Grant: Discovery Grants Program - Individual

INTRODUCTION: Smoke from biomass burning, including wildfires, consists of mostly organic aerosol, referred to as biomass-burning organic aerosol (BBOA). Wildfires inject BBOA mostly into the troposphere (altitude less than approximately 15 km). Large wildfires also periodically inject massive amounts of BBOA into the stratosphere (altitude between approximately 15 km and 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. Furthermore, this BBOA burden is expected to increase as climate change causes forest fires of growing frequency and size. KNOWLEDGE GAPS: Recently (within the last year), studies have suggested that reactions occur on or in BBOA in the stratosphere that lead to unexpected and unprecedented changes in the concentrations of gases in the stratosphere, including gases that play a crucial role in depleting stratospheric ozone. 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. BBOA can also influence the formation of polar stratospheric clouds, further impacting the stratospheric ozone layer. Nevertheless, the effects of BBOA on stratospheric chemistry and polar stratospheric clouds is highly uncertain due to the lack of laboratory studies on this topic. SHORT-TERM OBJECTIVES: In the next five years, we will focus on BBOA particles in the stratosphere due to the worrying predictions that they will destroy stratospheric ozone. We will 1) quantify rates of reactions on and in BBOA in the stratosphere, 2) identify key BBOA properties that influence these reaction rates, and 3) determine the effects of BBOA on polar stratospheric clouds. METHODS: We will quantify rates of reactions using aerosol flow tube reactors. We will identify key BBOA properties that influence these reaction rates by comparing BBOA properties, such as water content and viscosity, to the reaction rates. We will determine the effects of BBOA on polar stratospheric clouds using optical and FTIR microscopes coupled to low-temperature and low-pressure flow cells. IMPACT: We will quantify reaction rates on and in stratospheric BBOA and quantify the pathways by which BBOA can influence polar stratospheric clouds. These studies will provide a much better understanding of the effects of BBOA on stratospheric ozone. We will collaborate with researchers to incorporate our results into models of stratospheric ozone chemistry and polar stratospheric clouds, leading to improved predictive capabilities. Ultimately, these upgraded models will inform decision-makers and provide guidance when developing policies to address climate change and increasing forest fires in a warming world.