About the case studies

In 2014 Air domain report we presented three national indicators of air quality. In some instances, we do not have robust or national-scale data to report on an indicator. For these, we used case studies where we have data that showed a significant component of a topic or a region. This page provides information on the case studies we used.

Case study

Daily PM10 concentrations 

Related topic Particulate matter (state)
Case study definition The number of airsheds where daily PM10 concentrations exceed the short-term national health standard – providing an understanding of how many locations experience short-term poor air quality.
Background

Exposure to high PM10 concentrations are linked to adverse health effects such as lung and heart conditions. PM10 is the air pollutant that most frequently exceeds national and international thresholds in New Zealand.

 

Reporting the number of airsheds that exceed national health standards provides an understanding of how many locations experience poor short-term air quality. Providing grouped information on how often these exceedances occur provides information on the frequency of exceedances.

Presentation of case study components
  • The number of airsheds that exceed the national health standard.
  • Grouped information on how often this standard is exceeded.
Methodology

The number of airsheds where daily PM10 concentrations exceed the short-term national health standard, and the number of days it exceeds, is obtained from regional council and unitary authority monitoring stations.

 

Monitoring information is only included if the site achieves greater than 75 per cent valid data collection and follows good practice approaches. This helps ensure the data is representative of the location.

Data coverage Approximately 40 airsheds which cover a number of locations. The population coverage is unknown, meaning a nationally representative average cannot be compiled.
Data source Regional council and unitary authority monitoring data.
Limitations to data and analysis, including level of confidence

Some of the monitoring occurs at locations expected to have the highest concentrations (for example close to road traffic or peak urban areas) in that area and may therefore not be representative of the whole population of the area it is located in.

 

The population experiencing the exceedances is unknown.

Changes to time series

The sample includes monitoring sites achieving 75 per cent valid data. The sample of monitoring sites varies year to year, with additional sites being included if best practice approaches are followed or omitted if not of adequate standard.

 

Generally, those airsheds that do exceed the standard are continually monitored until they regularly no longer exceed the standard. Therefore, the trend in the number of airsheds exceeding the standard reflects changes in airsheds exceeding the standard rather than a change in monitoring sites.

 

Case study PM2.5
Related topic Particulate matter (state)
Case study definition Annual average PM2.5 concentrations for seven sites. The concentrations are compared against the World Health Organization (WHO) long-term guideline.
Background Particulate matter less than 2.5 micrometres in diameter (PM2.5) is a subset of PM10. On average, PM2.5 is largely emitted from human activities, with a much smaller contribution from natural sources than PM10. Some research shows that certain health effects (eg cardiovascular disease and mortality) caused by PM10 are more likely to be associated with the PM2.5 component (WHO, 2013; European Environment Agency, 2013).
Presentation of case study components

Annual average concentration (micrograms per cubic metre).

 

Frequency of daily PM2.5 concentrations above the WHO short-term guideline.

Methodology

PM2.5 concentrations are determined from council monitoring stations.

 

Annual averages are reported as they indicate long-term health risks. Information is only included if the site achieves a greater than 75 percent valid data rating to help ensure the data is representative of the location. The monitoring must also use reference methods and follow good practice methodologies.

 

The sites selected are those that have greater than 75 percent valid data for 2012 and at least one other year.

 

The number of times the WHO short-term guideline is exceeded is reported as they indicate the short-term state and health risks.

 

The WHO long-term guideline is set at 10 micrograms per cubic metre.

 

The WHO short-term guideline is set at 25 micrograms per cubic metre.

Data coverage Whangaparoa, Patumahoe, Penrose, Takapuna (Auckland); Masterton; St Albans, Woolston (Christchurch); Timaru. (2008–12)
Data source

Auckland Council [Auckland Council website]

 

Greater Wellington Regional Council [Greater Wellington Regional Council website]

 

Environment Canterbury [Environment Canterbury website]

Limitations to data and analysis Average PM2.5 concentrations across measured sites are not nationally representative.
Changes to time series None

 

Case study Nitrogen dioxide
Related topic Concentration of gases (state)
Indicator definition Annual average nitrogen dioxide concentrations at three location types: state highways; (busy) local roads; and urban background sites.
Background

Nitrogen dioxide is a gas and can be directly emitted into the air. It is more commonly formed, however, from nitric oxide being emitted into the air and then reacting with other air pollutants. Both nitrogen dioxide and nitric oxide (collectively known as nitrogen oxides) are emitted from the combustion of fossil fuels (coal, gas, and oil) and from natural sources such as volcanoes.

