Detection, Spatial Analysis and Source Identification of Hazardous Air Pollutants using Mobile Mass Spectrometry

<p dir="ltr">Air pollution exposure in urban areas has been a major source of concern. There is a growing need to understand the spatial variability of air pollutants within urban cities. Hazardous air pollutants (HAPs), or Air Toxics, can cause serious health problems like cancer and birth defects, along with other major health challenges. Several compounds are classified as HAPs, including some Volatile Organic Compounds (VOCs) and Polycyclic Aromatic Hydrocarbons (PAHs). There has been limited information on how VOCs and PAHs vary within cities. This is partly due to a lack of real time high temporal and mass resolution instrumentation. We explore in this dissertation the usage of high temporal and mass resolution spectrometry, such as aerosol mass spectrometry and proton transfer reaction mass spectrometry, to detect PAHs and VOCs in urban environments.</p><p dir="ltr">We conducted mobile sampling in the city of Pittsburgh to detect air pollutants and assess neighborhood-scale variations. The PAH driving routes were designed to capture different traffic densities and source activities, while the VOC routes aimed to include both traditional sources such as traffic and industrial emissions, and non-traditional sources such as gas stations, salons, dry cleaners, and cooking emissions. The non-traditional sources were included due to recent studies showing that volatile chemical products tend to contribute to urban air pollution. We also demonstrated the broad applicability of high-resolution mass spectrometry by applying it to a post disaster event such as the East Palestine train derailment. </p><p dir="ltr">Polycyclic Aromatic Hydrocarbons exhibited both intra and inter-neighborhood variability. For example, the median total PAH concentration in Downtown (0.15 µg/m3) was more than twice that of Oakland (0.07 µg/m3), while Downtown Pittsburgh exhibited a high interquartile range (Q3/Q1 ratio = 3.4). Spatial analysis of PAHs identified distinct hotspots along major highways, industrial areas, and the Downtown neighborhoods, suggesting contributions from traffic and industrial emissions. When compared to Black Carbon (BC), PAHs showed greater inter-neighborhood variability than BC. For instance, cumulative distributive function of PAHs indicated a maximum spread of 39% between neighborhoods, whereas BC had a maximum spread of 15%. Ratio-to-ratio plots (e.g., PAH/BC) further suggested contributions from traffic emissions. Additional potential sources include metallurgical coke emission and asphalt paving emission. </p><p dir="ltr">Volatile organic compounds, on the other hand, exhibited both shared and distinct VOC signatures. For example, isoprene showed a similar cumulative distribution function across neighborhoods, suggesting contributions from biogenic sources. Southside and Strip District exhibited elevated acetone levels relative to benzene, suggesting area-wide emissions possibly from solvent usage. Additionally, Neville Island displayed the highest styrene concentrations with the peak exceeding 600 times the campaign median, suggesting contribution from industrial sources. Spatial analysis of VOCs using exposure and quantile-based thresholds identified hotspots along major highways, Downtown Pittsburgh and industrial areas like Neville Island, suggesting contributions from traffic and industrial emissions. Correlation plots revealed various clusters such as strong correlation (Pearson r = 0.81) among combustion related species (C3H6 - Propyne), and moderate correlation (r = 0.5 - 0.7) among aromatic VOCs such as benzene, toluene and xylene, suggesting contribution from mixed sources such as gasoline combustion and solvent usage possibly in saloons. We also identified weakly correlated solvent VOC such as acetone (r <0.1). This suggests unique sources, such as cleaning operations or emissions from nail or hair salons. </p><p dir="ltr">Applying high-resolution mass spectrometry to post-disaster response such as the East Palestine train derailment, demonstrated the capability of highly sensitive, non-targeted mobile monitoring to detect both known and unknown VOCs after a disaster. Results showed that levels of targeted compounds such as benzene, toluene and xylene were similar to the EPA monitoring data and below minimal risk levels for chronic exposures. Non-targeted analysis identified compounds such as acrolein as being high compared to the local rural background, with other compounds displaying similar spatiotemporal patterns to that of acrolein. Overall, this study demonstrates the usage of high-resolution mobile monitoring to identify VOCs and PAHs in urban areas. It also provides their spatial variations within neighborhoods in a city. These tend to help inform exposure assessment, policymakers and urban planning.</p>