National Environmental Standards for Air Quality: Airsheds

This page provides information on air quality airsheds – areas where air quality could reach levels higher than the National Environmental Standards for Air Quality.


Although New Zealand’s air quality is mostly good, there are times when the air in urban areas is affected by pollution. The pollutant most commonly affecting our urban air is from smoke and soot (fine particles called PM10).


Air pollution can affect people’s health so National Environmental Standards for Air Quality were introduced in 2004 to set acceptable levels for air quality.

Identifying airsheds

In September 2005, regional councils and unitary authorities identified 42 areas where air quality could reach levels higher than the national air quality standards. These areas are called airsheds.


Airsheds have been identified based on councils knowledge of existing air quality data and the location of significant sources and factors that affect the spread of pollution (such as local geography and weather). These airsheds have been published in the New Zealand Gazette.


All but one of the 42 airsheds were gazetted because of known or potential concerns about levels of smoke and soot PM10) at certain times of the year. The remaining airshed at Marsden Point in Northland has the potential to breach the sulphur dioxide and PM10 standard.


Gazetted airsheds include areas where the PM10 standard is regularly breached each year, and a smaller number that have the potential to breach the standard unless carefully managed.


Seven gazetted airsheds do not appear to breach the standard, but monitoring to date is inconclusive, or emissions are expected to increase in the airshed. A further six airsheds lack any historical monitoring and have been gazetted because of their potential to breach the standard.


Councils have taken a number of approaches to defining airsheds in their region. An airshed may be based on one of the following:

  • urban areas where pollution levels may be high
  • a portion of the region covering more than one urban area
  • an area with separate, but similar, urban areas grouped together.


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The path towards complying with the PM10 standard

The PM10 standard sets a maximum concentration of 50 microgrammes per cubic metre (50µg/m3) over a 24 hour period. Levels above the standard, when concentrations are unacceptably high, are known as exceedences. The PM10 standard permits only one exceedence in a 12 month period.


Councils managing airsheds that breach the standard must plan for how to improve air quality. Air quality will be tracked along a straight or curved line path; a target set by councils that tightens every year until the standard is met by 1 September 2013.


If PM10 levels track on or above the straight or curved line path councils will not grant resource consents for any process that makes the levels worse. However, the resource consent could be granted if the proposed emissions are offset by reductions elsewhere in the airshed.


After 2013, no resource consents to discharge PM10 will be granted if the air quality standard is still being breached.

Monitoring air quality in airsheds

To track air quality in airsheds councils carry out monitoring. Monitoring is carried out where pollution levels are highest in an airshed. It is impractical to measure air quality everywhere as the air quality standards require ‘high tech’ round-the-clock monitoring.


To comply with the air quality standards many councils have had to upgrade monitoring equipment. Equipment that typically measured one day in three has been replaced by fully automated equipment that monitors continuously.


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Following progress in airsheds

The Ministry has developed a reporting framework for air quality in airsheds. This shows the location of airsheds around New Zealand and reports annual summary air quality information provided by regional and unitary authorities. This information is updated yearly.


The summary information shows:

  • peak levels of PM10 plotted against the airshed’s straight or curved line path (if the standard has been breached)
  • the number of times the PM10 standard is exceeded each calendar year
  • the most recent estimated PM10 emissions in the airshed

PM10 in the urban air

PM10 is ‘particulate matter’ that is smaller than 10 micrometers across – small enough to enter the tiniest passage of people’s respiratory systems. Some PM10, such as sea salts and dust, occur naturally and some is produced when people burn fuels such as coal, wood, oil, petrol and diesel. The main sources in the urban environment are home heating and vehicles, as well as some industrial processes.


The level of PM10 in the air depends on how much pollution is being produced (the emissions). However, other factors like the weather and local geography have a big effect. For example, windy conditions help move pollution away but features such as valleys can cause pollution to linger.


Temperature inversions that occur during cold, calm conditions can trap in pollution causing levels to be high. Years where there have been a lot of temperature inversions often have worse air quality than colder windier years even though people may have used their wood burners more often, and produced more PM10 in the colder year.


It is important to remember these effects when trying to assess improvements in air quality. Councils take this into account when setting the starting point of their straight or curved line path.

 

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Last updated: 8 February 2012