Air pollution in urban centres is increasing, with burgeoning population and increased traffic and industry. The detrimental impact on population health has been the focus of many epidemiological studies. Some cities are fortunate to have one, or at most a few, sparsely spaced fixed air quality monitors, which provide much needed daily data. However, fixed monitors do not accurately depict the spatial distribution of air pollution over the extent of an urban area nor can they target areas for focused surveys. We have used mobile monitoring to improve spatial coverage of pollution concentrations over the city of Hamilton, Ontario and to enhance our knowledge of the short-term bursts of pollution to which the population is exposed. Mobile surveys have been carried out in the city of Hamilton, Ontario, Canada since 2005. Results for two pollutants, oxides of nitrogen (NO(x)) representing traffic sources, and sulfur dioxide (SO2) representing industry sources, are presented. The data demonstrate very high levels of NO(x) exceeding 600 ppb, near major highways with SO2 levels up to 249 ppb near industrial sources. Both values significantly exceed the hourly maxima recorded by fixed monitors. The results also highlight the effect of wind direction on SO2 and NO(x) levels, and the affected population in each scenario.