In this research we wanted to ask, what is the magnitude, distribution, and fate of non-point carbon pollution in a low-density, urban area? To answer this question, the goal of the project is to: 1) characterize and quantify combustion-derived carbon compounds in soils near roadways across the Phoenix valley, 2) explore the dynamic fate of Polycyclic Aromatic Hydrocarbons (PAHs) in soils, and 3) assess the importance of microbial community structure in PAH storage and dynamics. We collected 63 soil samples near highways across the Phoenix valley to characterize and quantify PAH compounds using extraction methods with Ultrasound Sonication and analyses by Gas Chromatography-Mass Spectrometry (GC-MS). Additionally, we measured a suite of soil properties and processes to explore the role of abiotic and biotic factors on the retention of PAHs in urban soil.

PAH concentrations in arid Phoenix soils ranged from 52 ug/kg dry soil to 8,296 ug/kg (mean 926 ug/kg), nearly an order of magnitude lower on average than expected based on data from other cities (Figure 1, Table 1). The project findings show the extent of these pollutants, an EPA-priority group of hazardous compounds, in urban soils. Although the most likely sources for PAH content in roadway soils are vehicle emissions, they were not correlated with traffic density (r2 = 0.024; p = 0.26) or highway age (r2 = 0.044; p = 0.13) across all sites. However, PAH concentrations were significantly correlated to soil organic matter (r2 = 0.36; p less than 0.001). These results suggest that PAH concentrations in roadway soils of desert cities may be controlled by factors associated with carbon retention, such as soil organic matter, rather than source or rate of deposition