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EPA Proposes New Secondary Standards For NOx, SOx

The U.S. Environmental Protection Agency has proposed secondary air quality standards to protect the environment from nitrogen oxides and sulfur oxides.

The agency is proposing both to retain the existing secondary standards for NOx and SOx, and to add new secondary standards.

The existing secondary standards are:

  • For NO2: 0.053 ppm (parts per million) averaged over a year; and
  • For SO2: 0.5 ppm averaged over three hours, not to be exceeded more than once per year

The EPA says that these standards protect plant life from the direct effects of exposure to these pollutants in the air. Such effects can include decreased growth and foliar injury, the agency says.

The EPA is also proposing to set an additional secondary standard for each pollutant. The new standards would be identical to the public health standards that the agency strengthened last year. The new secondary standards would be:

  • For NO2: 100 ppb (parts per billion) averaged over one hour; and
  • For SO2: 75 ppb averaged over one hour

These standards would reduce the amount of NOx and SOx in the air, and the harmful effects that the pollutants have on sensitive lakes and streams, the EPA says.

The agency is already taking a number of steps to reduce NOx and SOx emissions, including the recently announced Cross-State Air Pollution Rule. This new rule will cut millions of tons of these pollutants from power plants each year, according to the EPA.

Nitrogen oxides are emitted from an array of sources, including vehicles, power plants, off-road equipment, and agricultural sources. Sulfur oxides are emitted from fossil fuel combustion by power plants, large industries, and mobile sources, and from some industrial processes.

The EPA will accept comments for 60 days after the proposed rule is published in the Federal Register and says it will issue a final rule by March 2012.

More information can be found here.

In April, the EPA proposed restrictions on sulfur dioxide emissions from a Pennsylvania power plant, in response to a petition by the state of New Jersey.

The rule required the Portland Generating Station in Northampton County, Pa., to reduce its sulphur dioxide emissions by 81 percent over a three-year period.

The New Jersey Department of Environmental Protection petitioned the EPA in September 2010 to find that the Portland power plant was impacting the state’s air quality and to require the facility to reduce its sulphur dioxide emissions.

Under the federal Clean Air Act, when a facility impacts air quality in another state, the affected state can petition the EPA and request that the facility be required to reduce its impact.

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3 thoughts on “EPA Proposes New Secondary Standards For NOx, SOx

  1. What does this statement mean: 0.5 ppm averaged over three hours, not to be exceeded more than once per year
    Lets say one has monitored for 1 month and the SO2 concentration is 10ppm, should one divide this by 30days and then by 3hrs or what please help?

  2. Tamba: Let’s say the concentration is measured by an automated device at a rate of one measurement per minute. The statement then means that three hours of measurements (i.e. 180 individual measurements) are then averaged together to produce a final number that is then to be compared to the standard of 0.5 ppm. The averaged final number cannot exceed that standard more often than once per year.

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