Ground-level air pollution changes during a boreal wildland mega-fire.

The 2011 Richardson wildland mega-fire in the Athabasca Oil Sands Region (AOSR) in northern Alberta, Canada had large effects on air quality. At a receptor site in the center of the AOSR ambient PM, O, NO, NO, SO, NH, HONO, HNO, NH and NO were measured during the April-August 2011 period. Concentrations of NH, HNO, NO, SO and O were also monitored across the AOSR with passive samplers, providing monthly summer and bi-monthly winter average values in 2010, 2011 and 2012. During the fire, hourly PM concentrations >450μgm were measured at the AMS 1 receptor site. The 24-h National Ambient Air Quality Standard (NAAQS) of 35μgm and the Canada Wide Standard (CWS) of 30μgm were exceeded on 13days in May and 7days in June. During the fire emission periods, sharp increases in NH, HONO, HNO, NH, NO and total inorganic reactive N concentrations occurred, all closely correlated with the PM changes. There were large differences in the relative contribution of various N compounds to total inorganic N between the no-fire emission and fire emission periods. While in the absence of fires NO and NO dominated, their relative contribution during the fires was ~2 fold smaller, mainly due to increased NH, NH and NO. Concentrations of HONO and HNO also greatly increased during the fires, but their contribution to the total inorganic N pool was relatively small. Elevated NH and HNO concentrations affected large areas of northern Alberta during the Richardson Fire. While NH and HNO concentrations were not at levels considered toxic to plants, these gases contributed significantly to atmospheric N deposition. Generally, no significant changes in O and SO concentrations were detected and their ambient concentrations were below levels harmful to human health or sensitive vegetation.