Our Children At Risk



Clean air is a delicate balance of nitrogen and oxygen, with small amounts of argon, carbon dioxide, neon, helium, and other gases. Unfortunately, pollutants are altering this mixture by adding myriad ingredients which alone and in concert pose health risks to everyone who breathes the air, particularly children. In fact, children represent the largest subgroup of the population susceptible to the effects of air pollution. Over the last ten years, a considerable number of scientific studies have reported adverse health effects associated with air pollution. The effects have ranged from respiratory symptoms and illness, impaired lung function, hospitalization for respiratory and cardiac disease to increases in mortality.

A recent study estimated that approximately 64,000 people in the United States die prematurely from heart and lung disease every year due to particulate air pollution -- more people than die each year in car accidents. Among children, air pollutants are associated with increased acute respiratory illness, increased incidence of respiratory symptoms and infections, episodes of longer duration, and lowered lung function.

Asthma, the most common chronic disorder of childhood, is on the rise in the United States and in other industrialized nations. During the 1980s, the prevalence of childhood asthma increased nearly 40 percent. Many different factors have been associated with asthma, including genetic makeup, environmental tobacco smoke, dust mites, cockroach allergens, and air pollution, both indoor and outdoor. Several studies have linked ozone and particulate air pollution with exacerbations of asthma in children afflicted with the disease.

Due to their greater respiratory rates, children breathe a proportionately greater volume of air than adults. As a result, children inhale more pollutants per pound of body weight. They also spend more time engaged in vigorous activity than adults. In addition, because of young children's height and play habits (crawling, rolling) they are more likely to be exposed to pollutants or aerosols that are heavier than air and tend to concentrate in their breathing zone near ground level. Children's physiological vulnerability to air pollution arises from their narrower airways and the fact that their lungs are still developing. Irritation caused by air pollutants that would produce only a slight response in an adult can result in potentially significant obstruction in the airways of a young child.

The harm caused by air pollutants has been recognized by medical scientists, government officials, and the public for some time. Historic air pollution disasters -- Meuse Valley, Belgium in 1930, Donora, Pennsylvania in 1948, and London, England in 1952 -- in which large numbers of people fell ill and died, have been clearly associated with high concentrations of particulate and sulfur dioxide pollution. Such acute air pollution episodes have killed children because of their heightened susceptibility to the damage that can be done by air pollutants.

Existing stationary sources of air pollution include coal combustion for power production, oil refineries, and industrial manufacturing facilities. Additional sources of air pollution have emerged; today automobiles are a major polluter of the air: Americans drive some 150 million private cars and nearly 50 million buses and trucks. The exhaust from these vehicles contains nitrogen oxides, and other ozone precursors, particulate matter, and carbon monoxide -- all deleterious to health, even in small quantities. Also of importance in vehicle exhaust are toxic organic compounds including formaldehyde, acetaldehyde, and benzene. And, even though new cars start out far cleaner than the cars of decades ago, we drive them far more and they fail to remain clean as they age.

To protect citizens, the federal government began setting standards for ambient air quality as early as the 1950s. In 1970, Congress passed the Clean Air Act, the first major national law for air pollution control throughout the United States. This Act, amended in 1977 and 1990, requires the EPA to establish national health standards for ambient air pollutants and to assure that states adopt effective programs for attaining these standards. The most successful parts of the Act, such as the acid rain program, the ozone depletion program, and the introduction of emission standards for automobiles and the reformulation of fuels, established very specific federal standards. Yet these standards are not enough. In 1995, about 127 million Americans -- half of the nation's population -- lived in regions with air quality that did not meet federal standards for certain pollutants. Based on U.S. Census Bureau estimates of the population by age group, 18 million children under the age of ten lived in these "nonattainment" areas. The health risks from air pollution are greatest in these regions, and those at greatest risk include children.

Citizens must seek additional remedies to assure the health of their families in the face of increasing air pollution threats. Toward that end, this chapter describes scientific research on the health effects of air pollutants on children, suggested measures that concerned parents and others can take, and model programs of local solutions that have worked throughout the nation, as well as government reforms that should be supported.


Children: The Most Vulnerable Among Us

The nation has failed to protect its most precious citizens -- its children -- from the adverse health effects of air pollution. Emission reduction efforts and federal air quality standards have been insufficient to shield children from potentially serious health damage. Ozone and particulate matter are of special concern. In June 1993, the Committee on Environmental Hazards of the American Academy of Pediatrics stated that the federal standard for ozone in effect at that time contained "little or no margin of safety for children engaged in active outdoor activity." In July 1997, the EPA revised both the ozone and particulate matter air quality standards in order to protect children and other members of the population. The American Lung Association estimated that 27 million children under the age of 13 reside in areas with ozone levels above EPA's revised standard, and that two million children with asthma, or half of the pediatric asthma population under the age of eighteen, lived in these areas.


