Guest Lectures

Spacious Western skies still obscured by pollution

By Mike Hannigan and Jana Milford
December 29, 2002

Everyone knows the terms "Western movie," "Western wear," "Western art," and heaven knows, "Western real estate."

It's time to shift some of our attention to the term, "Western air." Our vision of the West is exactly that: a vision. Our dreams for the West rise from a vision of open spaces under clear, dazzling skies, and this vision is inexorably linked to the quality of our Western air.

When asked to be part of the University of Colorado Chancellor's Community Lecture Series titled "Healing the West," we thought, "Why not Western air?" When we started to think about what we'd say in our lecture, we realized that we had better give the attendees the knowledge to answer a few basic air-pollution questions. We are teachers, after all, and the more Westerners know about the air they're breathing and looking at, the better.

For those who didn't attend the lecture, we'll present this as an interview: the Western public is asking the questions and we, two air-pollution researchers from the local ivory tower, are answering.

Q. We heard that Denver is now in compliance with federal air-pollution standards. So, can we stop worrying about air pollution?

A. No. Keep worrying.

Here's why. In August 2002, Denver became the first major metro area to reach the goal of "attainment." The EPA defines attainment as compliance with the federal standards for the six "criteria pollutants" designated by the Clean Air Act (lead, sulfur dioxide, nitrogen oxides, ozone, carbon monoxide, and PM10 — particulate matter with a diameter less than 10 microns; there are 10,000 microns in one centimeter). The federal government regulates these pollutants because they are ubiquitous and can cause adverse human health effects.

Each pollutant has unique origins and patterns of distribution. Sulfur dioxide itself has never posed a regulatory problem in Denver. Since lead was removed from gasoline in the mid-1970s, very few urban areas have had lead problems. In the 1970s, carbon monoxide concentrations in Denver regularly exceeded the standard. As the passenger-vehicle fleet has changed from no vehicles with catalytic converter technology in the early 1970s to almost all vehicles with catalysts in the late 1990s, carbon-monoxide emissions have plummeted, and Denver has not exceeded the carbon monoxide standard since 1995. PM10 has been a regular problem for Denver, but currently Denver is staying below the standard. The primary reason for the improvement is the reduction in street sanding during the winter.

So why can't we stop worrying? First, we remain on the edge of the ozone standard, and we have seen no reduction in ozone levels.

Second, some pollutants can endanger health even while registering below the standard. The newest criteria pollutant, PM2.5, particles with a diameter less than 2.5 microns, is a perfect, if unhappy, example. This pollutant could have acute and chronic health effects, even when it registers well below the federal standard. PM2.5 has received much attention (from experts, but it behooves the public to pay attention too) because of these adverse effects.

In a recent article in the Journal of the American Medical Association, Arden Pope and colleagues found the increased chronic health risk associated with typical U.S. urban PM2.5 levels to be comparable to the health risks associated with being moderately overweight. (Denver currently meets the new federal standard for PM2.5, and with limited information, we would be hard pressed to report an annual trend.)

And, third, we need to keep working on the problem of visual air quality in national parks and wilderness areas, and in cities like Denver. The brown cloud is still looming over us, after all.

Q. Wait a minute, if Denver is in compliance with federal standards, why can we still see the brown cloud?

A. The federal government does not regulate Denver's visibility problems. The state created its own visibility standard in the early 1990s based on public definitions of acceptably clean air. This "standard" is really just a "goal," and it carries no penalty for violations. Denver violates the visibility standard roughly half of the time, and this has been more-or-less constant since Denver began measuring this 11 years ago. Just placed on the EPA-generated criteria pollutant list in the past five years for health reasons, PM2.5 is also the principal cause of the poor visibility. Since this is a newly regulated pollutant and Denver is in compliance with the federal health standard, there has been no regulatory pressure to reduce the airborne levels.

Q. What's up with visibility in the national parks? Are the pollutants that affect visibility there the same ones that exacerbate asthma in urban areas?

A. Yes. PM2.5 causes most of the visibility reduction in the national parks and is linked with several adverse health effects in urban areas. You might detect a trend here: PM2.5 is our big challenge. Usually, these particles are generated during combustion, or created by chemical reactions in the atmosphere involving gases from human-caused combustion and natural sources. The dominant sources of PM2.5 in the national parks and wilderness areas include power plants, biomass burning, motor vehicles, and natural emissions. Some of these sources are located in the parks and wilderness areas, while others are as distant as several states upwind. The dominant sources of PM2.5 in urban areas include gasoline-powered vehicles, diesel vehicles, road dust, power plants, wood burning, and food cooking. In Denver, sources associated with vehicle use contribute more than half of the total airborne PM2.5.

Q. Is visibility in national parks and wilderness areas improving or getting worse?

A. The picture is mixed. In recent years, the clearest days have gotten a little clearer but the worst days are unchanged. Again, PM2.5 causes most of the poor visibility. The federal government has begun to tackle this problem. In 1999, the EPA issued new Regional Haze Regulations, calling for states to design and implement programs that will return the air in national parks and wilderness areas to natural conditions in 60 years. Opponents are challenging these regulations, and they may be in the courts for a while. In any case, the key to visibility improvement will be the reduction of PM2.5 from power generation, biomass burning, and motor vehicles.

Q. Won't it be hard to restore visibility in scenic areas to natural conditions?

A. You bet. The definition of "natural conditions" is a subject of debate. The National Park Service estimates that we will need to reduce sulfate PM2.5 (primarily emitted from power generation) by 90 percent, organic PM2.5 (from biomass burning, natural processes, power generation and motor vehicles) by 25 percent, and soot PM2.5 (from motor vehicles, biomass burning, and power generation) by 90 percent. Experts project that total energy use in the West will increase by 30 percent in the next 15 years. Thus, to meet national goals for visibility improvement, we either need to reduce energy consumption so that those projections are not realized, or drastically reduce the amount of pollutants produced per unit of energy generated.

Q. OK, so we've made progress and, in terms of many pollutants, our Western air is cleaner now than it has been. Where do we go from here?

A. We still have big challenges in front of us: ozone in metropolitan areas and PM2.5 everywhere. If clear vistas and healthy air are part of our vision for the West, we need to send strong signals to public officials that we want these values protected. The goals of reducing PM2.5 and ozone and improving visibility in the West challenge government, industry and all of us as consumers to find cleaner power and transportation systems, and to use energy more efficiently. Wouldn't this be a great contribution to healing the West?

Mike Hannigan is a research associate and adjunct professor and Jana Milford is an associate professor in the Mechanical Engineering Department at the University of Colorado. They specialize in the study of air pollution. Both are involved with the Center of the American West.