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The U.S. EPA has set safety levels for environmental exposure to NO₂ at 100 ppb, averaged over one hour, and 53 ppb, averaged annually.

However, NO₂ concentrations in vehicles and near roadways are appreciably higher than those measured at monitors in the current network. In fact, in-vehicle concentrations can be 2–3 times higher than measured at nearby area-wide monitors. Near-roadway (within about 50 metres (160 ft) concentrations of NO₂ have been measured to be approximately 30 to 100% higher than concentrations away from roadways.

The Basics of Detecting Nitrogen Dioxide

Properties | Exposure | Reduction

Nitrogen dioxide is an important atmospheric trace gas, not only because of its human health effects but also because as it absorbs visible solar radiation and contributes to impaired atmospheric visibility; as an absorber of visible radiation it could have a potential direct role in global climate change if its concentrations were to become high enough.

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. Indoors, exposure arises from cigarette smoke and butane and kerosene heaters and stoves.
– EPA (United States Environmental Protection Agency)

How Does Nitrogen Dioxide Effect Human Health?

NO₂ along with other NO_x reacts with other chemicals in the air to form both particulate matter and ozone. Both are also harmful when inhaled due to effects on the respiratory system.
– EPA (United States Environmental Protection Agency)

When side effects do happen, they often occur as the result of inhaling too much of the gas or inhaling the gas too fast.
Common short-term side effects include;

• Excessive sweating
• Shivering
• Nausea
• Vomiting
• Dizziness
• Fatigue

How Does Nitrogen Dioxide Effect The Environment?

NO₂ and other NO_x interact with water, oxygen and other chemicals in the atmosphere to form acid rain. Acid rain harms sensitive ecosystems such as lakes and forests. Together they can form secondary pollutants and can result in environmental problems such as acidification and nitrogen enrichment.