When wildfires burn, the choking smoke that billows upward has a life of its own. Depending on a multitude of conditions such as wind speed, cloud density and forest type, combustion byproducts move and change unpredictably in the atmosphere.
The study of these smoke particles - their size, composition, dispersion and interaction with clouds and atmospheric processes - has a rich interdisciplinary history at Colorado State University.
For more than a decade, CSU researchers have led groundbreaking experimental inquiries into understanding smoke from fires - everything from how breathable particles grow and beget new particles to how such smoke limits regional air quality and visibility. Sonia Kreidenweis, University Distinguished Professor and professor of atmospheric science, and Jeffrey Collett, professor and chair of the Department of Atmospheric Science, have led several studies using data from open biomass burns at the Missoula Fire Sciences Lab. They looked at physical, chemical and optical properties of combustion emissions from 33 plant materials in over 250 laboratory burns starting in the early 2000s.
Now, Shantanu Jathar, assistant professor of mechanical engineering, and Jeff Pierce, associate professor of atmospheric science, are taking that foundational work many steps forward, thanks to support from a handful of grants.
Earlier this year, the National Oceanic and Atmospheric Administration (NOAA) jointly awarded Jathar and Pierce about $250,000 to study the complex, dynamic chemistry and microphysics of both primary and secondary organic aerosols from wildfire smoke.
The three-year award will fund research into modeling how aerosols from fires in the West travel and react in the air. Their efforts will build on previously collected and future data from the Fire Influence on Regional and Global Environments Experiment (FIREX), a multi-institution, NOAA-funded effort to understand various aspects of wildfire science.
As part of the FIREX effort, Jathar and his team have simulated wildfires using a custom-built mobile smog chamber, which they deployed at the Missoula Fire Sciences Lab last year. To build the smog chamber, the CSU Office of the Vice President for Research provided critical start-up funds, Jathar said.
Jathar is a mechanical engineer who studies emissions from mobile sources, such as vehicles and gas and diesel engines. He has found that many of his techniques can be applied to wildfire research, which is also a combustion process - albeit infinitely more complex.
"Gasoline and diesel fuels are designed to burn efficiently, and we have engineered them to do so," Jathar said. "Unfortunately, forests are not like gasoline or diesel."
Jathar and Pierce are developing box models that recreate how organic particles associated with wildfires transform in the atmosphere, under different scenarios. They will then compare those results with data from NOAA-led field campaigns during prescribed and natural burns in 2019, to validate their results.
"One big milestone will be to understand if we can successfully simulate wildfires in the lab," Jathar said. "For the wildfire community, there is a gap between trying to simulate something in the lab and observing the same phenomena in the field."
Jathar will lead analysis of the organic aerosols' chemical makeup, while Pierce will focus on the microphysics of the particles as they evolve in the atmosphere.
In addition, the two scientists have received a nearly $520,000 grant from the Department of Energy Office of Science (Atmospheric Science Research program) to study organic aerosols, including but not limited to those from wildfires. This work will focus on how the particles interact with clouds and climate, both regionally and globally.
They will work with Christopher Cappa at the University of California, Davis to better understand how atmospheric aerosols could impact the Earth's radiative budget, which is related to climate change.
Pierce, who specializes in atmospheric particles and their interactions with both climate and health, has also been awarded two additional grants in collaboration with Jathar.
A $272,000 project will focus specifically on climate impacts of aerosols from biomass-burning wildfires. Pierce is teaming up with scientists at Massachusetts-based Atmospheric and Environmental Research to examine the sizes of aerosols from smoke and how they evolve via coagulation and evaporation within the first 24 hours of burning. For these experiments, they will also rely on data from FIREX lab studies.
An additional $372,000 grant from the National Science Foundation will focus on evaluating and improving scientists' ability to predict wildfire aerosol size distributions.
Through these and other studies, Colorado State University researchers are seeking to understand all the atmospheric properties of biomass-burning organic aerosols, among the most complex challenges faced by the West and other fire-prone areas.