Engines produce a range of exhaust emissions, some of which have a negative impact. Depending on the emission in question and the application, the negative impact may be felt either in close proximity to the exhaust or more widely in the environment. The emission which has received the most publicity in recent years is carbon dioxide. This is a greenhouse gas and many scientists believe it is partly responsible for global warming, however it is not directly harmful to human health (we all breathe out carbon dioxide !). Unfortunately the only ways to emit less carbon dioxide are to either use fuel more efficiently, or to use renewable fuels such as biogas or biodiesel.
Another category of exhaust emissions have a direct, adverse effect on human health i.e. they are toxic. Toxic exhaust emissions include carbon monoxide, hydrocarbons, oxides of nitrogen and particulate matter. The way in which their toxicity manifests itself varies, depending on the durability of the substance and the place it is emitted. Some toxins are primarily of concern in confined spaces, whilst others can have a negative impact several miles from where they were emitted (especially in a city). There are also some toxins which can cause problems hundreds of miles away from the source e.g. acid rain. However, on this website we will focus on two types of toxin which have an effect closer to home: carbon monoxide and particulate matter.