Airborne Measurements of Secondary Organic Aerosol Formation in the Oil Sands Region of Alberta

Abstract:

The Alberta oil sands (OS) region represents a strategic natural resource and is a key driver of economic development. Its rapid expansion has led to a need for a more comprehensive understanding of the associated potential cumulative environmental impacts. In summer 2013, airborne measurements of various gaseous and particulate substances were made in the Athabasca oil sands region between August 13 and Sept 7, 2013. In particular, organic aerosol mass and composition measurements were performed with a High Resolution Time of flight Aerosol Mass Spectrometer (HR-ToF-AMS) supported by gaseous measurements of organic aerosol precursors with Proton Transfer Reaction (PTR) and Chemical Ionization (CI) mass spectrometers. These measurement data on selected flights were used to estimate the potential for local anthropogenic OS emissions to form secondary organic aerosol (SOA) downwind of precursor sources, and to investigate the importance of the surrounding biogenic emissions to the overall SOA burden in the region. The results of several flights conducted to investigate these transformations demonstrate that multiple distinct plumes were present downwind of OS industrial sources, each with differing abilities to form SOA depending upon factors such as NOx level, precursor VOC composition, and oxidant concentration. The results indicate that approximately 100 km downwind of an OS industrial source most of the measured organic aerosol (OA) was secondary in nature, forming at rates of ~6.4 to 13.6 μgm^-3hr^-1. Positive matrix factor (PMF) analysis of the HR-ToF-AMS data suggests that the SOA was highly oxidized (O/C~0.6) resulting in a measured ΔOA (difference above regional background OA) of approximately 2.5 – 3 despite being 100 km away from sources. The relative contribution of biogenic SOA to the total SOA and the factors affecting SOA formation during a number of flights in the OS region will be described.