Particulate matter

This section provides monitoring data on particulate matter (PM10 and PM2.5) levels in New Zealand, including long-term exposure (annual averages) and short-term exposure (daily levels). Concentrations are measured against the National Environmental Standard for Air Quality (NESAQ) and WHO guidelines for PM exposure. 

National Environmental Standards for Air Quality (NESAQ) for PM and WHO guidelines have been developed to provide some level of protection against health risks. However, currently there is no evidence for a threshold below which health effects do not occur [1]. Moreover, at this time, New Zealand does not have a national standard for PM2.5.

What is particulate matter?

The most significant impacts on human health from air pollution are due to exposure to particulate matter (PM). PM consists of small airborne particles, including solid matter and liquid droplets. PM can affect more people than any other pollutant and the relationship between health impacts and PM air pollution is therefore well researched [1].

PM2.5 refers to particles with a diameter of less than 2.5 micrometres (Figure 1). These particles are mainly produced by combustion of fossil fuels (eg, motor vehicle emissions, burning wood and coal for home heating) and through transformation of other particles such as NOx, SO2, and organics.

PM10 refers to particles with a diameter of less than 10 micrometres, which is the major air pollutant monitored in New Zealand (Figure 1). These particles are derived primarily through suspension of dust and soil and other materials from roads, farming, construction, or mining activities, and combustion of coal and oil. PM10 also includes sea salts, mould, pollen and other plant parts [1, 2].

PM increases the risk of respiratory illness

Coarse particles such as PM10 deposit in the upper airways, whereas small particles such as PM2.5 deposit in the very small airways deep in the lungs [2].

Short-term and long-term exposure to PM10 and PM2.5 is associated with a wide range of health impacts. Mild impacts include shortness of breath or coughing. More severe impacts include premature death from cardiovascular and respiratory problems and an increased risk of lung cancer. Exposure to PM10 can also worsen asthma symptoms. Exposure to PM2.5 is associated with asthma, diabetes and adverse birth outcomes such as low birth weight, preterm birth and small-for-gestational-age births [1, 3].

Children, the elderly, and people with pre-existing conditions such as cardiovascular or respiratory diseases are particularly vulnerable to health impacts from PM air pollution [3].

Read more on the health effects of air pollution webpage.

Standards and guidelines

National Environmental Standards for Air Quality (NESAQ) for PM [3] and WHO guidelines [1] have been developed to provide some level of protection against health risks. However, currently there is no evidence for a threshold below which health effects do not occur [1]. Moreover, at this time, New Zealand does not have a national standard for PM2.5.

Exceedances of the 24-hour average threshold

Between 2006 and 2016, 45 out of 93 monitoring sites had valid data for PM10 exposure. Of the 45 monitoring stations, 38 exceeded the national 24-hour average standard on almost 3,700 occasions between 2006 and 2013 (Figure 1).

Figure 1: Number of exceedances of the NESAQ’s PM10 threshold (24-hour average) in New Zealand, 2006-2016

Between 2008 and 2016, 8 out of 35 monitoring stations had valid data for PM2.5 exposure. All eight monitoring stations with valid data exceeded the WHO daily guideline between 2008 and 2016. The guideline was exceeded on average 88-times per year (2008-2016). Timaru (Canterbury) exceeded the guideline the most, on average 62-times per monitored year (2012-2016).

Most PM exceedances occur in the colder months

More than three quarters of exceedances of the 24-hour average PM2.5 and PM10 threshold occur in the winter months (Figure 2 and Figure 3). During the cooler months, home heating emissions increase, contributing to worse PM concentrations and therefore exceedances.  Furthermore, calm and frosty weather conditions in the winter months more easily allow for a build-up of air pollutants [3].

Figure 2: Number of exceedances of the NESAQ’s PM10 threshold (24-hour average) in New Zealand, by month, 2006-2016

Figure 3: Number of exceedances of the WHO PM2.5 threshold (24-hour average) in New Zealand, by month, 2008-2016

Exceedances of the annual average WHO guideline

22 out of 45 monitoring stations exceeded the WHO annual average PM10 guideline between 2006 and 2016. In 2007, the monitoring station Arrowtown (Otago) had the highest annual average PM10 concentration (32.2µg/m3) of all monitoring stations between 2006 and 2016. Between 2006 and 2016, the annual average PM10 concentration (averaged across all 45 monitoring stations with valid data) decreased by 4µg/m3, from 19.6 µg/m3 to 15.6 µg/m3 (Figure 4).

Figure 4: Annual average PM10 concentration in New Zealand, 2000-2016

Fig 4: Annual average PM10 concentration in New Zealand, 2000-2016

Source: Ministry for the Environment and Stats NZ 2018 [3]

Between 2008 and 2016, four out of eight monitoring stations exceeded the WHO annual average PM2.5 guideline: Timaru (Canterbury), St Albans (Canterbury), Masterton West (Wellington) and Woolston (Canterbury). Takapuna (Auckland), Penrose (Auckland), Wainuiomata (Wellington) and Patumahoe (Auckland) did not exceed the guideline.

Information about the data

Particulate matter (PM₁₀) – annual average and daily values

Source: Ministry for the Environment – New Zealand’s Environmental Reporting Series: Our Air 2018

Definition: Number of monitored sites that exceeded the WHO annual average guideline for PM10 (exceedances occur when annual average concentrations are greater than 20µg/m3) and number of monitored sites that exceeded the national environmental daily (24-hour) average standard for PM10 (exceedances occur when daily average concentrations are greater than 50µg/m3; one exceedance per 12-month period allowed).

Particulate matter (PM2.5) – annual average and daily values

Source: Ministry for the Environment – New Zealand’s Environmental Reporting Series: Our Air 2018

Definition: Number of monitored sites that exceeded the WHO daily (24-hour) average standard for PM2.5 (exceedances occur when daily average concentrations are greater than 25µg/m3) and number of monitored sites that exceeded the WHO annual average guideline for PM2.5 (exceedances occur when annual average concentrations are greater than 10µg/m3).

References

  1. Ministry for the Environment and Stats NZ. 2018. Our air 2018. Data to 2017. Wellington: Ministry for the Environment.
  2. Pope CA & Dockery DW. 2006. Health effects of fine particulate air pollution: Lines that connect. Journal of the Air & Waste Management Association 56:709–42.
  3. WHO. 2013. Review of evidence on health aspects of air pollution – REVIHAAP Project. Copenhagen: WHO Regional Office for Europe.
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