Nitrogen oxides (NO_x ) is a group of highly reactive gasses, including nitrogen dioxide, nitrous acid, and nitric acid. For standards-setting, EPA uses nitrogen dioxide (NO₂ ) as an “indicator pollutant,” meaning, if nitrogen dioxide pollution exists in the air, so do other nitrogen oxides.

In particular, nitrogen dioxide commonly comes from fuel combustion, such as mobiles, power plants, and off-road equipment. The nitrogen oxides that form from these sources combine with volatile organic compounds (VOCs) to form ground-level ozone, the bad kind of ozone. The smallest, most harmful particulate pollution, known as PM_2.5 , is also formed from nitrogen oxides in combination with VOCs, sulfur oxides, ammonia, and particulates.

Ultimately, nitrogen oxides pollution impacts visibility, breathing abilities, water quality, acid rain, and the Earth’s temperature. 

Health and Welfare Effects

Nitrogen dioxide itself has been shown to lead to adverse respiratory effects including airway inflammation and asthma. Those living near major roadways are at high risk, considering NO₂  emissions are approximately 30-100 percent higher than areas away from roadways. 

The nitrogen oxides family can react with ammonia, VOCs, and other compounds to form PM_2.5 pollution that easily penetrates into sensitive and deep parts of the lung causing respiratory diseases like emphysema and bronchitis. NO_x also can aggravate a pre-existing heart disease, leading to premature death. 

The bad type of ozone, ground-level, is formed from when NO_x and VOCs react with sunlight and heat. Ground-level ozone acts as a dense barrier blocking pollution from escaping the higher atmosphere. This pollution grows closer to Earth and traps heat and decreases visibility. Certain groups like children, the elderly, and people with lung diseases are especially at risk of ground-level ozone, which can cause poor breathing and other respiratory issues.

Nitrogen Oxides Plans

There are no nonattainment areas in the country for the 2010 NO_x standards. Since all areas in the country are attaining the standards, Arizona has submitted the required infrastructure-SIP.  

2010 NO₂ Infrastructure SIP | Download >