Air quality assessment in a highly industrialized area of Mexico: Concentrations and sources of volatile organic compounds

Parallel to the economical benefits brought by the oil industry in Mexico, there have been some negative environmental effects due to emission of pollutants to the atmosphere. Salamanca, a city located inside one of the most important industrial corridors of the country, has been frequently affected by elevated concentrations of sulfur dioxide and particle matter. However, little is known about volatile organic compounds (VOCs), which in this study are analyzed along with criteria pollutants and meteorological parameters during February–March 2003 at urban, suburban and rural sites. Although sulfur dioxide average levels were ∼0.017 ppm, a high concentration event (∼0.600 ppm), attributable to emissions from the oil refinery and the thermoelectric power plant, was observed at the urban site at night time. The VOCs concentration varied from 170 ± 50 ppbC (rural) to 699 ± 212 (urban) and were constituted by 40% alkanes, 13% aromatics, 11% olefins and 11% of halogenated. The most abundant species were propane (167 ± 40 ppbC), n-butane (91 ± 23 ppbC), toluene (51 ± 10 ppbC) and i-pentane (44 ± 7 ppbC), that are related to combustion processes. Freon-114, methyl bromide and 1,2-dichloroethane which are likely emitted by application of pesticides, soil fumigation and fabrication of chemicals, showed high concentrations (48 ± 10, 50 ± 10 and 32 ± 6 ppbC respectively) in the rural sites, highlighting the importance of control measurements implementation for these species, as they represent a potential hazard for public health. Moreover, these halocarbons showed similar ratios regardless the monitoring site, suggesting same source. Modeling results indicated that meteorological conditions generally transport air masses to the northeast rural areas where the highest concentrations of ozone were calculated.