• The variability of 8 air pollutants at 20 monitoring sites in Tehran was investigated • Shorter time (seasonal, weekdays, and diurnal) cycles were quantified • CO/PM 2.5 ratio suggest petrol vehicles as major pollution source in Tehran • The spatial variation of NO was the highest in Tehran • Decreasing trends in PM 2.5 , PM 10 , CO, and SO 2 were observed. Determination of spatial-temporal variations and trends in air pollutant concentrations permits assessment of the effectiveness of air quality improvement programs. Real-time hourly average concentrations of eight air pollutants for 2015 to 2021 at 20 monitoring sites across Tehran (Iran) were used for this evaluation. Likely source locations were identified with meteorology-based techniques. The annual average concentrations of PM 2.5 , PM 10 , and NO 2 at all sites substantially exceeded WHO annual air quality guidance limits. The pollutant concentrations were highest in the cold seasons, except for O 3 that was highest in summer. The diel cycles of most pollutants (PM 2.5 , PM 10 , NO, NO 2 , NO x , and CO) showed bimodal patterns driven by vehicular emissions. O 3 showed unimodal patterns. The CO/PM 2.5 ratio indicated spark-ignition vehicles as the main combustion-related pollutant source. The spatial variation of NO driven by traffic was the highest followed by O 3 , NO x , CO, SO 2 , PM 2.5 , PM 10 , and NO 2 . Cross correlations exhibited strong correlations at 0 lag for CO, NO, NO 2 , and NO x while the O 3 -solar radiation correlation exhibited peak correlations at +2 h and +3 h lags. Decreasing PM 2.5 trends at most sites suggested the 2017 Clean Air Law was effective, but more is needed to achieve health-based standards. Graphical Abstract. .