Seasonal variation of polycyclic aromatic hydrocarbon exposure levels in Mexico City.

This work presents the results obtained when determining the priority polycyclic aromatic hydrocarbon (PAH) concentration contained in particulate matter 10 microm in aerodynamic diameter or less (PM10) and in the gas phase in Mexico City's atmosphere by means of a field study conducted during 2005. PM10 and vapor-phase PAHs were collected on prebaked quartz fiber filters and PUF-XAD-4 resin and quantified by gas chromatography (GC)-mass spectrometry. Vapor-phase PAHs comprised 86-97% of the total PAH mass, and naphthalene was the most abundant PAH determined, contributing 84-93% to the total mass. The benzo[a]pyrene content was on average 7% of the PAHs' particle phase and 0.2-1% of the gas phase. The PAH concentrations measured where large industrial areas are located were 2-8 times greater during the fall/winter months (dry-cold season), when winds bear north- northeasterly, than in spring and summer. In contrast, the largest partition gas/particle ratio occurred during the dry-warm season (March-May). The results of statistical analysis using multivariate techniques suggest that motor vehicles are the main PAH contributors. The toxicity equivalence factors (TEFs) related to the carcinogenic benzo[a]pyrene potency were used for the assessment of the carcinogenic potential risk because of the measured airborne PAHs. Benzo[a]pyrene equivalent (BAPeq) concentrations were determined through multiplication of the individual PAH concentrations by their corresponding TEF value. The estimated total BAPeq for the whole field study considering only PM10 PAHs was 1085 pg m(-3). However, when taking into account the PAHs in both phases, the estimated total BAPeq was 1250 pg m(-3); in either case, the values were greater than the 1000-pg m(-3) limit proposed by European countries.