Black Carbon Belchers? | Chemical & Engineering News
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Web Date: February 24, 2012

Black Carbon Belchers?

Pollution Monitoring: Cars may produce more climate-warming particles than previously thought
Department: Science & Technology
News Channels: Environmental SCENE, Analytical SCENE
Keywords: black carbon, soot, monitoring, laser spectral detection, diesel engines, climate change
Start Your Engines
Gasoline-burning cars produce more black carbon than suspected, according to a new study
Credit: Shutterstock
Traffic on a highway in Toronto.
Start Your Engines
Gasoline-burning cars produce more black carbon than suspected, according to a new study
Credit: Shutterstock

Tiny particles known as black carbon can pack a heavy punch when it comes to climate change, by trapping heat in the atmosphere and by alighting atop, and melting, Arctic ice. With an eye toward controlling these emissions, researchers have tracked black carbon production from fossil fuel combustion in gasoline-burning cars and diesel-burning trucks. Once thought to be minor players, gasoline-burning engines could put out twice as much black carbon as was previously measured, according to new field methods (Environ. Sci. Technol., DOI: 10.1021/es2033845).

Black carbon particles, which come from many combustion processes, have become a focus this month of an international agreement to control climate impacts from short-lived but powerful actors such as methane, hydrofluorocarbons, and black carbon (C&EN, Feb. 20, page 8). The new findings could lead to controls on gas-burning vehicles, long considered to produce less black carbon than diesel-burning trucks and cars.

A team of Canadian government scientists stumbled upon the hidden black carbon emissions after deploying a new laser-based method to monitor soot and other tiny particles in the chaos of traffic. In 2010, John Liggio and his colleagues from Environment Canada and the National Research Council Canada deployed the new device along highways around Toronto.

The instrument’s pulsed laser beam heats black carbon particles up to thousands of degrees Celsius, making them light up like “red-hot glowing charcoal,” says project leader Jeffrey Brook. A photometer measures the brightness of the particles to estimate their mass in real time. The team compared their device to a commonly used single-particle analyzer, known as SP2, which they set out at the same time.

The researchers followed 30 heavy-duty, diesel-burning vehicles and collected samples of their exhaust. They found that the trucks belched out levels of black carbon similar to those documented by prior studies.

While the scientists were chasing trucks, stationary monitors measured particles moving downwind of the same multi-lane highways. Video monitoring helped the team track the number and types of vehicles passing by. After measuring the mass of black carbon as it fluctuated over 17 days, the scientists compared those data with estimates of total black carbon based on expected black carbon emissions of diesel- and gasoline-burning vehicles. But their estimates always fell short of the actual black carbon measurements.

Gasoline-burning vehicles would have to emit more to take up the slack, the researchers concluded. They calculated that such vehicles must emit about 75 mg of black carbon per kilogram of fuel, about twice the amount that other scientists have reported and that the SP2 measured. They surmised that, unlike the new device, other methods miss tiny black carbon particles as small as 7 nm.

Researchers should be aware of the limitations of SP2, an instrument that is growing in popularity despite its lower sensitivity, says Dan Lack of the National Oceanic and Atmospheric Administration. However, other monitoring techniques such as absorption filters can track smaller particles, he says. For now, the discovery of a hidden well of black carbon holds true only for the team’s Toronto sites, he points out.

Mark Jacobson of Stanford University comments that if the results hold true elsewhere, they “imply an even greater urgency for taking measures to reduce particle emissions from vehicles.”

Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
Roman (February 25, 2012 5:16 AM)
So you measure emissions from some diesel trucks, never from cars, and then your conclusion is - cars emit too much black carbon?
1. Why didn't you measure emissions from cars?
2. Are you sure your conclusion is correct, and this 'black carbon' isn't a result of say tires rubbing against the road?
phil (February 28, 2012 6:46 AM)
In 2010, John Liggio and his colleagues from Environment Canada and the National Research Council Canada deployed the new device along highways around Toronto.
Carb Gossman (February 25, 2012 11:10 AM)
The article does not indicate whether the researchers controlled for existing carbon thrown up into the air from vehicle motion on the roadway, and new carbon from tire dust.
Chris G (February 25, 2012 11:24 AM)
I dont think their study is accounting for variation in the production across all vehicles. It's wrong to assume that all gasoline vehicles are producing twice as much when it could be that certain vehicles are producing 3, 4, or 5 times as much. We have all been stuck behind that guy in his 1970 beater that is choking us out or seen that jacked up dually diesel truck that the owner has tuned so when he steps on the gas he gets a cloud of black big enough to block out the sun. This study lacks comparison to controlled data, a set of new vehicles with all emissions systems in tact being driven under normal conditions, then compared to highway data to determine a variation between controlled and realized data. The realized would allow for a variation percent to be used against a measurement.
Brian (February 25, 2012 1:45 PM)
So lets get this straight. This article is written on the premise of faux science, rather than actual science then? Gasoline vehicles were not actually tested - rather, there was a pretty bold assumption made that gasoline vehicles "must have" accounted for the measurement discrepancy.
Lester (March 1, 2012 6:39 PM)
Hey Roman and Carb: There is a big difference between black carbon from combustion of fuel and rubber from tires...the biggest difference is that rubber from tires is NOT black carbon. Also, turns out that if you read the original paper, cars were tested from this highway. I guess its not faux science after all.
James (July 29, 2015 10:06 AM)
I dont see this as faux science - clearly more needs to be done - but it is new and provoking

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