Health Impact Assessment Of Air Pollution On Asthma In London

A project quantifying the effects of NO2 and PM2.5 on asthma and COPD admissions in London


The Greater London Authority (GLA) commissioned King’s College, London (King’s) and Imperial College, London to investigate the size of the link between asthma and air pollution in London following publication of a similar investigation in New York. It is accepted that air pollution is linked to exacerbation of asthma with ongoing debate on causation. This report concentrates on asthma admissions to hospital, particularly in children but also covers asthma admissions in adults and asthma/chronic obstructive pulmonary disease (COPD) admissions in the elderly. The report can be here.

Key Findings:

Exacerbation of asthma by air pollution is estimated to lead to around 1,000 asthma admissions from 2014 - 2016 in children in London, 10% of all asthma admissions in children in London. (Asthma admissions may have more than one cause e.g. air pollution may worsen response to an allergen.)

Children are more sensitive than adults, so the numbers for adults are smaller (over 600 adult asthma admissions from 2014-2016)

Chronic obstructive pulmonary disease (COPD), another respiratory disease similar to asthma particularly found in smokers, is more common in the elderly and difficult to distinguish from asthma. Results for the elderly therefore combined asthma and COPD.

Exacerbation of asthma and COPD by air pollution is estimated to lead to over 2,500 asthma/COPD admissions from 2014-2016 in the elderly in London.

The total across these age groups is over 4,000 air pollution-associated asthma admissions, with asthma admissions in children accounting for approximately one quarter of all admissions.

The above estimates are based on levels of nitrogen dioxide (NO2) above 10 µg m-3. Whether concentrations below 10 µg m-3 have effects is much less certain given the more limited data at lower concentrations.

Calculations were also done for PM2.5 concentrations above 5 µg m-3. This gave smaller results that probably overlap to some extent with those for NO2. In fact, as NO2 is a traffic pollutant, it may represent traffic PM better than PM2.5 does (total PM2.5 is heavily but not totally influenced by regional sources).

As the background evidence for effects of air pollution on asthma is mainly based on nitrogen dioxide, diesel PM and proximity to traffic, using the results for NO2 as an indicator for traffic pollution was chosen for the overall summary of the results.
This is not to say that calculations using PM2.5 do not provide an indication of effects on asthma admissions. It was estimated that reduction of current PM2.5 levels down to the WHO guideline of 10 µg m-3 could have led to a reduction of 100 asthma admissions in children and around 850 asthma/COPD admissions in the elderly from 2014-2016. This may be a conservative estimate because policies reducing concentrations to 10 µg m-3 would probably reduce concentrations further in some places.


Dr Heather Walton
David Dajnak
Dimitris Evangelopoulos
Daniela Fecht

Full Paper


© Imperial College London, Environmental Research Group. All rights reserved 2020.