Stratospheric pollution from Canadian forest fires

Abstract. Forest fires in British Columbia in August 2017 caused a pyrocumulonimbus event that injected a polluted airmass into the lower stratosphere. The Microwave Limb Sounder (MLS) on the Aura satellite first observed the polluted airmass on 14 August 2017 and continued to observe it for 60 days (100 days in water vapour). We estimate the mass of CO injected into the stratosphere to be 2–3 Tg. Events such as this are rare: this is the third of four such events in the 16 years since the launch of Aura, the second-largest of the four events, and the only one in the Northern Hemisphere. Unlike the preceding two events, but like the most recent event, the polluted airmass described here had an unusually high water vapour content.