Distribution of Polycyclic Aromatic Hydrocarbons in Leaked Crankcase Oil of Parking Facilities

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants that are produced in the environment naturally or anthropogenically. Many high-molecular weight PAHs are considered carcinogens or possibly carcinogenic to humans. Used crankcase oil is one of the major PAH sources in urban environments. When engine runs, PAHs are generated and accumulate in oil and when crankcase oil leaks onto parking surfaces, oil stains become PAH sources. This study measures PAH concentrations and estimates their distributions in leaked crankcase oil of two parking facilities: a covered concrete parking structure and an open asphalt parking lot. A total of 120 samples of oil stains, parking background, and parking dust were collected from the covered parking structure and the open parking lot and analyzed for PAHs by gas chromatography-mass spectrometry (GC-MS). Additionally, the chromatogram unresolved complex mixtures (UCM) of crankcase oil stains were examined by applying baseline filtering method (baseline estimation and denoising with sparsity; BEADS algorithm). In the covered parking, used oil is the predominant source of PAHs and PAH concentrations decreases significantly as oil stains age. In addition, in the covered parking, PAHs ratios suggest that biodegradation is the major process of PAH attenuation. In the open parking, asphalt pavement and coal-tar sealant are the predominant sources of PAH and this PAH signal overwhelms any PAH signal derived from leaked crankcase oil. For the open parking, comparison of gas-chromatographic retention time at the second quartile suggest a significant and early loss of low-molecular weight hydrocarbons of base oil, suggesting efficient base oil attenuation processes. In contrast, covered parking samples exhibit a very limited increase in retention time at the second quartile with increasing stain age, demonstrating the limited process of attenuation affecting base oil in stains of the covered parking. It can be concluded that biodegradation is the predominant natural attenuation mechanism for PAH degradation and crankcase oil loss in the covered parking structure. In open parking, however, natural attenuation processes are dominated by water-washing.