Air Pollution from Home Heating

PM₁₀ Particles are Smaller Than Human Hair

The Ministry for the Environment has set a National Environmental Standard  (NES) of 50 micrograms of PM₁₀ per cubic metre of air (averaged over 24 hours) with only one exceedence per year allowed by 2013. Another way of saying that is that the second highest concentration each year has to be lower than 50 micrograms per cubic metre of air by 2013. The NES requires regional councils to demonstrate that PM₁₀ concentrations are trending downwards in accordance with a “straight-line path”.

Other pollutants from home heating are carbon monoxide (CO) and sulphur dioxide (SO₂). The Ministry for the Environment has also set National Environmental Standards (NES) for CO and SO₂.

Carbon monoxide from home fires exceeds the NES occasionally,  but sulphur dioxide from home heating does not usually exceed the NES. Read more about other air pollutants.

Find out where we monitor and about PM10 exceedences

What Causes the PM₁₀ Pollution?

In all air sheds burning wood and coal for home heating causes most of the PM₁₀ pollution.  pollution. Some pollution is also caused by transport and industry. The amount emitted from these sources is estimated in emissions inventories.

PM₁₀ Emissions on a Typical Winter’s Day

	Home Heating (%)	Industry (%)	Transport (%)
Christchurch	82	9	9
Timaru	92	5	3
Kaiapoi	95	1	3
Rangiora	78	20	2
Ashburton	81	15	3
Waimate	98	1	1
Geraldine	Data Not Available	Data Not Available	Data Not Available

Home heating with wood and coal in combination with calm days can cause the pollution to build up during the winter months, especially in the evening when the wind often dies down on clear nights.

Although most of the pollution happens in winter, you may still see what looks like a pollution haze at other times of the year. As PM10 pollution is measured year-round monitoring can confirm the concentrations during such days do not breach the NES and the haze is more likely to be caused by natural particles such as dust, sea salt and moisture.

What Influence has the Weather?

The weather does not cause the pollution but can influence whether pollution will be blown away or not.

On still, cold winter nights a temperature inversion can occur: when the ground cools quicker than the air above, the air closer to the ground is colder than air higher up. As warm air rises, the cold air will stay close to the ground. This means that smoke from home chimneys will not keep rising up or get blown away , but gets trapped close to the ground, causing high levels of pollution.

This means that smoke from home chimneys will not rise as it would normally do, but gets trapped close to the ground, causing high levels of pollution. If there is wind, pollution will generally be blown away and diluted and pollution levels don’t generally reach high levels. This means the weather forecast is an important factor in forecasting air pollution. 

Inversion layers are typically formed when there is little or no wind and the sky is clear[1].

When the ground cools rapidly in the evening, the air close to the ground cools [2], relative to the air above [3].
Any pollution produced during this time is then trapped in the inversion layer.

What Happens if Pollution Levels Still Exceed the NES by 2013?

If the NES is still breached more than once a year by 2013 Environment Canterbury will not be able to issue any more air discharge consents for that particular air shed. If the exceedences are not trending downwards according to the straight-line path Environment Canterbury may not be able to issue any more air discharge consents for that particular air shed earlier than 2013. This may affect local industry but also solid fuel boilers in schools, hospitals etc.

Read more about the health effects of winter air pollution.

Read more about what actions Environment Canterbury is taking and what you can do to reduce the problem of winter air pollution.

Pollution Hotline

If you would like to report any pollution please call the pollution hotline on 03 366 4663 (Christchurch), 03 688 3320 (Timaru) or 0800 765588. The pollution hotline operates 24 hours a day, 7 days a week.