Air pollution

Air pollution comes from natural events (such as wildfires, windstorms, pollen and smoke from wood heaters) and from human activities (including industrial processes, motor vehicle emissions, the use of unpaved roads and the burning of fuels). Pollutants include gases, chemicals and airborne particles such as dust and pollen.

Cities often experience their worst air pollution on days of light winds and stable conditions, when a wide area can be affected. Low-lying areas tend to have worse air quality than higher ground, because pollutants settle in valleys, particularly on calm nights. People living on or within about 100 metres of major roads also tend to have reduced air quality.

Airborne contaminants vary from place to place, depending on factors such as population, industry, climate and the types of fuels burned. In many areas, air quality has steadily improved over recent decades as emissions have been reduced and monitored.

Air pollution events#

On days with an air pollution or air quality alert, people with respiratory conditions (such as asthma) and people with heart disease should avoid strenuous exercise.

• Air pollution events with high levels on warm, sunny days arise from the effect of sunlight on airborne pollutants, producing “photochemical oxidants” such as ozone.
• Air pollution events in colder weather arise when pollutants, particularly particles, build up around a city and are not blown away because of calm weather conditions.

Fuel combustion and air pollution#

In many cities, the main source of air pollution is motor vehicle emissions, caused by burning petrol or diesel. Burning other fuels, such as gas, wood and coal, also contributes significantly to air pollutant levels.

The main pollutants resulting from fuel combustion include carbon monoxide (CO), nitrogen dioxide (NO₂), ozone (O₃), particulate matter (fine particles suspended in the air) and sulfur dioxide (SO₂). The health effects associated with breathing in these contaminants include:

• carbon monoxide – reduces the ability of the blood to carry oxygen
• nitrogen dioxide – may trigger asthma attacks and other respiratory disorders
• ozone – may trigger asthma attacks and other respiratory disorders
• particulates – the effects depend on the chemical composition of the particles
• sulfur dioxide – may irritate the airways

Ozone depletion due to air pollution#

The ozone layer sits around 10 to 50 kilometres above the surface of the planet. Its main function is to moderate the amount of ultraviolet radiation from the sun that reaches the earth’s surface.

Ozone is produced by the action of sunlight and other chemical reactions on oxygen, and is naturally destroyed by a range of rising gases. In nature, the production and destruction of ozone is in balance, but human activity is depleting ozone faster than nature produces it. Gases including chlorofluorocarbons (CFCs) and halons (compounds containing bromine) create “holes” in the ozone layer, allowing greater amounts of ultraviolet radiation to reach the surface.

Health risks from depletion of the ozone layer include a greater incidence of eye problems, such as cataracts and pterygia (growths on the eye), and a greater incidence of skin cancer.

Air pollution and the greenhouse effect#

The earth insulates itself with greenhouse gases, which help to hold the warmth from the sun. Since the industrial revolution, human activity has increased the amount of greenhouse gases in the atmosphere, including carbon dioxide, methane, nitrous oxide, CFCs and halons. The generation of greenhouse gases has risen sharply in the last several decades, mainly due to the combustion of fossil fuels.

An increase in greenhouse gases makes the earth warmer and causes changes to weather and climate worldwide. These changes will affect health and wellbeing in many ways.

Indoor air pollution#

People spend most of their time indoors, which makes indoor air pollutants an important risk factor for health. Significant indoor pollutants include:

• outdoor air pollution penetrating indoors
• cigarette smoke
• emissions from faulty or unserviced gas heaters and fuel-burning appliances (which can lead to carbon monoxide poisoning)
• emissions from stoves without extraction fans
• chemical odours from freshly applied paint, glues, cleaners or solvents
• animal fur or dander
• moulds
• dust

Other home environment air pollution#

The outdoor environment around a home can be polluted with fumes, particulates and odours. These can be a nuisance that may or may not affect you or your neighbours. The main contributors include wood heaters, open fires and lawn mowers.

Dust storms and air pollution#

Dust storms reduce air quality and visibility, and may affect people’s health, particularly those who already have breathing-related problems such as asthma and emphysema. The most common symptoms experienced during a dust storm are irritation of the eyes and upper airways.

• Small, coarse airborne dust particles (PM10) generally only reach as far as the inside of the nose, mouth or throat.
• Finer particles (PM2.5) can reach deeper into the sensitive regions of the respiratory tract and lungs. In some people with pre-existing breathing-related problems, this can trigger allergic reactions and asthma attacks, and cause serious breathing difficulties.

Long-term exposure to airborne dust can lead to chronic breathing and lung problems, and possibly heart disease.

Hazardous substances and air pollution#

Some hazardous substances can become airborne:

• Arsenic – a substance found naturally in rock. It has been used to preserve timber and as an ingredient in chemicals such as pesticides and weed-killers. Small amounts of arsenic are normally taken into the body from low levels naturally present in water, air and soil. Swallowing a large amount of arsenic can cause severe health effects or even death.
• Asbestos – a silicate mineral made up of tiny fibres that form a dust when disturbed. Fibres breathed into the lungs can cause a range of health problems, including lung cancer and mesothelioma. Asbestos was once a common building material because of its fire-resistant and insulating properties, but because of the known health risks its use has been phased out in many countries.
• Cadmium – a mineral bound with elements such as oxygen, sulfur and chlorine. It is found naturally at low levels in most foods and is one of the ingredients of cigarette smoke. Smelting other metals, such as zinc and copper, produces cadmium. High exposure to cadmium, by either breathing or eating it, can cause a range of ill effects, including lung damage and kidney disease.
• Lead – a metal that can be found in paints in many older homes and in contaminated soil. The natural concentration of lead in the air is very low (less than 0.1 microgram per cubic metre). Lead gets into the air naturally through soil erosion, volcanic eruptions, sea spray and wildfires. It can also enter the air as a by-product of lead smelting, mining operations and waste incineration. In the home, lead air pollution is a risk when renovating a house painted with lead-based paint. Children are particularly sensitive to the effects of lead exposure. Acute poisoning is rare, but it can occur if a young child breathes in high levels of airborne particulate lead, or swallows lead paint dust or lead paint chips from old houses.

Key points#

• In many cities, the main source of air pollution is motor vehicle emissions, caused by petroleum combustion.
• The generation of greenhouse gases has risen sharply in the last several decades, mainly due to the combustion of fossil fuels.
• An increase in greenhouse gases makes the earth warmer and causes changes to weather and climate worldwide.
• Around the home, the main contributors to air pollution include wood heaters, open fires and lawn mowers.
• Fine airborne particles can trigger allergic reactions and asthma attacks, and cause serious breathing-related problems.

Where to get help#