In this study we investigate the use of ΔPM 2.5 /ΔCO and ΔNO y /ΔCO normalized enhancement ratios (NERs) in identifying wildfire (WF) smoke events in urban areas. Nine urban ambient monitoring sites with adequate CO, PM 2.5 , and/or NO y measurements were selected for this study. We investigated if WF events could be distinguished from general urban emissions by comparing NERs for wildfires with NERs calculated using yearly ambient data, which we call the ambient enhancement ratios (AERs). The PM 2.5 /CO and NO y /CO AERs represent typical urban concentrations and can provide insight into the dominant emission sources of the city. All 25 WF events were distinguished because they had ΔPM 2.5 /ΔCO NERs that were significantly greater than the PM 2.5 /CO AER for each site. The ΔPM 2.5 /ΔCO NERs for the WF events ranged from 0.057-0.228 µg m -3 ppbv -1 . In contrast, we were only able to calculate useful ΔNO y /ΔCO NERs (correlations with R 2 > 0.65) for 4 of 17 events (only 17 of 25 events had NO y data). For these 4 events, ΔNO y /ΔCO NERs ranged from 0.044-0.075 ppbv ppbv -1 , not all of which were significantly different from the NO y /CO AERs at the site. We conclude that ΔPM 2.5 /ΔCO NERs are a very useful tool for identifying WF events, but that the high and variable NO y concentrations in urban areas present problems when trying to use ΔNO y /ΔCO NERs.