Current state and trends

• PM₁₀ particulates

• nitrogen dioxide

• carbon monoxide

• sulphur dioxide

• ozone.

In addition to these five key air pollutants, this section also looks at PM_2.5 particulates, benzene, and lead.

PM₁₀ particulates

State of PM₁₀ particulates in gazetted airsheds during 2005

This section provides an overview of the state of PM₁₀ particulates across New Zealand.

As most of New Zealand is expected to have good air quality, only 1.5 per cent of New Zealand’s total land area has been gazetted as airsheds to date. However, about 65 per cent of New Zealanders live in a gazetted airshed as a result of New Zealand having a highly urbanised population (see chapter 2, ‘Our environment and people’). Furthermore, about 53 per cent of New Zealanders live in a gazetted airshed that has breached the PM₁₀ particulate ambient standard.

Elevated PM₁₀ particulate levels

About 30 locations in New Zealand experience periods of poor air quality⁵ each year resulting from elevated levels of PM₁₀ particulates. Elevated PM₁₀ particulate levels are not restricted to large centres of population (see photo below). Even very small communities can experience poor air quality during winter, where domestic coal and wood burning is prevalent and conditions prevent adequate dispersion of pollutants. Auckland is particularly affected by emissions from road traffic as well as by emissions from home heating in the winter.

Air pollution in a rural community during a winter temperature inversion.

Source: Courtesy of Greater Wellington Regional Council.

Poor air quality in winter

Air pollution episodes during winter in Christchurch are generally well known. However, smaller settlements around the country such as Alexandra, Tīmaru, Nelson, and Richmond also experience poor winter air quality from elevated PM₁₀ particulate levels. Reefton, with a population of about 990, is New Zealand’s smallest gazetted airshed that experiences high winter PM₁₀ particulate levels.

Exceedences in monitored airsheds during 2005

Figure 7.3 shows the frequency and extent of exceedences of PM₁₀ particulates in monitored airsheds during 2005 (that is, the number of times levels of PM₁₀ particulates were higher than the level allowed by the ambient standard and the highest 24-hour concentration experienced).

During 2005, several airsheds, including Nelson, Tīmaru, Alexandra, and Christchurch, experienced a large number of exceedences of the ambient standard for PM₁₀ particulates.

The greatest number of exceedences (51) was experienced in the Nelson South airshed. Although Nelson South exceeded the ambient standard most frequently, monitoring in other airsheds recorded higher 24-hour concentrations. The highest 24-hour concentration in the Nelson South airshed for 2005 was 96 micrograms per cubic metre, compared with 198 micrograms per cubic metre and 154 micrograms per cubic metre in the Invercargill and Christchurch airsheds respectively.

The ambient standard for PM₁₀ permits one annual PM₁₀ particulate exceedence in 12 months. Therefore, the ambient standard was not breached in Dunedin, Taupō, and the Wairarapa for 2005 (each of which had one exceedence in 2005). The ambient standard was also not breached in the locations in Figure 7.3 for which no exceedences are shown.

The majority of the exceedences shown in Figure 7.3 are limited to the winter months, with PM₁₀ particulate levels usually meeting the ambient standard for the rest of the year. This pattern is demonstrated for Christchurch in Figure 7.4.

Figure 7.4: PM₁₀ particulate levels in Burnside, Christchurch, 2005

 

Note: µg/m3 = micrograms per cubic metre.

State of PM₁₀ particulates outside gazetted airsheds

Areas outside gazetted airsheds are sparsely populated, and, as a result, little PM₁₀ particulate monitoring occurs in the rural environment and areas free from emissions caused by human activity. However, data collected outside of the airsheds does confirm that New Zealand is expected to have good air quality in most locations.

The National Institute of Water and Atmospheric Research (NIWA) measures aerosol optical depth (AOD) in Lauder, Central Ōtago. AOD is a measure of the clarity, or visibility, of the air, and is affected by the amount of particles and light-absorbing gases in the air. Measurements of AOD at Lauder are among the lowest observed in the world (up to 10 times lower than at sites in the northern hemisphere that are considered clean), and are often similar to measurements in Antarctica and Hawaii, indicating that New Zealand has comparatively excellent air quality by world standards.

