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EPA proposes stringent new limits on sulfur dioxide, smog

Posted by Barbara Gottlieb on January 14, 2010

The Environmental Protection Agency has proposed rules to strengthen the National Ambient Air Quality Standards for two primary pollutants under the Clean Air Act:  sulfur dioxide and ozone pollution (smog).  Coal-fired power plants contribute significantly to both. 

The proposed changes would help clean the air and protect the health of millions of Americans, especially those who suffer from asthma and other respiratory diseases.

PSR’s director of environment and health, Kristen Welker-Hood, called the proposals changes “critical to protect the public's health from pollutants that cause needless disease exacerbation and death every year.”


Last week the EPA unveiled the strictest standards to date on ground-level ozone, also known as smog.  Ozone is the most widespread gas polluting the U.S. and one of the most dangerous -- linked to serious health problems ranging from aggravation of asthma to increased risk of premature death. 

Ground-level ozone forms when nitrogen oxide emissions and volatile organic compounds (both of which are emitted by coal-fired power plants) react together in the presence of sun and heat. 

Reduction in ground-level ozone will be particularly important in protecting the health of children, especially those with asthma.  While children are at the greatest risk, adults with asthma or other lung diseases and older adults are also sensitive to ozone, and ozone can harm healthy people who work and play outdoors. 

The EPA proposed a “primary” standard for ozone levels, to protect public health, at a level between 0.060 - 0.070 parts per million (ppm) measured over eight hours.  EPA is also proposing a separate “secondary” standard to protect the environment, especially plants and trees. Repeated ozone exposure can reduce tree growth, damage leaves, and increase susceptibility to disease.

Moreover, ozone reduces green plants’ absorption of carbon dioxide, thus diminishing their effectiveness as a “carbon sink” to slow global warming.

The proposal would yield health benefits estimated by the EPA at between $13 billion and $100 billion.  These would be due to reductions in premature deaths, aggravated asthma, bronchitis cases, hospital and emergency room visits, and days lost from work or school due to ozone-related symptoms. Estimates of the cost of implementing the proposal range from $19 billion to $90 billion.

The EPA will hold public hearings on ozone Feb. 2 in Arlington, VA and Houston, TX, and Feb. 4 in Sacramento, CA and will finalize the proposed ozone regulations in August.

Limits on sulfur dioxide

EPA’s proposed rule for sulfur dioxide (SO2) would revoke the current 24-hour and annual average standards to replace them with a more health-protective one-hour standard.  It would apply a stringent new limit of between 50 and 100 parts per billion over one hour. 

Current limits on SO2 are based on averages of emissions over 24-hour and one-year periods, which allow plants to emit high concentrations amounts of pollutants over short periods of time.  The new standard would utilize one-hour measurements, which would detect such emissions spikes.  Recent studies have shown that exposure to high levels of SO2, even for a very short time period, make people sick.

 Coal-fired power plants are the major emitters of SO2, which can cause permanent and irreversible damage to the lungs, particularly in children, adults over 65, and people with heart or lung disease.  SO2 is also a major contributor to acid rain. 

The EPA estimated that if the rule were put in place at the 50 ppb level, the benefits in 2020 would include 4,700 to 12,000 fewer premature deaths a year and 3.6 million fewer cases of worsened asthma. It also calculated that the implementation costs of $1.8 billion to $6.8 billion would be greatly outweighed by the health benefits from such things as fewer emergency room visits or lost days of work.

A public hearing on the proposed sulfur dioxide regulations was held last week in Atlanta, and the new rules will become final by June.

EPA web resources on SO2 from coal

Using interactive charts and Google Earth satellite maps, the EPA website offers new interactive tools for tracking changes in sulfur dioxide emissions from individual coal-fired power plants. For example, their interactive map of pollution control technologies shows that in recent years, more and more coal-fired power plants are installing advanced controls, such as scrubbers, which dramatically reduce pollution. 


jfghrt said ..

not useful info...

September 3, 2013

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