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The pressures on our air quality

Human activities and natural pressures affect the quality of our air. This section describes these pressures, and the changes we are seeing in air quality over time.

Human pressures

This section sets out the main human sources of air pollution and their relative contribution: home heating, industry, and road motor vehicle emissions.

Main human-made sources of air pollution and their relative contribution

Burning wood or coal for home heating, emissions from road motor vehicles, combustion of fossil fuels by industry, and outdoor burning of garden and other waste by households are the main human-made sources of air pollution in New Zealand (see figure 3).

Figure 3:


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Note: Industry emissions data use data from 2008 to 2013. Estimates of other sources use data from 2013. PM10 – particulate matter 10 micrometres or less in diameter; PM2.5– particulate matter 2.5 micrometres or less in diameter; NOx – nitrogen oxides; SOx – sulphur oxides; CO – carbon monoxide. Sulphur oxide emissions are not estimated for road motor vehicles. These emissions are expected to be low.

This graph shows the relative contribution of the main human-made emission sources (household outdoor burning, road motor vehicles, industry, and burning wood or coal for home heating), to the estimated annual emissions of PM10, PM2.5, nitrogen oxides, sulphur oxides, and carbon monoxide air pollutants in 2013. Visit the MfE data service for the full breakdown of the data.

Emissions from home heating were the main source of PM10 and PM2.5 nationwide. Road vehicles (passenger vehicles and heavy commercial vehicles) were the major source of nitrogen oxides and carbon monoxide emissions. Industry was the source of 95 percent of sulphur oxides emissions.

We do not have information on the estimated emissions for other sources at a national level. Limited local studies show that emissions from other sources (shipping, aviation, rail, and off-road machinery) are generally minor.

For more detail see Environmental indicators Te taiao AotearoaRelative contribution of key human-made emission sources.

Home heating is the biggest contributor to particulate matter in our air

In New Zealand, 37 percent of households use wood for home heating and 4 percent use coal. A higher proportion of households use wood or coal for home heating in the South Island than the North Island. Illustrating this pattern, the highest proportion is in the West Coast (72 percent use wood, 56 percent use coal). In contrast, the proportion in Auckland is much lower (23 percent use wood and 2 percent use coal).

Burning wood or coal for home heating is the main human-made source of PM10 and the main source of PM2.5 emissions. In 2013, 96 percent of PM10 and PM2.5 exceedances of the short-term (daily) standard/guideline occurred during winter. These exceedances are linked to emissions from home heating, exacerbated by calmer winter conditions that slow the dispersal of pollutants.

From 2006 to 2013, estimated annual emissions of PM10 and PM2.5 from home heating decreased (24 percent and 23 percent, respectively) (see figure 4). This decrease was due to fewer households burning wood and coal for home heating and lower emission requirements for new burners. These requirements were introduced nationally in 2004 as part of the National Environmental Standards for Air Quality, but some regional and unitary councils implemented wood burner requirements before 2004, or have tougher requirements than the national standard.

Figure 4:


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Note: The left axis shows the estimated annual emissions for particulate matter 10 micrometres or less in diameter (PM10), particulate matter 2.5 micrometres or less in diameter (PM2.5), sulphur oxides (SOx), and nitrogen oxides (NOx). The right axis shows the estimated annual emissions for carbon monoxide (CO). Percentage changes show the change in emissions from 2006.

This graph shows the contribution of the key pollutants (PM10, PM2.5, sulphur oxides, nitrogen oxides, and carbon monoxide) from burning wood or coal for home heating in 2006 and 2013. Visit the MfE data service for the full breakdown of the data.

As well as a decrease in particulate matter, estimated annual sulphur oxides emissions also decreased (53 percent) from 2006 to 2013. This was due to a decrease in the use of coal for home heating.

Despite these reductions, home heating still causes levels of PM10 and PM2.5 that exceed standards and guidelines in some locations. Home heating also causes levels of arsenic (produced by burning treated-timber) and benzo(a)pyrene that exceed (or are ‘likely’ to exceed when screening methods are used) standards and guidelines in some locations. These pollutants are associated with adverse health effects ranging from respiratory irritation to cancer.

