Temporal variations of black carbon and nitro polycyclic aromatic hydrocarbons in Morelos, México

Carbonaceous species such as nitro-polycyclic aromatic hydrocarbons (NPAHs) are toxic ubiquitous pollutants contained in the organic fraction of airborne particles, since several of them have mutagenic and carcinogenic properties. Black carbon has been recognized as a short live climatic pollutant which must be controlled in order to mitigate climatic change. Morelos is a little state of Mexico located at the South of the Metropolitan Area of Mexico City which has grown in the last years, but only few studies related with atmospheric pollution have been performed, then, with the aim to have better information related with carbonaceous compounds contained in the PM_2.5 of the two main cities of Morelos, a monitoring campaign was carried out in Cuernavaca City, from 2016 to 2018, whereas in the Cuautla city the campaign was performed from 2017 to 2018. PM_2.5 were collected with HighVol Tish equipment every six days. Elemental and organic carbon were analyzed with a Sunset Lab and toxic NPAHs were extracted with dichloromethane and sonication and further analyzed by gas chromatography–mass spectrometry (GC-MS). Median annual PM_2.5 concentrations were 22.5 ± 7.2 mg m^-3 and 19.6 ± 6.1 mg m^-3, for Cuautla and Cuernavaca, respectively. Black carbon concentrations were higher in Cuautla than in Cuernavaca with 1.9 ± 0.5 mg m^-3, and 1.3 ± 0.4 mg m^-3 respectively, since Cuautla is a rural zone with frequent biomass burning The highest NHAPs concentrations were found in Cuautla with medians of 280.74 pg m^-3, 90.67 pg/m^-3 and 156.61 pg m^-3, for the warm dry season (March-June), the rainy season (July-October) and the cold dry season (November-February) respectively. In Cuernavaca, the NHAPs presented lower concentrations in the three seasons with 116.41 pg m^-3, 63.82 pg/m^-3 and 128.99 pg m^-3, respectively. 1-nitronaphtalene, 2-nitrophenentrene and 2-nitroanthracene were the most abundant compounds in both sites. Although PM_2.5 Mexican Standard was not exceeded, the high concentrations of black carbon and NPAHs are of concern since black carbon is a climatic pollutant and some of the NHAPs compounds are carcinogenic.