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EPA to Maintain Current Nitrogen Oxide (NOx) Standards
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EPA to Maintain Current Nitrogen Oxide (NOx) Standards


On April 10, EPA issued its final rule keeping two major air quality standards for nitrogen oxides (NOx). The agency left the one-hour standard at 100 parts per billion (PPB). The annual benchmark, based on an average of yearly NOx concentrations, will remain at 53 ppb.


EPA Administrator Scott Pruitt decided that the status quo should remain based on a review of existing scientific evidence. The rule was endorsed by the Clean Air Act Scientific Advisory Committee.


Pruitt signed the rule in keeping with a timetable set last year in response to a 2016 suit brought by the Center for Biological Diversity and the Center for Environmental Health, despite his opposition to sue-and-settle lawsuits.


The last review of the primary nitrogen oxides standards was concluded in 2010. While EPA is supposed to revisit the benchmarks for NOx and the other five criteria pollutants every five years, the agency has been routinely late.


The annual 53 ppb standard has been in place since 1971; the agency set the hourly 100 ppb threshold as a result of the 2010 review.

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