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CHILL (Children’s Health in London and Luton)

The science

Air pollution

Air pollution and air quality: what is the difference?

  • Air pollution: presence of gases or molecules that pollute the air we breathe.
  • Air quality: amount of pollutants in the air.

Air quality is extremely important as it impacts our health and the environment. Unfortunately, air quality is not easy to control since pollutants can travel over long distances affecting the air we breathe.

What are primary and secondary air pollutants?

  • Both primary and secondary air pollutants cause a reduction in lung health. 
  • Primary air pollutants: emitted directly from a source.
  • Secondary air pollutants: form when primary air pollutants react with themselves or other components of the atmosphere.
  • Pollutants can be inhaled deeply into the lungs where they can deposit in the lining of the airways.
  • They can also diffuse into the blood stream and travel to other organs.
  • This can cause inflammation and damage to lungs and other organs.

Air pollution can come from many different sources

Traffic pollutionTraffic - Well known cause of pollution, with diesel powered vehicles being the most polluting. It is this type of pollution that the CHILL study is most interested in, as we are studying whether the Ultra Low Emission Zone (ULEZ) in London improves air quality and children’s health. Did you know that it isn’t just the fumes coming out of a car's exhaust that impact air quality? Tiny bits of metal are shaved off as the tyres wear down, and particles from the road also enter the air as the roads slowly wear down too.


Planes outside an airport terminal buildingAirports – Most airport pollution comes from holiday makers driving their cars to the airport. Pollution also comes from planes taxiing around and working inefficiently. Once in the air they have a relatively low impact on air pollution.


Log burning fires and BBQs – An increasing number of people are converting back to log burning fires.




Indoor pollutants – More research is finding that there are lots of pollutants indoors. Photocopiers emit ozone and everyday products (ie deodorants, cleaning products) release harmful particles. These are then trapped indoors.



Power plant pollutionPower plants and industry – Well known cause of pollution. Wind currents carry all types of air pollution hundreds of miles. Air pollution generated in the UK frequently causes problems for mainland Europe.



Lung function

Lung function is a term used to describe the overall healthiness of the lungs. When someone performs a lung function test (spirometry) they are having their expiratory volumes and flows measured.

  • Forced vital capacity (FVC) – maximum volume of air that can be forcibly blown out (after inhaling as deeply as possible).
  • Forced expiratory volume (FEV1) – the maximum volume of air that can be forcibly blown out in one second (after inhaling as deeply as possible).
  • Peak expiratory flow (PEF) – maximum flow of air that can be forcibly blown out (after inhaling as deeply as possible).
  • FVC tells us how big the lungs are.
  • FEV1and PEF tell us how healthy the airways are. 

A person's lung function results are then compared to a reference population of healthy persons of the same age, gender, height and ethnicity to determine how healthy (or normal) their lungs are. Air pollution negatively impacts these parameters of lung function in healthy and unhealthy persons, increases worsening of symptoms in persons with pre-existing medical conditions, and can stagnate lung growth in children.

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