Recent trends in PM₁₀ particulate levels in the main centres

Total suspended particulate levels

The earliest data for particulate matter dates back to monitoring established in Auckland in 1964 to measure total suspended particulate (TSP) levels. TSP encompasses a wide range of particle sizes, and includes any particles with a diameter up to 50 microns. This measurement has been superseded by PM₁₀ particulate monitoring, which focuses on the more specific size range of particles associated with negative health effects.

Figure 7.5 shows a significant decrease in TSP levels over the past 40 years. Though the amount of particulates released into the air has fallen over this period, it is not known what proportion of the TSP was made up of PM₁₀ particulates. This factor makes it difficult to quantify the extent to which PM₁₀ particulate levels have fallen over the 40-year period, although some correlation would be expected.

Poor air quality in the Auckland airshed

Monitoring of PM₁₀ particulates at 12 sites in the Auckland airshed indicates that the region experiences incidences of poor air quality, including at the residential site, Takapuna (see Figure 7.6). Levels at other residential sites in Auckland show similar or slightly lower levels of PM₁₀ particulates.

Monitoring of PM₁₀ particulates at busy transport corridors in Auckland shows higher levels than in residential areas, though annual average levels at two roadside sites appear to be improving. However, this trend may have been influenced by reduced traffic flows resulting from nearby road improvements, rather than representing an overall improvement in the region.

High peak levels of PM₁₀ particulates in Christchurch

Of the five main centres of population, Christchurch experiences some of the highest peak levels of PM₁₀ particulates, mostly during winter temperature inversions. Monitoring at the residential site, St Albans, shows incidences of poor air quality each year, with more than 50 exceedences recorded in 1999 and 2001 (see Figure 7.6). The topography of the Canterbury Plains is particularly vulnerable to temperature inversions, so several other airsheds in the region have similar incidences of poor air quality during the winter.

Winter exceedences of PM₁₀ particulates in Hamilton and Dunedin

Hamilton and Dunedin experience exceedences of the ambient standard for PM₁₀ particulates during the winter. Residential monitoring sites in Hamilton and Dunedin have experienced poor air quality in recent years (see Figure 7.6). Note that the Dunedin data is based on monitoring equipment that is unable to monitor on a daily basis. Continuous monitoring equipment has recently been installed that will provide a better picture of annual PM₁₀ particulate levels than was previously possible.

No exceedences recorded in Wellington

No long-term data on air quality in residential areas is available for central Wellington. However, monitoring at busy roadside locations around Wellington indicates no exceedences of the ambient standard to date.

Monitoring of PM₁₀ particulates in residential areas is carried out in other parts of the Wellington region, such as Upper Hutt (see Figure 7.6). Though potentially susceptible to wintertime pollution episodes, this site has had no exceedences of the ambient air quality standard recorded.

Sources of PM₁₀ particulates

Emissions vary depending on the time of year

The quantity and main sources of PM₁₀ particulate emissions caused by human activity change seasonally, depending on the type of activities at different times of the year. Winter emissions have the greatest effect on air quality because this time of year tends to be when emissions are highest. For example, Auckland produces an estimated 29 tonnes of PM₁₀ particulates each day during the winter, with 64 per cent of emissions coming from home heating sources. In the summer, this level falls to an estimated 10 tonnes each day, with most emissions coming from the transport sector.

Home heating is a main source of PM₁₀ particulates in winter

Home heating is the biggest source of PM₁₀ particulates during winter in all five main centres of population. In metropolitan Christchurch and Dunedin a particularly high proportion of winter PM₁₀ particulates come from home heating.

Method of home heating affects PM₁₀ particulates

Although home heating is the main source of winter PM₁₀ particulates in Hamilton, emissions are lower than for many other urban areas in the region. A large proportion of Hamilton households (64 per cent) use gas to heat their main living areas, and only 1 per cent of households burn coal (Environment Waikato, 2006b). (Particulate emissions from gas appliances are negligible.)

