NOx gases are usually produced from the reaction among nitrogen and oxygen during combustion of fuels, such as hydrocarbons, in air; especially at high temperatures, such as occur in car engines. In areas of high motor vehicle traffic, such as in large cities, the nitrogen oxides emitted can be a significant source of air pollution. Small amounts of NOx gases are also produced naturally by lightning. Nitrogen dioxide (NO2) and particulates (PM10 and PM2.5) are another major road related haze issue. Road transport is the biggest source of both of these.
The Cobham, Woking, Weybridge, Guildford and Borough of Guildford hazes of the 1980s was a unpleasant, but minor air pollution incident in the county of Surrey. It was photogenic haze (a mild form of smog) that occurred on a few days during the 1980s due to some perticly hot and still summer weather, which allowed London's drifting car fumes (including a lot of NOx and diesel particulates), local high pollen levels and ground ozone to mix in to a mildly toxic ground level 'haze' cloud. There were only a few asthma deaths, mostly in the late 1980s.
- Photogenic smog
- The Great London Smog of 1952
- Central London hazes of the 1990s and 2010s
- Slough-Windsor-Datchet-Heathrow-Southall hazes of the 1980s
- Birmingham and Sandwell Borough hazes of the 1970s and 2000s
- UK tabloid press in the late 1980s, 1990s and early 2000s