A growing body of research is shedding light on the ways that air pollutants impinge on the health of the American public. Indeed, the Environmental Protection Agency highlighted this concern in December when, after reviewing the evidence, it ruled that greenhouse gases are detrimental to human health, particularly because they can aggravate asthma and other respiratory illnesses and can produce longer, more intense heat waves that endanger the poor, sick, and elderly. But it's not just lungs that suffer.
To be sure, clean-air advocates have worked to improve the nation's air quality, and the health risks that a particular individual might face directly from breathing polluted air are low. But research consistently is finding that, when spread out over a given population—be it residents of a certain city or those with a particular disease—the quality of the air has a very significant impact on public health. When vehicles, factories, power plants, and other machines burn fuel, the chemicals they release into the atmosphere react with one another (and other compounds in the air) in ways that can amplify health hazards. "Greenhouse gases actually increase air pollution and therefore [raise the] potential for more adverse events for people with pre-existing respiratory conditions or heart conditions," says Kent Pinkerton, chair of the environmental health policy committee at the American Thoracic Society.
The EPA's ruling dealt only with greenhouse gases, including carbon dioxide, nitrous oxide, and methane. But a constellation of air pollutants concern researchers who study their effects; one major offender is particulate matter, which wreaks havoc on human health, says Norman Edelman chief medical officer of the American Lung Association. We have no natural defenses against them. The fine and ultrafine particulates in air pollution are so small (fine particulates are about one-thirtieth of the width of a human hair, according to the EPA, and ultrafines can be up to 25 times smaller) that they can slip by the respiratory system's defenses. Over time, particulate exposure can raise rates of chronic obstructive pulmonary disease, lung cancer deaths, and asthma attacks.
And in recent years, research has revealed more about how far air pollution's harms go beyond the respiratory system. "People thought that when we inhale pollutants the lung is the main target, but the lung is surprisingly resilient. It turns out the cardiovascular effects are predominant," says Aruni Bhatnagar, an environmental cardiology researcher at the University of Louisville. One major study, which followed subjects for 16 years, found that people living in cities with higher levels of fine particulates were at greater risk of cardiovascular death. A difference of 10 micrograms per cubic meter increased the risk of dying from ischemic heart disease (narrowed arteries) by 18 percent, arrhythmia by 13 percent, and cardiac arrest by 21 percent, the study revealed. It seems air pollutants incite processes that lead to high blood pressure, blood clotting, and electrical instability in the heart, which can translate into heart attack, stroke, and sudden cardiac death. Even short-term exposure can be hazardous. Research shows spikes in cardiac deaths, emergency room visits, and hospital admissions in the hours and days that follow a spike in cities' levels of particulate matter.
One question: Who is most vulnerable to the effects of bad air? Emerging research suggests one group that could be at risk is those who are overweight or obese—even young adults. Considering the number of people in the United States who fit those designations, this risk is "an important public health issue," says Stephanie London, an internist and a senior investigator at the National Institute of Environmental Health Sciences. Her research found that among 18-to-35-year-olds exposed to ozone, a greater body mass index correlated with diminished lung function. Air pollution has been found to exacerbate health problems in the young, the elderly, and those with such chronic conditions as respiratory disease, heart disease, and diabetes.
Air pollution might actually cause disease as well. Separate research by London found that kids ages 9 to 16 who played at least three sports and lived in areas with high ozone concentrations had a 30 percent increased chance of developing asthma. And other work indicates that infants whose mothers were exposed to air pollutants while pregnant might be at a slightly greater risk of low birth weight, pre-term birth, and even death. Researchers also are investigating air pollution's effects on miscarriage rates and sperm quality in men.