The Environmental Protection Agency (EPA) has put forward revisions to the nitrogen oxide (NO2) air quality standard in what would be the first adjustment since 1971.
The proposals would add a one hour NO2 standard as well as additional monitoring requirements that aim to protect public health by reducing exposure to high, short-term concentrations of NO2. The proposals will also ensure that NO2 concentrations remain below levels that can cause public health problems.
According to existing scientific evidence, NO2 exposures, ranging from 30 minutes to 24hours, can cause respiratory problems, particularly for people with asthma.
Concentrations in vehicles and near major roads tend to be higher than those that are measured in the current network. Indeed in-vehicle concentrations can be as high as two-three times more than those measured as nearby community wide monitors. Near road concentrations have been measured at anything from 30-100 per cent higher than concentrations away from major roads. As a consequence individuals who spend time on or near major roads can experience short-term NO2 exposures.
Now, the EPA has proposed that for the first time, a one-hour NO2 standard at a level between 80 and 100 parts per billion (ppb) be implemented. It wants to see the current annual average NO2 standard of 53ppb retained and wants to add NO2 monitoring within 50 metres of major roads in cities with at least 350,000 residents.
After the proposal is published in the Federal Register, the EPA will accept public comments for 60 days.