Figure 7.7 shows typical PM₁₀ particulate emissions from different types of home heating appliances. Both Auckland and Christchurch have reported lower PM₁₀ particulate emissions in recent years. Over the same period, homeowners have changed to methods of home heating that produce less pollution.

Total home heating emissions in metropolitan Christchurch decreased by 15 per cent between 1999 and 2002 (despite an increase in the number of households). This decrease in emissions coincided with a regional decrease in the use of open fires, coal, and wood and an increase in the use of electricity, oil, and gas (Environment Canterbury, 2004).

Road traffic emissions as a source of PM₁₀ particulates

Road traffic is another significant source of PM₁₀ particulates, and is the main source of PM₁₀ particulate emissions in Auckland over an entire year. About 73 per cent of PM₁₀ particulate emissions from motor vehicles come from diesel exhaust alone (Auckland Regional Council, 2006b). The use of diesel fuel is expected to increase, particularly in commercial vehicles (Ministry of Economic Development, 2006).

Contribution to emissions from diesel vehicles

Badly tuned vehicles contribute a significant amount of air pollution. It is estimated that 10 per cent of all vehicles produce about 40 per cent of total vehicle emissions (Ministry of Transport, 2007). Emissions are made worse when an engine is poorly tuned. A diesel engine can continue running in a more neglected state than can a petrol engine.

Both diesel and petrol contain small amounts of sulphur that is not removed during the refining process. Sulphur in diesel leads to the formation of sulphate particulates. Reducing the sulphur content of diesel reduces emissions of PM₁₀ particulates and ensures fuel is suitable for the introduction of newer-technology vehicles that produce lower emissions.

Nitrogen dioxide

Recent trends in nitrogen dioxide levels in the main centres

Sites close to major roads or industrial sources are the most likely locations to be affected by elevated levels of nitrogen dioxide. The roadside Khyber Pass Road site in Auckland (see Figure 7.8) is located alongside a heavily congested road, carrying more than 27,000 vehicles each day. This site experiences periods of poor air quality each year. In 2001, the site experienced an unusually high number of exceedences (53 exceedences over 23 days), illustrating the effect that atmospheric conditions can have on pollution levels in different years.

Monitoring at two recently commissioned roadside sites in Wellington reports higher levels of nitrogen dioxide than in residential areas, but nevertheless indicates good air quality.

Levels of nitrogen dioxide in residential areas of Christchurch and Wellington also indicate good air quality (see Figure 7.8). Though the Christchurch site has experienced poor air quality in the past, nitrogen dioxide levels have been good over the past 10 years.

Figure 7.8 also shows nitrogen dioxide levels at the industrial Penrose site in Auckland. This site is fringed with residential properties that are likely to experience higher levels of nitrogen dioxide than are other Auckland residential monitoring sites. The industrial Penrose site has not exceeded the ambient standard more than the nine times permitted by the standard. However, this site has experienced exceedences of the ambient standard for nitrogen dioxide during some years.

No long-term, continuous nitrogen dioxide monitoring occurs in Hamilton or Dunedin. Monitoring surveys conducted in Hamilton during 1998 and 1999 indicate that nitrogen dioxide levels were low. Monitoring methods used in Dunedin differ from methods used at sites in Figure 7.8, so results from Dunedin cannot be assessed in the same way as the result of other main centres.

Sources of oxides of nitrogen

Most emissions are not emitted as nitrogen dioxide but mainly in the form of nitric oxide. Once released to the atmosphere, nitric oxide can be further oxidised to form harmful nitrogen dioxide. Estimates of emissions are for this reason always expressed as oxides of nitrogen.

Transport is the main source of oxides of nitrogen in all main centres of population, accounting for about 80–90 per cent of emissions. It is interesting to note that a significant proportion of oxides of nitrogen emissions in Wellington come from shipping.

