Sulphur dioxide (SO2) vertical column density measurements by Pandora spectrometer over the Canadian oil sands

Vitali E. Fioletov, Chris A. McLinden, Alexander Cede, Jonathan Davies, Cristian Mihele, Stoyka Netcheva, Shao-Meng Li, Jason O'Brien
2016 Atmospheric Measurement Techniques Discussions  
Vertical column densities (VCDs) of SO<sub>2</sub> retrieved by a Pandora spectral sunphotometer at Fort McKay, Alberta, Canada, from 2013&ndash;2015 were analysed. The Fort McKay site is located in the Canadian oil sands region approximately 20 km north of two major SO<sub>2</sub> sources (upgraders) with total emission of about 45 kt yr<sup>&minus;1</sup>. Elevated SO<sub>2</sub> VCD values were frequently recorded by the instrument with the highest values of about 9 DU (1 DU =
more » ... /sup> molecules•cm<sup>&minus;2</sup>). Comparisons with co-located in-situ measurements demonstrated that there was a very good correlation between VCDs and surface concentrations in some cases, while in the others elevated VCDs did not correspond to high surface concentrations suggesting the plume was above the ground. Elevated VCDs and surface concentrations were observed when the wind direction was from south to southeast, i.e. from the direction of the two local SO<sub>2</sub> sources. The statistical error of the Pandora SO<sub>2</sub> VCDs from the spectral fitting uncertainty is under 0.05 DU for optimal observation conditions. The precision of the SO<sub>2</sub> measurements, estimated from parallel measurements by two Pandora instruments at Toronto, is 0.17 DU. The total uncertainty of Pandora SO<sub>2</sub> VCD, estimated using measurements when the wind direction was away from the sources, is under 0.26 DU (1-σ). Comparisons with integrated SO<sub>2</sub> profiles from concurrent aircraft measurements support these estimates.
doi:10.5194/amt-2016-54 fatcat:o7xqdz5ktvba7kupf5wmu3gfga