Quin Shea of the Edison Electric Institute urges a re-think on plans to tighten particulate matter standards across the United States.

The US Environmental Protection Agency (EPA) is proposing new standards for particulate matter (PM) that promises the public little, if any, real benefits. The Edison Electric Institute (EEI) believes that the scientific basis for tightening EPA’s PM standards is weak and the EPA should continue to implement the current (1997) standards, which requires state plans in 2008 and compliance in 2010.

PM is the generic term for a broad class of chemically and physically diverse substances that exist as distinct particles (liquid droplets or solids) over a wide range of sizes. These particles may be emitted directly from combustion sources such as coal combustion, motor vehicle emissions, and oil and vegetative burning, or formed in the atmosphere by transformations of gaseous emissions such as sulphur dioxide (SO2), nitrogen oxides (NOx), and volatile organic compounds.

In the electric utility industry, the emissions-control equipment used at power plants captures over 99 per cent of the particulate matter emitted from power plant stacks. However, reactions in the atmosphere involving power plant SO2 and NOx emissions create sulphates and nitrates – two of the many types of fine particulate matter.

The EPA is scheduled to issue its final rule on PM in late September 2006. Its last review of PM air quality criteria and standards was completed in July 1997. In that decision, the EPA revised the National Ambient Air Quality Standard (NAAQS) for PM in several respects, most importantly creating a new measure for the ‘fine’ (small) fractions of PM – less than 2.5 microns in diameter (PM2.5), with two new standards, an annual-average limit of 15 micrograms per cubic meter (ug/m3), and a daily limit of 65 ug/m3. In January 2006, the EPA proposed to keep the annual standard the same, but lower the daily PM2.5 limit from 65 to 35 ug/m3 (although the agency is under pressure to also lower the annual standard).

The EPA’s proposed fine particulate matter standard is so stringent that it is estimated it will cost industry $20-$60 billion every year to comply. This would make it the most expensive federal regulation since the Office of Management and Budget began keeping records in 1981. Hundreds of communities that fail the new standard would become non-attainment areas. Attracting new businesses or expanding existing plants in these areas will become difficult. Some industrial plants might have to shut down or relocate. New or expanded plants would have to obtain offsets for every tonne of new emissions.

EEI supports the establishment of air quality standards based on a complete and thorough review of the current body of scientific literature. Unfortunately, the scientific evidence upon which the EPA is relying is inconsistent and does not justify the stricter standard the agency has proposed. An internal EPA staff memo, which characterized the mortality risk of fine particles over short time periods and was clearly influential in targeting 35 ug/m3, omitted ten studies that show mostly no effect or mixed effects of PM2.5.

When the complete set of studies from the EPA’s particulate matter Criteria Document is considered, only three out of about 20 show consistently statistically significant effects of exposure to PM2.5 at levels below the current daily standard. Even if the EPA ignores the great majority of the studies and focuses only on three, these three studies suggest the need for a more modest tightening of the standard – one of the three studies suggests that the 24-hour standard should be set at about 60 ug/m3, (i.e., just below the current level of 65 ug/m3) and two suggest setting the standard at about 40 ug/m3.

Another key is that co-pollutants confuse the often reported associations between PM2.5 and health impacts. In other words, it is challenging to untangle the effects attributable to various pollutants within an air pollution mixture. More often than not, if gaseous air pollutants are considered alongside particles in statistical models to try to explain the relationship between health and air pollutants, the particle effect becomes insignificant.

Also of crucial importance is the failure to identify specific types of particles, or other pollutants present in the air along with PM2.5, that may be more significantly associated with health concerns. Without knowledge of which of the components of PM2.5 are of greatest health importance, EPA and states cannot develop strategies to reduce emissions and achieve desired health benefits with any degree of certainty. Given this uncertainty, the health benefits for strategies targeting sub-components of PM2.5 (e.g. sulphates and nitrates) could be zero.

The agency has still to completely apply its current standard for PM2.5. In fact, state plans to attain the current standard are not due until April 2008. These plans will implement programmes to bring more than 200 current non-attainment areas into compliance with the current PM2.5 standards by April 2010.

For all of these reasons we are urging EPA to keep the current PM2.5 standards in place until we know that tightening the standard will yield benefits that outweigh the costs. The US has made remarkable progress in improving its air quality. Between 1970 and 2004, the country’s total emissions of the six principal air pollutants have dropped by 54 per cent, even though demand for electricity and the country’s gross domestic product have almost doubled. Environmental regulations based on sound science are needed to ensure that this progress can continue.

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Quin Shea, executive director, environment, of the Washington-based Edison Electric Institute