Cellular Damage

Even short-term exposure to low levels of pollutants can damage lungs at the cellular level. For instance:

  • Sulfuric acid compounds can interfere with the lungs' mucociliary clearance system, and ozone at levels below the pre-1997 federal ozone standards may hinder the immune system's ability to defend against infection.
  • Ozone exposure at levels below the pre-1997 federal standards contributes to persistent inflammation of airways, sometimes days after exposure ceases. Exposure to acidic aerosols may aggravate the effect.
  • Sulfur dioxide can induce bronchial constriction in asthmatics.
  • Even short-term ozone exposure increases lung cell permeability, which may hinder the body's ability to regulate the movement of gases and liquids between the lungs and the bloodstream. This effect potentially facilitates the body's uptake of inhaled substances and may promote enhanced allergic sensitization.

Reduced Lung Function

Lungs must inhale and exhale an adequate volume of air to remove carbon dioxide and replenish oxygen to maintain health, but studies show that even brief exposure to pollutants can result in impairment of lung function. These effects are generally temporary, but they are still of great importance, for two reasons. Chief among these is that the impairment of lung function may be a sign of invisible, sub-clinical damage inside the lungs, such as inflammation produced deep in the lungs from ozone, as discussed above. Though the impairment of lung function generally disappears after exposure, it may mask continuing cellular damage. Secondly, people whose lung function is already compromised may be unable to tolerate additional impairments caused by air pollution, however modest or temporary they might be. The medical literature shows that ozone, sulfur dioxide and sulphate aerosols, and airborne particulate matter affect lung function, and that chronic exposure to air pollutants can impair lung function permanently.

Respiratory Illness and Asthma

Breathing polluted air increases a person's chances for respiratory illness. Epidemiological studies show a significant correlation between exposure to air pollution and the frequency of respiratory symptoms -- ranging from cough symptoms to hospital admission.

Currently affecting at least 6 percent of American children, asthma is the number one cause of absenteeism for school children. During the 1980s, asthma incidence among children increased by nearly 40 percent. One study estimated the total costs -- both direct and indirect -- related to asthma in the young and old in 1990 to be $6.2 billion. Asthmatics suffer recurrent attacks of breathing distress caused by temporary inflammation and constriction of the airways. In many cases, asthma is caused by an allergic response that develops as a result of the airways becoming sensitized to one or several substances.

Common air pollutants, especially ozone, sulfur dioxide and particulate matter, present a challenge to asthmatics. A considerable body of scientific evidence links increases in levels of these pollutants to worsening of asthma (increased emergency room visits, increased medication use, increased hospitalization, and increased symptoms.) Some of the investigations reveal asthma exacerbations occurring at pollutant levels at or below the pre-1997 federal air pollution standards. In one case, hospital emergency visits rose by 37 percent on days when ozone reached hourly concentrations of 0.11 parts per million (ppm), which is below the pre-1997 federal standard.

Higher Mortality Rates

Research on mortality rates in heavily polluted areas reveals statistically significant links between high levels of air pollutants and increased numbers of deaths, primarily among the elderly. Particulates show the clearest link, and elevated death rates have been found even at particulate concentrations that are well below the pre-1997 federal health standards; death rates start to inch upward when particulates reach levels below the pre-1997 federal standard.

In December 1993, Harvard researchers published the results of a sixteen-year-long community health study that tracked the health of 8,000 adults in six U.S. cities with differing levels of air pollution. After adjusting for age and smoking, researchers found that residents of the most polluted city had a 26 percent higher mortality rate than those living in the least polluted city. This translated into a one- to two-year shorter lifespan for residents of the most polluted cities. Another major study corroborated these findings. The study correlated American Cancer Society data on the health of 1.2 million adults with air pollution data in 151 U.S. metropolitan areas. The study found that people living in the most polluted area had a 17 percent greater risk of mortality than people living in the least polluted city.

Long-Term Effects of Chronic Exposure

A variety of animal studies suggest that long-term exposure to air pollution damages lung cells. In one animal study, researchers found that low-level ozone exposure resulted in the progression of lung injury into structural changes. Acute inflammation in the animals' lungs evolved into chronic inflammation, with healing by a process known as fibrosis, or scarring that stiffens the lung and may make it less capable of efficient gas exchange.

Corresponding evidence from epidemiological research includes one study of humans who were exposed to elevated ozone levels over several days. Lung function loss persisted for a week after exposure, which suggested to researchers that cell death and inflammatory reactions were involved, not just reflex airway constriction.

