|In May, in a two-to-one split decision, the U.S. Circuit
Court of Appeals for the District of Columbia declared parts of the Clean Air Act
unconstitutional. The decision could jeopardize implementation of the Environmental
Protection Agency's 1997 air quality standards, which are based on health effects and
include standards for particles only 2.5 micrometers in size. Yet the court also stated
that "evidence demonstrating a relationship between fine particle pollution and
adverse health effects amply justifies establishment of new fine particle standards."
Thus it seems unlikely that national standards for fine particulate matter will be delayed for long. In June, EPA Administrator Carol Browner testified before Congress: "We stand by these standards. We stand by the science. We stand by the process."
At Berkeley Lab, Lara Gundel of the Environmental Energy Technologies Division (EETD) emphasizes that "there are lots of unanswered questions about how particulate matter affects health," and she is busy developing and implementing a means to help answer some of these questions.
"Particle size is one factor," she says, "but particles are of very different kinds -- acid droplets, metals from incinerators, toxic compounds from gasoline and diesel fuels, soot from unburned fuel, and many others."
Moreover, many pollutants exist in both particle and gas phases, including polycyclic aromatic hydrocarbons, which are ubiquitous in urban areas because of sources such as vehicle exhaust, and pesticides which abound in agricultural areas.
"A major scientific problem has been getting good measurements of the partitioning of these chemicals between the gas phase and airborne particulate matter. Here at the Lab, we have the tools to answer these questions." These tools include some of the most advanced and versatile in the field, which is one reason why the EPA has kept Gundel busy as an expert on sampling.
The tools are available because 10 years ago Gundel, her colleague Joan Daisey, head of EETD's Indoor Environment Program, and their associates began addressing similar problems in studies of indoor air quality. "We had a special interest in the physical and chemical characteristics of second-hand tobacco smoke," she says. "Tobacco smoke is an aerosol that dries fast. We realized we didn't know much about its gas-particle partitioning, and we needed a way to measure it."
Gas and particles are deposited differently in the lungs and have different physiological effects. According to Gundel, the partitioning, over time, of the phases of a semivolatile organic substance such as nicotine "has thrown a monkey wrench into many measurements" aimed at determining health effects.
Most phase measurements have been made by trapping solid particles on a filter and then collecting gases from underlying adsorbent beds. The filter itself, however, can absorb gases, and the particles may give up gases after they are trapped; both vaporization and condensation effects can thus lead to errors.
That's why Daisey suggested that Gundel and her colleagues in the tobacco study use a "denuder" -- a device that traps gas and allows particles to be collected separately. Denuders are not commonly used with organic chemicals but, Gundel says, "as soon as Joan mentioned a diffusion denuder, I said, `I know how to do that,' and I vizualized the solution. It was a leap of faith."
Her idea was to use sticky resin beads whose pores were the right size to trap molecules of organic gases -- small enough to adhere through friction alone to the sand-blasted inner surface of a glass tube.
"Solid particles are relatively massive and travel straight through the denuder," Gundel explains. "The gas molecules are moving all over the place, like toddlers; eventually they hit the wall and stick. The trick is to calculate the airflow and the length of the tube -- to make it short enough so the particles stay airborne but long enough for the gas to get trapped."
After an air sample is sucked through the denuder, the particle filter is removed and the gas trapped on the resin beads is analyzed.
Gundel had a working model of a denuder, which she later named the Integrated Organic Vapor/Particle Sampler, or IOVPS, built for the tobacco-smoke study. "We tried it in a room-sized chamber that held smoke from a single cigarette. In about 30 seconds we knew it was going to work."
Gundel refined the IOVPS as part of a successful Cooperative Research and Development Agreement with URG Corporation in North Carolina, increasing the denuding surface and designing new features for collecting vapor subsequently released from trapped particles. A few years ago a Canadian researcher, Douglas Lane of the Atmospheric Environment Service, collaborated with Gundel to modify the IOVPS for much higher flow rates and continuous operation -- up to 48 hours at time -- which would allow it to be used for testing the atmosphere outdoors.
The resulting Integrated Organic Gas and Particle Sampler (IOGAPS) comes in several sizes, the largest of which uses two denuder tubes with about 30 times the coated area of a single-channel IOVPS.
Groups around the country have employed this sampling technology in studies of semivolatile organic compounds. Among these have been investigations of the atmospheric behavior of dioxins and the contribution of diesel, other vehicle exhausts, and wood smoke to smog formation -- all under different weather conditions, in different parts of the country, and at different times of the day or night.
The EPA recently tested various air-sampler designs in cities throughout the country. As a kind of control for this test, the denuders were installed on what Gundel calls "old pieces of sampling equipment taken out of mothballs. The denuders are fitted on them like nozzles on vacuum cleaners." Air samplers with denuders got better results than samplers without, and now the IOGAPS devices are being used in other field studies in Seattle, Nashville and Atlanta.
Gundel has also been testing "vacuums" with denuder "nozzles" for other interesting applications, such as cleaning the air in buildings. And to serve a wider range of uses, Gundel and her associates are evaluating various denuder designs -- some durable and pricey, others lightweight and based on common products available in hardware stores. A patent for the IOVPS technology was awarded in 1998, and Gundel and her associates are actively seeking licensing partners through the Lab's Technology Transfer Department.
Already researchers armed with Lara Gundel's resin-coated denuders are finding out exactly what's in the air -- and in what phase -- all over the nation.