The pollutant is among those the EPA is required to examine periodically to determine that concentrations are at a level to ensure healthy air. Nitrogen dioxide can cause respiratory problems and is of special danger to children and people suffering from asthma and other respiratory illnesses.
The federal air quality standard for nitrogen dioxide, as it applies to health, has not been changed in 35 years.
EPA Administrator Lisa Jackson said in a statement the proposal to tighten the requirement reflects the latest scientific findings on what is needed to protect people's health.
"We're updating these standards to build on the latest scientific data and meet changing health protection needs," Jackson said. She said the proposal, if adopted, would "fill gaps in the current standard and provide important additional protections where they are needed most."
The EPA especially wants to assure that the federal requirement addresses health concerns from short term exposure of an hour or less. The proposal would maintain the current long-term concentration requirements, monitored over a year, but establish a new standard based on one-hour monitoring.
While the annual standard of a maximum 53 parts per million nitrogen dioxide concentration in the air would remain the same, the EPA wants to limit short-term concentrations - based on hour-long monitoring - to between 80 ppm and 100 ppm to provide added protection from short-term exposure.
"Current scientific evidence links short-term exposure, ranging from 23 minutes to 24 hours, with increased respiratory effects, especially in persons with asthma," the EPA statement said. These exposures, it said, often occur close to heavily traveled roadways and lead to increased visits to emergency rooms, hospital admissions and respiratory illnesses, particularly in children, the elderly and asthmatics.
The EPA set its first air quality standard for nitrogen dioxide in 1971, establishing both a standard to protect health and a secondary standard to protect public welfare. All parts of the country are well below the annual standard, but the short-term requirements need to be addressed, the agency said.
Under the ambient air quality rules, which cover a number of pollutants, the agency cannot take into account economic cost in establishing a federal standard, which is used to determine whether the air in a certain designated area is to be considered healthy. If an area has unhealthy air it risks the loss of federal highway funds and possibly other sanctions.
The EPA said it will accept public comment over the next 60 days on its nitrogen dioxide proposal and also plans to hold several hearings. It said it anticipates a final rule to be issued by January.
