We investigate the effects of temperature inversions on the levels of nitrogen dioxide (NO2) and fine particulate matter (PM2.5) in the atmosphere over the Hamilton Census Metropolitan Area and environs in Ontario, Canada, for the period 2003 to 2007. Vertical temperature profiles extracted from data acquired by the Atmospheric Infrared Sounder (AIRS) were used to determine the occurrences of daytime and nighttime temperature inversions over the region. NO2 and PM2.5 data were obtained from three in situ air quality monitoring stations located in the study area. The results indicate increases of 49% and 54% in NO2 and PM2.5 respectively, during nighttime inversion episodes. Daytime inversions resulted in an 11% increase in NO2 but a 14% decrease in PM2.5. Decreases occurred predominantly in the summer. We discuss these results and possible explanations for the reduced PM2.5 concentrations on inversion days. Weekday and seasonal analysis, with associated meteorological parameters are also discussed.