New legislation was passed (the Clean Air Act) to reduce air pollution and has led to a dramatic drop in smoke and sulphur dioxide levels. Today industry and domestic fuel burning is responsible for a minor amount of air pollution in Camden.
Emissions released from motor vehicle exhausts account for over two thirds of Camden's air pollution problem. More details on the air pollutant emissions of most concern in Camden are detailed below. Actions to reduce these emissions are outlined in Camden's Air Quality Action Plan.
Nitrogen oxides, NOx (including nitrogen dioxide and nitric oxide) are released directly from combustion sources such as vehicle engines and gas boilers. A larger proportion of nitrogen dioxide is formed in the atmosphere through chemical oxidation of nitric oxide.
During hot and sunny weather NOx and volatile organic compound (VOCs) emissions (primarily produced by vehicles and industrial processes using solvents), react in the atmosphere to form ground level ozone. Ozone is one of the main constituents of photochemical smog.
Particles vary in size, with those measuring 10 micrometers (µm) or less referred to as PM10. Primary particles arise directly from natural and man-made sources. Natural sources include pollen, sea salt and sand particles. Man-made sources of particles are predominantly produced from combustion sources such as motor vehicles, diesel trains, gas and wood fired boilers and bonfires.
These particles are released in the fine size fraction (<2.5µm) referred to as PM2.5. Coarse sized particles (2.5-10 µm) arise from industrial processes, such as cement batching plants, and construction sites.
The wearing of vehicle tyres and brakes, plus the re-suspension of deposited particles on road surfaces, are being given increasing attention as important sources of coarse particle emissions in urban areas.
Secondary particles are produced from the chemical reactions in the atmosphere involving gases such as nitrogen oxides and volatile organic compounds. These exist as PM2.5 and have a regional rather than local influence.
Consequently a large proportion of the particulate matter emissions in the UK arrive from Europe and on occasions more distant locations such as Africa and the United States.