Smoke from wildfire not only degrades air quality but can also impact climate through the release of particulate matter into our atmosphere, especially in the free troposphere. The free troposphere represents the part of the atmosphere where the majority of weather happens. Some smoke particles can affect cloud formation by serving as ice nucleating particles (INPs). In particular, INPs impact cloud radiative properties and precipitation development.
While the scientific community is well aware that wildfire emissions can be a source of INPs, there has been little work done to quantify the abundance of INPs with wildfires. Using INP data sampled from wildfire across the US in the 2018 Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN) campaign, this study is the first to quantify INPs within wildfire smoke plumes in the free troposphere. Notably, it is also the first study to provide measurements from the troposphere rather than lab or ground-based measurements.
Funded in part by CPO’s Atmospheric Chemistry, Carbon Cycle, & Climate (AC4) program, the study explores the effect of wildfire plumes on ambient INP concentrations in the atmosphere, the composition of INPs in those plumes, and the variability in INP emissions among fires. The study authors note that these new observations “shed light on INPs from wildfires at altitudes that can readily affect cloud formation and be transported long distances.” The study, published in Journal of Geophysical Research: Atmospheres, catalogues the size, type, and source of INPs, finding that INP characteristics combined with temperature and fire qualities determined their observed abundance. The wildfires that had the highest observed INP concentrations were fires involving sagebrush shrubland and aspen forests fuel.
The study authors concluded that while wildfire smoke is not an efficient source of INPs, the sheer number of wildfires and their emissions in the western US summertime does regionally elevate INP concentrates in the free troposphere. Thus including wildfires as a source of INPs in climate models is critical for assessing the climatic impacts of more frequent wildfires.