Concentration and characterization of airborne particles in Tehran's subway system.

Particulate matter is an important air pollutant, especially in closed environments like underground subway stations. In this study, a total of 13 elements were determined from PM10 and PM2.5 samples collected at two subway stations (Imam Khomeini and Sadeghiye) in Tehran's subway system. Sampling was conducted in April to August 2011 to measure PM concentrations in platform and adjacent outdoor air of the stations. In the Imam Khomeini station, the average concentrations of PM10 and PM2.5 were 94.4 ± 26.3 and 52.3 ± 16.5 μg m(-3) in the platform and 81.8 ± 22.2 and 35 ± 17.6 μg m(-3) in the outdoor air, respectively. In the Sadeghiye station, mean concentrations of PM10 and PM2.5 were 87.6 ± 23 and 41.3 ± 20.4 μg m(-3) in the platform and 73.9 ± 17.3 and 30 ± 15 μg m(-3), in the outdoor air, respectively. The relative contribution of elemental components in each particle fraction were accounted for 43% (PM10) and 47.7% (PM2.5) in platform of Imam Khomeini station and 15.9% (PM10) and 18.5% (PM2.5) in the outdoor air of this station. Also, at the Sadeghiye station, each fraction accounted for 31.6% (PM10) and 39.8% (PM2.5) in platform and was 11.7% (PM10) and 14.3% (PM2.5) in the outdoor. At the Imam Khomeini station, Fe was the predominant element to represent 32.4 and 36 % of the total mass of PM10 and PM2.5 in the platform and 11.5 and 13.3% in the outdoor, respectively. At the Sadeghiye station, this element represented 22.7 and 29.8% of total mass of PM10 and PM2.5 in the platform and 8.7 and 10.5% in the outdoor air, respectively. Other major crustal elements were 5.8% (PM10) and 5.3% (PM2.5) in the Imam Khomeini station platform and 2.3 and 2.4% in the outdoor air, respectively. The proportion of other minor elements was significantly lower, actually less than 7% in total samples, and V was the minor concentration in total mass of PM10 and PM2.5 in both platform stations.