Now, however, SO 2 is less of a problem due to the emission controls on stacks and a reduction of fuel burning in industry. These newer threats are largely a result of traffic in urban areas. CO does not travel over long distances as it oxidises after approximately one month to CO 2 . Hence CO can be classed as a localised pollutant. This reaction is heat dependant, and at high temperatures, such as those during combustion, NO is produced which then oxidises to NO 2 in the form of OH w radicals.
Ozone tends to be lower in urban areas than rural.
When combustion occurs, incomplete particles of the fuel are released into the atmosphere. This is how most smoke is formed. However, some particulate matter is formed when condensation occurs in the atmosphere. Particulate matter may be carcinogenic. The majority of primary particulate matter is produced by diesel rather than other sources of fuel.