Hold your breath: NRC’s discovery of ash in marine engine soot particles highlights potential toxicity


If you take a deep breath in a crowded seaport, near an oil refinery, or on a busy street, chances are you’ll inhale soot made up of tiny nanoparticles emitted from the burning of fossil fuels made from carbon dioxide. hydrocarbons. These emissions may also contain traces of metallic compounds (ash), which make the substance even more dangerous for the body. Few studies have looked at the ash content of engine emissions or measured the proportion of ash combined with soot, because these properties are difficult to access.

But an important discovery will change the way researchers approach ash measurements for engine emissions. During a routine exercise to measure the amount of soot (black carbon) in aerosol samples taken from various internal combustion engines, scientists from the Metrology Research Center of the National Research Council of Canada (NRC) discovered tiny dots of much denser material in the soot of marine engines. . After reviewing images from transmission electron microscopy (TEM) instruments, the Black Carbon Metrology team concluded that the dots were likely metallic compounds, but wanted more specific confirmation.

“We asked our colleague Dr. Martin Couillard from the NRC’s Center for Energy, Mining and the Environment to examine these nanoparticles to see if he could find traces of ash in the samples”, explains the Dr. Stéphanie Gagné, Research Officer, Metrology Research Center. “Fortunately, they had a powerful new technique – an annular dark-field scanning transmission electron microscope (ADF-STEM) that could visualize the mixing of ash and soot particles.” This was definitely a novel idea, as conventional TEM imaging could not detect the tiny nano-sized ash particles or determine their composition individually. ADF-STEM had been used mainly in other industries such as semiconductor.

Dr. Gagné reports that the results were surprising. “When we looked at emissions from residual fuels used only on ships, we realized that the ashes were not present as distinct spheres in the soot, as they are for distillate fuels such as diesel, natural gas and the Jet A-1,” she said. “Instead, they had formed a layer of ash on top of the soot particles that other techniques had never detected.” This coating appeared to be stained, so the team dubbed it “ash-painted” soot. When ash paints the surface of soot nanoparticles, the resulting composite particles behave like soot, remaining suspended in the air for days and posing a threat to the human body. Once inhaled, they can trigger toxic reactions in the body.

Although NRC researchers routinely study engine emissions from many transportation sectors, expanding their studies to the marine sector has been a major contributor to this discovery. Ships use residual fuel – the only type of fuel known to produce ash-painted soot. “The black carbon particles from these engines tend to contain ash with amounts of around 100 mg of vanadium alone per gram of carbon,” says Dr. Joel Corbin, Research Officer, Center for Metrology Research. “That’s considerably more than what comes out of the engines of vehicles such as planes or cars.”

Purify the air

“During this study, we used new or traditional tools in different ways, uncovering new clues with each technique,” ​​adds Dr. Corbin. “Once we put all the pieces together, we were able to confirm that the ash and soot were coming together in a mixture that could be hazardous to our health.”

An important contribution was the expertise in mass spectrometry of Dr. Zuzana Gajdosechova and her work with the team to develop new methods for analyzing particle surfaces. “Thanks to this, we gained certainty that the ash was on the surface of the particles and could therefore trigger a toxic response in the lungs”, notes Dr Gagné.

These findings provide answers that will help Canada and the International Maritime Organization design effective policies to protect our air. Polluted air contributes to more than 15,000 premature deaths in Canada every year. It also intensifies asthma and other respiratory conditions, costing our economy $114 billion a year overall.

Dr. Gagné confirms that for all ideas to come together and change the way people think about ash and soot emissions, NRC needed the right combination of people, scientific knowledge and technical expertise to interact . The team’s background included aerosols, heavy metal mass spectrometry and microscopy imaging.

“We ended up with a unique group that came up with something really unexpected.”

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