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TSP, PM10 and PM10/TSP ratios in the Mexico City Metropolitan area: a temporal and spatial approach.

Data for PM10 and TSP collected from SEDUE's (Secretary of Urban Development and Ecology) five principal air monitoring stations from March of 1988 to March of 1989 were analyzed with an emphasis on spatial and temporal distributions. The Mexico City sites consisted of a mixed residential and industrial setting in the NW, a highly industrialized area in the NE, the commercial and administrative district downtown, and areas in the SW and SE dominated by residential neighborhoods. High volume samplers for TSP and PM10 running in parallel were used following a protocol similar to the one specified by the U.S. Environmental Protection Agency. The individual data collected ranged from 24 to 1494 micrograms/m-3 for TSP and from 17 to 607 micrograms/m-3 for PM10. The PM10-to-TSP ratios ranged from 0.104 to 0.914 for a one year period, 0.495 being the overall mean ratio. Seasonal and geographical differences in this ratio may reflect the range of sources, transport and transformations of primary and secondary particles. High concentrations of particles were found during the winter and early spring, followed by relatively low concentrations during the summer. Statistically significant differences were found for the two most contrasting sites, the NE and SW areas of the city. The northern and eastern parts were the most impacted by particulate matter, while the area at the southwestern edge of the city was least polluted by fine and total suspended particles. Two interesting observations have emerged from this analysis. First, there is the exceedingly high daily and annual values for both TSP and PM10, relative to the Mexican and U.S. standards and WHO criteria for particulate matter. Second, although the SW area of Mexico City had the lowest fine suspended particle concentrations, it is in this area that the highest concentrations of ozone have been observed.