1) Carbon Monoxide (CO) - A colourless, odourless gas which reduces the oxygen-carrying capacity of the blood and can lead to headaches, nausea and dizziness.
2) Nitrogen Oxides (NOx) - A group of gases which contribute to the formation of ground-level ozone and smog.
3) Hydrocarbons (HC) - Unburned fuel compounds which contribute to the formation of ground-level ozone and smog.
4) Particulate Matter (PM) - A complex mixture of solid particles and liquid droplets which can cause respiratory problems and exacerbate asthma and heart disease.
