Particulate matter 2.5 micrometres or less in diameter (PM2.5)

Key point

In 2012, PM2.5 concentrations met the World Health Organization (WHO) long-term guideline in all but one location, but four of the seven monitored locations exceeded the WHO short-term health guideline between 1 and 38 days.

PM2.5 and why it’s important

Particulate matter 2.5 micrometres in diameter or less (PM2.5) is a component of PM10. PM2.5 is included in PM10 measurements, but they are not separately recorded. PM2.5 comes mainly from human activities (home heating, transport, industry), and is much less influenced by natural sources than PM10.

Research shows that many of the main health effects (eg cardiovascular morbidity and mortality) attributable to particulates are more likely associated with the finer PM2.5 component than the coarser particles within PM10 (World Health Organization, 2013). This is because the smaller particles penetrate more deeply into the lungs and can be absorbed directly into the bloodstream. As a result of these findings, international interest in and monitoring of PM2.5 concentrations is increasing, and more monitoring networks are focusing on PM2.5.

Case study: The WHO long-term PM2.5 guideline is generally met, but the WHO short-term guideline is exceeded at some locations

In New Zealand, several locations are monitored for long-term (annual) and short-term (daily) PM2.5 concentrations.

Annual PM2.5 concentrations are generally lower than the WHO long-term guideline of 10µg/m3. In 2012, one exceedance was recorded.

Annual average concentrations of PM2.5 at five Auckland locations meet the WHO long-term guideline (see figure 14). In 2011, annual average concentrations in Christchurch (St Albans) exceeded the WHO guideline, but did not do so in 2012. PM2.5 annual average concentrations in Masterton exceeded the WHO guideline in 2011 and 2012.

The Christchurch and Masterton sites are ‘peak sites’ where concentrations are expected to be high due to surrounding emission sources. The Patumahoe and Whangapararoa sites are ‘background sites’ where low concentrations are expected due to few emission sources. The remaining Auckland sites are between peak and background sites.

Figure 14

This graph shows Annual average PM<sub>2.5</sub> concentration – selected locations 2008–12

This graph shows Annual average PM2.5 concentration – selected locations 2008–12. Visit the data files page for the full breakdown of the data.


In 2012, the WHO short-term guideline for PM2.5 concentrations was exceeded one day at Penrose and four days at Takapuna. The daily WHO guideline was exceeded in Masterton on 38 days while in Christchurch it was exceeded on 31 days.

Ninety-five percent of exceedances at these sites occurred from May to August, which suggests they are largely due to home heating emissions and weather conditions that prevent the dispersal of pollutants. This is supported by studies that showed home heating as the main source of winter PM2.5 at Masterton and Christchurch (Mitchell, 2012; Environment Canterbury, 2011b).

Masterton and Christchurch sites experienced relatively high PM10 concentrations, which can be attributed to home heating (Mitchell, 2012; Environment Canterbury, 2011b). Given there are a number of other sites in New Zealand with high PM10 concentrations due to home heating, it is likely that they also have high PM2.5 concentrations.

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Published by - Mfe and Statistics