Chronic exposure to air pollutants may reduce lung capacity. The most comprehensive study was performed on populations living in two different parts of the Los Angeles Basin. People living in the more polluted area had substantially worse lung function than when they were initially tested, and they showed a significantly more rapid deterioration of lung function over time. Chronic exposure to a mixture of air pollutants, as shown in this study, results in less rapid growth of lung function in children and a greater rate of deterioration in adulthood.

In addition, a lifetime of exposure to air pollution may lead to premature aging of the lungs. The aging process in the lungs, which occurs naturally throughout adulthood, is marked by increased deposits of scar tissue, and it may render the lung tissue less elastic and less efficient in delivering oxygen to the blood. Ozone is strongly implicated in the premature aging of lungs. For instance, research on laboratory animals shows that common ozone exposure can lead to a variety of changes in lung tissue, including changes in the structure of the cells that line the smallest airways, such as death of the ciliated cells that are critical in the lung's defense system against particles and bacteria, reduced ability to remove foreign material, inflammation, biochemical changes that suggest damage to tissues and greater permeability of the air sacs, and stiffening of the lung due to the formation of scar tissue.

An autopsy study performed on 107 young accident victims (fourteen to twenty-five years of age) in Southern California, most of them lifelong residents, showed evidence of lung disease. Though few had outward signs of breathing disorders when alive, the lungs of 104 of them showed early signs of chronic lung disease, including low-level bronchitis, chronic interstitial pneumonia, and an unprecedented rate of severe chronic inflammation of the respiratory bronchioles. While the results of this study are not definitive since the subjects were not screened for the use of tobacco or marijuana, one of the researchers commented that the subjects "had lungs of older people," saying that, "air pollution is highly suspect for a substantial contributory role."

Special Vulnerability of Children

During the last decade, hundreds of published reports have documented the effects of air pollutants on children, who are more susceptible than adults to the adverse effects of air pollution. Children's greater sensitivity is a function of both greater exposure to air pollutants and unique physiological susceptibility.

Greater Exposure and Susceptibility

Children breathe more air relative to their body weight and lung surface area than do adults; consequently, they also receive proportionately higher doses of air pollutants. Children spend more time outdoors, often during midday and afternoons when pollutant levels are generally highest. Children are three times more active than adults while outdoors, significantly increasing their oxygen demand and consequently raising their breathing rates.

Young children generally spend more time low to the ground by virtue of both their shorter stature and the nature of their typical physical activity. Children, therefore, experience greater exposure to pollutants emitted close to the ground, such as automobile exhaust and high-density pollutants brought downward by gravity. In addition, when the sources of air pollutants such as automobiles are close to playgrounds and other areas where children play, children and infants in strollers may be heavily exposed.

Children often fail to recognize the significance of respiratory symptoms such as coughing, wheezing, and shortness of breath, and they frequently fail to move indoors or curtail exercise during air pollution episodes. Children tend to breathe more through the mouth than through the nose due to their increased physical exertion, thus reducing the effectiveness of one level of filtration. In addition, young children's small noses are easily blocked by congestion, constriction, or other illnesses.

Children's airways have small diameters. Environmental irritants capable of obstructing air passages are more likely to do so in children than in adults. Early in life, children have far fewer alveoli than adults, creating less "reserve volume" from which to draw oxygen. They also have relatively less reserve surface area in their lungs available for times of stress or increased metabolic demand. In adults, air moves from one alveolus to another through holes in the alveoli and channels between the small airways and the alveoli, allowing air to be distributed deeply throughout the lung, circumventing obstructed areas. Infants and young children have few such pathways that provide for this restorative air drift.

Children at greatest risk from the effects of air pollution include: children with sensitized respiratory systems, such as allergic or asthmatic children, children who live near industrial pollution sources, areas of heavy traffic, or in homes with cigarette smokers, and children who lack adequate medical attention, nourishment, or sanitary living conditions.

Adverse Health Effects in Children

Data gathered by a researcher from a variety of recent studies reveals that air pollutants are associated with a wide variety of adverse health effects in children, including:

  • increased death rates in very severe pollution episodes and increased mortality risks for those living in highly polluted areas,
  • increased risk of acute respiratory illness,
  • aggravation of asthma, increased respiratory symptoms, and increased sickness rates (as indicated by kindergarten and school absences), and
  • decreases in lung function.