In Auckland, estimates of oxides of nitrogen emissions have increased slightly since 1998. This is attributed to an increase in the number of diesel vehicles in the region (Auckland Regional Council, 2006b). Diesel vehicles produce higher oxides of nitrogen emissions than an equivalent petrol engine. At a national level, the number of diesel vehicles on the roads has increased by 39 per cent between 2001 and 2006 (see chapter 4, ‘Transport’).

In contrast, estimates of oxides of nitrogen emissions from motor vehicles in Christchurch have decreased by 5 per cent, despite a 12 per cent increase in the number of vehicle kilometres travelled. This is thought to be the result of an increase in the number of vehicles with emission control equipment in the region (Environment Canterbury, 2004).

Recent emission estimates for Dunedin do not include motor vehicle emissions.

Carbon monoxide

Recent trends in carbon monoxide levels in the main centres

Results of monitoring at Auckland and Christchurch sites

Levels of carbon monoxide at the Auckland and Christchurch monitoring sites appear to have fallen over the past 10 years (see Figure 7.10). This trend has been particularly noticeable at Auckland’s roadside Khyber Pass Road site, which is strongly affected by traffic emissions. The site experienced a large number of exceedences of the ambient standard for carbon monoxide in the second half of the 1990s (including 190 exceedences over 47 days in 1997), but has experienced no exceedences since 1999.

Carbon monoxide levels measured in a residential area of Christchurch have also noticeably reduced. No data is available for roadside sites in Christchurch.

Results of monitoring at Hamilton and Wellington sites

Carbon monoxide levels in Hamilton and Wellington remain below the ambient standard. Monitoring was established in central Wellington in 2004 to assess the influence of transport emissions in a heavily trafficked area. Although levels are higher than those of the Lower Hutt site, levels of carbon monoxide at the central Wellington site remain well below the limit set by the ambient standard.

Dunedin screening surveys

No permanent monitoring has been established in Dunedin, but screening surveys suggest that carbon monoxide levels in Dunedin meet the ambient standard.

Sources of carbon monoxide emissions

Transport as a source of carbon monoxide emissions

Transport is the main source of carbon monoxide in New Zealand. Emissions estimates indicate that transport contributes 85 per cent of annual carbon monoxide emissions in Auckland and 51 per cent of winter emissions in metropolitan Christchurch.

Carbon monoxide emissions in both Auckland and Christchurch have fallen in recent years despite increasing numbers of vehicles and vehicle kilometres travelled. Although private vehicles and congestion increased in metropolitan Christchurch between 1999 and 2001, emissions estimates indicate that carbon monoxide from motor vehicles fell by 15 per cent (Environment Canterbury, 2004). The fall in carbon monoxide emissions is thought to result from the increasing numbers of vehicles with emission control equipment.

Home heating as a source of carbon monoxide emissions

Changes in home heating also influence emissions of carbon monoxide. In Christchurch, 48 per cent of carbon monoxide emissions are estimated to come from home heating. Between 1999 and 2002 domestic emissions of carbon monoxide decreased by 13 per cent. This decrease was due to increased use of gas and electricity and a decrease in coal and wood burning, although wood remains a popular fuel choice in Christchurch (Environment Canterbury, 2004).

Sulphur dioxide

Recent trends in sulphur dioxide levels in the main centres

Figure 7.9 shows a steady fall in sulphur dioxide levels during the 1970s and 1980s as a result of the declining use of coal and heavy fuel oils in Auckland. Monitoring at other locations around New Zealand indicated a similar improvement in levels and was gradually discontinued. In the mid-1990s, sulphur dioxide levels in Auckland increased again, coinciding with an increase in the registration of new and imported diesel vehicles (particularly heavy goods vehicles).

In recent years, improved monitoring methods have shown that the Penrose site in Auckland has had good air quality with respect to the ambient standard for sulphur dioxide (see Figure 7.11). The fall in sulphur dioxide levels at this site between 2001 and 2002 coincides with a significant reduction in the sulphur content of diesel fuel in the Auckland region. However, since 2002 the annual average has increased each year.

Levels at the residential Christchurch site (see Figure 7.11) have fallen since the early 1990s, and indicate that levels of sulphur dioxide are not of concern. However, other monitoring sites in the Canterbury region near industrial sources (such as Woolston and Hornby) have occasionally recorded high levels of sulphur dioxide.

