Levels, Sources and Risk Assessment of Carbonaceous and Organic Species Associated with PM2.5 in Two Small Cities of Morelos, Mexico

A study of carbonaceous species, polycyclic aromatic hydrocarbons (PAHs), and nitro-PAHs associated with PM2.5 was conducted to assess their carcinogenic potential and associated health risks in the two main cities of the State of Morelos: Cuernavaca and Cuautla. The annual median concentrations in Cuernavaca of organic carbon (OC) and elemental carbon (EC) were 6.2 mu g m-3 and 0.6 mu g m-3, respectively, whereas in Cuautla, OC concentrations averaged 4.8 mu g m-3 and EC 0.6 mu g m-3. OC/EC ratios, total carbonaceous aerosols (TCA), primary (POC) and secondary organic carbon (SOC), as well as elemental carbon reactive (ECR) were estimated, also showing prevalence of primary emissions such as biomass burning. The seventeen PAHs recommended by the EPA and twelve nitro-PAHs were measured using gas chromatography-mass spectrometry. The annual median sum of PAHs was 9.7 ng m-3 in Cuernavaca and 11.2 ng m-3 in Cuautla, where carcinogenic high-molecular-weight compounds were the most dominant; the annual median sums of nitro-PAHs were 287 pg m-3 and 432 pg m-3, respectively. Diagnostic ratios were applied to identify potential sources of PAH emissions, suggesting that fuel combustion is the major contributor in both sites, followed by coal biomass burning and agricultural activities. The annual carcinogenic potential as benzo(a)pyrene equivalent was 2.2 ng m-3 for both sites. The lifetime excess cancer risk from PAH inhalation was estimated to range from 1.8 x 10-4 to 2 x 10-4 in Cuernavaca and from 1.5 x 10-4 to 2.2 x 10-4 in Cuautla, similar to values observed in other urban regions globally.