U.S. Environmental Protection Agency Administrator Scott Pruitt plans to retain the current primary National Ambient Air Quality Standards, or NAAQS, for sulfur dioxide, citing the most recent science and advice from the agency's science advisory panel.
"The U.S. is making tremendous progress reducing SO2 concentrations, and the proposal to retain the existing standard is based upon the best available science and the recommendations of our independent science advisors," Pruitt said in a May 29 statement.
The NAAQS for various pollutants must be reviewed every five years and can be retained or modified at the administrator's discretion. SO2 and other sulfur dioxides are typically produced by the burning of fossil fuels, specifically coal-fired power generation, and can contribute to acid rain and haze.
The primary standard for SO2 was last updated in 2010. After a court agreed that the EPA had failed to conduct the next review on time, the agency agreed to a consent decree requiring it to release a proposed decision by May 25 and a final decision by Jan. 28, 2019.
At this time, the EPA chief has opted to retain the primary standard of 75 parts per billion averaged over three years, according to a May 25 notice signed by Pruitt. The Clean Air Scientific Advisory Committee concurred with the EPA decision "that the current scientific literature does not support revision of the primary NAAQS for SO2," the agency said in a press release.
"The health effects evidence newly available in this review ... reaffirms the conclusions from the last review," the notice said. Therefore, the administrator has determined that the current standard is "requisite to protect public health, with an adequate margin of safety."
The notice recalled that when the primary standard was last updated in 2010 the EPA "significantly strengthened" the SO2 pollution limits. Specifically, the agency established a one-hour standard and revoked the previous 24-hour and annual standards "to provide protection from respiratory effects associated with exposures as short as a few minutes." The decision was based on evidence from public health studies that documented respiratory effects in people with asthma exposed to SO2 pollution for 5 to 10 minutes when breathing at elevated rates. The EPA also revised ambient air monitoring and reporting requirements.
SO2 pollution declined nationally by as much as 82% from 2000 to 2016, the EPA noted. This trend is likely related to Clean Air Act regulations "as well as changes in market conditions, e.g., reduction in energy generation by coal," the EPA said.
The proposal only impacts the primary SO2 standards. The EPA's Clean Air Scientific Advisory Committee continues to review "welfare-based" secondary NAAQS for sulfur oxides, nitrogen oxides and particulate matter, the EPA said. The EPA is also working on broader reforms to NAAQS reviews, which Pruitt said will "ensure we continue the dramatic improvement in air quality across the nation."
Comment on the proposed SO2 standard decision will be accepted for 45 days once it is published in the Federal Register.
