Nitrogen Dioxide (NO2) and Nitrogen Oxides (NOx)

Nitrogen oxides are highly reactive gasses. They contribute to the formation of ground level ozone, and also have their own adverse effects on the respiratory system. NO2 is generally considered an indicator for this group of chemicals, but the family also includes nitric oxide, nitrous acid, nitric acid and others. Where there are emissions from transportation, NO2 forms rapidly in the air.

NOx forms small particles when it reacts with ammonia, humidity, and other compounds. These particles can engender or aggravate respiratory diseases like emphysema and bronchitis when they penetrate deeply into sensitive areas of the lungs. They can also lead to hospital visits and premature deaths by worsening existing heart disease.

Short-term exposure to NO2 can cause airway inflammation in healthy people, and for people with asthma it can cause increased respiratory symptoms. It has been connected to increased visits to emergency rooms for respiratory problems and asthma.

NO2 concentrations are considerably higher inside vehicles and near roadways than at monitors farther from roads. Concentrations inside a vehicle can be 2-3 times greater than at nearby monitors. Concentrations near roadways can be 30% to 100% times more than at the monitors. Especially at risk are children, the elderly, and people with asthma.

When NOx combines with volatile organic compounds in the presence of sunlight and heat they form ground level ozone. Ozone can cause aggravated respiratory illnesses, asthma, reduced lung function, and increased respiratory emergency room visits, hospital admissions, and premature deaths. Especially at risk for ozone are people who work or exercise outside, children, the elderly, and people with lung diseases like asthma.

Emissions that create NO2 also generally lead to the creation of other NOx. Emission control measures that control NO2 can also help to control all NOx. This can reduce the formation of ozone and also of fine particles that affect the lungs.