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Frequently asked questions on airsheds

Why is air quality important?

Smoke and soot (PM10) in the air can affect health. It is estimated that, if the quality of air meets the new national standard, 625 lives could be saved in the next 14 years.

What can I do to improve air quality?

Our worst air pollution happens on cold, still winter nights when many of us are huddled around our wood burners or open fires. We can’t do much about the weather but we can re-think how we heat and insulate our homes. The warm homes project provides information about how to use your wood burner more effectively and cleaner ways to keep your home warm. We can also keep our cars tuned and in good condition to keep pollution to a minimum.

What is a gazetted airshed?

A gazetted airshed is a specific area identified by a council where air quality standards are (or may be) breached. These areas have been made public through the New Zealand Gazette and are known as gazetted airsheds. Maps with legal definitions are available to the public through Land Information New Zealand.

Do the standards apply outside gazetted airsheds?

Yes. Each region is an airshed in itself, and the standards apply anywhere in that region that is in the open air and where people are likely to be exposed. The standards do not apply within the boundary of a property where exposure is already covered by health and safety legislation.

What is a breach of an air quality standard?

Each air quality standard sets an acceptable maximum concentration for the pollutant concerned. For example, the air quality standard for PM10 is 50 microgrammes per cubic metre (µg/m3) measured over a 24 hour period. Levels above these concentrations are called exceedences. The standards allow a certain number of exceedences in any 12 month period. In the case of PM10 one exceedence is allowed over this time. If there are more exceedences than allowed the standard is considered to have been breached.

Is air quality bad all the time in a gazetted airshed?

Typically no - most breaches of the PM10 standard happen during cold, calm conditions in the winter when the emissions from domestic heating are higher.

To understand why pollution levels vary during the year see What makes air pollution increase? Large cities such as Auckland experience year-round emissions from traffic and can experience exceedences of the nitrogen dioxide and PM10 standards any time of the year.

What is the difference between concentration and emissions?

Concentration is the measurement of actual levels of pollution in the air we breathe.

Emissions are estimates of how much pollutant is being released into the atmosphere. Though concentration and emissions are linked, the relationship is complicated by the effects of weather. For example, in still conditions emissions linger and concentrations may be higher. Conversely, windy conditions blow emissions away and keep concentrations down.

Do Straight or Curved Line Paths apply to all pollutants covered by national standards?

No, the Straight or Curved Line Path only applies to PM10.

Why might a Curved Line Path be used instead of a Straight Line Path?

A Curved Line Path can be used if it is included in the regional plan. It might be used where a strategy to reduce pollution won’t come into effect during the initial years and reductions in pollution may not take effect immediately.

Why is there no data for some airsheds for 2005?

Monitoring equipment in some airsheds was being upgraded to meet the requirements of the national air quality standards. Data for 2006 will be more complete.

Councils are only required to monitor in airsheds where the levels of PM10 level has breached the standard. A small number of airsheds that either do not seem to breach, or lack historical data, had no monitoring in place during 2005. These airsheds are scheduled for future monitoring.

Why are there big airsheds in some regions and lots of small airsheds in another?

This is simply down to the approach taken by each regional or unitary authority. It is not possible to monitor everywhere and there are different approaches to dealing with this. One approach is to gazette a large airshed that covers a number of towns and cities. Monitoring is carried out at the worst location in this airshed.

Another approach is to individually gazette towns and cities of concern. Monitoring is carried out in the worst town and is used to represent the air quality in other similar but geographically separated areas. This is the approach taken by Otago Regional Council in which 22 separate areas have been grouped into four airsheds of similar characteristics.

Last updated: 3 November 2006