TIME EVOLUTION OF TOTAL SUSPENDED PARTICLES IN URBAN ZONES: A VERTICAL EVALUATION OF URBAN DUST FROM ARID ENVIRONMENTS
During the last decades, Hermosillo city, located in NW Mexico, has experienced a noticeable population and industrial growth. Low annual precipitation and extreme high temperatures characterize the region. Previous studies demonstrate high metal concentrations in urban and suspended dust. The city has experienced high concentrations of TSP, which can be related to any of the economic activities in the region or to geogenic sources. In order to evaluate the vertical distribution of TSP, a study was performed in central area of the city, where high metal concentrations and high anthropogenic activity are present. For the investigation, High Volume samplers were located at ground level and on a 7 m height building. Despite the differences of concentrations of TSP found in the experiment, a noticeable parallel distribution in time is observed. An average annual of 144.8 and 117.5 μg/m3 were obtained for the ground level and 7 m height samplers, respectively. The Mexican legal limits of the TSP were exceeded during spring and reached during fall, but exceeded almost twice the accepted values in the WHO guidelines. The TSP correlates inversely proportional to humidity, which is expected since less humidity in the environment favor the re-suspension of particulate matter; the only exception occurs during the ending of fall and beginning of winter season, probably suggesting thermal inversion processes. The obtained results indicate that TSP at ground level is the result of a complex and dynamic anthropogenic activity. This study shows that the routine TSP measurements may underestimate the real TSP concentration, and therefore, underestimate the real impact on human health, especially in urban zones from arid environments.