The Long-Lived Plume of the Pacific Northwest PyroCb Event: MLS Observations and Modeling of Composition Evolution

On 12 August, 2017, smoke and other combustion products from intense wildfires in British Columbia and Washington state were lofted to the tropopause by pyroconvection and then rapidly advected northward. This plume, first observed by the Microwave Limb Sounder (MLS) on the Aura satellite a day later over northwest Canada, was extraordinary both in its unprecedented trace gas mixing ratios and in its persistent coherence as a relatively compact airmass as it was radiatively lofted to an altitude of 23 km (31 hPa) and advected around the globe over the ensuing three months. CO mixing ratios of 1600 ppbv at 215 hPa and 1100 ppbv at 147 hPa in the days immediately following the injection event are the highest seen at these levels in the 13-year MLS record. Water vapor mixing ratios of 19 ppmv at 100 hPa are also as high as any at this level in the record. The persistence of extremely high water vapor and CO in the plume as it evolved simplifies the tracking of the airmass and facilitates investigation of the evolution of correlated signatures in the plume of numerous trace gases measured by MLS, including ozone (O3), methyl cyanide (CH3CN), methyl chloride (CH3Cl), methanol (CH3OH), hydrogen cyanide (HCN), and chlorine monoxide (ClO). In this work, we use a sectional microphysics model, the Community Aerosol and Radiation Model for Atmospheres (CARMA), coupled with the NCAR/DOE Climate model (CESM) in conjunction with the MLS observations to study the dynamical and compositional evolution of the plume.