Understanding the Sources and Transformations of Ice Nucleating Particles and Trace Reactive Gases in Biomass-Burning Emissions

The ability of a very small fraction of particulate matter to act as ice nucleating particles and initiate cloud glaciation has important impacts on cloud microphysics, precipitation, radiative forcing, and climate change. In recent years, the Sullivan group has investigated biomass-burning aerosol as a source of ice nucleating particles. My contributions towards measuring the aerosol chemical composition using aerosol mass spectrometry throughout biomass-burning experiments has improved our understanding of how atmospheric chemical aging influences the ice-nucleation activity of biomass-burning aerosol. We discovered that as biomass-burning aerosol ages, organic matter on the particle surfaces can evaporate or dissolve to reveal preexisting mineral-based ice-active sites, increasing the overall ability of biomass-burning aerosol to nucleate ice as it is undergoes transport and aging throughout the atmosphere. Some aging mechanisms, such as ozonolysis, result in the production of secondary organic aerosol which can have the opposite effect and result in no change or even a decrease in the ice-nucleation activity. While previous literature exists regarding how the ice activity of some types of ice nucleating particles change with atmospheric aging, no other work has investigated biomass-burning aerosol to the extent that my research has. My work introduces a new framework for the evolution of ice nucleating particles from biomass burning where the aerosol becomes more ice active as the smoke plume dilutes with transport. This results in a larger contribution to the ice nucleating particle budget, the resulting cloud microphysics, and climate forcing induced by wildfires than is currently considered.