Blame growing view-blocking pollution haze in the Great Smoky Mountains and Shenandoah national parks in the 1980s on increased sulfur dioxide emissions from nearby sources, say researchers from the University of California, Davis. And credit a recent change toward improved views during the past three years to reduced sulfur dioxide emissions from several power plants -- although it's too early to tell if this is a reversal of the trend toward hazier skies -- says Thomas Cahill, head of the UC Davis Air Quality Group and professor emeritus of physics and atmospheric science.
Cahill will present a new analysis and data linking regional haze in eastern national parks with nearby emissions on Monday, June 24, at the Air & Waste Management Association annual meeting in Nashville, Tenn. The meeting is believed to be the largest annual gathering of air pollution and waste-management environmental professionals in the country, representing industry as well as federal and state regulatory agencies.
The new study also answers lingering questions about a key scientific assumption behind the 1990 Clean Air Act amendments -- that air quality will improve in proportion to reduced emissions.
"There's no substitute for removing the problem at the source," Cahill says.
Minute particles of sulfate have been the main culprit robbing the eastern scenic areas of their stunning views. Almost all sulfate originates as sulfur dioxide emissions from coal-burning power plants and other industrial sources.
"A large part of the U.S. population lives under a sulfate haze every summer," Cahill says. "Anybody can see it. It does not require a professor. You cannot hide the haze."
Increased regional affluence and rapid growth of whole-house air conditioning (from 27 percent to 38 percent during the 1980-90) apparently skewed the electricity demand toward greater summer sulfur dioxide emissions from power plants, Cahill speculates. During particularly bad summer episodes, typically several weeks in July and August, the regional haze peaks with higher electricity demands for air conditioning during especially hot, humid days -- the same weather conditions that maximize the conversion of sulfur dioxide gas into the tiny sulfate particles that scatter and reflect light and muddy distant images.
After escaping from smokestacks, invisible sulfur dioxide molecules can transform into much larger, view-busting sulfate molecules, especially in humid regions. Sulfate also is a main ingredient in acid rain.
The new analysis confirms that the East has been steadily losing its struggle to maintain postcard-perfect views of favorite summer vacation spots, even though U.S. sulfur dioxide emissions have been decreasing slightly. From 1982-1992, summer sulfate hazes in Great Smoky Mountains National Park, Tenn., soared almost 40 percent. Air quality in Shenandoah National Park, Va., was even worse. Summer concentrations at the eastern sites peaked in 1990 and 1991 and have began to level off or drop.
In addition, the study answers some puzzling questions raised by the same research group. Two years ago, Cahill and his colleagues published the first study of its scope to track seasonal trend in haze-producing sulfates over large regions of the United States. The study was based on 12,000 samples collected at the more remote -- and presumably the most pristine -- areas of the country from 1982-92 as part of an interagency research program to preserve visibility at national parks and monuments.
According to the 1994 UC Davis study, published in the international journal Atmospheric Environment, there were dramatic reductions in atmospheric sulfates at some western sites, presumably because of a sharp decrease in local sulfur dioxide emissions. Yet, sulfate levels rose in the east, just as dramatically in some cases, despite a gradual reduction in sulfur dioxide emissions. The results raised the question, if national sulfur dioxide emissions were decreasing, why weren't eastern views improving proportionately?
The unanticipated findings generated considerable comment in scientific literature and motivated other studies challenging the results. So, Cahill and his colleagues reanalyzed their original samples (archived at UC Davis), double-checked their statistics, added two more years of seasonal data, conducted two summer studies for the National Park Service at the Great Smoky Mountains, and expanded their analysis to look for possible causes for the increased eastern haze.
Using emissions data from the Tennessee Valley Authority as a representative sample of regional power plants, Cahill and his colleagues found that regional sulfur dioxide emissions increased proportionally with summer sulfate haze in the 1980s. But recently, summer sulfate levels have held steady at Shenandoah and dropped by roughly 30 percent at Great Smoky Mountains. In 1994, the large TVA Cumberland power plant was efficiently "scrubbed," reducing annual sulfur dioxide emissions from roughly 200,000 tons a year to 20,000 tons a year. Because this plant used to spew forth 1 percent of the total U.S. sulfur dioxide emissions, Cahill speculates that this control effort already has reduced summer sulfates at Great Smoky Mountains and other sites in the Appalachian Mountains.
"Since sulfates annually average over half of all fine mass at Great Smoky Mountains, and since the close association between sulfates and visibility has been demonstrated, we can expect future improvements in visibility," he says.
In previous studies in the western United States, the UC Davis Air Quality Group has found similar reductions in regional sulfate levels with reduced or eliminated sulfur dioxide emissions from nearby sources. The air over public lands has special visibility protection. When it revised the Clean Air Act in 1990, Congress mandated sulfur-dioxide emission controls, believing the visibility problem, as well as the acid rain problem, would decline in proportion to the reduced emissions. The new UC Davis study suggests that it may, indeed, be that simple.
