Abstract
Quantile‐quantile plots have been employed to compare ozone concentrations on weekdays and Sundays at two rural sites in north‐west England. One site is influenced by local NOx emissions, possibly from traffic on a nearby motorway. The other site shows no significant difference between weekdays and Sundays at concentrations expected to result from the advection of anthropogenic precursors from distant sources. Weekday‐Sunday differences provide a quick and easy method of assessing a site for local NOXpollution.