investigation of air quality index and pm10 and pm2.5 in arak

background and purpose: in this study, the air quality index and concentration of particles such as pm10 and pm2.5 were investigated in arak. materials and methods: to determine the concentration of pm10 and pm2.5, 60 samples were collected by laser tsi model 8520 in summer and winter 2012. the collection site was around arak city center. results: during the sampling period, as a matter of pm10, the cleanest and the most polluted month were december and june with the average of 34.33 µg m-3 and 100.1 µg m-3, respectively. the concentration of pm2.5 was 12.93 and 53.17 µg m-3 for december and june, respectively. meanwhile, in terms of air quality index (aqi), in 98.3% and 70% of cases, the concentrations of pm10 and pm2.5, respectively were less than normal (aqi100). conclusion: the concentration of pm10 in the study period was less than environmental protection agency (epa) 2006 guideline. meanwhile, the concentrations of pm2.5 in 30% of air samples were greater than epa guideline. the average pm2.5/pm10 ratio during the sampling period was 0.41 compared to range 0.15 to 0.25 reported by epa.