Hotline, Fall 2002
by Peter Adams
If you have been to Schenley Park in the last year, you may have been annoyed to see a rather ugly trailer (with what appears to be antennas on top) on the hill near the corner of Schenley Drive and Tech Avenue. The inside of this mundane structure holds a surprise. It is full of sophisticated gadgetry and computer equipment. It makes you feel as if the set of Star Trek has been mixed up with the Beverly Hillbillies. Another surprise is that all this high technology wrapped in an ugly exterior actually does something good for the environment.
The trailer is the central location for the Pittsburgh Air Quality Study, one of approximately a dozen “Supersites” nationwide funded by the Environmental Protection Agency (EPA) to study airborne particulate matter (PM). The Pittsburgh Supersite consists of a team of researchers led by three Carnegie Mellon University professors with participation from twelve universities around the country.
Airborne PM consists of tiny liquid and solid particles suspended in the air, most of which are 10 microns in size or smaller (a period on this page is roughly 600 microns across). These particles are the main contributors to acid rain and cause reduced visibility on hazy days. Perhaps the most disturbing thing about PM is that it has been associated with increases in respiratory illness and death. In 1952, a severe episode in London resulted in thousands of deaths, and this tragedy led to serious public concern about particulate matter. Even today, however, it is estimated that airborne particulates are responsible for tens of thousands of deaths in the United States each year. Children and the elderly are most susceptible. In 1997, the EPA formulated a new air quality standard for PM2.5 (particulate matter smaller than 2.5 microns) when evidence indicated that the previous PM10 standard alone was not sufficient to protect Americans’ health.
Understanding the sources and effects of particulates is not an easy task, however. Hundreds of different chemical compounds are found in PM. While it is widely assumed that some are more harmful than others, it is not yet clear which are the culprits. Part of the difficulty is that regular air quality monitoring measures total PM concentrations without providing information on the chemical composition. Also, particulates come in a range of sizes with the largest being around 10 microns in width and the smallest less than a thousandth of that size. Monitoring the range of particle sizes is difficult, but essential, because particle size largely determines the atmospheric behavior of particles as well as their ability to penetrate deep into sensitive lungs. Other difficulties are that some kinds of particulates have natural sources and particles can be transported for hundreds or thousands of miles.
The Pittsburgh Air Quality Study was designed to address these issues. A collection of state-of-the-art instruments from around the country was assembled to measure every possible characteristic of Pittsburgh’s PM and has done so for a bit more than the past year. The timeline of measured characteristics such as particle sizes, composition, numbers, and mass will be compared against hospital admissions to provide clues about which kinds of particles are most harmful. This data set will also be used to understand what sources contribute most to PM concentrations in Pittsburgh and the surrounding region. Because many parts of the Midwest and Northeast are expected to violate the new PM2.5 standard, knowing the main sources is necessary to formulate effective control strategies. Historically, control strategies have focused on reducing sulfur dioxide emissions because its atmospheric product, sulfate, is a principal component of PM. Paradoxically, research at Carnegie Mellon has shown that, because of the complexities of PM chemistry, many times such emissions reductions do nothing to reduce PM levels or may even lead to slightly increased concentrations. A final goal is to evaluate the instruments used to monitor PM levels across the country and to develop a new generation of instruments. Some of the new instruments being tested at the Supersite provide measurements on a nearly continuous basis (traditional techniques give only one measurement per day) and greater information about the chemical composition of PM. One monitor can even sample individual particles.
Over the past year, most of the effort at the Schenley Park Supersite has been put into making measurements. Data collection activities will be completed this fall, but analysis of the data will continue for several years. However, some preliminary findings are already available. It is becoming clear, for example, that the standard monitoring techniques give measurements that are systematically too high under certain conditions and too low under others. Another interesting finding is that, even in the heart of Pittsburgh, much of the particulate matter comes from outside Pennsylvania, pointing to a regional problem that will require the cooperation of several states to solve. So, while the little trailer in Schenley Park may not be pretty, it is helping to understand a class of air pollutants that are a serious threat to people’s health. What is more, the trailer will be gone and the site restored to its original condition by the end of the year.
More information about the Pittsburgh Air Quality Study can be found online at http://homer.cheme.cmu.edu.