How2Day: Types of Exhaust Gas

A car exhaust. Motorcycle exhaust image by Crisps85 from Fotolia.com
Exhaust gases are produced by the chemical reactions involved in burning fuel in engines. Some exhaust gases are harmless and some are toxic. The internal combustion engines that power most automobiles are designed so as to minimize the proportion of their exhaust gases that are of the toxic variety. Exhaust gases are subject to clean air regulations in many legal jurisdictions, and, as such, automobile manufacturers must meet basic standards of exhaust gas quality.

When hydrocarbons are burnt with oxygen in an engine, energy is produced, and one of the main resultant molecules is water. A large part of the visible component of exhaust gas is in fact water vapor.

The other main component of exhaust gases is carbon dioxide. Carbon dioxide is odorless, colorless and tasteless. This consists of one carbon atom and two oxygen atoms bonded together. Carbon dioxide is not toxic in and of itself and exists in the atmosphere naturally in small amounts. However, carbon dioxide is also a greenhouse gas, and substantial increases in the atmospheric levels of carbon dioxide may lead to climate change.

When the fuel in an internal combustion engine is not burnt correctly, some carbon monoxide may be produced. Carbon monoxide is odorless, colorless and tasteless. Carbon monoxide is toxic to human beings and animals, so engine makers and automobile manufacturers try to minimise the amount of carbon monoxide present in their engine exhausts.

Nitrogen is a noble gas and is highly unreactive. Nitrogen forms the bulk of atmospheric gas and forms the bulk of most exhaust gases. Nitrogen typically appears as a molecule consisting of two nitrogen atoms bonded together.

Sometimes hydrocarbons appear in exhaust gases. The presence of hydrocarbons in exhaust gases suggests the engine is not functioning properly as some of the fuel is not being burnt. This situation is known as "incomplete combustion." Hydrocarbons can subsequently react with sunlight to form ozone.

Nitrogen oxides can appear in exhaust gases if the temperature of combustion is too high. Nitrogen oxides are any molecules that consist of nitrogen and oxygen atoms bonded to each other. Nitrogen oxides can subsequently react with sunlight to form ozone. Nitrogen oxides can harm vegetation, reduce visibility and discolor fabrics.

Ozone is a molecule that consists of three oxygen atoms bonded together. Ozone can have damaging effects on the respiratory systems of animals and humans. Ozone is not created directly by the combustion process in an engine but is in fact created by the reaction of first-order pollutants like hydrocarbons or nitrogen oxides with sunlight.

Soot, also known as "particulate matter," are tiny particles of solid matter suspended in the air. Soot is made out of carbon atoms and is another result of incomplete combustion of the hydrocarbon fuel.

How2Day