TIME EVOLUTION OF SUSPENDED PARTICULATE MATTER IN URBAN ZONES FROM ARID ENVIRONMENTS: INSIGHTS FROM NATURAL EROSION PROCESSES VS. ANTHROPOGENIC ACTIVITIES

Air quality is a worldwide health concern. The evolution of the concentration of suspended particulate matter (PM) in time is a required parameter to understand dust-generating processes. Spatial distribution of the PM is a useful tool to monitor air quality within the urban zones, but also to trace geogenic/anthropogenic PM production from distal zones (i.e. mining, agricultural, livestock). Desertification processes certainly has a negative economic impact, but also, a collateral negative response is the generation of PM. Hermosillo city, located in NW Mexico, is a rapidly growing city located within the Sonoran dessert province (low annual precipitation and extremely high temperatures). Previous studies show high metal- and pesticide-concentrations in urban and suspended dusts. Several diseases as those related with respiratory problems have increased dramatically in the last years. A total of 1,386 measurements of PM10 and TSP were carried out in Hermosillo in a monitoring period from 2000 to 2012. The determination of the evolution in time of particulate concentration (PC) during this period is analyzed, in conjunction with historic climate data and calculated aridity index (AI) and erosion potential (EP). The climate factor that has the clearest influence on the PC is the relative humidity (RH). An important peak of RH is reported in 2005, and correlates with a drop in PC in all the monitoring stations. An increased of percentage of dusty days is observed from 2000 to 2004, which apparently follows a predictable increase in AI and EP. However, a decrease in AI and EP is observed after 2004, which fails the expectable decrease in PC. This is an inflexion point where dust production was mainly controlled by erosion processes, and then anthropogenic processes is probably a contributing source in the last years. The concentration of PM varies geographically but the data is consistent during the studied period, implying that particulate sources are punctual and local. The worst air quality is located in the northern area, which correlates with scarce asphalting and artisanal brick production. High PM10 concentrations are reported for the southern zones, a high-industrialized area, and metallic and non-metallic activity to the SE zones. Hence, anthropogenic activities seem to be the main PM sources in Hermosillo.