Why air quality matters

Good outdoor air quality is fundamental to our well-being. On average, a person inhales about 14,000 litres of air every day, and pollutants in this air can adversely affect people’s health. People with pre-existing respiratory and heart conditions, the young, and older people are particularly vulnerable.

Air quality can also affect our economy through its impact on people’s health through higher medical costs and lost productivity. It also affects the environment. When air pollutants settle on land or waterways or wash into waterways, they can pollute these environments. Certain air pollutants can also affect our climate.  Some have a warming effect while others have a cooling effect.

(Source: https://environment.govt.nz/publications/environment-aotearoa-2015/)

What is air pollution?

Air pollution is a complex mixture of gases and particles arising from many different sources. Air quality is affected by many substances produced by human activities (e.g., burning of fuels) and by natural sources (e.g., volcanic eruptions, windblow dust, pollen and sea salt).

Airborne particles

Airborne particles are generated by human activities and arise from natural sources. Common activities that lead to particles being released into our air include burning wood for home heating, vehicle exhausts (particularly diesel), road dust and quarrying. Natural sources include sea salt, pollen and wind-blown soil particles, including liquefaction dust. Collectively all airborne particles are called particulate matter abbreviated to PM. We commonly classify particles by their size:

• PM₁₀ particles are smaller than 10 micrometres (µm) across

• PM₂.₅ particles are smaller than 2.5 micrometres (µm) across.

The diagram below compares the size of PM₁₀ and PM₂.₅ particles to a strand of hair and a grain of fine beach sand. They are tiny – too small for the human eye to see. Note that PM10 includes the smaller PM₂.₅ particles.

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The size of particles is also important for health impacts. Generally, the larger sized particles (between 2.5 µm and 10 µm) when breathed in remain in the upper airways. Whereas smaller particles (PM₂.₅ and smaller) can lodge deeply in the lungs and even enter the bloodstream. The PM₂.₅ particles are typically produced by human activities, such as the burning of wood and fossil fuels.

In the short term PM₁₀ mainly affects people’s lungs and heart, ranging from reduced lung function, impaired activities (e.g., sick days off school or work), more doctors’ visits and hospital visits. Long term effects are reduced life expectancy. Large studies overseas that have looked at impacts of PM10 on population health have not been able to reliably identify a level of PM10 in air below which there are no adverse health effects. In New Zealand, all regional councils and unitary authorities measure PM10 and some also carry out PM₂.₅ monitoring.

Particulate matter (PM) are small airborne particles composed of solid and/or liquid matter. These airborne particles are less than 10 micrometres in diameter (about a fifth of the thickness of human hair). These include fine particles (less than 2.5 micrometres) – known as PM₂.₅, and coarse particles (between 2.5 and 10 micrometres) – together fine and coarse particles are known as PM10. 

PM₂.₅ and PM₁₀ are pollutants that are most commonly caused by the combustion of wood and fossil fuels such as home heating and traffic. Other natural sources include dust, pollen and sea spray. 

These airborne particles are small enough to be breathed in and penetrate the human lung. This can cause negative health effects for people’s respiratory and cardiovascular systems. 

PM₁₀

PM10 include fine and coarse airborne particles less than 10 micrometres across (about a fifth of the thickness of a human hair). They are produced by the combustion of wood and fossil fuels, as well as by various industrial and natural processes. These concentrations are measured in micrograms per cubic metre (µg/m3) of air.

These particles can easily be breathed in. When the largest particles are inhaled, they get trapped in the nose and nasal passages and can irritate. The smaller particles (PM2.5, less than 2.5 micrometres across, and included in PM₁₀ measurements), can enter our lungs and also reach the bloodstream, potentially leading to respiratory diseases, heart attacks, and lung cancer.

PM₂.₅

PM₂.₅ are fine airborne particles less than 2.5 micrometres across (these are a component of PM₁₀). They can be easily breathed deep into the lungs where the smallest particles can enter the bloodstream. These concentrations are also reported in micrograms per cubic metre (µg/m3) of air.

Health effects include respiratory diseases, heart attacks, and lung cancer. Most particulate matter from natural sources is larger than 2.5 micrometres across.