Increased Mortality Risk

The most serious effect of air pollution is death. Although the elderly are at greater mortality risk from air pollution, children are also susceptible. In the London air pollution episode in December 1952, mortality in children increased. A new study has found an association in the United States between particulate pollution and an increased risk of infant mortality. A recent report from S‹o Paulo, Brazil, indicated that death in children under the age of five due to respiratory diseases from 1990 to 1991 was positively associated with air pollution levels of nitrogen oxides. In the Czech Republic, the risk of respiratory mortality among infants increased in relation to worsening air pollution (particulates, sulfur dioxide, and nitrogen dioxide) after adjusting for socioeconomic factors. Researchers in Taiwan, China found a higher rate of infant mortality from sudden infant death syndrome (SIDS) at times of elevated particulate air pollution as measured by reduced visibility.

Increased Acute Respiratory Illness

Several studies indicate that air pollution is associated with increased acute respiratory illness, as measured by hospital admissions and other indices. Two epidemiological studies, conducted in central Utah, on the relationship between hospital admissions for respiratory illness and ambient air pollution found that admissions were strongly correlated with particulate levels, and that the correlation was especially pronounced in preschool-aged children. In one study, bronchitis and asthma admissions for preschool children were twice as frequent when the local pollution source (steel mill) was operating than when it was shut down. Another study in the same region also indicated that hospital admission for respiratory illness is strongly associated with particulate air pollution and that the association is stronger for children than adults. During months with peak particulate pollution levels, average hospital admissions for respiratory illness in children nearly tripled, whereas for adults comparable hospital admissions increased by 44 percent.

Similarly, researchers found that summertime hospital admissions in Ontario for children are associated with increases in ambient ozone and sulfate levels. Other researchers report that over a six-year period, respiratory admissions were closely associated with ozone levels at 168 hospitals in Ontario. They also showed that 15 percent of summer hospital admissions for infants were associated with air pollution, as compared with 4 percent of such admissions for elderly patients. Studies of hospital admissions in Toronto suggested that increases in ozone, sulfates, aerosol hydrogen ion levels, and particulate air pollution with a diameter of 10 microns or less (PM10) can all be directly correlated to increases in hospital admissions.

In a diary study of 625 Swiss children between birth and five years of age, respiratory symptoms were associated with particulate concentrations, while the duration of symptoms was associated with levels of nitrogen oxide. These symptoms included coughing, upper respiratory episodes, and breathing difficulty.

Another study compared the frequency of upper respiratory infections in Finnish children residing in a polluted city with that in children living in two less polluted cities. The researchers found a significant association between the occurrence of upper respiratory infections and living in an air-polluted area. The finding was consistent in both the fourteen- to eighteen-month-olds and six-year-olds when comparing the polluted city with the reference cities and when comparing the more and less polluted areas within the polluted city. A study in East Germany found that levels of sulfur dioxide, particulate matter and nitrogen oxides were associated with an increased risk of developing upper respiratory infections in nine- to eleven-year-olds.

Increased Respiratory Symptoms

Elevated levels of various air pollutants have been linked with an increased incidence of respiratory symptoms in children. In an ongoing study comparing air pollution in six U.S. cities and the respiratory health of individuals living in those cities, the frequencies of coughs, bronchitis, and lower respiratory illnesses in preadolescent children were significantly associated with increased levels of particulates and acidic fine particles. Illness and symptom rates were higher by approximately a factor of two in the community with the highest air pollution concentrations compared to the community with the lowest concentrations. A follow-up study reported that rates of chronic cough, bronchitis, and chest illness during one school year were positively associated with particulate pollution. Another study in these six cities also found a significant association between particulate pollution and the incidence of coughing and other lower respiratory symptoms. One study suggested that though all children are at risk for increased respiratory symptoms due to particulate pollution, children with preexisting respiratory conditions (wheezing, asthma) are at greater risk.

Decreased Lung Function

To maintain a normal rate of gas exchange -- the removal of carbon dioxide and replenishment of oxygen -- the lungs must be able to inhale and exhale an adequate volume of air. In determining how well a person's lungs function, researchers take measurements of the lungs at rest, the volume of air that can be inhaled and exhaled, and the time it takes to exhale.

Numerous studies have showed that even brief exposure to air pollutants can impair lung function. One study in Utah Valley indicated that elevated particulate levels were associated with a decline in lung function among elementary school-age children as measured by peak expiratory flow (the maximum rate at which air is exhaled from a maximum inhalation). Another study examined the health effects of exposure to acidic air pollution among children in twenty-four communities in the United States and Canada and found that acidic air pollution is associated with reductions in pulmonary function, as measured by forced vital capacity (the volume of air forcibly exhaled from a deep inhalation) and forced expiratory volume (the volume of air exhaled over a specific period of time from a maximum inhalation).

