RESUMO
The Mexico City Metropolitan Area (MCMA) was the object of a chemical elemental characterization (Ti, V, Cr, Mn, Co, Ni, Cu, Mo, Ag, Cd, Sb, Pb, La, Sm, Ce, and Eu) of PM2.5 collected during 2013 and analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Sampling campaigns were carried out at five locations simultaneously-northwest, northeast, center, southwest, and southeast-during dry-warm season (April), rainy season (August), and dry-cold season (November). By means of enrichment factor (EF) and principal component analysis (PCA), it was possible to attribute the analyzed elements to geogenic and anthropogenic sources, as well as to identify a group of elements with mixed provenance sources. The highest concentrations for most metals were found in northwest and northeast, and during dry-warm (DW), confirming the trend observed in PM2.5 samples collected in 2011. Despite similarities between 2011 and 2013, an increase of 17% in PM2.5 mass concentration was observed, mainly attributable to geogenic sources, whereby the importance of wind intensity to the impact of emission sources is highlighted. The effect of wind intensity was revealed, by means of polar plots, as the controlling mechanism for this increase. This allowed us to conclude that high-speed episodes (5 m s-1) were responsible for raising geogenic metal concentrations rather than wind direction.
Assuntos
Poluentes Atmosféricos/análise , Monitoramento Ambiental , Material Particulado/análise , Cidades , Metais/análise , México , Estações do Ano , VentoRESUMO
In this study, atmospheric mercury concentration in airborne particulate matter with an aerodynamic diameter ≤ 2.5 µm (PM2.5) was analyzed by ICP-MS. Samples were collected in the Mexico City Metropolitan Area (MCMA), during 2013, in five locations, Northwest, Northeast (NE), Central, Southwest and Southeast, along three seasons: dry warm, rainy, and dry cold (DC). It can be observed that NE shows the highest mercury concentration (p < 0.05), where pollution events were identified. The seasonal distribution shows that samples collected during DC present the highest concentration (p < 0.05). These results are in agreement with the distribution of important mercury industrial sources located in the northern urban area as well with the temperature and wind conditions during 2013. The comparison of data obtained in this work with those of similar previous studies clearly indicates a decrease, between 2006 and 2013, of mercury content in PM2.5 collected in MCMA.
Assuntos
Poluentes Atmosféricos/análise , Monitoramento Ambiental/métodos , Mercúrio/análise , Material Particulado/análise , Cidades , México , Tamanho da Partícula , Estações do Ano , VentoRESUMO
The study of airborne metals in urban areas is relevant due to their toxic effects on human health and organisms. In this study, we analyzed metals including rare earth elements (REE) in particles smaller than 2.5 µm (PM2.5), collected at five sites around the Mexico City Metropolitan Area (MCMA), during three periods in 2011: April (dry-warm season, DW), August (rainy season, R), and November (dry-cold season, DC). Principal component analysis allowed identifying factors related to geogenic sources and factors related to anthropogenic sources. The recognition of the high impact of geogenic sources in PM2.5 is in agreement with the REE distribution patterns, which show similar behavior as those shown by igneous rocks, confirming the influence of the regional geogenic material. Metals associated to geogenic sources showed higher concentration (p < 0.05) at NE of the MCMA and a significant correlation with prevalent winds. Geogenic metals show similar seasonal distribution, with the highest concentration during DW (p < 0.05), suggesting a possible metal resuspension effect which affects more significantly at lower relative humidity (RH). The metals associated with anthropogenic sources are in agreement with the urban complexity of the area, showing homogenous distribution throughout MCMA (p > 0.05) and no similar seasonal pattern among them. These unexpected results exposed outstanding information regarding the identification of different geogenic sources as the main contributors of metals in the atmospheric environment in the MCMA and highlighted the importance of meteorology in the spatial and seasonal metal patterns.