Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants produced by incomplete combustion sources such as home heating, biomass burning, and vehicle emissions. PAH concentrations in soils are influenced by source inputs and environmental factors that control loss processes and soil retention. Many studies have found higher concentrations of these pollutants in soils within cities of temperate climates that have a centralized urban core. Less is known about the factors regulating PAH abundance in warm, arid urban ecosystems with low population densities but high traffic volumes. The relative importance of sources such as motor vehicle traffic load and aridland ecosystem characteristics, including temperature, silt, and organic matter content, were explored as factors regulating PAH concentrations in soils near highways across the metropolitan area of Phoenix, Arizona (USA). Highway traffic load is high compared to other cities, with an average of 155,000 vehicles per day. Soils contained low but variable amounts of organic matter (median 2.8 ± 1.8% standard deviation). Across the city, median PAH concentrations in soil were low relative to other major cities, 523 ± 1,886 ?g•kg-1, ranging from 67 to 10,117 ?g•kg-1. Diagnostic ratio analyses confirmed that the source of PAHs in Phoenix highway soils is predominantly fuel combustion (i.e. vehicle emissions) rather than petrogenic, biogenic, or other combustion sources (e.g. coal, wood burning). However, in a multiple regression analysis including traffic characteristics and soil properties, soil organic matter content was the variable most strongly related to PAH concentrations. Our research suggests that dryland soil characteristics play an important role in the retention of PAH compounds in soils of arid cities.