Seasonal and interannual trends in PM levels and associated inorganic ions in southeastern Spain

Concentrations of PM1, PM2.5, PM10, and associated inorganic ions were measured between October 2008 and October 2009 in the city of Elche (southeastern Spain). The levels of the inorganic components in PM2.5 and PM10 were compared with those measured in the same city during the period December 2004-November 2005. A reduction of 12% and 24% in the annual concentrations of PM2.5 and PM10, respectively, was observed from 2004-05 to 2008-09. The decrease in PM2.5 was mainly attributed to a steep reduction in (NH4)2SO4 levels caused by a significant decline in SO2 emissions, higher precipitation rates, and a lower occurrence of winter PM episodes under high atmospheric stability conditions. In the PM10 fraction, NH4+, Ca2 + and SO42 − experienced the largest decreases. The drop in Ca2 + levels, higher in winter than in summer, was mainly attributed to the increase in precipitation and the reduction in construction activity. The PM1 annual average concentration in 2008-09 was only 9.2 μg/m3. Slightly higher PM1 levels were measured in summer (10.1 μg/m3) than in winter (8.8 μg/m3), due to the low frequency of local pollution episodes during winter 2009. The PCA analysis identified the contribution of three sources of ionic compounds in the submicron fraction: secondary (NH4)2SO4 and NH4NO3, traffic emissions, and dust resuspension. NO3− size distribution exhibited a marked seasonal pattern, with a lower proportion associated with particles smaller than 2.5 μm in summer than in winter, due to the thermal decomposition of NH4NO3. In contrast, the SO42 − size distribution was approximately constant throughout the year.