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USEPA Proposes New Sulfur Dioxide NAAQS

On November 16, 2009, the U.S. Environmental Protection Agency (USEPA) proposed new, tighter National Ambient Air Quality Standards (NAAQS) for sulfur dioxide (SO₂), finding the existing standards are not adequate to protect public health.

NAAQS are designed to protect human health and the environment, with an adequate margin of safety. Once the NAAQS are established, USEPA then designates areas as "attainment" or "nonattainment" based upon monitored air quality. States are then required to promulgate regulations to achieve and maintain the NAAQS as part of their State Implementation Plans. If adopted as proposed, the change to the SO₂ NAAQS will likely result in an increase in the number of areas designated as nonattainment, which in turn will likely require additional state regulations to achieve and maintain the SO₂ NAAQS.

USEPA has not updated the air quality standards for SO₂ since they were originally established in 1971¹ at 0.14 parts per million (ppm) averaged over a 24-hour period, not to be exceeded more than once per year, and 0.030 ppm measured over an entire year. In its latest review of the SO₂ standard, however, USEPA concluded that the standard required a shorter averaging time to provide additional health protection for sensitive groups. Moreover, based on new scientific evidence and risk and exposure information, USEPA determined that a 1-hour standard would better protect against the health effects associated with shorter-term SO₂ exposures.

USEPA proposes a 1-hour SO₂ standard within the range of 50 - 100 parts per billion (ppb), based on the three-year average of the annual 99th percentile (or fourth highest) of one-hour daily maximum concentrations.² USEPA also proposes to revoke the current 24-hour and annual standards, recognizing that the new standard will have the effect of generally maintaining concentrations well below the levels of the current 24-hour and annual standards.

USEPA alternatively solicits comments and support for setting the standard as high as 150 ppb. However, if the new standard is set at greater than 100 ppb and up to 150 ppb, then USEPA proposes to retain the existing 24-hour standard.

As required by judicial order (Center for Biologic Diversity v. Johnson (Civ. No. 05-1814) (D.D.C. 2007)), USEPA must sign the final primary NAAQS for SO₂ by June 2, 2010. Assuming this deadline is met, USEPA intends to complete the initial area designations by June 2012, based on three years of complete, quality assured, certified air quality monitoring data from the current monitoring network. The comment period will close 60 days following publication in the Federal Register.

The largest sources of SO₂ emissions — those most likely impacted by the proposal — include cement manufacturing facilities, industrial boilers, industrial processes such as petroleum refining and metal processing, as well as fossil fuel combustion at electric generating units.

¹ 36 FR 8187.

² USEPA is proposing a new "form" for the SO₂ standard, similar to the new form of the ozone standard with the introduction of the eight-hour standard. USEPA proposes a concentration-based form, averaged over three years, rather than an exceedance-based form, because the concentration-based form gives proportionally greater weight to years when one-hour daily maximum SO₂ concentrations are well above the level of the standard, than to years when one-hour daily maximum SO₂ concentrations are just above the level of the standard.

RECENT ENVIRONMENTAL PUBLICATIONS

"New State Legislation Increases Funding, Availability and Scope for Green Energy Bonds in Illinois," Environmental Update (November 18, 2009)
"USEPA Continues Its Pursuit Of Greenhouse Gas Regulation," Environmental Update (October 30, 2009)
"Greenhouse Gas Emissions a Nuisance, Yes or No?" Environmental Update (October 23, 2009)
"USEPA Tightens Emissions Standards for Coal Preparation Plants and Processing Facilities," Environmental Update (October 13, 2009)

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