There are several types of air pollution with varying types of sources. Particulate Matter (PM) and Nitrogen Dioxide (NO2) are both major components of urban air pollution, however there are several different types:

Particulate Matter (PM): a generic term used to describe a complex mixture of solid and liquid particles of varying size, shape, and composition.

• Particulate Matter is classified by size:
  • PM10 (coarse particles that are less than 10 micrometres in diameter).
  • PM2.5 (fine particles that are less than 2.5 micrometres in diameter).
  • PM0.1 (ultrafine particles that are less than 0.1 micrometres in diameter)

• Sources: Combustion of fuels (vehicle, industry and domestic) and other human-made activities – mining, wood burning, various industrial processes and tyre and brake wear from vehicles. Naturally occurring sources include wind-blown soil and dust, pollen and sea spray particles, and fires involving burning vegetation.
• Health effects: Due to the small size of many of the particles that form PM, some of these toxins may enter the bloodstream and be transported around the body, entering the heart, brain, and other organs. Short term exposure to PM may cause irritation of the eyes and respiratory symptoms, such as irritation of the nose and throat, coughing, shortness of breath and chest tightness. Long-term exposure to PM reduces life expectancy by contributing to the development and progression of cardiovascular and respiratory diseases, as well as exacerbation of symptoms in those who already have these diseases.

Nitrogen Dioxide (NO₂): a gas that is mainly produced during the combustion of fossil fuels, along with nitric oxide (NO). NO₂ can also be formed when NO reacts with specific gases in the atmosphere, such as ozone, which is harmful to health. These reactions take place very quickly and are reversible. Together they are referred to as Nitrogen Oxides (NOx).

• Sources: Vehicle emissions from transport, with the largest source being emissions from diesel light duty vehicles (cars and vans). Other sources include power generation, industrial processes and domestic heating.
• Health effects: Short term exposure to NO₂ can cause inflammation of the airways leading to – coughing, production of mucus, and shortness of breath. NO₂ can also exacerbate the symptoms of those with lung or heart conditions.