The role of organic films and the effect on hydrophobic organic compounds in urban areas: An hypothesis

Urban areas experience a convergence of multiple chemical discharges into a highly disturbed environment characterized by impervious surfaces. It is hypothesized that an organic film comprised of surfactant-like compounds coats impervious surfaces. This film, which is analogous to the organic film on surface waters and the cuticular surface of leaves, provides a medium into which gas-phase hydrophobic organic compounds (HOCs) can partition and particle-sorbed HOCs are trapped. The hypothesis is supported by reports in the literature citing films on roadways, fog droplets and urban particulates. The film is comprised of primary emissions from vehicles and secondary organic aerosols (SOA) formed by atmospheric oxidation of primary emissions of volatile organic compounds (VOCs). It is suggested that the film provides a layer into which HOCs can partition, thereby elevating HOC concentrations and amounts that may enter surface waters upon film washoff and urban air at elevated ambient temperatures.