Nitrogen Dioxide

Nitrogen dioxide (NO2) is a gas formed from one nitrogen atom and two oxygen atoms.

Nitrogen dioxide is formed to a small extent directly in combustion processes. However, most nitrogen based combustion products are emitted as nitric oxide (NO). Nitric oxide is relatively unstable and is rapidly oxidised to nitrogen dioxide in air. When low level ozone (another atmospheric pollutant) is present, it is often the ozone molecule that contributes to this process. The relative proportions of nitric oxide and nitrogen dioxide generated from any source can be very variable and as such when both gases are being emitted they are often referred to as ‘oxides of nitrogen’ (NOx) The most significant source of these gases is road transport which accounts for 40% of the total UK emission.

Since 1989, total NOx emissions have declined by 45% as a result of a 52% decrease from road transport, due to the introduction of catalytic converters and stricter regulations and a 47% reduction from power stations.

The principal health effects of nitrogen dioxide relate to impaired lung performance from changes in structure and function and suspected hyper reactivity to allergens (causes of allergic response). Effects are reversible; however, ongoing exposure may lead to poorer lung function later in life. Exposure to high concentrations for short periods is considered more toxic than low concentration exposure for long periods.

Oxides of Nitrogen (Nox) Uk Emission Graph

Data and Graph provided by UK National Atmospheric Emission Inventory