New Science on Particles Counters Industry Arguments
In 1997, the U.S. EPA established the first air quality standards for PM2.5, particulate matter so fine that it can be inhaled and lodge deep in the lungs. Community heath studies demonstrated that fine particle air pollution was associated with increased use of asthma medication in children, decline in respiratory function, increased emergency room visits and hospitalization for respiratory and cardiac problems, and premature death.
The combustion of fossil fuels is the major source of fine particulate air pollution, hence industries such as the trucking, auto, petroleum, steel, and electric utilities led the opposition to the new standards. Industry groups cited cost, scientific, and legal arguments in opposition to the new standards. Industry groups continue to challenge the standards in federal court, despite a Supreme Court decision rejecting many of their claims.
In part in response to industry concerns, the federal government established a major program to fund scientific research on fine particle air pollution and its health effects. A National Academy of Sciences panel was convened to identity research priorities and to assess scientific progress. A million a year research program was established, with research centers at four major universities. In addition, the Health Effects Institute, jointly funded by EPA and the auto industry, undertook an independent review and reanalysis of two important long-term studies that had been the subject of industry attacks, as well as funding other key research.
As a result of this infusion of research dollars and talent, significant progress has been made in answering many questions and in reducing the uncertainties about the health effects of fine particles. The American Lung Association® believes that there was sufficient information about the adverse health effects of fine particle pollution to justify the standards established by EPA in 1997, and that an even stronger case exists today, as EPA proceeds with a review of the standards.
This fact sheet describes new research findings that effectively put to rest the major industry criticisms of the science.
Industry Argument: Most of the positive findings have been reported by the same author and for just a few cities.
Response: Since 1997, over 70 new studies showing a relationship between short-term increases in particulate pollution and mortality have been published. The findings are consistent among multiple investigators and over multiple locations. Further, the National Morbidity, Mortality and Air Pollution Study (NMMAPS), an independent study of 90 U.S. cities using uniform methodology nationwide, reported that contemporary levels of particulate air pollution are contributing to mortality.
Industry Argument: The studies and underlying data have not been validated by independent investigators.
Response: The most important studies have now been extensively reanalyzed and validated by independent investigators and the original conclusions have been fully upheld.
Industry Argument: The epidemiologic studies cannot prove that air pollution is killing people.
Response: Laboratory studies of effects on humans are limited because sensitive individuals, those most likely to suffer effects, cannot be included for ethical reasons. Epidemiological studies provide a way to study the effects of pollution on representative populations. Scientists use a number of criteria to assess the body of evidence before making conclusions about causality. These criteria include the strength of the association, consistency of the association, temporal relationship, dose-response relationship, biological plausibility, specificity of the association, coherence of the association with other known facts, analogy, and other factors. Many prominent scientists have concluded based upon these criteria that particulate air pollution causes death and disease.
Industry Argument: The people dying from air pollution are very frail, and probably would have died in a few days, even in the absence of air pollution (the “harvesting” theory).
Response: Studies have now shown that chronic exposure to fine particle pollution may lower life expectancy by several years or more. The “harvesting” hypothesis has been disproven by studies that show that increases in the death rate after an air pollution episode are not followed by decreases in the death rate.
Industry Argument: The effects observed in these studies are due to weather, not air pollution.
Response: Extreme weather conditions such as heat are associated with an increase in the death rate. The statistical design of recent epidemiological studies has been able to demonstrate an independent effect of air pollution.
Industry Argument: Effects may be due to other confounding factors that have not been evaluated in the studies.
Response: The two major long-term epidemiological studies, the American Cancer Society Study and Harvard Six City study, took into account the most obvious confounding factors such as smoking, occupational exposures, and body-mass index. The Health Effects Institute reanalysis of these studies considered the role of 20 additional potential confounders including other pollutants, climate, and socio-economic factors. The sensitivity analysis largely confirmed the original findings that particulate air pollution increases the risk of premature death, particularly death from cardio-pulmonary causes.