The data come from a fine-particle monitoring network based at the UC Davis Crocker Nuclear Laboratory. Funded by a small grant from the Environmental Protection Agency, the UC Davis network began with three sites in Utah in 1977. The UC Davis program has grown into an ad-hoc international network involving 17 countries, yielding valuable new information for global climate research. The UC Davis group's archive of air samples now numbers close to 100,000. Techniques and protocols developed by the UC Davis team have been adopted by the United Nations' new Global Atmospheric Watch program.
The latest analysis was supported by the Interagency Monitoring of Protected Visual Environments, the National Park Service and UC Davis. Background: 1996 Eastern Haze Trend Analysis Air Quality Group Crocker Nuclear Laboratory University of California, Davis 21 June 1996
Major Findings
Sulfate increases in eastern national parks can be quantitatively linked to regional sulfur dioxide emissions. The study also confirms that, as sulfur dioxide emissions are lowered, sulfates will also decline and visibility will improve.
Significance
When Congress revised the Clean Air Act in 1990, it mandated sulfur controls in hopes of cleaning up the acid haze in proportion to the emission reduction. This study suggests that sulfate haze trends are explained by sulfur dioxide emissions, confirming the science behind the 1990 legislation.
The study also shows the importance of continuing consistent long-term monitoring programs. Such trends could not be determined before from shorter term studies because of the typically big annual swings in weather patterns, seasonal emission patterns, and multiyear meteorology cycles.
About Sulfates
Individual sulfate particles in the air are so small they cannot be seen even by the standard microscope, but the human eye can easily see the combined effect of many sulfate particles. Sulfate aerosols cloud scenic views in two ways -- by scattering the light coming through the haze, muddying distant images, and by reflecting light back to the eye like bright headlights in dense fog. Sulfates also are a main ingredient in acid rain. Procedures and The UC Davis researchers employ consistent research methods and Equipment good quality control to ensure accurate comparisons of the 12,000 air samples analyzed for the study.
The air sampling units developed at UC Davis collect air particles so small they cannot be seen by a standard microscope (smaller than 2.5 microns). During the decade, two additional filters were added to each sampler to measure carbon and nitrates. Two 24-hour samples are collected each week from the units and shipped through U.S. mail to UC Davis. There, a team of research staff and students weigh the filters using a machine called an electromicrobalance, which is sensitive to .0000001 gram. Using a laser, they measure how dark the filters have become. Then, using a device known as a particle accelerator or cyclotron, they precisely measure the quantity of many elements, including sulfur, that have accumulated on the filters. The non-destructive test is called the Particle-Induced X-ray Emission (PIXE).
The group developed another specialized test to measure hydrogen. To measure nitrates and carbon, two important air pollutants, they send the filters to other labs, but the UC Davis researchers are responsible for quality assurance of all six measurements.
Program History
The Clean Air Act of 1977 designated most U.S. national parks and wilderness areas as class I visibility areas, where visibility must be protected. It gave the monitoring responsibility to federal land management agencies. From 1979 to 1981, UC Davis monitored remote sites for the Environmental Protection Agency. In 1982, the National Park Service expanded its visibility monitoring program by adding the UC Davis small-particle samplers and analyses into a national network extending coast to coast. In 1988, the UC Davis particle-monitoring network expanded again, becoming part of the Interagency Monitoring of Protected Visual Environments (IMPROVE), a cooperative program involving the NPS, EPA, Forest Service, Bureau of Land Management, Fish and Wildlife Service and more.
The UC Davis Air Quality Group now analyzes air quality at more than 100 remote sites for IMPROVE, NPS and other government agencies. Recently, the UC Davis program has grown into an international network involving 17 countries, yielding valuable new information for global climate research. The UC Davis group's archive of air samples now numbers close to 100,000. Last year, techniques and protocols developed by the UC Davis group were adopted by the United Nations' new Global Atmospheric Watch program.
The Cyclotron
The technical centerpiece of the UC Davis air quality testing program is a particle accelerator constructed from parts salvaged from a pioneering cyclotron built at UC Berkeley in 1939, once used to discover plutonium, which powers atomic bombs, and other elements. Ensconced at the UC Davis Crocker Nuclear Laboratory since the mid-1960s, the particle accelerator now works on such projects as measuring U.S. and global air-quality trends, authenticating important but fragile historical documents, researching new methods of preserving foods, and assisting with medical treatments. To measure various aspects of air quality, the cyclotron generates fast-moving protons that zaps the filter and excites the atoms, which release energy in the form of X-rays as they relax back to their former states. Each element gives out a characteristic X-ray, a sort of "fingerprint." The researchers count up the energy readings to find the composition of the air sample. The technique is accurate and relatively inexpensive.