In addition to the key pressures covered in this report, we have some background information on other pressures that affect our air quality. We intend to examine these pressures on a case-by-case basis to assess their significance to future environmental reporting. We will consult, assess, and advise ministers and councils on the costs and benefits of improving this information
See improving environmental reporting data web page for more information.
Emissions from fuel used off road
Off-road emissions from liquid fuels (diesel and petrol) affect air quality. Off-road fuel is used in shipping, rail, aviation, recreational boating, tractors, construction vehicles, and equipment (eg lawnmowers, chainsaws, generators).
We do not have information on the quantity of emissions at the national level.
Some manufacturing, construction, and electricity production activities produce emissions of air pollutants. The most common pollutants are sulphur dioxide, PM10, and nitrogen oxides. While we do not have information on emissions from all industries, emissions from the transport industry are captured, from on-road activity, in the on-road vehicle emissions national indicator, but cannot be separated from non-industry emissions.
The contribution of industry emissions to air pollutant concentrations varies by areas, depending on how much industrial and other air pollutant emitting activities exist. For example, in 2010–11, industry contributed 5 percent of winter-time sulphur dioxide emissions in Hastings, compared with 48 percent in Gore. Likewise, industry accounted for 17 percent of winter-time nitrogen oxides emissions in Invercargill, but only 1 percent in Napier (Wilton, 2011; Hawke’s Bay Regional Council, 2010).
Primary sector emissions
Many primary sector activities can release substantial levels of air pollutants:
- pollutants from biomass burning
- pollutants dispersed from using fertilisers and pesticides
- wind-borne dust (from logging activities, tilling soil, quarrying, mining).
We do not have information on how much the primary sector contributes to our air quality.
Weather conditions can affect the quantity, patterns, and dispersal and removal rates of emissions.
The state of air quality is not only influenced by the pollutants emitted but also by the extent to which the pollutants are dispersed and removed from the air. Weather conditions play a key role in determining the quantity of emissions (eg home heating, release by ‘cold start’ of vehicles, sea spray, wind erosion) and 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 prevent pollutants from dispersing therefore allowing them to build up. Low wind speeds and cold temperatures can cause temperature inversions (see figure 28), which can further inhibit pollutant dispersion.
The impact of wind speed can be large. This is evident in small towns that emit lower quantities of pollutants than larger towns, but report higher concentrations of them.
Conversely, high wind speeds can also increase concentrations of pollutants in some conditions. For example, strong wind can create and disperse spray from the sea, or raise dust, which contribute to PM10 concentrations.
Sunlight and temperature also play a key role in producing, transforming, and breaking down air pollutants. Concentrations of ground-level ozone, for example, show a strong diurnal and seasonal pattern, driven by these factors.
Weather conditions can vary from year to year, which can cause changes in pollutant concentrations.
Topography can also influence local air quality, largely by its influence on weather conditions. For example, valley locations can be more favourable for temperature inversions. Topography can also influence wind patterns and therefore pollutant dispersal.
Figure 28: How temperature inversions trap pollution
Source: Ministry for the Environment
This image shows how temperature inversions trap pollution. In a normal situation pollution readily disperses into the atmosphere as the air cools with altitude. A temperature inversion occurs when pollution levels are trapped near ground level under a layer of warmer air.