Industry Argument: Even if air pollution is contributing to premature death, it may be pollutants other than particulate matter that are the real problem.
Response: The major studies of the last several years have looked at the full range of air pollutants and have found that the effect of particle pollution is significant and robust.
Industry Argument: There have been only a few studies of fine particle pollution (PM2.5), and we are already regulating PM10 pollution so there is no need for a separate, new standard for PM2.5.
Response: We need standards to protect against the effects of both coarse and fine particles. The PM10 standards have proven to be ineffective in controlling combustion sources of fine particle air pollution, so a new separate standard is needed for PM2.5. Many studies have examined the effects of PM10 because more extensive monitoring data was available than for PM2.5. PM2.5 is a subset of PM10, so the two pollutants are very closely related. Two major long-term epidemiological studies, the Harvard Six City Study and the ACS Study, both of which were recently validated by the Health Effects Institute, reported strong associations between long-term exposure to fine particles and premature mortality. In addition, a number of new short-term studies have focused on PM2.5 effects.
Industry Argument: We don’t know what component of PM2.5 is responsible for effects, so if we regulate now, we may be controlling the wrong sources.
Response: PM2.5 is comprised of primary pollutants such as diesel particulate, and aerosols such as sulfates, nitrates, and carbonaceous compounds that are formed in the atmosphere from gaseous emissions from fossil fuel combustion. Controlling the major sources of fine particle pollution such as diesel trucks and coal-fired power plants will reduce a number of major air pollutants providing multiple benefits to public health.
Industry Argument: Epidemiological studies of the effect of outdoor air pollution on people’s health are irrelevant because people spend most of their time indoors.
Response: Both indoor and outdoor air pollution are important sources of health risks. Furthermore, ambient fine particles are relatively stable in the atmosphere and can readily penetrate indoors. Studies have demonstrated that measurements taken at outdoor monitors are actually quite good predictors of indoor fine particle concentrations. NMMAPS researchers used statistical techniques to explore the issue of measurement error, and concluded that it is more likely to result in underestimates, than overestimates, of risk.
Industry Argument: Causality cannot be proven because the biological mechanisms are not completely understood.
Response: Mechanistic information is not needed to demonstrate causality. In other words, scientists can conclude that air pollution is killing people even though they don’t know exactly how it is doing so. For instance, tobacco was connected with death and disease before the biological mechanisms were fully identified. As with tobacco, prudent public health practice dictates curbing exposure to fine particle pollution. As the Health Effects Institute concluded in a review of recent research, “epidemiologic evidence of PM’s effects on morbidity and mortality persists even when the alternative explanations have been largely addressed,” and that this is the true test of a cause and effect relationship.
Industry Argument: The studies have not identified a threshold for effects.
Response: Scientific studies show that a linear, no-threshold model best characterizes the PM-mortality relationship. This means that exposures have not yet gone below the no-effects threshold, if such a threshold exists.
Industry Argument: The NMMAPS study reported higher risk levels in some regions of the country. Until these regional differences are explained, there is too much uncertainty to regulate particle pollution.
Response: There are a number of possible explanations for these differences. One factor under investigation is the increased use of air conditioning in certain regions of the country. Another factor may be differences in access to health care in different cities. The NMMAPS study provided important confirmation that contemporary levels of particle air pollution are killing people and need to be regulated.
Industry Argument: Even if air pollution does have an effect, the relative risk is so small as to be insignificant.
Response: A lower relative risk has public health significance if the frequency of the disease is great, or if large numbers of people are exposed, as with air pollution. In the case of fine particle pollution, tens of millions of people in the United States are exposed to unhealthy concentrations.
Industry Argument: Air pollution is declining so it can’t be responsible for the rise in asthma.
Response: At this point in time, we do not claim that outdoor air pollution causes asthma, however, we know that air pollution can exacerbate asthma. The reason for the rise in the number of people diagnosed with asthma is unknown. Air pollution and other factors (e.g. cold air, respiratory infections, and allergens) are known triggers for flare-ups in asthma patients.