 

Exposure to high nitrogen dioxide concentrations are linked to asthma symptoms and reduced lung development and function in children.

Presentation of indicator components Annual average concentration of nitrogen dioxide (micrograms per cubic metre) at three location types:
 
  • state highways
  • busy local roads
  • urban background sites.
Methodology

Information is obtained from the New Zealand Transport Agency’s (NZTA) nitrogen dioxide monitoring network.

 

The network consists of approximately 130 monitoring stations over 2010–12. Monitoring stations are located in each region and cover all the main urban areas, as well as other urban areas. The network uses passive monitoring to determine nitrogen dioxide concentrations.

 

Information is only included if the site achieves a greater than 75 percent valid data rating to help ensure the data is representative of the location.

 

For more information on the monitoring methodology used for the NZTA monitoring network see the National air quality (NO2) monitoring network information on NZTA’s website.

Data coverage Approximately 130 monitoring sites that cover many locations. The population coverage of the monitoring network is unknown, meaning a nationally representative average cannot be compiled.
Data source NZTA monitoring network
Limitations to data and analysis, including level of confidence

Only one gas is reported.

 

The NZTA monitoring network uses a screening method which provides results that cannot be compared directly to WHO long-term guidelines.

 

For more information on this and other limitations see the National air quality (NO2) monitoring network information on NZTA’s website.

 

The population coverage of the monitoring network is unknown.

Changes to time series Minor changes in monitoring sites during the reported period.

 

Case study Ground-level ozone
Related topic Gases (state)
Case study definition Eight-hour maximum ozone concentration at ground level at three sites in Auckland. The concentrations are compared against the World Health Organization (WHO) short-term guideline.
Background Ozone at ground level is linked to increased health risks, like respiratory and cardiovascular diseases. Ozone is not directly emitted into the air, rather it is formed by chemical reactions involving nitrogen oxides, volatile organic compounds, sunlight, and time. There is much international interest in ozone as in many countries ozone concentrations are increasing and regularly exceed WHO short-term guideline values.
Presentation of case study components Eight-hour maximum concentrations (micrograms per cubic metre) at three Auckland sites.
Methodology

The ground-level ozone concentrations are determined from Auckland Council monitoring stations. Auckland Council is the only council that regularly monitors ozone.

 

Eight-hour maximum ozone concentrations are presented as this is the time period the WHO short-term guideline is based on to provide a set level of protection against adverse health effects.

 

Monitoring information is only included if the site achieves greater than 75 percent valid data collection and follows good practice approaches (Ministry for the Environment, 2009). This helps ensure the data is representative of the location.

 

The WHO short-term guideline is set at 100 micrograms per cubic metre.

Data coverage Auckland: Musick Point, Whangaparoa, and Patumahoe, 1996–2012
Data source Auckland Council [Auckland Council website]
Limitations to data and analysis The monitoring of ozone occurs at sites where concentrations are expected to be the highest. The ozone concentrations reported cannot be taken to represent all of Auckland, or outside of Auckland.
Changes to time series None

 

Case study Number of households that burn wood or coal for home heating
Related topic Home-heating emissions (pressure)
Case study definition

This case study presents the number of households that burn solid fuel (wood or coal) for home heating. Tracking these values over time illustrates whether, at a national level, a key component of home heating emissions is increasing or decreasing.

 

This is based on information from the national census that determines the fuel type used to heat occupied private dwellings. More than one fuel type may be used, for example, electricity, gas, coal, and wood.

