during SOA formation in the presence of PAH vapor. These SOA particles grew larger, resulting in up to a 600% mass loading increase over SOA formed without PAH vapor present, and had longer atmospheric lifetimes. This indicated that the presences of PAHs during particle growth increases the formation less-volatile organic compounds, which remain condensed in the atmosphere. High-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS) showed that SOA particles formed in the presence of PAH vapor had increased signals of mass to charge ratios (m/z) at higher m/z. Other studies have demonstrated a large number of oligomers in SOA which could have the m/z signals measured here, suggesting a synergistic effect on SOA non-volatile compound formation.
In the second part of this dissertation, ambient PM2.5 samples (collected in collaboration with the Swinomish Indian Tribal Community of the Northwest coast of the US State of Washington) were found to contain the same PAH oxidation products measured in our SOA experiments. The presence of these compounds in ambient samples proved the real world application of the experimental data collected in the first part of this dissertation. Along with these oxidation products, measured concentrations of ~130 PAHs in the ambient PM2.5 analyzed in this dissertation were used to assess the air quality of the Swinomish Reservation during different atmospheric conditions. Significant differences in PAH concentrations were found during changes in wind direction, the presence of regional wildfires, and during atmospheric inversions. Excess Lifetime Cancer risk assessment was performed on PM2.5¬ samples to demonstrate that during inversions, the inhalation cancer risk rises to levels above WHO safety guidelines.
The oxidative potential (OP) of atmospheric fine particulate matter (PM2.5) has been linked to the organic content of PM2.5, including polycyclic aromatic hydrocarbons (PAHs). Using the results from individual PAHs in the assay, computational modeling was performed to calculate the free energy of reaction (ΔGrxn) for each PAH in the consumption assay. Significant correlations were found between the DTT50 and the ΔGrxn of subclasses of PAHs, the molecular weight (AMU) of PAHs, the assay response (linear slope), and various physical structural components of the PAHs. While mixtures of the 16 PAHs currently found on the US EPA Priority Pollutant List tested in this study appeared to show an additive mixture effect in the DTT assay, whole mixtures of PAHs prepared to match ambient PM2.5 PAH measurements did not. The compounds in the mixtures appear to either have antagonistic effects, or a non-linear relationship in oxidative potential at the low concentrations measured in PM2.5 samples. Extract measurements were significantly less
This dissertation used advanced aerosol instrumentation, analytical characterization, and chemical assays to demonstrate ways to improve our understanding of PAH fate and transport in the atmosphere, as well as potential impact on human health. The results of this research illustrate both the presence of a large number of PAHs in ambient PM2.5 and their implications on atmospheric lifetimes and PM2.5 exposure induced oxidative stress.