Particulate air pollution and health: the facts

provided by American Lung Association

ow does particulate air pollution harm human health? Fine particles are easily inhaled deep into the lungs where they can remain embedded for long periods of time. Particulate matter air pollution is especially harmful to people with lung disease such as asthma, chronic bronchitis, and emphysema, as well as people with heart disease. Young children and the elderly are at greatest risk.

    Exposure to particulate air pollution can trigger asthma attacks and cause wheezing, coughing, and respiratory irritation in individuals with sensitive airways. Hundreds of studies from around the world have linked particulate air pollution with more serious health outcomes, including emergency room visits, hospital admissions, and premature death from cardiopulmonary causes, even at relatively low concentrations.

    Particulate air pollution shortens the lives of people who live in more polluted areas by one to three years, according to long-term community health studies.

    How do the recently announced revisions to a major study change what we know about the health effects?

    First, there have been no changes to the overall conclusions: Exposure to contemporary concentrations of particulate matter in the United States increases the risk of premature death. Other studies have linked particulate pollution with additional serious health outcomes such as asthma attacks, breathing difficulty, lung cancer, and heart attacks. The weight of evidence is overwhelming and incontrovertible. The study in question is the National Morbidity, Mortality and Air Pollution Study, released in 2000 that looked at daily effects of particulate pollution in 90 US cities. Researchers have found an error in a standard statistical software program they used to analyze the data in that study. When they reran the data, researchers found that the average daily effect of particles on mortality was reduced by about half of what had been previously reported. In some cities, risks increased; in others, it declined. However, the reanalysis showed that the risk of premature death clearly exists and is significant. Even at the lower rate of risk, this study confirms that particulate air pollution remains a very serious public health problem, given the tens of millions of people exposed to unhealthy concentrations.

    These revisions do not change the underlying results of the landmark long-term studies of particles, the Harvard Six Cities Study and the American Cancer Society study, which were both reanalyzed in depth and upheld in 2000. These studies found that prolonged exposure to particulate air pollution significantly increases the risk of dying from cardiopulmonary causes.

    The National Morbidity, Mortality, and Air Pollution Study is a daily time series study, which examined deaths immediately following exposure to increased particulate matter concentrations. It was not designed to measure the effects of living in a polluted region, day in and day out. The Harvard Six Cities Study and the American Cancer Society studies, by contrast, are longitudinal studies, which examine changes over a period of years. Those studies did not use the same software as the National Morbidity and Mortality Air Pollution Study. The estimates of tens of thousands of premature deaths associated with particulate matter are based on the long-term studies and are not affected by the revised study results.

    What needs to be done now that this software problem is known? Studies using the software are being reanalyzed to see what, if any, effect this change will have on their results. Only recent studies used this statistical software, so the validity of EPA's 1997 standards for particulate matter cannot be called into question. As with all science, new information and refinement of current tools advances our understanding.

    The American Lung Association supports basing environmental health public policy on the most accurate science available and, therefore, strongly supports reviewing those studies that used the software in question. However, the severity of the health risks involved requires that review to be as rapid as possible. The underlying threat to human health remains. That threat won't be alleviated until we clean up the air.