Air Pollution Epidemiology

Exponent scientists have had considerable experience in the analysis and evaluation of epidemiological and toxicological data on the impact of components of air pollution on human health. Exponent expertise includes analyses of time-series, cohort (semi-ecologic), case-crossover, and panel studies of air pollution and health. Our scientists have been involved in reviews of various EPA criteria documents and staff papers. Exponent scientists, supported both by trade groups and the EPA, have also published research on air pollution and health in various peer-reviewed journals.

Air pollution is an environmental problem stemming from multiple sources, both anthropogenic and natural.  The potential human health effects associated with air pollution are of particular concern to susceptible populations; however, its ubiquitous nature may impart health risks to the population at large.  In the United States, average ambient air pollution concentrations have been decreasing in recent years as a result of policies and regulations that have resulted from the Clean Air Act, which regulates six criteria air pollutants: carbon monoxide, lead, nitrogen dioxide, ozone, sulfur dioxide, and particulate matter.   In developing countries such as China and India, and in urban areas experiencing rapid growth, levels of these air pollutants may still be increasing.  Even in areas where regulations and technologies are in place to control pollution levels, these may not be sufficient to keep up with the increased pollution load.

Agencies at both the national and international levels have concluded that outdoor air pollution increases morbidity and mortality outcomes in humans.  In 2012, the International Agency for Research on Cancer (IARC) classified diesel exhaust as a Group 1 carcinogen (i.e., “carcinogenic to humans”).  Shortly afterwards in 2013, IARC also classified outdoor air pollution as a Group 1 carcinogen.   These assessments and government regulations result from hundreds of studies investigating the association between air pollution and a myriad of health outcomes, which include low birth weight, cardio-pulmonary diseases, and a number of different cancers.  In some cases, the reported associations are complicated by a host of endogenous and exogenous factors relating to study design, statistical methodology, and the resulting interpretation.  The works conducted by Exponent scientists, including some of the aforementioned studies, have added to our understanding of the likely risks that exposure to ambient air pollution imparts on human populations.

One of the major difficulties of air pollution epidemiology is that populations with the highest health risk have an inherently higher likelihood of experiencing larger exposures to air pollution.  This causes a serious problem when estimating the magnitude of these health effects, in part, because the effect of air pollution tends to be much smaller than traditional health risk factors such as smoking, poor diet, and occupational exposures. When this problem is coupled with the difficulty of accurately assessing exposures and the assumptions required by statistical models, it may be difficult to accurately and precisely estimate the health effects attributable to air pollution.  There are, however, a number of methodologies that are able to diagnose problems and arrive at defensible estimates of health risk due to air pollution exposure; Exponent scientists have substantial experience in these methods.