Much of the evidence that air pollution reduces lung function in children focuses on summertime exposure to acidic particles or acid aerosols.Reductions in pulmonary function in children have also been linked to ozone exposure. One study found a significant decline in forced expiratory volume after ozone exposure, a change that appeared to persist for sixteen to twenty hours.

Exacerbation of Asthma

Approximately 4.8 million children in the United States under the age of 18 have asthma, the most common chronic illness among children. The incidence of the disease is on the rise, increasing nearly 40 percent among U.S. children between 1981 and 1988. Other countries are also observing rising rates of asthma. Blacks, Hispanics, and people living in urban areas appear to be at greatest risk for the disease. Asthma is a complex disease associated with many factors including genetics, allergies (cockroaches and dust mites), mildew, molds, and the environment. Asthma is a condition of the airways characterized by chronic inflammation and episodic limitation of the flow of air into and out of the lungs. Symptoms of the disease include coughing, tightness in the chest, shortness of breath, and wheezing. Exacerbations of asthma have been linked with exposure to ambient air pollutants, indoor air pollutants, as well as allergens.

Based on increased hospital admissions, increased hospital emergency room visits, and increased medication use, ambient air pollution is associated with aggravation of asthma. In a recent study of children at an asthma summer camp, ozone air pollution was significantly correlated with an increase in the use of asthma medication and the worsening of other asthma symptoms. The children were 40 percent more likely to suffer asthma attacks on high pollution summer days. In another study, researchers reported a 37 percent increase in hospital emergency visits for childhood asthma after periods of maximum ozone pollution levels. A study in Mexico City showed an association between increased levels of particulate matter and ozone and a worsening of respiratory symptoms among mildly asthmatic children. Hospital admissions among children with asthma in Toronto were higher after days with elevated ozone levels.

Children of Color

While dirty air is a threat to all Americans, communities of color often suffer disproportionately from air pollution. This is also true of low-income communities. Such communities have historically been used as dumping grounds for the toxic by-products of industrial society. Several studies have demonstrated that proportionately more landfills, power plants, toxic waste sites, bus depots and rail yards, sewage treatment plants, and industrial facilities are sited in them. In a landmark report prepared by the United Church of Christ's Commission for Racial Justice, investigators discovered that three of the five largest hazardous waste landfills in the United States are in Black or Latino neighborhoods and that the mean percentage of people of color in areas with toxic waste sites is twice that of areas without toxic waste sites. An update to this report found that, in 1993, the percentage of people of color remains three times higher in areas with the highest concentration of commercial hazardous waste facilities than areas without commercial hazardous waste facilities.

The health risks from air pollution are likely to be more serious for children who are already exposed to toxic chemicals, because they live or attend school near landfills, toxic waste sites, bus depots and rail yards, industrial plants, or similar facilities. Because of low-quality housing, overcrowding, and lack of air conditioning, children in low-income communities may also spend more time outdoors on smoggy summer days. (In the absence of air conditioning, indoor concentrations of ozone can approach 80 percent of outdoor levels.) In addition, children in low-income families are less likely to receive sufficient health care.

Scientists at the Argonne National Laboratory have found that minority population subgroups experience greater exposure to substandard outdoor air quality. In particular, their research indicates that minorities live in greater concentrations both in areas with above-average numbers of air polluting facilities and in air quality non-attainment areas. For instance, 52 percent of all whites live in counties with high ozone concentrations. For African-Americans the figure is 62 percent, and for Hispanics it is 71 percent. Population group distributions were found to be similar for carbon monoxide, sulfur dioxide, nitrogen dioxide, lead, and particulate matter, with higher percentages of African-Americans and Hispanics than whites residing in counties with excessive levels of these pollutants. Moreover, 57 percent of all whites, 65 percent of African-Americans, and 80 percent of Hispanics live in counties that failed to meet at least one of the EPA's ambient air quality standards. Five percent of whites, 10 percent of African-Americans, and 15 percent of Hispanics live in counties that exceed standards for four air quality standards.

To compound the greater likelihood that children of color reside in the areas of worst air pollution, Black and Hispanic children are potentially more susceptible to air pollution due to their increased rates of asthma. Black and Hispanic children have a higher incidence of asthma than white children. Black children are more likely to have asthma than white children. Moreover, Black children aged five to fourteen years are four times more likely than whites to die from asthma, and African-Americans under the age of twenty-four are 3.4 times more likely to be hospitalized for asthma. Children of Hispanic (mainly Puerto Rican) mothers have a rate of asthma two and a half times higher than whites and more than one and a half times higher than Blacks. Within the Hispanic-American population, the highest prevalence of asthma among children was in Puerto Ricans (11.2 percent), followed by Cuban-Americans (5.2 percent), and Mexican-Americans (2.7 percent). By comparison, the asthma incidence in non-Hispanic Blacks is 5.9 percent and in non-Hispanic whites it is 3.3 percent.



