The characteristics of indoor air quality (IAQ) parameters such as PM mass (PM10, PM2.5, PM1) and particle number concentrations (PNC), carbon monoxide (CO), carbon dioxide (CO2), temperature (T) and relative humidity (RH) in multilevel urban classrooms of a school in tropical climate were studied. The PNC in the range 0.35-22.5 μm was monitored for 2 days in each classroom during the working hours using environment dust monitor and converted to mass concentrations. The 8hr-mean concentrations of PM10, PM2.5, PM1 mass, CO, CO2, T, and RH inside ground floor (GF) classroom were found to be 942.84 ± 248.49, 61.59 ± 17.19 and 16.13 ± 3.65 μg/m3, 458.86 ± 58.60 ppm, 34.80 ± 0.81 °C, 55.06 ± 4.10%, 0.93 ± 0.43 ppm, respectively. The PM10 mass concentrations were found to decrease by 8.35 and 46.67%, respectively in first and second floor classrooms. Similarly, PM1 and PM2.5 values were increased by 4.60 and 12.99%, respectively in first floor and decreased by 32.35 and 16.61%, respectively in second floor classrooms. The PNC for particles of size 0.3-1 μm were 58.04, 71.24 and 55.47 particles/cm3 for ground floor, first and second floor classrooms, respectively. The PNC of coarse particles were found to decrease with increase in floor heights. The thermal comfort parameters namely; CO2, T, and RH were more or less showing same trend in all the three classrooms. The distribution of PM10, PM2.5 and PM1 mass data in ground and first floor classrooms fitted with lognormal 3-parameter (3-P) distribution while the second floor PM mass data best fitted to the log-logistic 3-parameter (3-P) distribution. © 2016 Elsevier Ltd.