Impact of urbanization on the ozone weekday/weekend effect in Southern Ontario, Canada

•Demonstrated statistical significant weekday/weekend effect for cities and towns in Southern Ontario.•Significant statistical relationship between weekday/weekend effect and population.•Southern Ontario is largely NOx saturated.

The ozone weekday/weekend effect has been examined for a suite of urban centers in Southern Ontario, Canada using 2010 data to explore the impact of urban size. The magnitude of the weekday/weekend effect was measured by comparing the difference in ozone concentrations at 7 h for weekdays and weekends. The results indicate a statistically significant relationship between this difference and degree of urbanization as measured by population.