Mark Zondlo: Portable sensors measure air pollutants

Nov. 21, 2013

Although not as well-known as carbon dioxide or methane, nitrous oxide is a significant greenhouse gas. One of its primary sources is the application of nitrogen-based fertilizers on farm fields. Yet measuring the levels of nitrous oxide in a field is difficult because today’s sensors are heavy and consume large amounts of power. A portable nitrous oxide sensor, easily carried from place to place, could radically change how scientists and regulators monitor this greenhouse gas.

Mark Zondlo, assistant professor of civil and environmental engineering, and his team have developed a fast, sensitive and portable nitrous oxide sensor that can be carried in one hand. The sensor uses a battery-powered laser, called a quantum cascade laser, to fire a beam of light through a sample of air, while a detector measures the light absorption to deduce the amount of nitrous oxide in the air.

The group has created similar sensors that measure ammonia and carbon monoxide. The portable sensors allow measurements to be taken quickly and frequently, which could greatly expand the understanding of how these pollutants are released and how this release can be controlled. The research team tested the sensors for several weeks earlier this year in California’s San Joaquin Valley and found that they performed well compared to stationary instruments.

To give accurate measurements in rapidly changing field environments, the sensors must be calibrated frequently by measuring a known concentration of gas. The calibration equipment contributes to the large size of today’s bulky sensors. The new Princeton sensor replaces the large calibration equipment with a finger-sized chamber of reference gas.

“Our sensors have precision and stability similar to the best sensors on the market today, but at a fraction of the size and electricity requirements,” said Zondlo, who is affiliated with the Mid-infrared Technologies for Health and the Environment (MIRTHE) center, a multi-institution center funded by the National Science Foundation and headquartered at Princeton. Zondlo’s co-inventors on the project include graduate students Kang Sun and David Miller as well as Postdoctoral Research Associate Lei Tao and former postdoctoral researcher Amir Khan.