Public interest in air pollution has fluctuated greatly in recent years, but is now at a high level with frequent reports in the press. While real progress has been made in reducing concentrations of some air quality pollutants, others remain at unacceptably high levels. An episode of very poor air quality in the second half of January stimulated a great deal of media interest, despite the fact that similar episodes have occurred many times in the past.

London was, for many years, one of the most polluted cities in the world. There are historical records of periodic bans of coal burning going back many hundreds of years. However, with improvements in the understanding of effects upon health, this came to a head in the 1950s with the Great Smog of December 1952 which led to a huge increase in the death rate in London, and is estimated to have caused around 4,000 excess deaths in a period of a week, with most probably a similar number dying from delayed effects over the subsequent weeks. As a result, the Clean Air Acts of 1956 and 1968 outlawed the emission of black smoke in towns and cities. This was around the time that piped gas became widely available, and the combination of the Clean Air Acts and a changeover to domestic heating by gas led to major improvements in air quality, to the extent that it was widely believed that the problem of air pollution from a health perspective had been solved.

This belief was shaken by new research using more advanced methods which emerged initially from North America in the early 1990s, which clearly demonstrated effects of air pollutants on health at concentrations previously believed to be safe. The current consensus in the scientific community is that there is no wholly safe level of exposure, and the more vulnerable members of the population are susceptible to the effects of air pollution exposure at levels well below legislated Limit Values.

So what was the level of risk in January? Concentrations of fine particles in London exceeded 100 micrograms per cubic metre for a 24-hour average, and in the West Midlands reached 60 micrograms per cubic metre. This far exceeds the World Health Organisation recommendation that a concentration of 25 micrograms per cubic metre (daily mean) should not be exceeded. As a consequence, Defra issued health advice that adults and children with lung problems, adults with heart problems and older people should avoid strenuous physical activity, and people with asthma may find that they need to use their reliever inhaler more often. If a concentration of 100 micrograms per cubic metre were to continue for a year (and very fortunately it does not), it is expected that this would lead to an increase of 60% in mortality rates relative to clean air.

Concentrations of fine particles in cities such as Beijing and Delhi regularly exceed 100 micrograms per cubic metre and can reach concentrations of a thousand micrograms per cubic metre over 24-hour and longer periods.

With support from the Newton Fund, air quality specialists in the School of Geography, Earth and Environmental Sciences at Birmingham are leading projects with collaborators from across the UK and local scientists from within China and India to investigate the causes of these air pollution problems, with a view to recommending cost-effective solutions. This is revealing physico-chemical processes which are not seen as significant in the UK atmosphere, but which are making a very major contribution to air quality degradation in those countries.

There has been much discussion in the scientific community of the likely consequences of Brexit for air quality. Some see Brexit as an opportunity for the UK to be a beacon of good practice and to move faster than the European Union in improving air quality. Unfortunately, there are good reasons to doubt this view. The EU has been a hugely powerful influence in forcing the rate of air quality improvement, and had the UK not been a member, it would almost certainly have progressed less rapidly than has been the case.

If, as seems likely, we simply transpose European regulations into UK law, even if we adopt subsequent tighter EU standards in the future, there will be less of an impetus to improve air quality. This is because the European Union has the right to impose unlimited fines on member states which fail to comply with air quality Limit Values. It is that threat from Europe which has motivated the UK government to implement many of its air quality improvement measures, and without the big stick, we may well see the UK lagging behind the remainder of Europe in bringing its air quality to ultimately acceptable levels.

Roy M Harrison
Professor of Environmental Health, School of Geography, Earth and Environmental Sciences, University of Birmingham