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_2.5, O₃, NO, NO₂, SO₂, NH₃, HONO, HNO₃, NH₄⁺ and NO₃^- were measured during the April-August 2011 period. Concentrations of NH₃, HNO₃, NO₂, SO₂ and O₃ 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_2.5 concentrations >450μgm^-3 were measured at the AMS 1 receptor site. The 24-h National Ambient Air Quality Standard (NAAQS) of 35μgm^-3 and the Canada Wide Standard (CWS) of 30μgm^-3 were exceeded on 13days in May and 7days in June. During the fire emission periods, sharp increases in NH₃, HONO, HNO₃, NH₄⁺, NO₃^- and total inorganic reactive N concentrations occurred, all closely correlated with the PM_2.5 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 NO₂ dominated, their relative contribution during the fires was ~2 fold smaller, mainly due to increased NH₃, NH₄⁺ and NO₃^-. Concentrations of HONO and HNO₃ also greatly increased during the fires, but their contribution to the total inorganic N pool was relatively small. Elevated NH₃ and HNO₃ concentrations affected large areas of northern Alberta during the Richardson Fire. While NH₃ and HNO₃ concentrations were not at levels considered toxic to plants, these gases contributed significantly to atmospheric N deposition. Generally, no significant changes in O₃ and SO₂ concentrations were detected and their ambient concentrations were below levels harmful to human health or sensitive vegetation.