Air Quality Guide for Nitrogen Dioxide

Air Quality Index Protect Your Health Near Roadways

Good

(0-50)

No health impacts are expected when air quality is in this range.

Moderate

(51-100) 

Individuals who are unusually sensitive to nitrogen dioxide 

should consider limiting prolonged outdoor exertion.

Unhealthy for Sensitive Groups

(101-150)

The following groups should limit prolonged outdoor exertion: 

• People with lung disease, such as asthma 

• Children and older adults

Unhealthy

(151-200)

The following groups should avoid prolonged outdoor exertion: 

• People with lung disease, such as asthma 

• Children and older adults 

Everyone else should limit prolonged outdoor exertion.

Very Unhealthy 

(201-300) 

The following groups should avoid all outdoor exertion: 

• People with lung disease, such as asthma 

• Children and older adults 

Everyone else should limit outdoor exertion.

What You Should Know About Nitrogen Dioxide and Your Health

• Nitrogen dioxide comes from vehicles, power plants, industrial emissions and off-road sources such as 

construction, lawn and gardening equipment. All of these sources burn fossil fuels.

• People who live or work near busy roadways can experience high exposures.

• Find out more about air quality through TV, radio, newspapers, AIRNow (www.airnow.gov) and 

EnviroFlash (www.enviroflash.info), so you can take steps to protect your health.
Revisions to the National Ambient Air 

Quality Standards for Nitrogen Dioxide

On January 22, 2010, EPA strengthened the healthbased National Ambient Air Quality Standard 

(NAAQS) for nitrogen dioxide (NO2). EPA set a 

1-hour NO2 standard at the level of 100 parts per 

billion (ppb). EPA also retained the annual average 

NO2 standard of 53 ppb. 

The 1-hour standard will protect public health by 

limiting people’s exposures to short-term peak 

concentrations of NO2 – which primarily occur near 

major roads. Community-wide NO2 concentrations 

will be limited to levels below those that have been 

linked to respiratory-related emergency room visits 

and hospital admissions. 

 

Additionally, EPA established ambient air monitoring 

and reporting requirements for NO2. In urban 

areas, monitors are required near major roads and 

in other locations where maximum concentrations 

are expected. EPA has placed a number of monitors 

in locations to help protect communities that are 

susceptible to NO2-related health effects. 

What is nitrogen dioxide and where does it 

come from?

EPA’s NAAQS for NO2 is designed to protect against 

exposure to the entire group of nitrogen oxides 

(NOx). NO2 is the component of greatest concern 

and is used as the indicator for the larger group 

of NOx. The sum of nitric oxide (NO) and NO2

is commonly called NOx. Other nitrogen oxides 

include nitrous acid and nitric acid. NOx reacts with 

volatile organic compounds to form ozone. 

NO2 forms from ground-level emissions related to 

the burning of fossil fuels from vehicles, power plants, 

industrial sources, and off-road equipment, such as 

construction vehicles and lawn and garden equipment. 

In addition to contributing to ground-level ozone 

formation, NO2 is linked with a number of adverse 

effects on the respiratory system. NOx reacts with 

ammonia, moisture, and other compounds to form 

small particles. These small particles can penetrate 

deeply into sensitive parts of the lungs. 

How does nitrogen dioxide affect health?

Scientific evidence links short-term NO2 exposures, 

ranging from 30 minutes to 24 hours, with adverse 

respiratory effects including airway inflammation in 

healthy people and increased respiratory symptoms in 

people with asthma. 

Studies also show a connection between short-term 

exposure and increased emergency room visits and 

hospital admissions for respiratory illnesses.

 

Who is sensitive to nitrogen dioxide? 

Individuals who spend time on or near major roads 

can experience NO2 exposures considerably higher 

than occur away from roads. These exposures are of 

particular concern for sensitive groups, such as people 

with lung disease including asthma, children and older 

adults.

Does my community have unhealthy NO2 levels?

Unlike ozone and particle pollution, which can be 

of concern over large regions, NO2 levels are 

appreciably higher in close proximity to pollution 

sources (e.g., vehicles on major freeways, factories). 

Health effects associated with NO2 are much less 

likely farther away from these pollution sources.

NO2 in heavy traffic or on freeways can be two times 

as high as levels measured in residential areas or on 

lesser traveled roads. Monitoring studies have shown 

that within approximately 50 meters of heavy traffic/

freeways, NO2 concentrations may be 30 to 100 

percent higher.

What You Can Do To Reduce NO2 Emissions

• Carpool or use public transportation.

• When air quality is healthy, bike or walk instead of driving. 

• Combine errands to reduce vehicle trips. 

• Limit engine idling. 

• When refueling, avoid spilling fuel. Tighten gas cap securely.

• Keep your car, boat, and other engines tuned up. 

• Inflate car tires to the recommended pressure. 

• Conserve energy at home and at work.

Office of Air and Radiation (6301A)

EPA-456/F-11-003

www.airnow.gov

February 2011