Sources of fine organic aerosol. 3. Road dust, tire debris, and organometallic brake lining dust: roads as sources and sinks
Particulate matter emitted to the atmosphere due to motor vehicles arises from several sources in addition to tailpipe exhaust. In this study, the organic constituents present in fine particulate (d_p ≤ 2.0 µm) road dust, brake lining wear particles, and tire tread debris (not size segregated) are analyzed using gas chromatography/mass spectrometry. The objective is to characterize such traffic-related sources on an organic compound basis and to search for molecular markers that will assist the identification of traffic-associated dusts in the urban atmosphere. More than 100 organic compounds are quantified in these samples, including n-alkanes, n-alkanoic acids, n-alkenoic acids, n-alkanals, n-alkanols, benzoic acids, benzaldehydes, polyalkylene glycol ethers, PAH, oxy-PAH, steranes, hopanes, natural resins and other compound classes. Paved road dust acts as a repository for vehicle-related particles, which can then be resuspended by the passing traffic. To evaluate the contributions from major urban sources to the road dust complex, source profiles representing different types of vehicle exhaust, brake dust, tire debris, and vegetative detritus are compared, and their fractional contributions are estimated using several groups of organic tracer compounds. Likewise, the close relationship between airborne fine particulate organic constituents and road dust organic matter is discussed.