FOCUS ON FIRE
IN THE FOREST
FUNCTION OF FIRE
A GRASP ON SMOKE
BEYOND THE BLAZES
By Vince Devlin
On a clear day from his home in the South Hills, Bob Yokelson has a gorgeous view across the city of Missoula and up into Rattlesnake Canyon.
On a smoke-filled day at the height of a bad summer for wildfires, Yokelson has a view of a mailbox across the street. Like thousands of Montanans, he endured the suffocating Augusts and Septembers of 2000 and 2003, when smoke from forest fires choked the valleys of western Montana.
Unlike many, Yokelson has a pretty good idea what he’s sucking into his lungs with every breath taken on those days.
While many others study the effects of fires on forests and grasslands, Yokelson’s research concentrates on the smoke emitted by fire. The adjunct associate professor of chemistry at UM has been involved in the research of biomass burning since 1993.
“The big picture is, when people started getting interested in air pollution, they were studying the effects of cars and industry,” Yokelson says. But in 1979, Nobel Prize winner Paul Crutzen realized that fires in the tropics probably contributed just as much to global pollution as vehicles and industry combined.
Early smoke research used instruments capable of measuring one or two types of compounds, which Yokelson compares to the story of the five blind guys and the elephant.
“One guy grabs a trunk and describes the elephant, another guy grabs a leg, another guy grabs the tail ... they can’t agree on what the elephant is really like.”
molecules absorb infrared radiation,” Yokelson says. “If
you shine that through the smoke, you can detect nearly
all types of compounds in there.”
A wide variety of reactive and stable compounds in smoke can be studied in real time using Fourier transform infrared spectroscopy (FTIR). In the beginning Yokelson’s group studied smoke from small fires in laboratories like the combustion facility at the Fire Research Center in Missoula. They soon graduated to other “open-path” devices that could be used in the field.
Today, Yokelson and other scientists will typically board a University of Washington Convair 580 research plane to fly through plumes of smoke directly above fires at different altitudes and at various distances downwind from them, allowing their sophisticated equipment to sample the air with closed-cell FTIR systems.
“What we’ve found consistently is that what’s in smoke is quite different from what people thought,” Yokelson says. “It used to be thought that smoke was primarily carbon dioxide, carbon monoxide and hydrocarbons.”
On a computer screen, Yokelson shows the result from one fire. Dozens of compounds are listed, including methanol, acetic acid and formaldehyde. “We’ve found that oxygenated organic compounds are about four times more abundant than hydrocarbons. What we used to think of as everything reactive and interesting in smoke turned out to be only about 20 percent of what was reactive — and it changes fast.”
What’s in fresh smoke depends on what’s burning. Fresh smoke from a savannah grassland fire in Africa is different from smoke from a stand of burning ponderosa pines in Montana. Smoke at the source of a fire is different from smoke 1,000 feet higher — and different again at every other elevation or distance downwind.
it interacts with sunlight and other chemicals, new compounds
are made and others destroyed,” Yokelson says. They have
learned that smoke many miles from a fire can carry more harmful
chemicals than smoke near the fire.
Billions of years ago, Yokelson says, life evolved about a meter below the ocean surface. Ultraviolet rays from the sun were too strong for anything to grow on land. But the plants gave off oxygen, which led to the creation of the ozone layer that blocked harmful UV rays. That allowed carbon-based life to spread from beneath the ocean surface to land.
With that came the fuels for fires to burn.
“Fires can consume everything,” Yokelson says. “Fire can consume just a few trees. In some fires, almost all the trees survive and just the ground fuels are burned. All scales of fire occur naturally. It’s part of the normal ecology.”
Fire, he says, has co-evolved with plant life on Earth. The resulting smoke can affect climate, human health and ozone production.
Ozone is one of the compounds smoke from fires can produce. It is not created at the source of a fire, but rather, as smoke travels through the atmosphere.
“The ozone layer is a good thing,” Yokelson says. “Ozone down here is a bad thing. It’s a greenhouse gas. It’s poison, basically. It eats away at tires on a car, so imagine the damage it can do to your lungs.”
Ironically, both fire and ozone are major sources of the chemicals that make the ozone layer go away. Knowing what’s in smoke is the key to determining what all the effects of all those compounds may be. Using the data gathered, Yokelson and his fellow scientists from around the world can build better models to determine how the pollution will affect things such as climate and rainfall.
“We basically take the smoke recipe and put it in a chemistry model to see how it changes over time,” Yokelson says.
Yokelson has a picture of that view from his house on a perfect day, the sky a bright blue. He has another during the wildfire season of 2003, when the world seems coated in gray and smoke swallows up any sight of the city or mountains.
Those who live in western Montana well remember the weeks the air was thick with that smoke. He also has a picture taken when smoke research took his team to Brazil. The photograph is of children playing a game of soccer in the city of Maraba. It makes the 2003 wildfire season in Montana look like a walk in the park.
The game was played at 11 a.m., but the photograph looks like it was taken after dusk. The air is so polluted you can’t even see the soccer goal. Measurements for solid particulate constituents in the air showed 5,000 micrograms per meter cubed.
In Missoula during the forest fire season of 2003, the measurement was 200 per. What Montanans endured for weeks, some people in the tropics endure at far greater levels for months on end. In Brazil, as they chop down the rainforest, they burn what they chop. Mahogany trees six feet in diameter go up in smoke.
Yokelson and other scientists — who have previously studied smoke from fires in Alaska, North Carolina, Africa and Indonesia — headed for Brazil to the state of Mato Grosso, which is Portuguese for “thick jungle.”
“Fly over it now, and it looks like Iowa,” Yokelson says. “It’s mile after mile of soybean fields.”
They headquartered in Alta Floresta (“tall forest” in Portuguese), a city that didn’t even exist until 1976. The first people who settled there, Yokelson says, came to extract the rubber from the rubber trees. When the rubber ran out, Alta Floresta was well on its way to ghost-town status when gold was discovered in the area.
But by the time the gold ran out, the ever-expanding soybean fields were approaching. Alta Floresta today has more people than Missoula.
Mato Grosso had 1,294 fires burning on a single day in September 2004 among 3,600 burning in Brazil. Outdoor air pollution in these places can be far dirtier than what industrial areas of the world experience.
In addition, half the planet’s population still cooks on open fires inside their homes. About 2 million to 3 million children under the age of five die every year from respiratory disease caused because there are no chimneys to vent the smoke.
Yokelson’s research is the first step toward knowing what the world breathes when fire occurs — whether it covers hundreds of thousands of acres or occurs in the space of a square foot inside a hut.
Where there’s smoke, there’s fire — but where there’s smoke, there’s also a lot more than anyone knew before.
For more information, e-mail Yokelson at firstname.lastname@example.org.