Glossary of air quality terms
Learn about monitoring and measuring protocols for each pollutant and parameters.
Carbon monoxide (CO)
Carbon monoxide is an odourless, colourless gas produced by incomplete oxidation (burning). Although any combustion process will contribute CO, in cities, motor vehicles are by far the largest human source. Other sources include wildfires, and natural processes such as the oxidation, in the oceans and air, of methane produced from organic decomposition.
Carbon monoxide enters the bloodstream through the lungs and inhibits transport of oxygen by blood, thereby reducing oxygen reaching the body's organs and tissues, especially the heart. People suffering from heart disease are most at risk, and may experience chest pain from CO exposure particularly while exercising.
Nitrogen dioxide (NO2)
Nitrogen dioxide is found at its highest concentrations near busy roads and can also be high indoors when un-flued gas appliances are used. It is a respiratory irritant which may worsen the symptoms of existing respiratory illness. Nitrogen dioxide makes people with asthma more susceptible to lung infections and asthma triggers like pollen and exercise.
Oxides of nitrogen (NOX)
NOX formed during combustion is composed predominantly of NO (90-95%) and a lesser amount (5-10%) of NO2.
Particles less than 10 micrometers in diameter (PM2.5)
Particles less than 2.5 micrometers in diameter. Sources include all types of combustion, including motor vehicles, power plants, residential wood burning, forest fires, agricultural burning, and some industrial processes. May also include sea salt.
Particles less than 10 micrometers in diameter (PM10)
Particles less than 10 micrometers in diameter. Sources include sea salt, crushing or grinding operations and dust stirred up by vehicles on roads.
Sigma theta
Standard deviation in wind direction. The variability of the wind direction can be used as an indicator of the amount of turbulence and therefore mixing of air. The term used is 'sigma theta', where sigma is a standard measure of variability and theta is a Greek letter commonly used to represent an angle in mathematics.
Solid particles
Solid or liquid particles may be suspended in the air and reduce visual amenity and adversely impact health. The size of a particle determines its potential impact on human health. Larger particles are usually trapped in the nose and throat and swallowed. Smaller particles may reach the lungs and cause irritation. Particles are measured in various size fractions (PM2.5, PM10 and TSP).
Temperature at 2 metres 1hr average
Ambient Temperature in degrees Celcius, measured at 2 metres above ground level.
Temperature at 10 metres 1hr average
Ambient Temperature in degrees Celcius, measured at 10 metres above ground level.
Wind direction
Vector wind direction in degrees (based on true north).
Wind speed
Vector wind speed in meters per second.
Visibility
Degree (measured in units of 'K') to which light is weakened as it passes through the air. K is a visibility attenuation coefficient, which is a measure of the degree to which a beam of light is weakened (attenuated) by as it passes through a volume of material (e.g. particles). A large value indicates that volume is relatively opaque to light; a small value indicates that the medium is relatively transparent to light.
Volatile organic compounds (VOC) as propane
Volatile organic compounds (VOC) can be formed as a result of incomplete fuel combustion. With the provision of emission management technology, VOC emissions from vehicles is very low. The main source of VOCs from fuel is via evaporation. Key VOC include benzene, toluene and xylenes. VOC are measured as equivalent propane as a simple way of comparing the emissions to the required overall limits rather than measuring each individual compound separately.