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On a Clear Day You Can See Foreverby |
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On a Clear Day You Can See Foreverby |
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December 5, 1952, dawned clear and cold in London, England. The air was damp and stagnant. Heavy black smoke rose from chimneys as Londoners lit the coal they burned to cook and heat their homes. Fog began to roll in. By dusk, the smoke-filled fog had turned an impenetrable yellowish black.
By the time the smoky fog lifted four days later, 2,000 Londoners were dead of heart and lung complications. Another 2,000 died during the following two weeks, as the persistent health impacts of the five-day fog continued. When researchers compiled statistics, they estimated that during the next two months, 8,000 more died of causes directly related to that deadly fog.
The culprit in London’s killer fog wasn’t the fog itself. It was thousands of tons of tiny particles that clung to the stagnant fog and filled residents’ lungs. Thick soot from the city’s coal-burning home hearths, diesel buses, and factories hung near the ground, trapped by a slow-moving temperature inversion. Black smoke concentrations measured during those five days reached more than 50 times normal levels.
For hundreds of years, Londoners have experienced discomfort related to particles in smoky fog (dubbed smog in 1905). Recently, it has become clear that those fine particles are more than uncomfortable.
The most serious effects of small particles are associated with aggravation of heart or lung disease. Numerous studies have related particles in the air to increased hospital admissions, emergency room visits, and mortality. Aggravation of lung diseases, including asthma attacks and acute bronchitis, has been correlated with short-term exposure. In people with heart disease, particles have been linked to heart attacks and irregular heart rhythms.
According to Dr. Joel Schwartz of the Harvard School of Public Health, it’s not a small problem. By one estimate, 70,000 people in the U.S., primarily older adults, die prematurely each year when fine particle pollution increases to unhealthy levels. “This,” says Schwartz, “is larger than the death rate from breast and prostate cancer combined.”
Minnesota is a long way from the London of the 1950s—or even the troubled cities of the industrial northeast United States. It has its own unique problems with smoke-related pollution, however, as documented in the following article.
The following material is excerpted from “Out of a Clear Blue Sky: Regional Haze Mars Scenic Vistas, Even in Minnesota” by Ralph Pribble, Minnesota Environment, Summer 2003, Vol. 3(3), p. 10.
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Figure 2. A Forest Service IMPROVE automated monitoring station just outside the BWCAW shows the distinct difference between a clear day (more than 125 miles visibility, above) and a hazy one (less than thirty, below). Photos: USDA Forest Service |
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Air pollution affects not only urban areas, but national parks and wilderness areas as well. On bad days, “regional haze” cloaks some of the United States’ most treasured “purple mountain majesties” in brown or white gauze. Many of the 280 million Americans who each year visit parks such as the Grand Canyon or Glacier National Parks are surprised to find they can’t get a clear view of the scenic wonders they have come to see.
The cause might surprise outdoor enthusiasts. It is fine particles similar to those that blight our urban skies. Some haze is natural, part of prevailing climate dynamics. After all, the Great Smoky Mountains were known by that name long before the mid-South industrialized. Dust, organic compounds, smoke from forest fires, and humidity figure into what is considered natural (unpolluted) visibility.
In pre-settlement days, the farthest a person could expect to see on a clear day was between 110 to 115 miles in the Western U.S., and 60 and 80 miles in the East. Today, however, typical visual range in the West is 60 to 90 miles. In the East, it’s only 15 to 30 miles. The culprit in this deterioration appears to be human activities.
In 1999, the U.S. Environmental Protection Agency (EPA) issued regulations designed to further reduce haze and protect visibility, as well as specific programs to reduce particle air pollution overall. For example, the U.S. Department of Agriculture National Forest Service’s IMPROVE (Interagency Monitoring of Protected Visual Environments) network collects air samples and provides monitoring data on visibility and fine particulates at 163 Class I locations, including Voyageurs National Park and the Boundary Waters Canoe Area Wilderness (BWCAW), both located in northern Minnesota.
The equipment at IMPROVE sites includes automated samplers to measure airborne particles and particle mass, along with light-monitoring equipment and a camera. According to Trent Wickman of the Forest Service’s Duluth office, “The contributions of pollutants at the [BWCAW] are clear. A large portion is ammonium sulfates, which are pretty clearly tied to coal combustion.” He added there’s not sufficient data yet to provide trend analysis, but that “we’re getting to that point.”
Regardless of their source, trying to describe fine particles is like trying to describe animals to someone from another planet. Just as animals can be large or small, feathered or furred, dangerous or benign, particles can be varying sizes, solid pieces or liquid droplets, man-made or natural, dangerous or benign.
Some particles are emitted directly into the air, and some form in the air from chemical reactions of nitrogen oxides, sulfur oxides, volatile organic compounds, and ammonia. Particles can cling to moisture droplets or simply drift in the air. Scientists call particles “particulate matter,” abbreviated PM. Regulators generally divide particulate matter into two categories on the basis of size: PM10 and PM2.5.
Date Posted: 05/09/05 nas
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