The Wood Buffalo Environmental Association (WBEA) is a multistakeholder, not-for-profit association located in Fort McMurray, Alberta. WBEA has been monitoring air quality in the Athabasca Oil Sands Region (AOSR) of north-eastern Alberta, Canada since 1997. In 2011, WBEA operated 15 air monitoring stations that used continuous and time-integrated techniques to report on ambient air quality. Ambient air quality continuously measured in 2011 at WBEA compliance, attribution, and community air monitoring stations are presented. Maximum 1-h SO 2 concentrations ranged from 56 to 122ppb at compliance stations and 12 to 83ppb at community stations. There were no exceedances of the Alberta Ambient Air Quality Objectives (AAAQOs) for SO 2 in 2011. Maximum 1-h NO 2 concentrations ranged from 52 to 154ppb at compliance stations and 42 to 66ppb at community stations. There were no exceedances of the 1-h AAAQO for NO 2. Maximum 1-h O 3 concentrations measured at community stations ranged from 77 to 89ppb. In 2011, there were 15 exceedances of the 82ppb AAAQO for O 3, all in the period of intense forest fire activity and smoke episodes. In 2011, ambient fine particulate matter (PM 2.5) levels were highly influenced by the heavy particulate loading in fire smoke resulting in periods of extremely reduced visibility. Maximum 1-h PM 2.5 concentrations ranged from 406 to 451μgm -3. In 2011, there were 97 exceedances of the 24-h AAAQO for PM 2.5 of 30μgm -3. Beta attenuation technology being evaluated by WBEA measured short-term concentrations as high as 900μgm -3. Ninety-four exceedances (97% of total) of these occurred during the fire event. Maximum 1-h H 2S/TRS concentrations ranged from 6 to 98ppb at compliance/attribution stations, and from 3 to 7ppb at community stations. Maximum 24-h concentrations ranged from 1 to 23ppb at compliance/attribution stations and from 1 to 3ppb at community stations. In 2011, there were 23 exceedances of the 1-h AAAQO. This was 74% less than in 2010 and 89% less than in 2009. There were no exceedances in 2011 at community stations. Time-integrated air quality measurements included canister sampling for 60 VOCs and 20 RSCs at nine air monitoring stations. Most frequently, measured VOCs were benzene, toluene, acetone, butane, isopentane, isobutane, m,p-xylene, 2-methylpentane, hexane, pentane, and ethylbenzene. Most frequently, measured RSC were carbonyl sulfide, carbon disulfide, H 2S, and dimethyl disulfide. Twenty-three polycyclic aromatic hydrocarbon (PAH) species were routinely measured in low concentrations at four community stations. Phenanthrene, acenapthene, acenapthylene, fluoranthene, fluorene, and pyrene had highest mean concentrations.Between October 21, 2010 and May 31, 2011, Environment Canada operated a gaseous mercury analyzer at the Patricia McInnes air monitoring station in Fort McMurray. Excluding data collected during the forest fire period in May 2011, average ambient total gaseous mercury (TGM) concentrations averaged 1.40±0.15ngm -3. This value is similar to average TGM concentrations measured elsewhere in Canada.Air quality monitoring observations in 2011 were dominated by a massive forest fire complex north of Fort McMurray that consumed some 700,000ha and burnt to within a few kilometers of the community of Fort McKay. Data presented on O 3 and PM 2.5 were particularly influenced and skewed to higher than normal values. Air quality health index (AQHI) values calculated for the four reporting WBEA air monitoring stations indicated that air quality posed a low risk to health between 96% and 99.3% of the time in 2011. AQHI values presenting a high health risk (0.9-1.3% of available 8760h per station) all occurred during the forest fire smoke episodes. While exceedances of the odor perception-based AAAQO for H 2S/TRS of 10ppb for 1h, and 3ppb for 24h have decreased significantly since 2009, odors, nevertheless, remain a concern in some communities.