Particulate matter 10 micrometres or less in diameter (PM10)

Key points

  • From 2006 to 2012, the national average PM10 concentration fell 8 percent, from 17.0 µg/m3 (micrograms per cubic metre of air) to 15.6 µg/m3.
  • New Zealand’s average national PM10 concentration was the seventh lowest of 32 Organisation for Economic Co-operation and Development (OECD) countries in 2011.
  • In 2012, 87 percent (48 out of 55) of PM10 monitoring sites met the World Health Organization (WHO) long-term guideline. Of the seven exceeding locations:
    • PM10 levels at two sites exceeded the annual guideline by 1–10 percent
    • PM10 levels at three sites exceeded it by 11–20 percent
    • PM10 levels at two sites exceeded it by 21–40 percent.
  • In 2012, 50 percent (19 out of 38) of airsheds experienced concentrations that exceeded the national short-term standard, down from a peak of 26 airsheds in 2008. Of these 19 airsheds:
    • eight exceeded the daily PM10 standard on 2–10 days
    • seven exceeded it on 11– 20 days
    • four exceeded it on 21–50 days.
  • From 2006 to 2012, average PM10 concentrations at monitoring sites decreased by:
    •  8 percent in cities
    •  11 percent in medium-sized towns
    •  19 percent in small towns.
  • Monitoring sites in rural areas had the lowest average PM10 concentration (10.1 µg/m3) while monitoring sites in medium-sized towns had the highest (17.0 µg/m3) in 2012.

PM10 and why it’s important

PM10 is a mixture of solid particles and liquid droplets found in the air that are 10 micrometres or less in diameter (see figure 5). Particulates can be a mix of combustion particles, organic matter, metals, sulphates, nitrates, sea salt, and dust.

PM10 is emitted from the combustion of fuels, such as wood and coal (from home heating and industry) and petrol and diesel (from vehicles). Natural sources such as volcanoes, pollen, wild fires, dust, and sea salt can also produce PM10. It is also formed in the air from reactions between gases or between gases and other particles.

PM10 is a pollutant of particular concern in New Zealand because:

  • it is associated with severe health effects such as cancer, respiratory problems, and cardiovascular disease
  • relative to other pollutants, it is the pollutant that most frequently breaches national standards and international guidelines.

Figure 5: The relative size of particulate matter

Figure 5: The relative size of particulate matter

Source: Ministry for the Environment

This image illustrates the relative size of particulate matter. It compares the size of PM10 and PM2.5 to a strand of hair and a grain of beach sand.

 

National indicator: Annual average PM10 concentrations are decreasing

From 2006 to 2012, New Zealand’s annual average PM10 concentration declined (see figure 6). Since a peak of 17.0 µg/m3 in 2006 and 2007, overall concentrations have fallen 8 percent to 15.6 µg/m3.

The increase in 2011 (up 0.3 µg/m3 from 2010) was influenced by higher concentrations in Christchurch. This was due to increased dust dispersion from liquefaction and damaged roads resulting from the Canterbury earthquakes (Environment Canterbury, 2011a).

We report on annual averages as they give the best indication of general air quality conditions and long-term exposure. Most PM10 health impacts are associated with long-term exposure to PM10.

Figure 6

This graph shows Annual average PM<sub>10</sub> concentration in air - New Zealand 2006-12.

This graph shows annual average PM10 concentration in air - New Zealand 2006-12. Visit the data files page for the full breakdown of the data.

 

See About the indicators for more information on this indicator.

 

Figure 7 presents a snapshot of annual average PM10 concentrations in OECD countries. New Zealand’s national PM10 concentration is low compared with other countries. The figure also illustrates the different air quality challenges different countries face.

This international comparison covers only urban areas selected by the WHO, unlike our estimate which covers all monitored urban areas. As a result the WHO estimate and our own differ. The WHO apply the same methodology to calculate each country’s estimate. However, countries can use different monitoring approaches, so international comparisons are indicative only.

Figure 7

This graph shows Annual average PM<sub>10</sub> concentration in urban areas - OECD countries, 2011.

This graph shows annual average PM10 concentration in urban areas - OECD countries, 2011. Visit the data files page for the full breakdown of the data.

 

Annual average PM10 concentrations at most sites meet WHO long-term guideline

 

This section reports on annual average PM10 concentrations at North and South Island cities, towns, and rural locations.

Local monitoring sites have a range of annual PM10 concentrations. Figures 8–11 show the averages for different urban groups, and compare them with the World Health Organization (WHO) long-term guideline.

