View all publications

3 Air Pollution – General

Any assessment of the health effects due to air pollution is extraordinarily complex. Firstly, assessing the level of air pollution is not a trivial exercise, as it is highly variable in space and time, affected by the weather, by what is being emitted through various activities, and by very location-specific features such as valleys and where people live and work in relation to the sources. The major source categories are summarised in Table 3.1, with further details provided in Appendix A.

Secondly, although the concept that ‘dirty air’ is bad for people has been known since ancient times, it is only within the last decade that the mechanisms have started to be identified. Furthermore, a great number of large-scale epidemiological studies have shown that effects can occur at quite low levels of pollution, over a wide range of people due to a number of different exposure scenarios – eg, which pollutant, over what time period, under which activity.

Finally, there is no one measure of ‘air pollution’. It is a common public perception that air pollution is a single thing – and most evidenced by visible pollution such as smoke. However air pollution comprises many components, not all of which are obvious or even detectable by people, and each of which can have different effects:

  • Particulates (commonly assessed as PM10) – very fine particles that can be visible, but are often not obvious – affects pre-mature mortality, and exacerbates a number of respiratory problems.

  • Carbon monoxide – a colourless gas – affects mortality slightly, but exacerbates heart disease, causes drowsiness and learning difficulties. Is strongly correlated with PM10 in cities.

  • Nitrogen dioxide – a slightly brown gas (only detectable when present over large areas) – causes breathing problems, exacerbates asthma and other respiratory problems. Tends to be well correlated with PM10.

  • Sulphur dioxide – a pungent gas – causes sore throat and eyes, and can have an effect on mortality. Not usually present in high concentrations in New Zealand.

  • Ozone – a colourless gas – present naturally, but can cause severe breathing problems in high concentrations. Not presently a serious problem in New Zealand.

  • Benzene – a component of petrol (along with numerous other hydrocarbons) – can lead to cancer.

  • Toxics – a whole range of other toxic compounds, including complex organic chemicals, process chemicals, and heavy metals. Little is known about many of these.

In summary, whilst some health effects are well known, others are not, and the state of knowledge is still developing rapidly.

This report treats air pollution and greenhouse gases as two separate entities. In addition to the source linkages between climate change and air quality, evidence exists which shows that air pollutants, especially troposphere ozone and particulate matter, play an important role in the climate system (Heywood and Shine, 1995). Air pollutants may affect climate in different ways. Tropospheric ozone is a greenhouse gas (GHG) and thus has a warming effect on the atmosphere. Particles have either a cooling effect on the atmosphere through scattering of shortwave radiation (sulphate and organic carbon particles) or a warming effect through absorption of shortwave radiation (black carbon particles). In addition to the direct effects of scattering or absorption, particles may indirectly influence climate by affecting clouds and the albedo of snow and sea ice.

Table 3.1: Breakdown of sources of air pollution (PM10) emissions (2005)

Source of emissions

Emissions
(kilotonnes per year)

Commentary

Domestic

13.5

Domestic sources are primarily emissions from the use of wood and coal in home-heating appliances. Home heating is the major source of winter air pollution in New Zealand’s towns and cities. Christchurch experiences 25 to 30 days on which the particles standard is exceeded each winter. In many areas (on both the North and South Island) domestic heating can contribute around 80–90% of the daily winter particle emissions.

Other domestic sources can include:

  • surface coating and thinners

  • aerosols

  • service stations / refuelling

  • fuel combustion

  • lawn mowing

  • cutback bitumen

  • natural gas leakage

  • off road vehicles

  • dry cleaning

  • domestic waste combustion (burn-offs)

  • other unaccounted for industrial/commercial emissions.

Industry

3.2

Large industrial installations can generate considerable quantities of air contaminants from a single source. Industrial sources include major industries such as power generation, the pulp and paper industry and dairy processing. Power generation from the burning of fossil fuels is a significant source of air pollutants. Reducing consumption of electricity has an immediate effect on air quality by reducing emissions. However, New Zealand has relatively few large industrial emitters; these are often located at some distance from heavily populated areas and are subject to local authority discharge rules.

Other industrial sources can include:

  • food manufacture

  • mining and quarrying

  • chemical manufacture

  • non-metallic minerals

  • metal manufacture

  • can coating

  • fabricated metals

  • printing

  • fuel storage.

Transport

2.1

Transport sources are primarily from internal combustion engines (vehicles) on the national roads, using petrol and diesel. Diesel effects are greatest, and are classed as cars, light commercial vehicles, heavy commercial vehicles and buses. Key generic issues of importance also effecting vehicle emissions include the composition of the fleet, the state of tuning of vehicles, congestion levels, weather factors and road design features. New Zealand has one of the highest vehicle ownership rates in the world.

Other transport sources can include:

  • marine pleasure craft/ shipping

  • rail

  • aviation.

Biogenic sources

n/a

  • Vegetation.

  • Soil

  • Sea spray.

3.1 Calculating air pollution emissions

The emissions figures given in Table 3.1 are estimates. There is currently no national emissions inventory, although a project is underway to develop the first one for New Zealand. Most regional councils have developed air pollution emissions inventories for their regions or for the major towns within their regions. These are used to track reductions measures and as input to air pollution studies such as airshed modelling (see summary in Appendix A). Some these are very detailed and have gone through several iterations. However there has been no serious attempt to accumulate all of the information and there are still regions of the country where a detailed emissions inventory has not been completed. The analysis is further complicated since different councils have used different categories – for example there is no consistent view on what sources should be included in the ‘industrial’ category, or whether the ‘transport’ category should include off-road vehicles or not, or aviation, etc.

For the purposes of this analysis, an estimate has been made on an adjusted population basis, using emissions data from those places where specific analyses have been done (listed in Appendix A). These include the major population centres of Auckland, Wellington and Christchurch as well as several other smaller towns and regions. There are regional variations that have been accounted for – such as the heavier traffic density in Auckland, the greater use of wood burning for home heating in more southern towns and those near forests, and the distribution of industries. This is a similar methodology that was used in the HAPiNZ Study (Fisher et al, 2007) to estimated PM10 concentrations in 67 cities and towns throughout New Zealand. It has proved reasonably robust for that purposes.

It should be noted that the kilotonnes per year figures given are for indicative purposes only – they are not used further in the co-benefits analysis, which is based on actual pollution concentrations in the air rather than on emissions per se (of course the two factors are closely related, but in a complex way that depends on the local meteorology and topography).