Air Pollutants

Carbon Dioxide (CO2)

– as a major product of animal respiration and fossil fuel combustion, carbon dioxide is one of the most abundant greenhouse gases in the atmosphere. CO2 molecules absorb heat radiation from the Earth and warm the atmosphere, contributing to climate change. Because atmospheric concentrations are so high, carbon dioxide is absorbed from the atmosphere by the ocean. Absorbing CO2 causes the ocean to acidify, damaging aquatic ecosystems and representing a major threat to our aquatic resources, like fisheries.

Carbon Monoxide (CO)

– Carbon monoxide is a by-product of fossil fuel combustion in an anaerobic (oxygen lacking) environment. CO is harmful to human health because it inhibits the ability of blood to deliver oxygen to the body’s organs. This can cause death at high enough concentrations. Transportation emissions contain large amounts of carbon monoxide.

Methane (CH4)

– Methane gas is largely produced by the decaying of organic matter and the flatulence of livestock animals. When organic kitchen waste is not properly composted, it ends up in a landfill and produces this strong greenhouse gas. While methane has a warming potential over 30 times greater than carbon dioxide, it only lasts about ten years before it decomposes. Unfortunately, during this decomposition, the methane (CH4) reacts with stratospheric ozone (O3) to produce carbon dioxide (CO2) and water vapour (H2O). Both these products have their own warming potentials, and depleting the ozone layer by removing ozone is disastrous for the planet and all the organisms that live on it.

Nitrogen Oxides (NOx)

– Nitrogen oxides, like NO2 (nitrogen dioxide), are usually produced during fossil fuel combustion. They are involved in the production of harmful fine particle pollution, as well as ground-level ozone. Nitrogen oxides are known for causing respiratory distress, and can increase susceptibility to respiratory infections.

Sulphur Dioxide (SO2)

– Sulphur dioxide is another by-product of fossil fuel combustion, particularly high-sulphur coal, but it is also released into the atmosphere by volcanic eruptions and forest fires. It is quite damaging to the respiratory system, and aggravates the symptoms of asthma. Like nitrogen oxides, sulphur dioxide reacts with compounds in the air to form fine particulate matter, which can embed in the lungs, and aggravate skin or heart conditions. Sulphur dioxide can also be transported to the upper atmosphere, where it transforms into sulphuric acid, a major component of acid rain.

Ground-Level Ozone (O3)

– Ground-level ozone is a secondary pollutant produced when nitrogen oxides react with volatile organic compounds (VOCs) in the presence of sunlight. It is important to understand that ground-level ozone is different from stratospheric ozone, which forms naturally and protects life on Earth from the sun’s dangerous UV rays. Ozone in the troposphere (ground-level) visibly contaminates the air, contributing to the hazy smog that characterizes many major urban areas. It also irritates the eyes, nose, throat, and respiratory systems of people and animals. Exposure can contribute to asthma, deregulate heartrate, and reduce resistance to infection. Ground-level ozone also damages the environment by changing the quality of water, habitats, and nutrient cycles. Concentrations of ground-level ozone are expected to increase as the climate changes because higher temperatures stimulate ozone production.


– Chlorofluorocarbons (CFCs) have been used in the past as both refrigerants and aerosol propellants. In 1989, an international treaty known as the Montreal Protocol was signed to ban the use of CFCs, as they had been shown to actively degrade the ozone layer, an important component of Earth’s atmosphere.

Lead (Pb)

– Lead particles are released into the atmosphere by industries like metal refineries, and through the combustion of lead-gasoline for transportation. Lead can affect cardiovascular and renal function in adults, and the developing nervous systems of children, impacting learning, memory, behaviour, and IQ.

Particulate Matter

– Particulate matter (PM) is the tiny solid or liquid particles that float in the air. Primary particulates are released into the atmosphere directly through actions like driving on an unpaved road or burning carbon fuels like wood or gasoline. Secondary particulates form in the atmosphere through chemical reactions with sulphur or nitrogen dioxide, VOCs, and ammonia. Particulate matter is often classified by size, with PM10 referring to particles that are between 2.5 and 10 microns (μm), and PM2.5 referring to particles that are less than 2.5 microns. A micron is one millionth of a meter; therefore these particles are incredibly small. Because of its size, particulate matter is invisible to the naked eye, and can be inhaled into the nose and throat. While PM10 will irritate the eyes or nasal passages, it is generally not small enough to be inhaled into the lungs. This is why PM2.5 is so dangerous. Small enough to penetrate the respiratory system, PM2.5 can easily become lodged in the lungs, potentially increasing the risk of asthma, bronchitis, emphysema, pneumonia, heart disease, and death.


– For those who suffer from allergic reactions to airborne allergens, climate change is expected to increase the risk of allergic or asthma attacks by increasing the production of pollen and fungal spores. The reason for this is twofold: a longer growing season and larger amounts of pollen produced per organism. A longer growing season caused by a warming climate means that pollinating plants will be pollinating for longer, extending the allergy season. Pollen production is increased because plants have been shown to produce more pollen when exposed to higher concentrations of atmospheric CO2. It’s also possible that the pollen produced will contain more allergenic proteins, meaning that allergy seasons will last longer, there will be more allergens present in the air, and the allergens themselves will be more potent. This is true for both the spring (most pollinating trees), and fall (ragweed) allergy seasons.