NITROGEN DIOXIDE

Nitrogen dioxide (NO₂) is a reddish-brown gas with a strong and irritating odour. It transforms in the air to form gaseous nitric acid and toxic organic nitrates. NO₂ also plays a major role in atmospheric reactions that produce ground-level ozone, a major component of smog. It is also a precursor to nitrates, which leads to more breathable particles in the atmosphere.

NO₂ can combine with water molecules to form nitric acid, which contributes to the formation of acid rain, acid snow and acid fog.

Sources

Nitrogen dioxide is one of the most common smog-causing pollutants.

The main source of nitrogen dioxide resulting from human activities is the combustion of fossil fuels (coal, gas and oil), especially gasoline used in cars.  All combustion in air produces oxides of nitrogen (NO_x), of which NO₂ is a major product.  Approximately 63 per cent of NO_x in Ontario comes from the transportation sector. A large part of the remaining 37 per cent comes from power generation, primary metal production and incineration. Natural sources of NO_x include lightning and the aerobic activity of soil bacteria. These natural sources, however, are small compared to emissions caused by human activity.

Effects on health and the environment

The main health effect of NO₂ is on the respiratory system. Inhalation of nitrogen dioxide by children increases their risk of respiratory infection and may lead to poor lung function in later life. There is also an association between nitrogen dioxide concentrations in the air and increases in daily mortality and hospital admissions for respiratory disease. Nitrogen dioxide can decrease the lungs’ defences against bacteria, making them more susceptible to infections, and can also aggravate asthma. Sensitivity increases for people with asthma and bronchitis, young children, and adults with heart and respitory disorders.

NO₂ chemically transforms into nitric acid and, when deposited, contributes to lake acidification. Nitric acid can corrode metals, fade fabrics and degrade rubber. It can damage trees and crops, resulting in substantial losses.