Nitrogen oxides (NO+NO2) is the generic term for a group of highly reactive gases, all of which contain nitrogen and oxygen in varying amounts. Nitrogen oxides are colourless and odourless. Nitrogen dioxide (NO2) along with particles in the air can often be seen as a reddish-brown layer over many urban areas.
Nitrogen oxides are formed when fuel is burned at high temperatures. Motor vehicles are the primary man-made sources of NOx, other sources include electric utilities, industrial, commercial, and residential sources that burn fuels. NOx can also be formed naturally.
Short-term exposures may lead to changes in airway responsiveness and lung function in individuals with pre-disposing respiratory illness. Long-term exposures could render sensitive populations at risk to respiratory infection and cause irreversible changes in lung structure.
NOx contributes to the formation of ground-level ozone that causes damage to vegetation and reduces crop yields.
NOx reacts with other substances like sulphur dioxide to form acid rain that causes damage and deterioration to cars, buildings and causes watercourses to become acidic. Excess nitrogen in watercourses also causes eutrophication which leads to oxygen depletion.
Nitrous oxide is a green house gas that contributes to global warming. NOx also reacts with common organic chemicals to form other toxic products. In most urban areas, NOx together with particles can cause visibility impairment.
Particulate matter is generally the mixture of solid particles and liquid droplets in air. Particle sizes range from those small enough that can only be detected with an electron microscope, others are large enough to be seen as dust.
PM10 refers to all particles less than or equal to 10 micro-metres in diameter.
Primary particles are those that are emitted directly into the atmosphere e.g. dust from roads. Secondary particles are formed in the atmosphere from primary gaseous emissions e.g. nitrates formed from NOx emissions from vehicles and other types of combustion sources.
Those particles that are small enough to get into the lungs are the PM10 particles (i.e. less than or equal to 10 micro-metres in diameter). These particles can cause illness or are linked to heart and lung disease. Various health problems have been associated with long-term exposure. Particles can exacerbate conditions such as asthma and bronchitis; and is associated with cardiac conditions.
People with heart or lung disease, the elderly and children are at higher risk from exposure to particles.
Air borne particles can have an adverse effect on vegetation and ecosystems. It can also cause some damage to paints and building materials. Particulate matter contributes to reduced visibility in many parts of the United Kingdom.
Should you have any concerns about air pollution affecting your health please consult your GP