Quantification of the Spatial Variation and Source Contributions to Ambient Particle-Bound PAHs Using Aerosol Mass Spectrometry.

Abstract

Polycyclic Aromatic Hydrocarbons (PAHs), a subset of air toxics, pose severe health risks even at low concentrations due to their carcinogenic and reproductive effects. Despite their significance, spatial distribution studies of PAHs remain limited, largely due to the absence of real-time, chemically specific methods. This study applies high-resolution aerosol mass spectrometry (AMS) for quantification and spatial analysis of particle-phase PAHs. Laboratory experiments were conducted with four PAH standards (anthracene, pyrene, 9-methyl anthracene, and acenaphthylene) to determine their mass spectra and ionization efficiency. AMS mass spectra of the PAH standards were highly correlated with NIST reference spectra (R² > 0.95), though the aerosol mass spectra exhibited greater fragmentation than the reference spectra. Subsequently, field sampling was carried out in the city of Pittsburgh. A mobile laboratory was driven over defined routes in areas of varying source activities (e.g., the downtown core, residential areas, and industrial areas). These measurements revealed significant spatial variability. The median neighborhood-scale total particle-phase PAH concentrations ranged from 70 ng/m³ to 150 ng/m³ indicating a 2.1-fold difference, with the downtown neighborhood exhibiting the highest intra-neighborhood variability (Q3/Q1 = 3.4). Compared to Black Carbon (BC), particle-phase PAHs showed greater spatial variability. Most of the detected particle-phase PAHs had low background concentrations and the time series of concentration was punctuated by high concentration spikes. These spikes occurred most frequently in high-traffic zones such as Downtown and on major highways, suggesting contributions from vehicle traffic. Additional spikes in industrial areas suggest contributions from industrial sources. Ratio-ratio plots (e.g., PAH/BC) and comparison of particle-phase PAH concentrations with the concentrations of hydrocarbon-like organic aerosol (HOA), an indicator of vehicle emissions, further indicate the importance of vehicle emissions on ambient particle-phase PAH concentrations. However, vehicle emissions cannot fully explain particle-phase PAH concentrations in the mobile sampling data. Other sources including metallurgical coke emissions and asphalt paving emissions may also be important.

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Supplementary information: The online version contains supplementary material available at 10.1007/s44408-026-00109-2.