Levels of sulphur dioxide in Hamilton, Wellington, and Dunedin are generally considered to be low and are not monitored.

Sources of sulphur dioxide

The main sources of sulphur dioxide vary across the country. In Auckland, the main source is transport emissions. In Christchurch, 80 per cent of daily wintertime emissions of oxides of sulphur come from industrial sources such as coal-fired boilers, and, to a lesser degree, diesel boilers. Vehicle emissions of sulphur dioxide in Christchurch are increasing and have been attributed to an increased number of diesel vehicles on the road (Environment Canterbury, 2004).

Figure 7.11 shows that 92 per cent of winter sulphur dioxide emissions in the Wellington region are from transport. Emissions inventories estimate that 93 per cent of these emissions come from commercial shipping (Air and Environmental Services Ltd, 2001). Motor vehicles are the largest source of winter sulphur dioxide in Hamilton (49 per cent), closely followed by industry (44 per cent) (Environment Waikato, 2006b). In contrast, the main source in Dunedin is industry (85 per cent), followed by home heating (15 per cent) (Otago Regional Council, 2005a). No data is available for transport in Dunedin.

Figure 7.10: Carbon monoxide (CO) levels and emissions in main centres of population

 

See figure at its full size (including text description).

Ozone

Recent trends in ozone levels in the main centres

Auckland, Christchurch, and Hamilton have been identified as having the highest potential for ozone pollution (photochemical smog) during the summer (National Institute of Water and Atmospheric Research, 1996). Ozone is a secondary pollutant that requires precursor pollutants and its formation is a slow and complex process. Consequently, the highest levels tend to be found some tens of kilometres downwind of the sources of precursor pollutants.

Auckland has four ozone monitoring sites including Musick Point (see Figure 7.12). No exceedences of the ambient standard for ozone have occurred during the course of the monitoring. The Musick Point monitoring site did, however, exceed the ambient guideline twice in 2002.

Ozone is not monitored in metropolitan Christchurch. Instead, it is measured in Lincoln, 20 kilometres south west of Christchurch, where levels are expected to be highest. Monitoring for ozone during the summers of 1998 and 2003 indicated no exceedences of the ambient standard.

A short screening survey carried out in Hamilton during the 2003 summer indicated that ozone levels were considerably below the ambient standard.

Figure 7.12: Ozone levels at Musick Point, Auckland, 1996–2005

 

Note:
µg/m³ = micrograms per cubic metre.

Data source: Auckland Regional Council, 2006a.

Text description of figure

Year	1hr max (µg/m3)	Annual average
1996	84.2	31.5
1997	111.8	30.4
1998	102.4	35.2
1999	92.2	40.8
2000	82.3	36.0
2001	90.3	35.5
2002	135.0	43.7
2003	134.0	43.6
2004	110.6	43.3
2005	100.1	46.6

Sources of ozone precursors

In Auckland and Hamilton, the main source of ozone precursors (oxides of nitrogen and volatile organic compounds) is traffic. In Christchurch, the main source of ozone precursors is traffic, but 60 per cent of the volatile organic compounds come from home heating (Ministry for the Environment, 2003).

PM_2.5 particulates

Monitoring indicates that the relationship between PM_2.5 and PM₁₀ particulate levels can vary during the year. For example, monitoring in Christchurch indicates that the levels of PM₁₀ and PM_2.5 particulates are similar in winter, but less so in summer. During summer, a larger proportion of the PM₁₀ particulates come from natural sources such as sea salt and soil particles, which are largely absent in PM_2.5 particulates. During winter, both PM₁₀ and PM_2.5 particulates in Christchurch come mainly from combustion sources such as home heating, so levels are more similar.

Most particulate monitoring in New Zealand is for PM₁₀ particulates rather than PM_2.5 particulates.

Figure 7.13: Levels of PM_2.5 particulates in Mount Eden, Auckland, 1997–2005

 

Note:
µg/m³ = micrograms per cubic metre.

