Shorthand for “particulate matter of 2.5 microns in size or less,” PM 2.5 is a class of pollutants based on dimensions rather than origin or chemical makeup. It would take about 30 of them lined up to cross the width of a human hair. It’s their size that’s the key problem: It allows them to get deep into the lungs and even cross into the bloodstream, causing heart and respiratory problems. In short, it’s a terrible pollutant.
Public comment on the proposal closed late last month, and the EPA is now deciding whether and how to implement revisions.
The EPA estimates a third of the PM 2.5 we breathe in this country is from wildfires. For those in the West during wildfire season, it can be 90%.
And if wildfire trends continue and worsen, as climate models suggest they will, then we’ve seen nothing yet.
To avoid the worst outcomes, Wara of Stanford points to the need to dramatically increase the use of prescribed fire in pyro-adapted landscapes.
“Some of the best hopes that we have for reducing public health impacts from wildfire and [general] impacts from wildfire have to do with substituting prescribed fire emission for high-intensity wildfire emission,” he said.
The rub: Wildfire smoke vs. prescribed fire smoke
The EPA enforces its clean air standards. If air districts do not achieve these clean-air goals, then the EPA can take over air permitting within a district and even impose a ban on new federal highway grants.
However, EPA officials recognize that sometimes air districts are out of compliance through no fault of their own. In this case, they are allowed to file for an “exceptional event.” In this bureaucratic process, the “event” is linked to the cause of pollution going over the legal limit. It is meant for events that are unforeseeable and are unlikely to occur in the same location again, like a volcanic explosion. If the link can be made, then emissions from that event can be subtracted from the total, and the air district is no longer in trouble with the EPA.
To use an analogy, if you couldn’t pay off your credit card bill some month because you had an unforeseen emergency expense, this would be the process by which you might convince the credit card company to waive that charge.
An aerial view shows neighborhoods in Monrovia enshrouded in smoke from the Bobcat Fire on Sept. 13, 2020. (David McNew/Getty Images)
It is a long, technically involved process. A California Air Resources Board (CARB) exceptional events filing (PDF) for ozone concentrations during the Northern California wildfires of 2020 runs 228 pages.
The problem, as seen by many in the wildfire science community, is that while this process essentially means air districts are not on the hook for wildfire smoke, they are on the hook for prescribed fire smoke. And prescribed fire — the most affordable, effective inoculation against future wildfires — has never been used as a basis for an exceptional event in California.
But fire scientists and those in fire agencies worry this new rule will stifle the state and federal plans to expand the use of prescribed fire as a core strategy to stem out-of-control wildfires.
“We’ve got to start doing larger prescribed burns if we want to make a difference to what is actually happening on our landscape,” said Scott Stephens, fire science professor at UC Berkeley. “That just means there’s going to be more smoke.”
Pro-prescribed-fire groups, including the National Association of Forest Service Retirees, have submitted comments detailing their concern (PDF) that the proposed rule “will reduce the Nation’s ability to implement strategies intended to reduce unwanted wildfire effects on communities and wildlands, including barriers to increasing the pace and scale of prescribed burning.”
Prescribed burns, like this one in Humboldt County, reduce the underbrush without destroying trees. (Lenya Quinn-Davidson/NPR)
A large group of fire specialists, including professors, cultural burners and ecologists, wrote in a comment letter to the EPA that its plan “would put the EPA on the wrong side of policies and actions planned by federal, state, local and Tribal entities to address the wildfire crisis and ultimately, to reduce harmful PM2.5 emissions and impacts by reducing wildfire smoke.”
Smoke from prescribed fires is less intense and less damaging than smoke from wildfires. Many scientists view it as a protective trade-off — some pollution now in exchange for greater fire safety (and less pollution) in the future.
Air districts supportive, with qualifications
Both the California Air Resources Board and the Bay Area Air Quality Management District (PDF) have submitted comments supporting a tightening of the PM 2.5 standard. In interviews with KQED, regulators from both organizations also expressed support for prescribed burning.
Charles Knoderer, meteorologist at BAAQMD, said that the air district views prescribed burning as a partner and ally in lowering the risk of wildfires.
“We can control when they’re doing the burning and we can minimize the amount of smoke that’s released,” he said. “Wildfires will put out a ton more smoke, and at that point there’s really no controlling it.”
Neither Bay Area nor California air regulators seem to share the worries of the fire community that the EPA will hamper the increased use of prescribed fire, however.
