Air pollution in Christchurch
Eighty percent of Christchurch’s winter air pollution comes from wood or coal burners and open fires. Only 10% comes from vehicles and 10% from industry.
To burn or not to burn
Professor Simon Kingham, from the University of Canterbury, talks about Christchurch’s very high air pollution levels in winter, mainly because people burn wood to keep their homes warm. The level of air pollution in Christchurch is by no means the worst in the world, but has been linked to ill health and increases in death related to respiratory illnesses.
The older and less efficient a fire is, the greater the quantity of emitted dangerous fine particulate emissions (known as PM10). On cold, still winter nights, these particles can form into a choking, brown smog.
Christchurch pollution problem
Professor Simon Kingham, from the University of Canterbury, talks about the high level of particulate air pollution in Christchurch, which can cause people who are already at risk of respiratory illness to die. People most at risk are the elderly, young people who have respiratory problems, such as asthma and people who have heart conditions or diseases.
For up to 50 days each winter, the level of PM10 particles in the air in Christchurch exceeds Ministry for the Environment guidelines. Research indicates each year this pollution is responsible for:
serious health problems for several thousand people, such as respiratory and cardiac illness (causing them to take time off work, which affects the local economy)
the premature deaths of more than 150 people due to respiratory or cardiac illness
higher health costs for everyone, due to heavier demand on the health system
a damaging effect on the public image of Christchurch.
Ill health and pollution
Associate Professor Simon Kingham, from the University of Canterbury, talks about how there is an association between the level of air pollution and people’s health. It seems that people who live in areas with higher air pollution are more likely to get illnesses related to air pollution such as colds, flu, asthma, emphysema, lung cancer, and even heart attacks.
In Christchurch, because there are hills close by, a layer of warmer air, known as an inversion layer, traps the smog down at street level. This directly affects the people who live there. Although the problem is at its worst in the evening, the smog is often clearly visible the next morning.
What is a temperature inversion?
You may think that, on a sunny day, it is the sun warming the air around you, but that’s not strictly true. What is actually happening is that the earth is absorbing the sunlight and then radiating that energy back out as heat. What this means is that normally the air is warmest at ground level and gradually gets colder in higher parts of the atmosphere. At the end of a cold calm winter’s day, the temperature of the earth can drop after the sun goes down. If the warm air is not moving because there are hills that prevent this, the air closer to the ground can be colder than a warmer layer above it and the two layers do not tend to mix. This is called temperature inversion. This effect traps any pollutants close to the ground, and you breathe these in, wherever it occurs.
Temperature inversion
Dr Peyman Zawar-Reza, Geography Department at the University of Canterbury, explains how temperature inversion occurs due to the heating of land during the day and cooling of air at night. He explains that, in Christchurch, temperature inversion is greater because the surrounding hills cause the cold air, which is denser, to drain down the slopes of the hills into Christchurch.
Things to think about
Temperature inversion
This diagram of a temperature inversion illustrates the way in which a layer of warm air traps a layer of cool air, and with it pollution, close to the ground. Without this inversion layer pollution would be able to rise into the atmosphere and disperse.
During a temperature inversion the cold layer closest to the ground is caused by cold dense air sinking down surrounding hills underneath the less dense warm air.
Cause and effect related to human health is hard to show.
If you were a scientist, what would do to show the link between air pollution and breathing problems?
What things would you need to think about before setting up experiments on people?
What other evidence could demonstrate that air pollution causes breathing problems?
Related content
The most common form of air pollution is from particulates – small particles released from burning material. Scientists, Professor Simon Kingham and Dr Peyman Zawar-Rezaare, are researching the link between human health and the level of particulates. Learn more about the issue of air quality.
The 2017 Connected article Sensing data describes how a team of researchers used technology and big data to help make Christchurch a healthier smarter city to live in.
Activity ideas
Explore air quality issues further with the activities Investigating air pollution and Sources and effects of air pollution.
Useful links
View data from the Environment Canterbury Regional Council monitoring air quality.
This visual guide details the major contributors to and health risks associated with air pollution, including effective ways of reducing pollution.
