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Frequently asked questions

Is London air bad for my health?

Yes.  COMEAP say it’s shortening Londoners’ lives by about nine months.   It is increasing the number of young and older people with asthma and COPD.   When air pollution is worse hospital admissions rise.   Go to Clean Air in London for details and airTEXT for forecasts. Janke’s Appendix  (2009) summarises effects of pollutants.  


What are the pollutants in traffic fumes and what do they do to us?

  • NO2 is a brown gas with a detectable smell.  It is highly toxic in significant concentrations.   It causes inflammation of the airways and can constrict the bronchial tubes.  As a primary pollutant, NO2 comes mostly from exhaust pipes of diesel vehicles, especially slow-moving vehicles.   It is also a secondary pollutant.  Nitric oxide (NO) is produced by burning fuel at high temperatures, reacts with oxygen in the air to form NO2.  Most NO2 comes from road transport but power stations and gas heating also produce significant quantities.  NO2 converts to nitrates (NO3) and nitric acid (HNO3) and return to Earth from the atmosphere through rain or gravity.
  • Particulate matter 2.5-10 μm is mostly soil, mineral dust or sea salt produced mechanically by construction, mining, farming and sea spray.   It settles quickly by gravity.   Fine particles 0.1-2.5 μm are produced mostly combustion processes and secondary particles from condensation of volatile compounds and ammonia (NH3).    They can stay in the atmosphere for periods of days to weeks and travel thousands of miles as they are too small to settle by gravity and too large to combine into larger particles.   They eventually return to Earth with rain.  Particles smaller than 10 μm can be inhaled but 60-80% of particles 5-10 μm are trapped in the nose and pharynx.  Smaller particles penetrate the trachea and primary bronchi and very small particles penetrate deeply into the lungs.   The WHO says adverse health effects are suffered at levels experienced by urban populations.   All the population is affected but effects vary with health and age.
  • Ozone (O3) is a bluish, pungent smelling gas, toxic and inflammatory at low concentrations.   It is a secondary pollutant formed by sunlight acting on volatile organic compounds in the presence of NO2.   It can travel long distances. It is broken down by nitric oxide (NO) so concentrations are higher in rural than urban areas.   However, the resultant pollutants are also a problem.    As sunlight is required for its formation, ozone is highest in summer.
  • Carbon monoxide (CO) is a colourless, odourless, poisonous gas.   It is produced by combustion where the oxygen supply is insufficient, mostly from idling or slow moving motor vehicles but also from burning of organic matter in power stations and waste incinerators.  It stays in the atmosphere for about a month before oxidising to CO2.   It reduces the body’s ability to use oxygen.
  • Benzene (C6H6)is an aromatic hydrocarbon.  Major sources are cigarette smoke, benzene-containing petrol (especially during refuelling and extended travel in motor vehicles where levels are raised), petrochemical industries and combustion.   It is a carcinogen, destroys red blood cells and mutations in chromosomes.
  • 1,3-Butadiene (C4H6)is a colourless, flammable gas found in cigarette smoke and fuel.  It is carcinogenic and mutagenic.
  • Polycyclic aromatic hydrocarbons (PAHs)are formed by incomplete combustion of oil, gas, coal and wood.  Sources also include cigarette smoke and unvented heating.   Together they form a huge range of chemicals.  The most commonly tested are carcinogenic, toxic to genes and immune and reproductive systems.

(Janke et al, 2009 and WHO, 2000 and 2005)


Why is there only one monitoring site in Hackney?

The Clapton monitoring site was closed in 2011 after a review found:

  • government criteria for siting urban background and roadside monitoring equipment was not met – it was too close to the road for the former and too far away for the latter
  • cheaper diffusion tubes could substitute for the NO2 monitoring carried out at the site
  • monitoring of CO or O3 there was unnecessary
  • the PM2.5 analyser would soon need replacing
  • future funding was refused.

However, the review recommended the Council seek additional funding to enhance monitoring.


The Council has future targets: how do they know what pollution levels will be in future?

The Central London Cluster Group commissioned the ADMS-urban dispersion model.   Data on all possible sources of pollution such as roads, traffic volumes, flows and speeds, factories, houses along with heat from buildings and the weather is entered and the model run to work out pollutant concentrations. Models simplify factors to make reality easier to understand, modelling is a complex process, assumptions have to be made and uncertainties arise but results are validated against continuous air quality monitoring.

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