US EPA strengthens air quality standard for nitrogen dioxide

26 January 2010

The US Environmental Protection Agency (EPA) announced a new national air quality standard for nitrogen dioxide (NO₂). For the first time ever, a one-hour standard has been adopted to control peak short-term exposures, such as those that occur near major roads. Short-term exposures to NO₂ have been linked to impaired lung function and increased respiratory infections, especially in people with asthma, said the EPA.

The new one-hour standard for NO₂ is set at a level of 100 ppb. EPA also retained the existing annual average standard of 53 ppb.

NO₂—a component of NOx—is formed from vehicle, power plant, and industrial emissions. NO₂ is also an undesired product formed over certain types of vehicle emission control catalysts and catalytic particulate filters via oxidation of nitric oxide (NO), the other component of NOx. NO₂ contributes to the formation of fine particle pollution and smog. Earlier this month, EPA proposed to tighten the ambient smog (ozone) standards.

EPA is establishing new monitoring requirements in urban areas to measure NO₂ levels around major roads and across the community. Monitors must be located near roadways in cities with at least 500,000 residents. Larger cities and areas with major roadways will have additional monitors. Community-wide monitoring will continue in cities with at least 1 million residents.

Working with the states, EPA will site at least 40 monitors in locations to help protect communities that are susceptible and vulnerable to elevated levels of NO₂.

Based on existing 2006-2008 data, the only area that would violate the new 100 ppb standard is Cook County (Chicago), Illinois. The EPA expects to designate areas not meeting the new standard, based on the existing monitoring network, by January 2012. New monitors must begin operating no later than January 1, 2013. When three years of air quality data are available from the new monitoring network, EPA intends to redesignate areas as appropriate.

Source: US EPA