Assessing the effects of oil sands related ozone precursor emissions on ambient ozone levels in the Alberta oil sands region, Canada

A study was undertaken to determine whether, and the extent to which, increased ground-level ozone (O-3) precursor emissions from oil sands development have impacted ambient air quality in the northeastern Alberta, Canada, over the period 1998 to 2012. Temporal trends in emissions of O-3 precursors (NOx and VOC) and ambient air concentrations of O-3 precursors, and O-3 were examined using the TheilSen statistical analysis method. Statistically significant correlations between NOx emissions and ambient NOx concentrations were found mainly near surface (open-pit) mining areas where mine fleets are a large source of NOx emissions. No statistically significant trends in the 4th highest daily maximum 8-hr average O-3 at any of the continuous and passive ambient air monitoring stations were found. A significant long-term decrease in monthly averaged O-3 is observed at some ambient monitoring sites in summer. A visual examination of long-term variations in annual NOx and VOC emissions and annual 4th highest daily maximum 8-hr O-3 concentrations does not reveal any indication of a correlation between O-3 concentrations and O-3 precursor emissions or ambient levels in the study area. Despite a significant increase in oil sands NOx emissions (8%/yr), there is no statistically significant increase in long-term O-3 concentrations at any of monitoring stations considered. This suggests that there is surplus NOx available in the environment which results in a titration of ambient O-3 in the areas that have ambient monitoring. The limited ambient O-3 monitoring data distant from NOx emission sources makes it impossible to assess the impact of these increased O-3 precursor levels on O-3 levels on a regional scale. As a precautionary measure, the increasing oil sands development O-3 precursor emissions would require that priority be given to the management of these emissions to prevent possible future O-3 ambient air quality issues. (C) 2017 Elsevier Ltd. All rights reserved.