Data source: Auckland Regional Council, 2006a.

Text description of figure

Year	Auckland (Mount Eden)
	24hr max (µg/m3)	Annual average
1996
1997	31.9	11.9
1998	24.6	11.4
1999	33.7	9.9
2000	29.2	10.4
2001	39.9	8.8
2002	21.2	6.9
2003	24.0	6.2
2004	24.4	7.2
2005	27.7	5.5

Monitoring for PM_2.5 particulates has been carried out at several sites around Auckland. Long-term monitoring from Auckland’s residential Mount Eden monitoring site indicates an overall decrease in the annual average (see Figure 7.13). Generally, Auckland experiences a few exceedences of the reporting guideline each year. The highest number of exceedences occurred at the Penrose industrial site. Exceedences of the reporting guideline are summarised in Table 7.3.

Table 7.3: Exceedences of the reporting guideline for PM_2.5 particulates around Auckland, 1997–2005

Note:

µg/m³ = micrograms per cubic metre.

Data source: Auckland Regional Council, 2006a.

Some PM_2.5 particulate monitoring has been carried out in Christchurch. Environment Canterbury estimates that during nights of high PM₁₀ particulate levels, 90 per cent of the particles are likely to be PM_2.5 particulates (Foster, 1998).

Winter PM_2.5 particulate levels are summarised in Table 7.4. In places where the source of PM₁₀ particulates is predominantly from home heating, PM_2.5 particulate levels are likely to exceed the reporting guideline (25 micrograms per cubic metre) more frequently than the PM₁₀ particulate levels exceed the ambient air quality standard (50 micrograms per cubic metre). For example, in 2001 there were 49 exceedences of the PM_2.5 particulate reporting guideline compared with 37 exceedences of the PM₁₀ particulate ambient standard.

Table 7.4: Winter PM_2.5 particulate levels at St Albans, Christchurch, 2001 and 2005

Note:

µg/m³ = micrograms per cubic metre.

Data source: Environment Canterbury, 2006.

Benzene

Annual benzene levels measured at an industrial Auckland site and residential Christchurch site (see Figure 7.14) are below both the current ambient guideline (10 micrograms per cubic metre) and the guideline limit of 3.6 micrograms per cubic metre that will take effect in 2010. Levels at roadside sites in Christchurch were higher than those in residential areas. While the Christchurch roadside levels of benzene met the current ambient guideline, annual average concentrations for 2004–2005 were greater than 3.6 micrograms per cubic metre.

Benzene levels at all Christchurch sites are decreasing (Environment Canterbury, 2005). Environment Canterbury attributes the decrease in benzene levels to improvements in vehicle emissions technology, changes in fuel specifications, and possibly, changes in the number of domestic wood burners in favour of electricity or gas. Benzene levels in petrol were reduced from 4 parts per million to 1 part per million in January 2006, which should help to further improve air quality.

Monitoring of benzene in Hamilton indicates improving air quality, with all monitored sites meeting the 2010 ambient guideline between September 2005 and September 2006 (Environment Waikato, 2006a).

Figure 7.14: Benzene levels in Auckland and Christchurch, 2001–2005

 

Note:

µg/m³ = micrograms per cubic metre.

Data source: Ministry for the Environment, 2006b.

Text description of figure

	Auckland (Penrose)	Christchurch (St Albans)
Year	Annual average	Annual average
2001	2.6	6.4
2002	2.1	3.8
2003	2.1
2004	2.2	2.4
2005	1.9	2.1

Emissions data for benzene has not been widely compiled in New Zealand, and emissions factors for different sources are not well established. However, data indicates the main source of benzene emissions in Auckland is from motor vehicles. In Christchurch, home heating is the main source (51 per cent) followed by road transport (42 per cent) (Ministry for the Environment, 2003).

Lead

Figure 7.15 shows a downward trend in airborne lead levels measured at three Auckland sites as a result of the reduction of lead levels in petrol, culminating in lead-free petrol in 1996. Monitoring in Christchurch indicates that levels are also well below the ambient guideline for lead.