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.
Birmingham and Sandwell Borough hazes of the 1970s and 2000s was a unpleasant, but minor air pollution incident in the Birmingham and Sandwell. It was photogenic haze (a mild form of smog) that occurred on a few days during the mid to 1970s and mid 2000s due to some perticly hot and still summer weather, high local car, ground ozone and factory fumes (including a lot of NOx and diesel particulates), to settle locally and to to mix in to a mildly toxic ground level 'haze' cloud. There were only a few tens of asthma deaths, mostly in the 1970s and 2010s
The 2018 Birmingham city center clean air zone, along with the new tram services and an expanded railway network have helped to reduce pollution since 2000, but air in places still remain toxic at many times.
The continuing crisis
Birmingham's 5 most polluted areas in 2018 (where the air is also most filled with toxic nitrogen dioxide gas) were:
- Outside the Brasshouse, in Broad Street
- Outside Birmingham Children’s Hospital
- Outside O’Neills also in Broad Street
- Kings Heath High Street
- Underneath Spaghetti Junction.
- Sections of the ring road, Tyburn Road, A34 and A452.
City council data showed seven out of 10 locations sampled were over EU limits for the gas.
It was never as bad as in Birmingham, Alabama in the 1960s and 1970s.
- Photogenic smog
- The Great London Smog of 1952
- Central London hazes of the 1990s and 2010s
- Birmingham, Alabama smogs of the 1960s and 1970s
- Slough-Windsor-Datchet-Heathrow-Southall hazes of the 1980s
- Cobham, Woking, Weybridge, Guildford and Borough of Guildford hazes of the 1980s
- UK tabloid press in the late 1980s and early 1990s.