  • In 2012, 87 percent (48 out of 55) of PM10 monitoring sites met the WHO long-term  guideline. Exceedances occurred at monitoring sites in each of the urban groups (cities, one site; medium-sized towns, three sites; and small towns, three sites).
  • On average, monitoring sites in medium-sized towns had the highest average concentration of the groups (17.0 µg/m3) in 2012. Three of the 10 monitoring sites in medium-sized towns exceeded the WHO long-term guideline in 2012.
  • On average, monitoring sites in rural areas had the lowest average concentration of the groups (10.1 µg/m3) in 2012. These low concentrations reflect the fewer emission sources in these areas. No rural sites exceeded the WHO long-term guideline in 2012. Rural monitoring is limited to the North Island only.
  • From 2006 to 2012, average PM10 concentrations at monitoring sites decreased by:
    •  8 percent in cities
    •  11 percent in medium-sized towns
    •  19 percent in small towns.
  • In 2012, average PM10 concentrations at monitoring sites were higher in the South Island than the North Island by:
    • 42 percent in cities
    • 33 percent in medium-sized towns
    • 32 percent in small towns.
  • Higher annual PM10 concentrations in the South Island reflect the greater use of wood and coal for home heating, and relatively settled winter conditions which means less pollutant dispersion.

The WHO provides an annual health guideline of 20 µg/m3 for PM10 concentrations. However, adverse health effects can be experienced at very low concentrations (even below the guideline). WHO recommends this guideline to provide a minimum level of protection against long-term health risks (WHO, 2006).

Figure 8

This graph showsAnnual average PM<sub>10</sub> concentration – cities(1) 2006–12.

This graph shows annual average PM10 concentration – cities 2006–12. Visit the data files page for the full breakdown of the data.

 

Figure 9

 

Annual average PM<sub>10</sub> concentration – medium-sized towns(1) 2006–12

This graph shows annual average PM10 concentration - medium sized towns1 2006-12. Visit the data files page for the full breakdown of the data.

 

Figure 10

 

This graph shows Annual average PM<sub>10</sub> concentration – small towns(1) 2006–12.

This graph shows annual average PM10 concentration - small towns1 2006-12. Visit the data files page for the full breakdown of the data.

 

Figure 11

 

This graph shows Annual average PM<sub>10</sub> concentration – North Island rural areas(1) 2006–12.

This graph shows annual average PM10 concentration – North Island rural areas1 2006–12. Visit the data files page for the full breakdown of the data.

 

Five locations in New Zealand have been monitoring and reporting annual average PM10 longer than many other locations. The information they provide shows their long-term trends in PM10 concentrations (see figure 12).

 

Figure 12 shows the PM10 concentrations for one site in each of the five main cities over the past 15 years. For cities with more than one monitoring site, we selected the site based on how long the site had been monitored and on advice from councils about representativeness.

For every city, the concentrations were lower in 2012 than 10 years before. Concentrations at the Christchurch site have been declining since 1997. The higher concentrations in Christchurch during 2011 were attributed to increases in dust and its dispersion due to liquefaction and damaged roads resulting from the Canterbury earthquakes (Environment Canterbury, 2011a). The Auckland and Hamilton monitoring sites recorded decreasing concentrations from 2006 to 2010.

Figure 12

This graph shows Annual average PM<sub>10</sub> concentration – selected urban centres 1997–2012.

This graph shows Annual average PM10 concentration – selected urban centres 1997–2012. Visit the data files page for the full breakdown of the data.

 

Case study: The national standard for daily PM10 concentrations are exceeded at some locations

PM10 concentrations across New Zealand are routinely monitored by local authorities. The National Environmental Standards for Air Quality (NESAQ) (Resource Management Regulations, 2004) includes a daily PM10 standard that defines the minimum requirements outdoor air quality must meet. Monitoring the number of times the national standard is exceeded helps us understand how often people are exposed to short-term poor air quality.

In 2012, daily PM10 concentrations were measured in 38 airsheds (an area defined for air-quality management purposes, generally based around urban and city areas). Of these, 19 exceeded the daily PM10 standard (experienced short-term poor air quality) on two or more days. This is a decrease from 26 airsheds (the highest number of airsheds exceeding the daily PM10 standard) in 2008 and 2009 (see figure 13).

The NESAQ requires the 19 airsheds to meet the daily PM10 standard by 2016 or 2020. (The different target dates reflect the extent of air quality issues experienced and the levels of effort needed to comply with the daily PM10 standard.)

Of these 19 airsheds, 15 are in the South Island and four in the North. Eight airsheds exceeded the daily PM10 standard on 2–10 days, seven exceeded it on 11–20 days, and four exceeded it on 21–50 days. There have been decreases in the number of airsheds exceeding the daily PM10 standard in the 2–10 days and 21–50 day categories since 2006 and an increase in the 11–20 days category.

Of the number of times the PM10 daily standard was exceeded, 95 percent occurred during May to August. This suggests they can largely be attributed to home-heating emissions, as supported by council studies (Auckland, Waikato, Hawke's Bay, Manawatu-Wanganui, Wellington, Marlborough, Nelson, Tasman, Canterbury, West Coast, Southland) (Airshed progress reports provided by regional councils to the Ministry for the Environment for compliance reporting).

Weather conditions – such as cooler temperatures, still days, and temperature inversions that prevent the dispersal of pollutants – can occur more often in the cooler months. These conditions are also important factors in these seasonal exceedances.

Figure 13

This graph shows Airsheds that exceeded PM<sub>10</sub> national standard on 2+ days a year 2006–12

This graph shows Airsheds that exceeded PM10 national standard on 2+ days a year 2006–12.

 

See About the case studies for more information on this case study.

 

 

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