Large wildfires periodically inject massive amounts of aerosol into the stratosphere (~15 km ≤ altitude ≤ 50 km), where they can linger for many months. Examples include the large-scale wildfires in British Columbia in 2017 and the Australian “black summer” fires in 2020. Recent studies have speculated that reactions occur on or in wildfire aerosol in the stratosphere, leading to unexpected depletion of the UV-blocking stratospheric ozone layer. Furthermore, scientists have speculated that in a warming world, these reactions could delay the recovery of the ozone layer for many years to come, leading to an increase in ultraviolet radiation exposure and cases of skin cancer. Wildfire aerosol can also influence the formation of polar stratospheric clouds, further destroying the stratospheric ozone layer. Nevertheless, the effects of wildfire aerosol on stratospheric chemistry and polar stratospheric clouds are uncertain due to the lack of laboratory studies on this topic. To address this uncertainty, we are investigating the reactivity of wildfire aerosol under stratospheric conditions in the laboratory and the effects of wildfire aerosol on polar stratospheric clouds.
Figure 1. A) Aging of wildfire aerosol in the stratosphere, also called biomass burning organic aerosol (BBOA). VOCs represent volatile organic compounds. B) Possible formation pathways of polar stratospheric clouds (PSCs). NAT represents nitric acid trihydrate. PSCs form at temperatures less than ≅200 K.