For more information see: The state of our air section.

For more detail see Environmental indicators Te taiao AotearoaHome-heating emissions.

Industry emissions are the biggest contributor of sulphur oxides

Nationally, industry is the main human-made source of sulphur oxides, and a smaller, but still significant contributor of nitrogen oxides and particulate matter.

For more detail see Environmental indicators Te taiao AotearoaIndustrial emissions.

We cannot report on changes in emissions from industry at the national level, as this information is not currently available. We have identified this data gap as an area for improvement.

For more information see: Data needs and improvements chapter.

Road motor vehicle emissions are a major source of some air pollutants

Nationally, road vehicles are the main source of nitrogen oxides (of which nitrogen dioxide is a component) and carbon monoxide emissions. Road vehicles are those used on public roads, and include passenger vehicles through to heavy commercial vehicles. Compared with petrol vehicles, diesel vehicles contribute more air pollutants (especially nitrogen oxides and particulate matter) (Parliamentary Commissioner for the Environment, 2015). This is despite making up only 27 percent of total vehicle kilometres travelled (compared with 73 percent for petrol vehicles) (NIWA, 2015).

Pollutant emissions from road vehicles are estimated to have decreased between 2001 and 2013, despite a 12 percent increase in vehicle kilometres travelled (see figure 5) (Ministry of Transport, 2015). This change represents a statistically significant decreasing trend, and is due to improvements in our vehicle fleet and fuel quality. Emission requirements for vehicles imported into New Zealand took effect in 2004 and later amendments were more stringent. Improvements in fuel quality have reduced sulphur and other pollutants in our fuel.

Figure 5:


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Note: This index reflects changes in estimated road vehicle emissions relative to a 2001 base-year value.

This graph shows the estimated annual emissions index of key pollutants (PM10, PM2.5, nitrogen oxides, carbon monoxide, and volatile organic compounds) from road transport between 2001 and 2013, indexed to their base values in 2001. Visit the MfE data service for the full breakdown of the data.

Despite these decreases, road vehicle emissions still cause levels of nitrogen dioxide (a form of nitrogen oxides) and benzene that exceed (or are ‘likely to’, when screening methods are used) standards and guidelines in some busy transport sites at major urban centres (Auckland, Hamilton, Wellington, and Christchurch).

For more detail see Environmental indicators Te taiao AotearoaRoad motor vehicle emissions.

Natural pressures

This section sets out the natural pressures on our air quality: natural sources, and weather and topography.

Natural sources can contribute significantly to airborne particulates

Sea salt, pollen, airborne soil, and volcanic ash are natural particulates that can influence our air quality.

Limited monitoring studies have shown that natural PM10 (sea salt and soil) contributes from 28 percent to 55 percent of annual PM10 concentrations at some urban locations. However, some of the airborne soil that makes up PM10 at some of these sites may be the direct result of soil disturbance caused by human activities such as construction or earthmoving (and therefore are not ‘natural’ sources).

Research on the health effects of natural particulate matter is inconclusive. However, for sea salt specifically, WHO (2013) concluded that there is little evidence that it poses a risk to health. Furthermore, the larger the size of particulate matter, the less harm it is likely to pose. Particulate matter from natural sources, such as sea salt and airborne soil, is generally large, and therefore less likely to be harmful to health.

For more detail see Environmental indicators Te taiao AotearoaNatural PM10.

Weather and topography can influence air quality

Weather conditions also influence air quality because they can determine how pollutants are dispersed and removed from the air. Weather conditions and topography play a key role in patterns and rates of dispersal and removal (by rain). High wind speeds can quickly disperse pollutants, preventing them from accumulating. Low wind speeds can slow the dispersion of pollutants, allowing them to build up.

Meteorological conditions, influenced by topography, can create ‘temperature inversions’, where a layer of warm air traps cooler air, and any pollution, underneath. This weather pattern explains why some small towns can report higher concentrations of pollutants, despite emitting lower quantities of pollutants than larger towns.