|Climate Protection and the National Interest (WRI, 1997, 56 pages)|
Although U.S. policy-makers have long recognized the public health threat of air pollution, they have often overlooked links between air pollution, energy security, and climate change. As Figure 7 shows, much of the air pollution in the United States arises from fuel burning in transportation, power plants, and buildings. (Air pollution from the burning of fuels is indicated by the black and white portions of the bars.) By far, most of the carbon monoxide, nitrogen oxide, and sulfur oxide emissions come from fuel burning.
According to the Environmental Protection Agency (EPA), about 80 million Americans live in areas where at least one federal air pollution standard was exceeded in 1995.39 Over the past 25 years, EPA and the Congress have devoted huge resources to combating this pollution and have made remarkable progress in reducing emissions to levels below historical trends. Yet, economic and population growth continually increase the number of energy (and hence pollution) sources and the number of people exposed to pollutants. Moreover, pollution controls deteriorate over time. As a result of both growth and deterioration, EPA expects emissions of carbon monoxide, nitrogen oxides, volatile organic compounds, and small particles to begin rising again.40 Only sulfur oxide emissions are projected to continue their long-term downward trend, the result of a congressionally mandated absolute limit on utility sulfur emissions.
Examples of the energy-pollution-climate connection abound. Sulfur dioxide (SO2) arises mostly from coal-burning electric-power production and is a serious air pollutant that contributes to acid rain. While in the atmosphere, SO2, with the help of moisture and other air pollutants, leads to the formation of small aerosols that have a regional cooling effect, offsetting some of the global warming by scattering sunlight back into space and by helping to form clouds that reflect sunlight. Conversely, ground-level ozone is both a harmful pollutant that arises mostly from fossil-fuel burning and a significant greenhouse gas that contributes to global warming. Carbon monoxide, a hazardous air pollutant given off by motor vehicles, is removed from the atmosphere by chemical reactions that have the effect of increasing concentrations of methane, a powerful greenhouse gas. Nitrous oxide (N2O) is a greenhouse gas and stratospheric-ozone depleter that arises, in part, from the use of catalytic converters that reduce motor vehicle air pollution emissions.41
Air pollutants can be roughly grouped according to their sources. Sulfur dioxide (SO2) pollution arises mainly from coal burning in power plants, while carbon monoxide and ozone (the principal chemical in smog) arise mostly from the emissions of cars, buses, and trucks. Nitrogen oxides (NOx) and small-particle pollution come from both motor vehicles and fuel-burning power plants; NOx contribute to both smog and acid deposition. Small particles from fuel burning, industrial processes, transportation, and other sources present serious health risks partly because they can penetrate deeply into the lungs. According to EPA, fugitive dust from roads and construction are a large source of PM2.5 emissions (particles with diameters less than 2.5 millionth of a meter), accounting for nearly 36 percent of primary releases. Home heating with wood is also a large source.42 Taking into account the small, secondary aerosols formed from utility SO2 emissions, power plants are the single largest source of PM2.5.
The chemicals involved in acid rain and smog pollution all occur naturally in the air. Sulfur dioxide, nitrogen oxides, hydrocarbons, and ozone all have natural sources such as volcanoes, lightning, and forest fires. The reason that emissions from human activities cause such pollution problems is that they are huge compared with natural emissions. In the United States, for example, sulfur dioxide emissions from human sources, almost all from fuel burning, are about 20 times natural sulfur emissions. Similarly, human-caused emissions of nitrogen oxides (essential for smog formation) are about 10 times natural emissions. With such high emissions, it should come as no surprise that we may be overwhelming natural sulfur and nitrogen cycles, causing health and ecological damage in the process.
Coal is the principal source of sulfur pollution in the United States and is an important source of small-particle air pollution. (Per unit of energy, coal also emits the largest amount of carbon dioxide.) Over the years, electric-power production has become the largest market for coal and the largest single source of SO2. A similar situation exists in parts of Eastern Europe and in China, where coal is the dominant source of power and is burned with few controls. In some parts of the world, especially in developing countries, SO2 pollution, primarily from local, ground-level sources, poses significant health risks. In Western Europe and the United States, the sulfur problem primarily involves the impacts of sulfate particles rather than SO2 itself. These acidic substances adversely affect human health, aquatic systems, forests, monuments, and the regional climate.
Acid deposition has been recognized as an environmental threat since at least the 18th century. The deleterious effects of acid rain on sensitive lakes, forests, soils, and ecosystems have been scientifically documented for more than 30 years. Of long-term concern is the leaching by acids of nutrients from soils. Weakened by nutrient deficiency, trees succumb to combinations of such natural stresses as insects, diseases, wind, drought, and ice storms. Studies suggest that despite the reductions in sulfur emissions required by the Clean Air Act there is still a long-term threat to some forests from the leaching by acid rain of nutrients from the soils and, potentially, from the input of excessive nitrogen.43
The effects of acid deposition go beyond damage to soils, trees, aquatic systems, and man-made structures. Recent studies (1994) show that acid rain is causing the decline of several species of songbirds in Europe.44 In the Netherlands, researchers found that up to 40 percent of certain song birds were laying defective eggs as a result of too little calcium. The birds eat certain snails that were declining because the soils lack calcium, a result of leaching by acid rain. When forests were treated with lime, the snails came back and the egg-thinning problem disappeared.
The reason that emissions from human activities cause such
pollution problems is that they are huge compared with natural
Ozone and photochemical smog result primarily from chemical reactions involving organic compounds (VOCs) and nitrogen oxides (NOx) in the presence of sunlight. VOCs and NOx arise from fuel combustion and from industrial and other sources. The ozone (smog) problem is of special concern for several reasons. The problem is widespread and appears likely to be long term. In 1995, 71 million Americans were living in areas where the ozone air quality standard was violated. And according to EPA, the current standard is not adequate to protect public health. Persons exposed to ozone suffer eye irritation, cough and chest discomfort, headaches, upper respiratory illness, increased asthma attacks, and reduced pulmonary function.
Crops and, indeed, all vegetation are damaged to some extent by ozone. Current ozone concentrations cause losses in crop productivity estimated at 5 to 10 percent45 and annual crop damages are estimated as high as 5 billion dollars. Many studies have demonstrated that photo-chemical pollutants damage forest ecosystems. Ozone has been shown to be the cause of major declines among pine trees (ponderosa and Jeffrey pines) in California and may be responsible for reduced forest productivity in many U.S. locations.46 Ozone also attacks various manufactured materials such as rubber.
Carbon monoxide (CO) has no known direct adverse impact on the environment though it can affect chemical reactions in the atmosphere, indirectly augmenting global warming. In 1995, about 85 percent of U.S. CO emissions came from fuel burning, more than 80 percent from motor vehicles. Indeed, over 90 percent of all human-caused CO comes from transportation sources.