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Welcome to PSR's Environmental Health Policy Institute, where we ask questions -- then we ask the experts to answer them. Join us as physicians, health professionals, and environmental health experts share their ideas, inspiration, and analysis about toxic chemicals and environmental health policy.


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Our Work On Air Toxics Goes Unfinished

Posted on April 14, 2011

By Kristen Welker-Hood, ScD MSN

This essay is in response to: What is the most important achievement we've gained through air pollution management? What remains to be done to safeguard public health from air pollution?

The Clean Air Act (CAA) is one of the most important and effective public health laws ever enacted.

This declaration might have given a few of you a pause – given that popular understanding is that the CAA is an environmental law. Let us, however, look at the evidence.

Since its passage, ambient air concentrations for the most common, dangerous air pollutants (also known as criteria pollutants) have dropped considerably.  Notable reductions achieved through CAA pollution controls include 75% decreased emissions in primary particulates (PM2.5 and PM10) released directly from utility and industrial smokestacks, 50% reductions of carbon monoxide (CO), primarily through motor vehicle controls, and 99% reductions of lead emissions from 230,000 tons to 3,000 tons.[1]  Continued emission reductions are anticipated for all criteria pollutants throughout the 2000 to 2020 period as a result of the 1990 CAA Amendments. The largest predicted reductions will be in SO2 and NOx emissions, by 70.4% and 68.2% respectively.[2] 

Reducing exposures to criteria pollutants saves lives and decreases human suffering. The reduction of PM2.5 (fine particulates) has prevented 160,000 premature deaths and 1,700,000 asthma exacerbations. Lowering ground-level ozone and PM2.5 has prevented 84,000,000 restricted activity days. As a former visiting nurse, these numbers mean something to me. I am grateful that critical pollution prevention efforts will ease the discomfort of my patients who frequently struggled to breathe on bad air days.

The under-realized potential of the CAA is most clear in the area of limiting our exposure to hazardous air pollutants (HAPs). To better protect public health, Congress enacted the 1990 CAA Amendments to establish highly protective emission standards for all major HAPs sources within ten years. Yet more than two decades later, EPA is just now issuing emission standards for some of the largest sources of hazardous air pollution: coal- and oil-fired electric power plants, cement kilns, and industrial boilers. These sources for too long have escaped regulation while they emitted mercury, arsenic, other toxic metals, and acid gases which are known neurotoxins, carcinogens, or contribute to the production of particulate pollution, and, consequently, to cardiovascular and respiratory illnesses.

Putting tardiness in rule setting for controlling air toxics aside, a glaring failure to prioritize reducing HAPs can be witnessed in the inconsistent approach to monitoring emission levels. This is particularly true for communities that bear the greatest burden of exposure to air toxics. Communities that abut refineries or industrial areas, or those communities of color in which industrial areas and high transportation areas are sited, are exposed to the highest levels of air toxics. Sadly, too few EPA air monitors are located in these communities. The EPA weaves together the limited available air toxic monitoring data with modeling studies to evaluate trends in hazardous air pollutants. One modeling study is the National-Scale Air Toxic Assessment (NATA) that combines ambient HAPs concentrations to model inhalation exposures and associated health risks for 180 of the 187 HAPs listed under the CAA. 

The air toxics data collected at industrial sites that feeds into the EPA NATA is part of a largely voluntary reporting program under the Toxics Release Inventory (TRI). Emissions reported to the TRI are notoriously underestimated. One CAA exemption that has enabled this under reporting is the “start-up and shut-down” clause for industry, in which emissions that are released during plant start-up and shut-down activities do not need to be reported. Start-ups and shut-downs happen whenever there are repairs to equipment at industrial sites, refineries, or power plants. They also occur when the equipment is malfunctioning. Both situations are frequent and can be responsible for greater-than-average releases of toxic emissions into local communities. It is precisely these types of peak exposures to carcinogens or neurotoxins that we want to capture to identify high-risk communities in need of air pollution interventions.

In its report, Our Nation’s Air, EPA estimates that nearly 285 million people in the US have a cancer risk greater than 10 in 1 million attributable to air toxics exposures. The national average cancer risk for 2002 was 36 in 1 million for all known causes. Thus, nearly 30% or 1 in every 28,000 cases of cancer is a result of breathing air toxics from outdoor sources over a lifetime of exposure. Reflecting on the 2010 President’s Cancer Panel report, which asserted that "the true burden of environmentally induced cancer has been grossly underestimated,” it is clear that the most important work left incomplete under the CAA is addressing the dramatic health damages caused by hazardous air pollutants.

[1] U.S. Environmental Protection Agency. (1997, Oct). Retrospective Study 1970-1990.  Retrieved April 11, 2011 from

[2] U.S. Environmental Protection Agency. (2011, Mar). The Benefits and Costs of the Clean Air Act from 1990 to 2020. Retrieved April 11, 2011 from


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