On a Clear Day You Can See the Bird's Nest

By Jade Boyd
Rice University

While the Beijing Olympics were the hottest global sports ticket this summer, researchers from Rice’s Laser Science Group with collaborators from Princeton University conducted their own world-class event in the Chinese capital — a first-of-its-kind air-quality study using new laser-based sensors designed and built by the Rice-Princeton team.

Rice’s Frank Tittel, the J.S. Abercrombie Professor in Electrical and Computer Engineering, and graduate student Rafal Lewicki used sensors near the Olympic stadium to monitor trace gases, before, during and after the games. They worked with colleagues from the Chinese Academy of Sciences in Beijing and Princeton University’s Mid-Infrared Technologies for Health and the Environment (MIRTHE) center in New Jersey. The Princeton effort was led by Assistant Professor Gerard Wysocki, formerly a faculty fellow in electrical and computer engineering at Rice.

“This has never been done before,” Tittel said. “Our system continuously made sensitive and selective measurements of nitric oxide, even in the presence of strongly interfering gases like water vapor and carbon dioxide.”

Nitric oxide, a molecule containing an atom of nitrogen and an atom of oxygen, is an ozone precursor or health-harming chemical compound that is found in vehicle exhaust fumes. Although

Smoggy day at the Bird's Nest

scientists have had the tools to measure it in air samples for years, machines needed to analyze the samples are large and expensive. That process is slow, using samples collected in the field and shipped to a laboratory where they went through a time-consuming analysis.

“The continuous monitoring of nitric oxide we did in Beijing has never been attempted before,” Tittel

said. “If the technique proves robust, it could open the door for new

Clear Day at the Bird's Nest

types of real-time atmospheric monitoring elsewhere.”

Tittel said Rice’s new sensors employed “quantum cascade” lasers, a unique type of laser invented in the mid-1980s. The lasers in the new sensors emit at a particular wavelength of mid-infrared light that is absorbed by nitric oxide. Using laser absorption spectroscopy, the sensors can measure nitric-oxide concentrations at the parts per billion level.

Tittel said the team collected data for almost two months. Findings will be thoroughly analyzed before conclusions are drawn about the technique or the concentration of pollutants in Beijing’s air. The results could be published as early as next summer.

The MIRTHE center was established in 2006 with a $15 million grant from the National Science Foundation. Rice is one of six partner institutions collaborating in the Princeton-based center. The collaboration is led by Claire Gmachl, professor of electrical engineering at Princeton. MIRTHE performed its field trials in Beijing, China, as guests of the Chinese Academy of Sciences, Institute of Atmospheric Physics, in the group of Dr. Zifa Wang.

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