Smoldering peat fire emits a hazy smoke over a tropical forest
Smoldering peat fires like this one in Indonesia can burn for months and even years. Credit: Aulia Erlangga/CIFOR, CC BY-NC-ND 2.0

Setting fire to a tropical peatland, it turns out, can be tough.

“After burning peat in the lab for 15 years, we were really confident. We actually claim we are the world experts in igniting peat,” said Guillermo Rein, a professor of fire science at Imperial College London. Rein and his team were in South Sumatra, Indonesia, setting alight a peatland for their European Union–funded HAZE project, which aims to analyze the emissions of smoldering peatland fires.

“And then we actually struggled to ignite it,” Rein said. “We got a fright because if you don’t ignite the peat, then you don’t have an experiment. It took us a week and a half.”

In the end, the researchers used one of the most common methods of ignition for peatland fires in Southeast Asia: slash and burn. They cut down vegetation, piled it on their peatland site, and set it on fire.

Studying a Fire from the Ground Up

Rein’s team is the first to ignite a peatland in the name of research.

Rein’s team is the first to ignite a peatland in the name of research. Scientists already knew that peatland fires emit a huge amount of particulate matter smaller than 2.5 micrometers (PM2.5). But the amount released in the first few days of burning hadn’t been measured previously because the fires often remain undetected early on. To effectively measure early emissions, scientists needed to be there when the fire started.

The researchers divided their plot into sections to create separate fires and then dug sand-filled trenches for firebreaks. Once the fires were alight, the scientists observed them for a month, using thermal cameras, temperature probes in the soil, and equipment to measure emissions.

Researchers discovered that peatland fires emit around 3 times more PM2.5 particles than previously thought. These data may help inform air quality forecasts and community health measures because PM2.5 particles can penetrate deep into the lungs and have been linked to cardiovascular issues, respiratory diseases, and cancers.

Not all atmospheric scientists are convinced by the new emissions data. Robert Yokelson, an atmospheric chemist and expert in global fire emissions at the University of Montana, said the research should be put in a larger context.

“I think it’s possible the particulate matter emissions are higher or lower than what is in the literature now based on a limited amount of sampling,” he said, “but I don’t believe that factor of 3. Nor has it been proven the current estimates are even biased low. The fires can burn a long time, so a brief enhancement at the beginning may not have a big effect on the overall emissions.”

Other Observations

Scientists also observed that “different stages of the smoldering fire have different smoke signatures. Earlier on, when it has just ignited, there are a lot of hydrocarbons, for example, and very little carbon monoxide and carbon dioxide,” Rein said. As the fire accelerates, emissions of hydrocarbons such as methane and benzene fall, but emissions of carbon monoxide and carbon dioxide increase.

As well as being hard to ignite, peatland fires are difficult to suppress. During the experiment, there were three massive rainstorms that broke the team’s tents. It was more rain than Rein had ever seen, yet to his surprise, the fires continued to burn. “We were like, ‘Okay, that’s it, the experiment is over,’” he said. “And the morning after, the fire is still there—this thing just doesn’t want to stop.”

At the end of the experiment, it took 3 days to put the fires out.

No Positive Outcomes

Peatland fires are “the largest and longest-burning fires on Earth,” Rein said. These slow, smoldering fires can burn for weeks and months and consume phenomenal amounts of fuel. Peatland fires are thought to be responsible for 15% of global greenhouse gas emissions every year—the same percentage as the European Union.

Peatland fires also produce a low-lying haze that can choke towns and cities for weeks. A recent study found that if current trends continue, air pollution from Indonesian fires will cause 36,000 excess deaths per year across Indonesia, Malaysia, and Singapore over the next decade.

Unlike forest fires, which can clean out dead brush, “these fires are not known to have any positive outcomes—to nature or to humans,” said Rein.

—Michael Allen (, Science Writer


Allen, M. (2020), Starting (and stopping) a fire to study it, Eos, 101, Published on 10 February 2020.

Text © 2020. The authors. CC BY-NC-ND 3.0
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