Exposures to carcinogens in ambient air can cause genetic damage that can be passed on to future generations. Findings reported by Columbia University researchers indicate that carcinogens in ambient air can be transferred transplacentally from the mother to the fetus. In fact, genetic damage to the fetus was found to be higher than damage to mothers, indicating the increased sensitivity of the developing fetus to the effects of carcinogenic exposures. Children in the study had decreased birthweight, length, and head circumference.



Below are summaries of the chief potential health impacts of major outdoor air pollutants. It is important to keep in mind that little clinical research has been done to determine the health effects of air pollutants in combination, and this fact is reflected in a common flaw in federal and state air pollution programs that generally fail to take into account the potential effects of the pollutant "soup." Ozone, particulate matter, nitrogen oxides, sulfur oxides, and carbon monoxide are "criteria" air pollutants for which the EPA has established maximum exposure limits.


Ozone is a highly reactive, unstable form of oxygen, formed in the atmosphere by the action of sunlight on nitrogen oxides and reactive hydrocarbons -- both of which are emitted by motor vehicles and industrial sources. Ozone levels, therefore, tend to be highest on windless, warm, sunny days, particularly in the afternoon when children are most likely to be playing outside. Ozone concentrations decrease rapidly when the sun goes down.

Ozone damages the cells that line the respiratory tract, causing irritation, burning, and breathing difficulty. When inhaled, even at very low levels, ozone can cause acute respiratory problems, aggravate asthma, cause inflammation of lung tissue, and impair the body's immune system, making people more susceptible to respiratory illness. Ozone exposure can cause temporary decreases in lung capacity of 15 to 20 percent in healthy adults. Inhalation of ozone can lead to hospital admissions and emergency room visits. According to the EPA, 10 to 20 percent of all summertime respiratory-related hospital visits in the northeastern United States are associated with ozone pollution.

Particulate Matter

Particulate matter is the term used for a mixture of microscopic solid particles and liquid droplets -- also known as aerosols -- found in the air. Coarse particles (larger than 2.5 microns in diameter) come from windblown dust and grinding operations. The combustion of fossil fuels is the principal source of emissions of fine particles (less than 2.5 microns in diameter), including the burning of coal, oil, diesel fuel, and gasoline. High-temperature industrial processes such as metal smelting and steel production are also significant sources of fine particles. Nationally, coal-fired power plants are the largest source of fine particle emissions, followed by industrial boilers and gasoline and diesel vehicles. Ultrafine particles, so small that several thousand of them could fit on the period at the end of this sentence, are of particular health concern because they easily lodge in the deepest recesses of the lung.

A battery of scientific studies has linked particulate matter, especially fine particles (alone or in combination with other air pollutants) with health problems, including premature death, respiratory-related hospital admissions and emergency room visits, the exacerbation of asthma, acute respiratory symptoms such as severe chest pain, gasping, and aggravated coughing, chronic bronchitis, and decreased lung function (which can be experienced as shortness of breath).

Nitrogen Oxides

Nitrogen dioxide and related nitrogen oxides are produced when fuel is burned, especially at very high temperatures, as in power plants and motor vehicles. Nitrogen dioxide is a strong oxidizing agent that reacts in the air to form corrosive nitric acid, as well as toxic organic nitrates. It also plays a major role in the production of ground-level ozone (or smog). Nitrogen dioxide can irritate the lungs and lower resistance to respiratory infections such as influenza.

Carbon Monoxide

Carbon monoxide is a colorless, odorless, and poisonous gas formed by incomplete combustion of coal, wood, charcoal, or petroleum. Autos are the chief source, releasing about 60 percent of all carbon monoxide emissions in the United States In cities, automobile exhaust can cause as much as 95 percent of all carbon monoxide emissions. Other sources include industrial processes and fuel combustion in boilers and incinerators.

Once inhaled, carbon monoxide passes immediately through the lungs into circulating red blood cells, binding tightly to hemoglobin and blocking the blood's ability to carry oxygen throughout the body. Intense, short-term exposure to carbon monoxide can lead to a loss of consciousness, as was known by physicians in the late nineteenth century who used it as an anesthetic. The health threat from exposure to carbon monoxide is most serious for those with cardiovascular disease. Exposure to elevated levels of carbon monoxide is associated with irritability, headaches, visual impairment, reduced work capacity, reduced manual dexterity, poor learning ability, and difficulty performing complex tasks.

