Characteristics of gaseous and particulate air pollutants at four different urban hotspots in Tehran, Iran.

• Gaseous and particulate pollutants measured at four distinct urban hotspots in Tehran, Iran. • The major source of gaseous and particulate pollutants was traffic emissions. • Particulate concentrations were higher in winter, especially the first three days of the work week. • HQ for both PM 2.5 and PM 10 in different age groups exceeded the acceptable limit. • HQ for PM 2.5 and PM 10 in both seasons for 4 bus terminals exceeded the acceptable limit. This study reports a characterization of outdoor gaseous and particulate pollutants and their associated health effects in four different urban hotspots in Tehran, Iran during winter and summer. Buses, taxis, and cars are prominent sources of toxic pollutants in Tehran. There is a significant level of exposure to emissions from diesel buses in bus terminals, especially with boarding, disembarking, and waiting. Mean concentrations (μg/m³) in summer and winter, respectively, ranged from 10 to 20.67 and 17–21 for PM 1 , 52.50–79.19 and 58.33–85.33 for PM 2.5 , 64.50–102 and 78.83–125.83 for PM 7 , 130.17–204.67 and 157–231.67 for PM 10 , 261–409.50 and 305.83–458.83 for TSP, and 372.50–418.33 vs. 351.27–373.47 for CO 2 (ppm). Particulate concentrations were higher in winter, especially the first three days of the week, assisted in part by the shallower mixing layer height as compared to summer. Mean hazard quotient (HQ) values for both PM 2.5 and PM 10 in both seasons for bus terminals in three scenarios ranged between 0.81 and 4.96, which exceeded reference levels (1 < HQ). The results of this study have implications for public health, especially in dense traffic areas. [ABSTRACT FROM AUTHOR]