A Decade of Change in NO₂ and SO₂ over the Canadian Oil Sands As Seen from Space

A decade (2005-2014) of observations from the Ozone Monitoring Instrument (OMI) were used to examine trends in nitrogen dioxide (NO₂) and sulfur dioxide (SO₂) over a large region of western Canada and the northern United States, with a focus on the Canadian oil sands. In the oil sands, primarily over an area of intensive surface mining, NO₂ tropospheric vertical column densities (VCDs) are seen to be increasing by as much as 10%/year, with the location of the largest trends in a newly developing NO₂ "lobe" well removed from surface monitoring stations. SO₂ VCDs in the oil sands have remained approximately constant. The only other significant increase in the region was seen in NO₂ over Bakken gas fields in North Dakota which showed increases of up to 5%/yr. By contrast, other locations in the region show substantial declines in both pollutants, providing strong evidence to the efficacy of environmental pollution control measures implemented by both nations. The OMI-derived trends were found to be consistent with those from the Canadian surface monitoring network, although in the case of SO₂, it was necessary to apply a correction in order to remove the residual signal from volcanic eruptions present in the OMI data.