Sulfur Dioxide

Sulfur dioxide is formed when sulfur-containing fuel, mainly coal and oil, is burned, primarily in power plants and diesel engines. Like nitrogen dioxide, sulfur dioxide can change in the atmosphere into acidic particles. Evidence suggests that exposure to sulfur dioxide, even at low levels, makes the airways in the lung more sensitive to bronchoconstrictors -- substances that cause the airways to tighten or constrict, which increases their resistance to the inflow and outflow of air. This in turn inhibits oxygen exchange and can result in wheezing, gasping, and shortness of breath.

The seriousness of the threat from exposure to sulfur dioxide was underscored in a recent study of air pollution and daily mortality in residential areas of Beijing, China. Researchers from the Harvard School of Public Health and the Chinese Ministry of Public Health found a highly significant association between sulfur dioxide and daily mortality, estimating that the risk of total mortality increased by 11 percent with each doubling of the sulfur dioxide concentration.

Toxic Air Pollutants

In addition to the criteria air pollutants, toxic air pollutants -- also known as hazardous air pollutants (HAP) under the Clean Air Act -- consist of airborne substances known or suspected of causing cancer, genetic mutations, birth defects, or other serious illnesses. Toxic air pollutants include metals, other particles, and certain vapors from fuels and other sources. Examples of toxic air pollutants released include benzene from gasoline, perchloroethylene from dry cleaners, methylene chloride from degreasers and paint strippers, and chromium from metal plating operations. Benzene and hexavalent chromium are known human carcinogens. Methylene chloride and perchloroethylene are probable human carcinogens.

Formaldehyde and acetaldehyde, which can be found in automotive exhaust as well as in consumer products, are strong irritants, reddening eyes and causing runny noses and respiratory irritation. The EPA has designated both substances probable human carcinogens. Another probable human carcinogen, emitted from motor vehicles, is 1,3 butadiene. The EPA estimates that mobile (car, truck, and bus) sources account for as much as half of all cancers attributed to outdoor sources of air toxics. Non-road mobile sources (tractors and snowmobiles) emit air toxics as well.

Heavy Metals

Waste incinerators emit fly ash, which can contain metals, including lead, nickel, cadmium, copper, and mercury, as well as dioxins and furans. Particulate matter contains a variety of carcinogenic or toxic heavy metals, including arsenic, barium, cadmium, chromium, copper, iron oxides, mercury, and others. Among the most pernicious airborne environmental threats is lead. After the EPA ordered the phasing out of leaded gasoline in 1976, scientists who charted blood-lead levels saw a close correlation between the decline in leaded gasoline use and the decline in levels of lead in blood. The phase-out of lead from gasoline was completed on January 1, 1996.


Air pollutants come from a variety of sources. At one point, the burning of coal was the greatest source. For instance, in 1952 more than four thousand people died in London due to a fog saturated with coal dust and acids. Since that time, government and business in the United States and in other countries have acted to reduce coal smoke emissions.

Though air pollution from coal has been substantially reduced in most areas of the country, citizens must be concerned about other sources of air pollution. Today, motor vehicles are the primary air polluter. Some pollutants are emitted directly into the atmosphere while others are produced by reactions that occur in the atmosphere between "precursor" substances. The following are sources of man-made pollutants common throughout the United States:

Cars and Trucks

Motor vehicles such as automobiles, trucks, and buses are the primary source of air pollution nearly everywhere in the United States In 1950 there were 53 million cars in the world; now there are 480 million. In the United States, there are nearly 150 million private cars and almost 50 million trucks and buses. Furthermore, the miles traveled by car continue to increase in excess of population growth. Automotive exhaust contains hydrocarbons, nitrogen oxides, sulfur dioxides, particulate matter, and carbon monoxide. Other important emissions from vehicles include toxic organic compounds such as formaldehyde, acetaldehyde, and benzene. Ozone is produced by sunlight-driven reactions between nitrogen oxides and hydrocarbons emitted from automobiles and other sources.

Recent evidence suggests that diesel engine emissions are more dangerous than previously considered. Two recent government reviews, one by the EPA and the other by California, have found diesel exhaust to be carcinogenic. A draft qualitative and quantitative cancer assessment of diesel emissions conducted by the EPA reportedly concludes that such emissions are probable human carcinogens. In March 1997, CalEPA issued a draft review of the health risks from diesel exhaust and found it carcinogenic.

Stationary Point Sources

In Los Angeles and its environs, all fourteen operating refineries emit approximately 30 tons of nitrogen oxides per day and 10 tons of reactive organic gases per day. Despite a long history of aggressive efforts to control emissions, power plants continue to expel large quantities of pollutants. Factories and high-tech industries -- everything from aerospace firms to label manufacturers -- also contribute. For instance, paper mills commonly release sulfates into the air, coal-burning power plants emit sulfates and acids, and municipal incinerators emit fly ash, a particulate mixture which can include heavy metals. Of particular concern are metal smelters, which sometimes emit lead, arsenic, and other metals.

