The emerging science of tracing smoke back to wildfires.

As smoke from wildfires crosses state and international borders more frequently, tracking and studying it is increasingly important for shaping air quality and health measures around the world.

An upcoming study from researchers at Stanford University offers a new way to trace far-flung smoke and pollution back to individual wildfires of origin.

What’s burning in a wildfire determines what kind of pollution is in the smoke. A forest fire burns differently from a fire in a swamp, or a fire that burns buildings. As smoke travels, its chemical composition may change with time and distance.

The findings could help officials to determine which wildfires are likely to have the biggest health consequences for the greatest number of people, and to allocate firefighting resources accordingly.

“We don’t find that fire suppression resources are often spent on the fires that are most damaging from a health perspective,” said Jeff Wen, a Ph.D. candidate in Earth system science at Stanford and the study’s lead author.

The researchers focused on a pollutant called particulate matter, made of very small solid particles floating in the air, which can enter people’s lungs and blood and lead to problems such as difficulty breathing, inflammation and damaged immune cells.

Using their new method, Mr. Wen and his team ranked all of the wildfires observed in the United States from April 2006 to December 2020 by the resulting smoke exposure. The worst fires in their ranking did not match up very well with the worst fires in traditional rankings, such as acres burned or buildings and infrastructure lost. More firefighting resources were not necessarily deployed to the smokiest fires, either.

“We often suppress fires mainly because of structures and immediate threat to life,” said Bonne Ford, an atmospheric scientist at Colorado State University who was not involved in this study. While it’s important to save lives and help rural communities in immediate harm’s way, it’s “short-term thinking” to focus only on those immediately dangerous fires and ignore others that may harm many people farther away through smoke exposure.