By Farrer Owsley-Brown, King’s College London
Leverhulme Wildfires researchers from King’s College London have published a new paper, “Can the remote sensing of combustion phase improve estimates of landscape fire smoke emission rate and composition?”, in Atmospheric Measurement Techniques. Our work takes a fresh look at a crucial, yet often overlooked, factor in wildfire emissions: combustion phase—whether a fire is flaming or smouldering.
Why Does Combustion Phase Matter?
Emissions from wildfires are complex. Generally, however, during the flaming phase fires burn intensely, converting nearly all carbon in the fuel into carbon dioxide (CO₂) through complete combustion. In contrast, smouldering fires are cooler and slower but can persist for much longer. Smouldering combustion releases slightly lower amounts of CO₂ but much higher levels of harmful pollutants like carbon monoxide (CO), methane (CH₄), volatile organic compounds (VOCs), and particulate matter (PM) relative to the amount of fuel burned.
Photos: images of wildfires from the FIDEX campaign. Credit: Farrer Owsley-Brown.
Current methods for estimating emissions using satellite data treat every fire in a particular biome as having a typical amount of flaming and smouldering activity. However, this is potentially leading to inaccuracies in smoke emission calculations, which play a vital role in air quality forecasts, carbon budgeting, as well as climate and fire modelling.
Remotely Measuring Combustion Phase
Scientists have speculated that remote sensing techniques might distinguish between flaming and smouldering fires, but no one has rigorously tested whether they can actually improve emission estimates… until now.
This study tested two remote sensing methods and found that one technique stood out: detecting the potassium emission line (K-line), a signal in the near-infrared produced only during flaming combustion. This is similar to the visible colours observed in Bunsen burner tests or fireworks, where hot atoms of specific elements produce certain colours.
The study intensively measured controlled burns at KCL’s Wildfire Testing Chamber with remote sensing and smoke analysis instruments. We found that by using the K-line measurements to notice when the fires were flaming led to a significant improvement in the accuracy of the emissions estimated from the fires.
We then tested their findings on airborne data of a real wildfire collected by the KCL team from a research aircraft. We found that current estimates which do not account for the individual combustion phase behaviour of a fire could be missing a lot of this crucial information.
A Future Application
Interestingly, an upcoming European Space Agency (ESA) satellite currently set to launch in 2026 is designed to measure solar-induced fluorescence (SIF), which can indicate the stress that plants are under. However, while designed for something completely different, it is incredibly well-suited to measure the K-line from space. This presents exciting potential for refining global emission estimates, which could enhance air quality predictions, for example.
Another Fiery Link with Potassium
Potassium, biomass, and fire already have a history. The word “potassium” originates from “potash” —a substance people have used for centuries—produced by burning wood, dissolving the ash in water in a pot, and evaporating the solution. Potash played a pivotal role in soap making, glass production, and even gunpowder and fireworks. In the 19th century, Cornish scientist Humphry Davy isolated potassium as an element, revolutionising its use. Modern fertilisers derived from potash (now mainly mined) help sustain half of the global population.
Photo: an experimental burn in the KCL Wildfire Testing Chamber, located at Rothamsted Research. Credit: Farrer Owsley-Brown
This study highlights how another link between potassium, biomass, and fire could serve this new purpose: helping us better understand wildfire emissions. While there is still much work to be done, this research opens up exciting possibilities. Watch this space!
Feature Image: Image of a wildfire in Northern Ontario captured below the research aircraft using a PhaseOne iXU-RS-1000 during the FIDEX campaign (read more about it here: https://airborne.geog.kcl.ac.uk/fire-detection-experiment-fidex/) in August 2023. Credit: KCL-NAEO.
Farer Owsley-Brown is a PhD student in the Department of Geography at King’s College London, studying the hyperspectral and thermal remote sensing of landscape fire properties.