Background Home heating emissions have been identified as a key source of air pollution, like particulate matter (Kuschel et al, 2012). The number of homes burning solid fuel is a key component for calculating home heating emissions, along with emissions factors (which account for appliance efficiency) and quantity of fuel burnt.
Presentation of case study components Total number of homes burning solid fuel and by type of solid fuel:
  • wood
  • coal.
Methodology

The number of households that burn solid fuel for home heating is determined from the census.

 

The census asks each household to say which heat sources are used to heat this dwelling. The two options, which emit outdoor air pollutants of concern, are wood and coal. The number of households that say they burn either wood or coal, either as the only heating source or in combination with any heating source, are reported as the number of households that burn solid fuel for home heating.

Data coverage National (1996, 2001, 2006, 2013)
Data source when possible Census (1996–2013) – Statistics NZ customised request.

More information on the fuel types used to heat dwelling variable is available from Statistics New Zealand [Statistics New Zealand website].

Limitations to data and analysis, including level of confidence

The fuel type by dwelling variable has been given a quality rating of ‘high’ by Statistics NZ and is fit for use with only minor quality issues.

 

The type of fuel used by non-respondents is unknown. In each census, a number of households (approximately 5.5 percent of total households in 2013) did not respond to this question. Of these households, we assume that the proportion burning solid fuel for home heating is the same as the dwellings that responded.

 

There are other factors that influence how burning solid fuel for home heating affects air quality. This includes the quantity of solid fuel burnt and the efficiency of the appliance being used to burn the fuel. These factors are known for some urban areas, but are not currently known at a national level. This is an improvement that will be considered for future reporting.

Changes to time series

The same question was asked in censuses in 1996, 2001, 2006, and 2013.

 

There was a two-year delay for the last census following the Canterbury earthquakes. This means absolute changes between earlier adjacent censuses (eg 2001–2006) cannot be directly compared with the change from 2006–2013.

 

Case study Contribution of natural sources to PM10 concentrations
Related topic Emissions from natural sources (pressure)
Case study definition For selected monitoring sites, this case study presents the natural and anthropogenic (human-made) components of total annual PM10 concentrations.
Background

Natural sources (eg sea salt, dust, bushfires, volcanoes, pollens, and other biogenic material) can contribute to the presence of air pollutants. However, the contributions of air pollutants from natural sources are expected to remain relatively stable in the absence of significant natural events, such as large volcanic eruptions or bushfires.

 

While impacts from PM10 include the effects of natural and anthropogenic (human-made) sources, the contribution of natural sources to PM10 concentrations is beyond the control of management or abatement strategies.

Presentation of case study components Annual average concentrations of PM10 (micrograms per cubic metre), for sites which have conducted source apportionment studies, by:
  • natural sources
  • anthropogenic (human-made) sources.
Methodology

Uses information from source apportionment studies conducted over time. Source apportionment studies analyse the particles collected at some monitoring stations.

 

Source apportionment studies have been conducted at many sites in New Zealand. This case study uses the results from these studies where the results are considered to be representative of that site (at least one year of monitoring).

 

See NIWA’s Indicators for Environmental Domain Reporting report for more information. The values used for this case study are those used for the health impacts indicator, as outlined in appendix B of NIWA’s report.

Data coverage

Blenheim (2006–07)

 

Nelson (2006–12)

 

Masterton (2002–04)

 

Tahunanui (2008–09)

 

Hastings (2006–07)

 

Upper Hutt (2000–02)

 

Dunedin (2010)

 

Wainuiomata (2011–12)

 

Kingsland, Auckland (2004–07)

 

Henderson, Auckland (2006–12)

 

Penrose, Auckland (2006–12)

 

Takapuna, Auckland (2006–12)

 

Khyber Pass, Auckland (2006–12)

 

Queen Street, Auckland (2006–12)

More information is needed before a national average can be compiled.

Data source Source apportionment data and analysis provided by GNS Science
Limitations to data and analysis, including level of confidence The data accurately represents the monitoring site but are not nationally representative.
Changes to time series The data covers different time periods for different sites.

 

Published by - Mfe and Statistics
Reviewed:
16/05/14