Small Businesses and Consumer Products

It is often easier to regulate large companies than a large number and wide variety of smaller businesses. Yet these businesses may be an important source of air pollution. Dry cleaners, for instance, emit carcinogenic solvent vapors, especially perchloroethylene; plastic molding plants can emit formaldehyde and other organics into the air; scrap metal recycling plants often emit lead, cadmium, and mercury into the atmosphere; plating shops emit chromium and nickel (as suspended particulate matter); and auto body shops release a variety of solvents and other toxic organics. In fact, in the Los Angeles Basin, auto body shops emit two tons of reactive organic gases per day.

Also of concern are consumer products. Hairspray, spray-on deodorant, and room fresheners expel individually only small amounts of gases, but these minute amounts are released several million times a day. In southern California, consumer products contribute almost 8 percent of the total daily volatile organic carbon emissions.


What You Can Do

The following are suggestions for protecting children and other family members during air pollution episodes.

Regularly check air pollution levels in your area and plan accordingly. Pollution patterns and concentrations can differ radically from one area to another. Some areas might be particularly susceptible to carbon monoxide violations, while for others it might be ozone. Be sure you are able to recognize the air district jurisdiction under which your area falls. Call your county health department to identify your local air pollution control agency. Pollution patterns also change over the course of a single day. During hot summer months in some areas, for instance, levels of ozone are five times higher in the afternoon than in the morning, while in the winter the mid or late afternoon may be the time of lowest pollution. Depending upon the area in which you live, newspapers and newscasts often discuss each day's air pollutant levels. You can also contact your local air district for specific information and advice.

Limit children's outdoor exercise when smog levels are high. Laboratory studies have revealed that heavy exercise during smog episodes contributes to adverse health effects. Though our bodies have a variety of protective mechanisms against the adverse affects of air pollution, children are especially vulnerable and should be encouraged to stay indoors during smog episodes. At these times, keep doors and windows closed whenever possible while taking into account the sensitivities of asthmatics and others with breathing difficulty that may be exacerbated due to indoor air pollutants.

Be sure your child's school is prepared for smog episodes. Every school should have plans for smog episodes, including alerting teachers, curtailing sports or exercise programs, and providing alternative activities that do not involve heavy physical exertion.

Encourage curriculum development on air pollution issues. Children need help identifying air pollution hazards and the health symptoms that might indicate sensitivity to air pollution. Encourage your child's school to develop curriculum units centered on these issues.

Be aware of sensitivities that put family members at increased risk. Children, people with asthma and other chronic lung diseases, the elderly, and the chronically ill are especially vulnerable to air pollution. During episodes of poor air quality, monitor the health of these individuals and contact a physician if needed.

Avoid highly polluted areas during smog episodes. If you must be outside during a smog episode, avoid busy streets and highways that can significantly increase your exposure. Sitting in a car during a hot summer day in the middle of a traffic jam can expose you to elevated levels of carbon monoxide.

Keep indoor air as clean as possible. Do not smoke cigarettes indoors. Keep your house free from dust and mildew. To control dust in the home, remove wall-to-wall carpets when possible and replace them with small area rugs that can be thoroughly cleaned. Periodically remove and launder heavy curtains. Be sure that fumes from gas stoves and heaters are properly vented, and reduce indoor sources of pollutants such as insecticides, wood fires, cleaners, solvents, and deodorizing sprays. When painting or using chemical cleaning agents, assure full ventilation.

Help get polluters off the road. Report vehicles with visibly excessive tailpipe emissions to your local air quality management district. In some areas, an anonymous 800 number is available for this purpose. Minimize your own use of the automobile. Take your car to a reliable service station if your automobile "smokes " or if the "check engine " light remains illuminated. Carpool whenever possible. Use public transportation, bicycle, or walk as frequently as you can.

Consult the Toxics Release Inventory. The Toxics Release Inventory (TRI), part of the 1986 Superfund Amendments Reauthorization Act, is a powerful tool for uncovering local sources of air pollution. The information, available thorough the regional US EPA office or state air pollution board, is free to any citizen who requests it. The TRI data identify by name and location industrial facilities that release toxic substances into the air, water, or land. Contact the EPA's Emergency Planning and Community Right-to-Know Information Hotline at 800/535-0202.

This article was published by the National Resources Defense Council, copyright 1997. It can be accessed online at the following link.

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