NRC Scientists Pinpoint Particulates - National Research Council Canada

Burning gasoline or diesel fuels in internal combustion engines produce waste gases such as carbon dioxide and it also produce microscopic bits of solids and condensed liquids, called particulate matter. A major part of these particulates is black carbon, or soot. These tail-pipe particulates contribute to urban smog and cause respiratory, cardiovascular, and other health problems when they're inhaled.

NRC researchers have created a technology that's helping enforce some of the world's toughest vehicle emissions standards for particulates. The technology is helping government regulators clear the air across North America. It's even being used to help assess the impact of particulates on climate change.

"Environmental agencies are setting emissions standards that are so low and detailed they can't be measured with many previously used technologies," says Greg Smallwood, who leads NRC-ICPET's Ottawa-based combustion research team. "This is why they're so excited about our technology."

Traditionally, measuring exhaust particulate emissions has been done by trapping the particulates on a filter and weighing them. However, forthcoming emissions standards in the U.S. and Canada are so low that filters do not provide the required precision. Moreover, California — a world leader in establishing strict emissions standards — is implementing "not-to-exceed" emission standards for diesel trucks in 2007. This means that the trucks can't exceed a maximum particulate emission level at any point while on the road, something that can't be measured with filters. So how do you measure these real-world, real-time emissions?

In spring 2005, the California Air Resources Board (CARB) used LII technology to conduct real-time particulate emission measurements for a heavy-duty truck, including evaluation of the new not-to-exceed standard. The testing was done on a dynamometer, a kind of treadmill for vehicles. These tests used a commercial version of the NRC-ICPET LII technology licensed to California-based Artium Technologies.

In 2005 Artium released a push-button simple, portable, brief-case-sized instrument based on the NRC-ICPET tabletop LII technique, making the technology readily accessible to a broad range of users. These include aircraft engine makers and even carbon black manufacturers who produce specific sizes of soot which tire manufacturers use to alter the properties of rubber.

Enter NRC Institute for Chemical Process and Environmental Technology (NRC-ICPET) patented technology. Based on laser-induced incandescence (LII), the technology uses a laser to zap a tiny sample of engine exhaust. This nanosecond burst of laser energy is absorbed by the black carbon particulates. They rapidly heat to about 3500 ºC, and start to glow, or incandesce, like a light-bulb filament.

"It's like we have thousands of nanoscale light bulbs going on," says Smallwood. "We record that light given off by these particles and can use this to calculate the concentration of particulates."

The intensity of the light from the super-heated particles is measured at two wavelengths. This enables the researchers to calculate both the temperature and concentration of the particles. "Since we can do all of this with a single laser pulse the technology can be used to measure real-time emissions," Smallwood says.

Based on the success of the dynamometer trials, NRC-ICPET researchers worked with CARB and Artium again in the summer of 2005 to conduct the first on-road, real-time particulate emission testing for diesel heavy-duty trucks.

"Usually emissions are measured in the lab with the vehicle on a dynamometer," says Smallwood. "But the question is what are the emissions out in the real world?" During the CARB on-road tests, samples were collected using special vehicle-mounted equipment, though Smallwood doubts the technology will ever be small or low-cost enough to become a standard vehicle feature.

NRC-ICPET is also using LII technology in collaboration with Environment Canada to measure the particulate emissions from advanced technology vehicles. These vehicles use new engine designs and fuels, such as those produced from Canada's vast oil sands resources. The LII tests provide key insights to the trade-offs between improved fuel efficiency and increased particulate emissions.

Additionally, the NRC-ICPET group is developing a unique, portable high-sensitivity LII-based sensor that Environment Canada researchers can use for detailed air quality measurements. The goal is to understand the role that atmospheric black carbon particulates, when heated by sunlight, play in climate change. Two university graduate students in the NRC-ICPET combustion labs are also using the technology to characterize particulates released by oil and gas flares.

At NRC-ICPET, researchers are going beyond their LII technology and they are pushing the boundaries of particulate science. Using LII and other laser-based techniques to develop ways to identify the size, concentration and the complex fractal, or tree-like, structure of particulates. This information will ultimately help in the understanding of the health impacts of these particulates. "We're learning a lot about the optical and thermal properties of the soot," says Smallwood. "The more experiments we do, the more questions we raise."