The National Science Foundation has funded a multimillion-dollar Engineering Research Center based at Princeton University that is expected to revolutionize sensor technology, yielding devices that have a unique ability to detect minute amounts of chemicals found in the atmosphere, emitted from factories or exhaled in human breath.

The center, dubbed MIRTHE, for Mid-Infrared Technologies for Health and the Environment, combines the work of approximately 40 faculty members and researchers, 8 post-docs, 77 graduate students, and 30 undergraduates from the six universities (Princeton, Johns Hopkins, Rice, Texas A & M, City College of New York, and the University of Maryland Baltimore County) that are located in areas that are struggling to meet air quality standards.

The center also is collaborating with dozens of industrial partners to turn the technology into commercial products, and is working with several educational outreach partners, which will use MIRTHE’s research as a vehicle for improving science and engineering education. The goal of the research is to produce devices that provide unprecedented high-performance and are so low in cost and easy to use that they transform aspects of the way doctors care for patients, local agencies monitor air quality, governments guard against attack and scientists understand the evolution of greenhouse gases in the atmosphere.

At the February 18 Lunch ‘n Learn, Claire Gmachl and Jim Smith talked about the work of the center and discussed an atmospheric field campaign that monitored Beijing air quality, clouds, and precipitation during the 2008 Olympic games. Of particular importance were analyses of the impacts of pollution reduction strategies implemented for the Games. Gmachl introduced two of the core technologies of the center, mid-infrared laser sources, and sensing applications for the environment. To verify that our environment is clean, safe, and sustainable, on local, national, and global scale, MIRTHE is developing grids of networked sensors in a dense grid that can allow for the integration of measurements of trace chemicals over large distances.

In the marketplace, there are carbon dioxide sensors that are easy to use and relatively inexpensive, but these are not sensitive enough for the needed sensor grids. There is also a high end market offering much more sensitive instruments, but these units are expensive, bulky, they require experienced handlers, and they tend to measure only one chemical per instrument.

And so MIRTHE is developing high performance, compact, easy-to-use, cost-effective, network ready sensors. The new technologies involve mid-infrared trace gas sensors. Any chemical in the air that exists as a vapor under normal temperature and pressure conditions consists of small molecules or atoms that vibrate and strongly absorb the infrared light at unique, characteristic frequencies. Sensors are thereby able to determine the amount of each chemical in the air, even trace amounts.

Gamchl described the MIRTHE research in Quantum Cascade lasers. Laser pointers, which involve driving a current through a semiconductor, all generate the same red light because they are made from one material. Chemical sensing requires a huge variety of frequencies. Rather than one layer of material, they take many thin layers, one on top of another, to generate a range of energy levels and colors that can detect a full range of trace gases.

Jim Smith described several applications of the new sensor technology, notably the monitoring of air quality a and regional climate during the recent Beijing Olympic games. Air quality in Beijing was visibly poor, as the following images of the Bird’s Nest Stadium well illustrate.

During the games, MIRTHE focused on monitoring ozone and aerosol emissions and their impact on regional climate change. Like many urban areas, Beijing is seeing increasing pollutants. Beijing faces the complicated factor of being situated within the industrial core of Eastern China and bordered to the west by mountains. Air quality remediation in Beijing might not overcome events in nearby cities. There are sodium dioxide emissions from power plants and emission of ammonia from agriculture and automobiles.

Smith noted that the global impact of aerosols is not well understood, in part because, unlike carbon dioxide, they exhibit dramatic variability. Over the past three decades, the increase in aerosol loadings in Beijing appears to have resulted in a reduction of precipitation perhaps because this cloud cover inhibits the formation of large water droplets or because the aerosols are heating the atmosphere and cooling the ground.

In preparation for the games, the Chinese reduced auto traffic by 40%, and shut down factories and local construction efforts. The MIRTHE sensors were part of a much larger effort to understand the environmental response and the impact on aerosol loadings. For the Beijing effort, MIRTHE deployed two environmental sensor systems. QCLOPS (Open Path Remote Sensing System) tracked multiple trace gases using a tunable laser and absorption spectroscopy. And an NO Point sensor measured trace gas plumes. The group has received and is reviewing its data.

Claire Gmachl earned her M.Sc. in Physics from the University of Innsbruck in 1991. She went on to receive her Ph.D. in Electrical Engineering from the Technical University of Vienna in 1995, graduating /sub auspiciis Praesidentis/ (with special honors by the president of the Austrian republic). Her studies focused on integrated optical modulators and tunable surface-emitting lasers in the near infrared. From 1996 to 1998, she was a Post-Doctoral Member of Technical Staff at Bell Laboratories. In 1998, she became a formal Member of Technical Staff at Bell Labs and in 2002 she was named a Distinguished Member of Technical Staff, in part due to her work on the development of the quantum cascade laser. In 2003, she left Bell Labs and took a position as Associate Professor in the Department of Electrical Engineering at Princeton University, where she is currently working. In 2004, Popular Science named Gmachl in its “Class of 2004 - Brilliant 10,” its list of the 10 most promising scientists under 40. She went on, in September 2005, to win the MacArthur Foundation’s “genius grant.” Recently, she was named the director of the new Mid-InfraRed Technologies for Health and the Environment (MIRTHE) Center, funded by the National Science Foundation.

James A. Smith is MIRTHE deputy director and Professor of Civil and Environmental Engineering at Princeton University. His research interests concern the hydrology, hydraulics and hydrometeorology of extreme floods. Hydrometeorological studies have centered on development of technologies for measuring rainfall from weather radar, stochastic modeling of the space-time structure of rainfall and microphysical studies of extreme rainfall from organized systems of thunderstorms. Smith’s research group has been involved in numerous hydrometeorological field campaigns, most recently in connection with the Baltimore Ecosystem Study (BES), a component of the NSF LTER program. Field studies in the BES have also examined the heterogeneity of hydrologic response in urbanizing watersheds, the stability of the channel-floodplain system in urban drainage networks and the hydraulics of extreme floods in urban rivers. In addition to field campaigns focused on intensively monitoring research watersheds, Smith and his colleagues have been extensively involved in field studies of major floods in the United States.

A podcast and the presentation are available.

Posted by Lorene Lavora