Nitrogen Dioxide (NO2) Pollution

Basic Information about NO2

On This Page: 

What is NO2 and how does it get in the air?

Nitrogen Dioxide (NO2) is one of a group of highly reactive gases known as oxides of nitrogen or nitrogen oxides (NOx). Other nitrogen oxides include nitrous acid and nitric acid. NO2 is used as the indicator for the larger group of nitrogen oxides.

NO2 primarily gets in the air from the burning of fuel. NO2 forms from emissions from cars, trucks and buses, power plants, and off-road equipment.

Top of Page

Effects of NO2

Health effects

Breathing air with a high concentration of NO2 can irritate airways in the human respiratory system. Such exposures over short periods can aggravate respiratory diseases, particularly asthma, leading to respiratory symptoms (such as coughing, wheezing or difficulty breathing), hospital admissions and visits to emergency rooms. Longer exposures to elevated concentrations of NO2 may contribute to the development of asthma and potentially increase susceptibility to respiratory infections. People with asthma, as well as children and the elderly are generally at greater risk for  the health effects of NO2.

NO2 along with other NOx  reacts with other chemicals in the air to form both particulate matter and ozone. Both of these are also harmful when inhaled due to effects on the respiratory system.

Environmental effects

NO2 and other NOx interact with water, oxygen and other chemicals in the atmosphere to form acid rain. Acid rain harms sensitive ecosystems such as lakes and forests.
The nitrate particles that result from NOx make the air hazy and difficult to see though. This affects the many national parks that we visit for the view.
NOx in the atmosphere contributes to nutrient pollution in coastal waters.

Top of Page

What is being done to reduce NO2 pollution?

EPA’s national and regional rules to reduce emissions of NO2 and NOx will help state and local governments meet the National Ambient Air Quality Standard (NAAQS).
EPA identifies areas where the air quality does not meet the national NO2 standards. For these areas, state, local, and tribal governments develop plans to reduce the amount of NO2 in the air.

Top of Page