Monitoring of total and off-road NO _<i>x</i> emissions from Canadian oil sands surface mining using the Ozone Monitoring Instrument

Abstract. The oil sands in Alberta, Canada, are a significant source of air pollution. Observations from the Ozone Monitoring Instrument (OMI) on the NASA Aura satellite have been used to quantify NOx emissions from the surface mining region of the oil sands. Two related emissions methods were utilized, one for point and one for area sources, where OMI vertical column densities of NO2 were combined with winds from a meteorological reanalysis and a two-dimensional exponentially modified Gaussian (EMG) plume model. This work better connects the two (point and area) emissions methods and discusses the interpretation of fit parameters and the ability of OMI (and other sensors) to resolve emissions between neighbouring sources. The two methods employed, in good agreement with each other, indicated an increase in emissions from about 55 to 80 kt [NO2] yr−1 between 2005–2011 and a flat trend thereafter. Reported emissions were within 15 % of reported emissions, consistent to within uncertainties. In an extension of this methodology, OMI observations were combined with reported point source emissions to derive the more uncertain emissions component from the large off-road mining fleet. These were found to make up about 60 % of total NOx emissions, also consistent with reported emissions. The OMI-derived 0.9 % yr−1 increase in fleet emissions and the 5.5 % yr−1 increase in bitumen mined, generally a good proxy for fleet emissions, can be reconciled by considering the evolution of the mine fleet over this period. OMI is therefore able to track the transition from US EPA Tier 1 standards, through Tier 4 standards, to the present and in doing so demonstrates the efficacy of this policy. Furthermore, this analysis shows that had the fleet remained at Tier 1, this source would currently be emitting an additional 40 kt [NO2] yr−1.