PM10 is particulate matter in the air that is 10 microns in diameter or less - that’s one-fifth of the diameter of a human hair. The National Environmental Standard of 50 micrograms of PM10 per cubic metre of air doesn't sound like a big deal, but in fact PM10 at that concentration is associated with significant respiratory health problems for people.
Smoke from domestic solid fuel burning causes over 80% of the PM10 pollution problems in Canterbury. The remainder is caused by transport and industry. The amount emitted from these sources is estimated in emissions inventories which are produced every few years.
During the winter, Canterbury often has cold but settled weather with many frosty and still evenings. These are the nights when our pollution levels are at their highest because the smoke from home fires is not being blown away by wind.
When there is very little wind and clear skies at night, the land cools fast. The air closest to the earth’s surface also gets cooled through the night, creating a layer of cool air that sits below any warmer air further up.
This is called a temperature inversion. Smoke gets trapped in this inversion layer, which can be tens of metres thick, and we breathe in the trapped smoke. The inversion layer lasts until the sun warms up the land and/or the wind picks up speed again.
Although most of the pollution happens in winter, you may still see what looks like a pollution haze at other times of the year. As PM10 pollution is measured year-round, our monitoring checks whether the concentrations during such days do not breach the NES. In the summer, the haze is more likely to be caused by natural particles such as dust, sea salt and moisture.
The Ministry for the Environment has set National Environmental Standards (NES) for particulate matter (PM10), carbon monoxide (CO), nitrogen dioxide (NO2), sulphur dioxide (SO2) and ozone (O3).
The National Environmental Standard for PM10 is 50 micrograms of PM10 per cubic metre of air (averaged over 24 hours). Environment Canterbury is responsible for assisting the Canterbury airsheds of Christchurch, Timaru, Ashburton, Kaiapoi and Waimate to meet no more than three exceedances per year by 1 September 2016 and one exceedance by 1 September 2020.
The airsheds of Rangiora and Geraldine must reach one exceedance per year by 1 September 2016.
The other main air pollution sources in Canterbury are:
In Canterbury towns, vehicles are not a major cause of air pollution. However, along busy roads such as Riccarton Road in Christchurch, air pollution may be high at times. Poorly tuned vehicles can also create smoke (and sometimes odour) nuisance.
In Canterbury towns, industry is not a major source of air pollution; although in industrial areas, air pollution from commercial sources may be high at times particularly in Christchurch. Some commercial activities create odour as well as smoke.
Large-scale agrichemical spraying generally only occurs periodically in rural areas. It then presents a short-term localised source of air pollution. Best practice limits the risk of humans or animals being exposed to potentially harmful chemicals.
Odour is one of the most frequently raised concerns regarding poor air quality in Canterbury. Odour, possibly more than any other form of pollution, directly affects the "amenity values" of an area. Amenity values are those qualities and characteristics that contribute to people's appreciation of an area.
Rural burning sometimes contributes to PM10 air pollution, but the data collected on high pollution days indicate that the main source is domestic home heating.
Apart from suspended particulate (PM10), Environment Canterbury monitors the following other air pollutants: carbon monoxide, nitrogen dioxide, sulphur dioxide, hazardous air pollutants such as benzene, and ozone.
Environment Canterbury is responsible for assisting airsheds to meet the National Environmental Standard for Air Quality. A number of different tools are used to help Canterbury towns and homeowners to achieve cleaner air, including:
Incentive programmes to encourage and assist homeowners to convert to cleaner forms of heating. Examples include the Clean Heat Project between 2002-09, and town-specific incentive programmes that are currently underway.
Planning and policy to set the strategic direction for air quality management and regulatory to help achieve air quality objectives. Key statutory documents include:
Education, communication and marketing programmes to raise awareness of air quality issues and causes, and encourage residents to take action.
Scientific investigations to improve our understanding of air quality science and enable more accurate projections for the future.
Air quality monitoring to enable us to observe trends in air quality.
Good air quality is of great significance to Tangata Whenua because of the inter-relationship between air and other resources such as water, flora and fauna, and its life-supporting capacity. For Tangata Whenua, air is a taonga.
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