In government-speak, the Waldo Canyon and Black Forest fires were “unplanned biomass burning events.” As such, they fall into a statistical and scientific abyss. Scientists and regulators know that wildfires release enormous quantities of pollutants, but they have yet to develop tools enabling them to accurately measure the quantity or nature of pollutants from individual wildfires.
Open biomass fires, including wildfires, agricultural burning and managed burns, make up a significant part of global emissions of certain pollutants. Such burning is estimated to make up 51 percent of global carbon monoxide emissions, as much as 76 percent of primary fine organic particulate matter and 20 percent of nitrogen oxides.
Measuring wildfire pollution is particularly difficult, because smoke plumes from large conflagrations may extend hundreds of miles from the source. Ground measuring devices near the blaze aren’t of much use as pollutants disperse in the upper atmosphere, settling hundreds or even thousands of miles from the fire’s location.
For five days in June, Colorado Springs was wreathed in pungent smoke from wildfires in southwestern Colorado and New Mexico. Pikes Peak was hidden, and the foothills scarcely visible. The sun disappeared into the haze early in the afternoon, visible only as a faint red disc.
We might as well have been in Beijing.
County and state health officials advised elderly residents, infants and those with respiratory problems to stay inside, minimizing the long-term health impacts of exposure to smoke.
“Many people may have respiratory symptoms when breathing smoky air. The good news is that most symptoms are short-lived, and resolve as smoke dissipates,” said Dr. Karin Pacheco at National Jewish Health respiratory hospital in Denver.
For city residents, it was déjà vu all over again. Even before the Waldo Canyon and Black Forest fires, smoky days were common during summertime. And while such conditions are no longer exceptional, air pollution spikes recorded by local monitoring sites are often not included in regional air quality assessments, especially if including them might cause “exceedences.” Local officials typically argue that such spikes are one-time events that do not reflect actual regional emissions.
“They do not throw out the data, and the days impacted by fires are not necessarily exempt from exceeding the air quality regulations,” said Dr. Christine Wiedinmyer of the National Center for Atmospheric Research in Boulder. “In fact, it is a very rigorous process that regions must go through to prove that there was an ‘exceptional event’ and that an air quality exceedence was the result of a wildfire and may not count as an official exceedence.”
Exceedences can have severe consequences. Multiple exceedences of certain pollutants during a calendar year may put a region into “non-attainment,” triggering various kinds of penalties for non-compliance. In practice such penalties are rarely enforced, but local governments have little interest in testing the resolve of federal regulators.
Yet as wildfires throughout the West become more common, scientists and regulators are increasingly concerned about the impact of such events.
In a recent NCAR study, Wiedinmyer and co-author Jason Neff found that “large-scale fires in a western or southeastern state can pump as much carbon dioxide into the atmosphere in a few weeks as the state’s entire motor vehicle traffic does in a year.”
Using satellite observations and a computer model that estimates carbon dioxide emissions based on the mass of vegetation burned, they estimate that wildfires in the continental United States and Alaska release about 290 million metric tons of CO2 annually.
That’s only about 6 percent of the nation’s total emissions from fossil fuels, but such fires contribute a much higher percentage of local CO2 emissions in several Western states.
Their estimates have a margin of error of about 50 percent, because of inexact data about the extent of fires and the amount of carbon dioxide emitted by different types of blazes.
Particularly large fires can release enormous pulses of carbon dioxide rapidly.
“A striking implication of very large wildfires is that a severe fire season lasting only one or two months can release as much carbon as the annual emissions from the entire transportation or energy sector of an individual state,” the authors write.
How much atmospheric pollution was released by the Waldo Canyon and Black Canyon fires? There’s no way of knowing. Wiedinmyer and Neff developed a formula for calculating CO2 emissions from wildfires, which seems simple enough: ECO2 = A(x,t) * B(x,t) * EFCO2(1), where A(x,t) is the area burned at location x and time t, B(x,t) is the biomass burned at location x and time t, and EFCO2 is an emission factor, or the mass of CO2 that is emitted per mass of biomass burned.
Similar formulae could be applied to all wildfire pollutants, but analyzing a particular incident is difficult. Broad assumptions about stand density, forest composition, percentage of biomass actually consumed by fire and other variables might not be applicable.
One thing seems certain, though.
This year’s prolonged and ferocious wildfire season, which incinerated hundreds of thousands of forested acres in Colorado and New Mexico, was a major contributor to regional air pollution. Earlier this week, the local skies were clear … or were they? Here’s Tuesday’s update from CDPHE.
“Various wildfires burning in the western U.S., particularly in Idaho, Wyoming and Utah, will contribute to background haze across Colorado on Monday and Tuesday, especially in the northern portion of the state.”
So shouldn’t regulators regard wildfire emissions as equivalent to transportation or stationary source emissions, a fact of life in the Mountain West?
“You make a good point about wildfires and their frequency,” said Wiedinmyer. “I think it is one that air quality managers are wrestling with across the West.”