Nitrogen dioxide

What is nitrogen dioxide?

Nitrogen dioxide is one of the family of chemicals known as nitrogen oxides; chemicals formed from nitrogen (N) and oxygen (O). Two of these chemicals, nitrogen dioxide (NO2) and nitric oxide (NO) are air pollutants, and are collectively known as nitrogen oxides (NOX).

These compounds are in the form of a gas, so are easily breathed in and can cause health effects, particularly to the lungs. Nitrogen dioxide can combine with different vehicle exhaust gases to form photochemical smog and ground level ozone, which also affect people's health.

In addition to these problems, nitrogen dioxide emissions contribute to acid rain, which can cause damage to trees, buildings (stonework), lakes and rivers.

Sources of nitrogen dioxide

Nitrogen dioxide comes from nature and people's activities. Natural sources include volcanic activity, and bacteria in the sea and soil. Nitrogen dioxide is also produced naturally from ammonia, which can come from farm animal waste.

Man made sources are combustion, such as burning coal and oil for electricity supply or heating, motor vehicles and industry. High levels of nitrogen dioxide indoors can be caused by the use of gas cookers and heaters, and by cigarette smoke. In London fumes from vehicles are the largest source of nitrogen dioxide, making up over half of total emissions (see chart below).

Sources of nitrogen oxides in London

Health effects of nitrogen dioxide

Nitrogen dioxide has been found to affect the lungs and cause breathing problems. It may also lead to infections of the lungs and airways. Young children and the elderly are more likely to affected by this pollutant, as are people who suffer from asthma.

Studies have shown that high levels of nitrogen dioxide indoors can cause lung problems and headaches. Further health effects are caused by the formation of photochemical smog, which occurs when nitrogen dioxide combines with other air pollutants in sunny weather.

This smog can lead to symptoms such as irritation of the eyes, nose and throat, coughing, shortness of breath, and headaches.

Levels of nitrogen dioxide in Camden

Nitrogen dioxide is routinely monitored at Swiss Cottage, Russell Square gardens (Bloomsbury) and Shaftesbury Avenue. These stations give up-to-the-minute information on pollution levels.

Results from these sites show that the levels of nitrogen dioxide are higher than the Government's Air Quality Standard of 21 parts per billion (see chart below). We also measure nitrogen dioxide at many other sites around the borough using ‘diffusion tubes'. These tubes provide average results once a month, and show that all sites close to busy roads have nitrogen dioxide levels above the air quality standard.

Only sites in background locations well away from any roads are below the standard.

Levels of nitrogen dioxide in Camden

What is being done to reduce the levels of nitrogen dioxide?

In 1995 the government brought in tighter emissions standards for diesel and petrol cars, with even tougher standards to be introduced in the year 2000. Since 1993, all new cars are now fitted with a catalytic converter which converts much of the nitrogen dioxide present in the exhaust gases into pure nitrogen and carbon dioxide.

Although this reduces emissions of nitrogen dioxide, catalysts result in more carbon dioxide being released, which is a harmful greenhouse gas.