Gases

Gases can also adversely affect our air quality and people’s health. We have good information on nitrogen dioxide concentrations in New Zealand based on monitoring carried out by the New Zealand Transport Agency (NZTA). Some regional councils and unitary authorities also measure nitrogen dioxide. Nitrogen dioxide concentrations are an indicator of air pollution from road motor vehicles. Exposure to nitrogen dioxide is linked to an increase in asthma symptoms and reduced lung function. Other gases, such as carbon monoxide, sulphur dioxide, benzene and ozone, are also monitored by some regional councils and unitary authorities at some sites in New Zealand.

Gases can adversely affect our air quality and people’s health.

The National Environmental Standards for Air Quality Regulations 2004 (commonly referred to as the NESAQ) include four gas contaminants that, when breathed in, can cause negative effects to people’s health:

• Sulphur dioxide (SO₂)
• Carbon monoxide (CO)
• Nitrogen dioxide (NO₂)
• Ozone (O₃)

These NESAQ guidelines are for short term concentrations of an hour, or eight hours for CO. There have been few breaches of these NESAQ at sites in New Zealand. Sites are selected to monitor these gases when there is a likelihood of people being exposed to harmful concentrations. Monitoring sites are commonly placed in industrial areas for SO₂ near roads for CO and NO2 and some distance downwind of cities for O₃.

Since 2007 Waka Kotahi NZ Transport Agency (NZTA) has monitored NO2 on state highways in New Zealand, to assess long term trends. They use passive sampling to measure monthly average concentrations, so these cannot be compared to the NESAQ hour average threshold for NO₂.

Other gases, such as benzene, are also monitored by some regional councils and unitary authorities at traffic sites in New Zealand.

Sulphur dioxide (SO₂)

A colourless, soluble gas with a characteristic pungent smell that forms sulphuric acid when combined with water. Sulphur dioxide is produced mainly from the combustion of fossil fuels that contain sulphur, such as coal and oil (e.g. coal being burnt in a home fireplace for heating and diesel-powered vehicles). Sulphur dioxide is also produced from some industrial processes (e.g., fertiliser manufacturing, aluminium smelting and steel-making). Natural sources of sulphur dioxide include geothermal activity.

Sulphur dioxide can cause respiratory problems such as bronchitis and can irritate your nose, throat and lungs. It may cause coughing, wheezing, phlegm and asthma attacks. Sulphur dioxide has been linked to cardiovascular disease. Measured concentrations are reported in micrograms per cubic metre (µg/m3) of air.

Carbon monoxide (CO)

A colourless and odourless gas formed by incomplete combustion of carbon-containing fuels, in particular from motor vehicles (petrol and diesel) and burning wood and coal for home heating or wildfires. Health effects include reducing the blood’s ability to carry oxygen and aggravating heart conditions. Measured concentrations are reported in milligrams per cubic metre (mg/m3) of air.

Nitrogen dioxide (NO₂)

Nitrogen dioxide is a reddish-brown, pungent, acidic gas that is corrosive and strongly oxidising. Nitrogen dioxide is not usually released directly into the air. The main source of nitrogen dioxide resulting from human activities is the combustion of fossil fuels (coal, gas and oil) especially fuel used in cars. It is also produced from making nitric acid, welding and using explosives, refining of petrol and metals, commercial manufacturing, and food manufacturing. Natural sources of other nitrogen oxides include volcanoes and bacteria.

The main health effect of nitrogen dioxide is on the respiratory system. Inhalation of nitrogen dioxide by children increases their risk of respiratory infection and may lead to poorer lung function in later life. There is also an association between nitrogen dioxide concentrations in the air and increases in mortality and hospital admissions for respiratory disease. Nitrogen dioxide can decrease the lungs’ defences against bacteria making them more susceptible to infections. It can also aggravate asthma. Measured concentrations are reported in micrograms per cubic metre (µg/m3) of air.

Ozone (O₃)

A colourless and odourless gas at ground level is formed by chemical reactions involving sunlight, volatile organic compounds, and nitrogen oxides (the main source being vehicle emissions). Ozone also occurs naturally in the upper atmosphere where it can move downwards, contributing to ground-level concentrations. Health risks include respiratory and cardiovascular diseases. Measured concentrations are reported in micrograms per cubic metre (µg/m3) of air.

Benzene

A volatile organic compound. Motor vehicles and home heatings are the main sources and some industrial activities. Benzene is found in petrol products and some solvents. Breathing in benzene over a long period can cause cancer and other diseases. Measured concentrations are reported in micrograms per cubic metre (µg/m3) of air.

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