Urban Organic Aerosol Exposure: Spatial Variations in Composition and Source Impacts

Area of Science:

• Environmental Chemistry
• Atmospheric Science
• Air Quality Monitoring

Background:

• Urban environments exhibit complex spatial heterogeneity in air pollution.
• Understanding the sources and composition of organic aerosol (OA) is crucial for assessing health impacts.
• Mobile sampling campaigns provide valuable data on localized pollution patterns.

Purpose of the Study:

• To investigate the spatial variability of organic aerosol (OA) components in an industrialized urban area.
• To identify specific organic carbon (OC) fractions as markers for fresh emissions versus secondary or aged aerosol.
• To develop land use regression (LUR) models for predicting OC fraction concentrations.

Main Methods:

• Conducted a mobile sampling campaign in Pittsburgh, PA, with 36 sites stratified by traffic, industrial density, and elevation.
• Collected and analyzed organic carbon (OC) using thermal-optical analysis, categorizing fractions by volatility (OC1-OC4, pyrolyzed carbon [PC]).
• Compared ambient OC concentrations with emission data from vehicles, cooking, biomass burning, and a traffic tunnel; developed LUR models.

Main Results:

• OC2 and OC3 fractions strongly correlated with primary emission sources, indicating they are markers for fresh pollution.
• OC4 and PC fractions showed more spatial homogeneity, suggesting secondary formation or aged aerosol.
• LUR models for OC fractions achieved an average R-squared of 0.64, demonstrating predictive capability.

Conclusions:

• OC2 and OC3 serve as effective markers for recent, primary emissions in ambient air.
• OC4 is indicative of secondary organic aerosol formation, while PC represents a mix of biomass burning and secondary aerosol.
• Exposure to higher total OC levels likely means greater inhalation of fresh OC2 and OC3 due to their stronger association with local sources.