What do these terms mean?
National Environmental Standards for air quality
The national environmental standards for air quality are regulations introduced by the Government in 2004 under the Resource Management Act (1991). These regulations set concentration limits for outdoor air quality. The primary purpose of the ambient standards is to provide a guaranteed level of protection for the health of all New Zealanders. They are not “safe” limits to pollute up to.
The standards are ambient, that is, they apply outdoors. They are further defined with reference to an averaging time (see below).
Ambient Air Quality Guidelines
In addition to the national environmental standards for air quality, New Zealand has ambient air quality guidelines. The primary purpose of the national ambient air quality guidelines is to promote sustainable management of the air resource in New Zealand. As such, the guideline values are minimum requirements that all outdoor air quality should meet in order to protect people and ecosystems from significant adverse effects. As with the national air quality standards, they are not “safe” limits to pollute up to.
Key differences between the national ambient air quality guidelines and the national environmental standards for air quality are as follows:
- The guidelines include a wide variety of pollutants, including toxics, whereas the national environmental standards include only 5 priority pollutants;
- The guidelines promote the protection of both ecosystems and human health whereas the national environmental standards are based on human health only;
- The guidelines recognise and promote the maintenance and enhancement of air quality through the use of environmental indicators (for example, the establishment of action and alert levels below the guideline values).
The national ambient air quality guidelines were last updated in 2002. Your regional council may have its own air quality guidelines. Regional guidelines may be more stringent than the New Zealand guidelines because you may have a particular air quality issue in your region. We recommend you refer to your regional air plan to find out more details for your region (see below).
Regional Air Quality Goals and Targets
Following the introduction of the regulations in 2004, all regional councils now have regional air quality plans either operative or in the final stages of becoming operative. The plans reflect particular regional circumstances and may range from being very straightforward, dealing primarily with issues of open burning, to the more complex with specific rules and plans for meeting the national environmental standards for air quality.
Regional air quality plans may further contain ambient air quality concentration limits, in the form of goals or targets, that are more stringent than either the national environmental standards for air quality or the national ambient air quality guidelines. In such cases, the more stringent concentration limit applies. Thus a regional air quality guideline that is more stringent than a national environmental standard supersedes the national standard. (The regional air quality guidelines cannot, however, be more lenient than the national environmental standards). We recommend you refer to your regional air plan to find out more details for your region.
Averaging times
An averaging time for air pollution provides a set period of time for consideration of how good or bad the air quality is. For example, the start up exhaust fumes from a dirty diesel truck is a puff of pollution that would register high concentrations over a 10 minute period. This same puff would, however, rapidly dissipate (particularly if the truck moves away) and would register lower concentrations if measured over a longer period of 8 hours.
To get a 24-hour average, the levels of a pollutant are measured at regular intervals, for example one hour or 10-minute intervals. This data is then averaged over a 24-hour period.
Carcinogen
A carcinogen is a substance that has been found to cause cancer in humans or animals.
Photochemical smog
Photochemical smog forms when gases in the air, such as nitrogen oxides and reactive organic compounds, react with sunlight to form other gases called photochemical oxidants, such as ozone.
Temperature inversion layer
Temperature inversion layers typically form just after the sun goes down on still winter nights when the temperature of the air at ground level rapidly decreases as the sun disappears. Because this layer of cool air is heavier than the warmer air above it, the cool air often becomes trapped close to the ground under the temperature inversion layer.
Inversion layers occur between 10 and several hundred metres above the ground depending on the weather conditions. Air pollution from human activities gets trapped under the inversion layer and builds up, causing air pollution levels to rise. In some places when there is little or no wind, inversion layers can linger for several days.
Last updated: 16 July 2009
