A forest of flare stacks pour out smoke at an oil field in Uzbekistan. One stack alone could be emitting as much soot as several hundred diesel buses running around the clock. In fact, nobody could tell for sure how much pollution was pouring out. Until now.
Matthew Johnson, an engineering professor at Carleton University in Ottawa, and his collaborators at National Research Council and Natural Resources Canada, have developed a technique called Sky-LOSA that can measure the amount of soot coming out of a flare stack. It's a deceptively simple approach to solving a big global problem.
"This is the first and only time a flare has been quantitatively measured," Dr. Johnson says. "Armed with this knowledge, you could say okay, I can invest in some kind of solution for this particular flare, and get measured and identified benefits that would be equivalent to trying to remove 500 city buses. So, pull your city bus fleet off the road or deal with a single flare. A whole new world of practical, implemental, potentially cost-effective solutions emerges now that we can see."
To measure the amount of soot (also known as black carbon) coming out of that stack in Uzbekistan, Dr. Johnson pointed two cameras at the smoke plume. One camera takes high-speed images to figure out how fast the smoke is moving and in what direction. The second camera is slower and feeds higher-resolution images to a computer.
The computer takes a cross-section of the plume and replaces the smoke with the photo's background. It then compares the amount of light coming through the plume to the amount naturally occurring in the background. The difference tells researchers how much light is being blocked by the soot. Together with data from the high-speed camera, the researchers are then able to calculate how much soot is coming out of the stack.
It's not a perfect technique; Dr. Johnson acknowledges that the margin of error is about 30 per cent. But until now, the method of measuring emissions was even less reliable - we just eyeballed it. A trained monitor would look at a plume and compare its opacity to known plume opacities. Dr. Johnson's method uses similar principles, but gives quantifiable results with far less of a margin for human error.
According to his data, that one stack in Uzbekistan is pumping out 275 trillion particles per second, as much black carbon per second as about 500 diesel buses. At times, however, that stack will pump out significantly more. (He points outs that this is a particularly large stack, and the flares at oil operations in Canada are much smaller.)
For decades, soot was considered a localized problem, contributing to smog and respiratory problems. But recently, researchers found that it's also a major contributor to global warming.
"My estimates are it is the second-leading cause of global warming after carbon dioxide and just ahead of methane," says Mark Jacobson, a civil and environmental engineering professor at Stanford University who has studied the effects of black carbon on global warming.
"There are different sources of carbon and co-pollutants that affect how strong the warming is," he adds. Soot from diesel engines and flares like the one Dr . Johnson studied are the worst.
Soot helps trap heat, as greenhouse gases do, but it only stays in the atmosphere for a couple of weeks, unlike carbon dioxide. However, it has another, longer-lasting effect on climate: Because black carbon is dark, when it settles on ice it cuts reflectivity and increases heat absorption. This makes ice melt faster, revealing darker-coloured land and ocean underneath ice caps, creating an accelerating warming cycle that's causing the Arctic to warm much faster than areas further south.
"It absorbs light," Dr. Johnson says. "It helps snow absorb, rather than reflect, and greatly speeds warming." "And everyone can see this every spring. If you look at a dirty snow bank on the side of the street, it has these dirt particles that seem to fall deep into the snow. Basically the particles are heating up, they're melting all the snow around them and you get that very fingered-looking snow bank structure."
"It [soot]is hard to measure, and this looks like a better mousetrap," says John Bachmann, former associate director for Science/Policy and New Programs, Office of Air Quality Planning and Standards at the United States EPA and expert in black carbon. "The one thing that's missing is getting the organic carbon portion," he says. Because different flares may have different ratios of black to lighter organic carbon, their effect on warming might not be universal. Still, he sees Sky-LOSA as a big step forward.
Although it will not solve the global climate problem, cutting soot emissions will cause a quick reduction in warming, Prof. Jacobson says, and reduce air pollution and related health effects.
With this new measuring technique, countries will be better able to estimate their contributions to global warming and the results of their efforts to curb emissions.
As for Dr. Johnson, he's now looking at other measuring problems, such as leaks from gas lines and storage tanks. Those leaks might account for four per cent of Canada's greenhouse gas emissions. But, as with soot from gas flares, we don't really know.
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