Why Should You Care About the Air?

Linda Brookes, MSc


September 10, 2015

In This Article

The State of Air Pollution in the United States

In the United States, levels of air pollution emissions from mobile and stationary sources are regulated by the US Environmental Protection Agency (EPA) under the Clean Air Act (CAA).[28] Despite continuing legal challenges to the regulations set by the EPA, progress is being made in reducing year-round air pollution across the nation, particularly in the East, owing to adoption of cleaner diesel fleets and cleaner fuels used in power plants.[1] Climate change is a significant factor in the rising risk for effects of air pollution on human health, particularly in the West, where high temperatures and drought create appropriate conditions for increased particle pollution.[1,29,30]

The EPA sets legally permissible levels for six common ("criteria") air pollutants: particulate matter (PM), ground-level ozone (O3), carbon monoxide (CO), sulfur oxides, nitrogen oxides, and lead.[31] "Those air pollutants have been studied the most widely and intensively, so the EPA establishes National Ambient Air Quality Standards for these pollutants because so much is known about their harmful effects with respect to health," Dr Balmes notes. The most widespread and most hazardous to health are fine PM (particles smaller than 2.5 μm in aerodynamic diameter, PM2.5) and O3, which are considered the most significant cause of early deaths related to poor outdoor air quality.[3] A recent study calculated that in the United States, combustion emissions (from electric power generation; industry; commercial and residential activities; and road, rail, and marine transport) are responsible for approximately 200,000 premature deaths annually related to exposure to increased PM2.5 concentrations and approximately 160,000 premature deaths related to increased O3 concentrations.[26]

But as Dr Balmes points out, "What we are starting to learn—and I think EPA knows this already—is that the six criteria air pollutants that are currently regulated do not necessarily represent all that is toxic in air pollution. For example, exposure to traffic emissions appears to be particularly harmful to health, but those are not just PM2.5 or oxides of nitrogen; they are a mixture of those pollutants plus many more." Of particular concern, Dr Balmes explains, are the polycyclic aromatic hydrocarbons (PAHs), a large group of more than 100 chemicals formed as a result of incomplete combustion of such organic materials as fossil fuels (diesel, gasoline, coal, and oil). PAHs in ambient air have become a cause of increasing concern because of their carcinogenicity and mutagenicity and their potent immunosuppressant effects. Sixteen PAHs are included in the EPA's list of designated "priority pollutants." Dr Balmes believes that it may be necessary to change the way the EPA currently regulates air quality. "Although it has led to improvement, at this point it may not be the only way we should be doing it," he suggests. "We are focusing on the multipollutant mixture, particularly traffic emissions, because that is where we have the best evidence that exposure to it as a whole is more harmful than to any one component," he points out.