Quantifying the Impact of Intense Pyroconvection on Stratospheric Aerosol Loading

Intense heating by wildfires can generate deep, smoke-infused thunderstorms, known as pyrocumulonimbus (pyroCb), which can release a large quantity of smoke into the upper troposphere and lower stratosphere. Recent work has shown that an extreme pyroCb event can significantly influence the lower-stratosphere in a manner similar to a moderate volcanic eruption. However, the seasonal impact of pyroCb activity on stratospheric aerosol loading remains almost completely unconstrained. This study quantifies the total aerosol particle mass injected into the lower stratosphere during active fire seasons in North America. The particle mass originating from a wide variety of individual pyroCb events is examined, as well as an accumulated fire season total. PyroCb smoke plume properties are analyzed using the combination of lidar and ultraviolet aerosol index observations. A systematic inventory of intense fire activity and ensuing pyroCb events is constructed to confirm the source of these plumes. Results highlight the spatial and temporal variation in the pyroCb source, and its correlation with total wildfire activity. These results indicate that pyroCb activity, occurring as either large singular events or smaller events accumulated over a fire season, can significantly influence the composition of the lower-stratosphere. Integration with meteorological data suggests that stratospheric injection of smoke particles can be expected every fire season in favored regions of the Northern Hemisphere. This work sets a foundation for understanding the relative contribution of pyroCb activity to seasonal and inter-annual variation in stratospheric composition, and their corresponding effects on circulation and radiative forcing.