Seeding ice clouds with wildfire emissions

Credit: CC0 Public Domain

For anyone who has ever witnessed a raging wildfire, ice is probably the last thing that comes to mind when recalling the experience. Yet nature works in mysterious ways, and researchers are beginning to reveal a link between wildfires and the frozen water droplets that make up clouds.

Cloud formation is a complex process that varies depending on temperature and atmospheric dynamics. Ice-containing (e.g., cumulonimbus, cirrus), which dominate continental precipitation, often depend on floating particulate matter to help kick off the crystallization process in the troposphere. Such ice nucleating particles (INPs) range from bacteria and bits of organic matter to mineral fragments and can influence cloud radiative properties and precipitation.

Because wildfires generate enormous amounts of particulate matter, they may considerably influence local cloud dynamics. Barry et al. sampled INPs from smoke plumes during the 2018 wildfire season in the western United States, the first measurements made at heights where smoke particles can directly affect cloud formation. Their results show that overall, INPs increase in quantity by up to 2 orders of magnitude in smoke plumes compared with background air. However, the specific types of particles and the exact degree to which they increased depended heavily on the conditions of a given fire (e.g., location and vegetation burned) and even how hot the fire was. For all samples, though, the INPs were dominated by organic material.

Electron microscopy also revealed that tiny spherical tar balls accounted for nearly a quarter of total INPs in certain conditions. The overall contribution of these tar balls to -derived INPs likely also depends on fuel and fire type and is "an open question," according to the researchers.

Wildfires are predicted to become more common with ongoing climate change, so understanding interplays between fires and the broader climate will become increasingly vital, the authors say. The new results confirm that wildfires generate abundant INPs in the troposphere, potentially modifying cloud formation and precipitation. But, the researchers note, more modeling and sampling studies are needed to understand in detail how fuel and combustion conditions contribute to regional INP concentrations and thus the range of ways that wildfires can affect the climate system at large.

Explore further

How wildfires may have larger effects on cloud formation than previously thought

More information: Kevin R. Barry et al. Observations of Ice Nucleating Particles in the Free Troposphere From Western US Wildfires, Journal of Geophysical Research: Atmospheres (2021). DOI: 10.1029/2020JD033752

Johannes Mülmenstädt et al. Frequency of occurrence of rain from liquid-, mixed-, and ice-phase clouds derived from A-Train satellite retrievals, Geophysical Research Letters (2015). DOI: 10.1002/2015GL064604

This story is republished courtesy of Eos, hosted by the American Geophysical Union. Read the original story here.

Citation: Seeding ice clouds with wildfire emissions (2021, March 1) retrieved 10 April 2021 from
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