The Primary Convective Pathway for Observed Wildfire Emissions in the Upper Troposphere and Lower Stratosphere: A Targeted Reinterpretation

The literature—spanning several recent decades—describes numerous attempts to characterize the efficacy of cumulonimbus “Cb” convection as a pollutant pathway connecting the planetary BL to the upper troposphere and lower stratosphere (UTLS). The relatively new discovery of wildfires triggering deep convection and Cb formation, referred to as pyrocumulonimbus “pyroCb,” has provided a new convective candidate for examination. Previous studies have shown that the pyroCb pathway offers a reinterpretation of supposed volcanic aerosol layers observed in the stratosphere. The community now questions whether this relatively unappreciated phenomenon has been overlooked or imprecisely characterized in published analyses of observed UTLS biomass burning constituents attributed to traditional convection, such as individual Cbs or larger mesoscale convective systems. Here we show that on at least two occasions, a reinterpretation of the literature is required. Both are in the context of coordinated measurement campaigns in summertime Central and North American domains. We provide a strategic review of prior studies and explore three selected works, wherein the pyroCb naturally explains observations of dramatically strong, remote, and high-altitude biomass burning pollution. We complete our discussion with the implications for including the pyroCb phenomenon in case studies and assessments of the primary convective pathway for smoke particles to enter the UTLS.