Despite huge improvements since the intense pollution smogs of the 1950s, the impacts of air pollution on human health remain a major problem in the UK. Before the Clean Air Acts of 1956 and 1968, triggered by the Great London Smog of 1952, the main concerns were emissions of sulphur dioxide and particles from coal burning. These have fallen substantially given strict legislation and wide-spread switching from coal to gas, and more recently solar and wind energy. However there has been growth of other pollutants, in particular from traffic, and from emerging trends such as domestic wood burning.
Understanding of the health impacts of air pollution has grown substantially since the 1980s through the publication of a large literature on epidemiological research in the UK and many other countries. Early work linked mortality and respiratory hospital admissions to exposure to fine particles. This has since expanded to include a broader range of pollutants and effects. With respect to exposure to pollutants in the ambient air, most attention in the UK and Europe is now focused on three pollutants, fine particles (PM2.5) which can penetrate deep into the lungs, nitrogen dioxide (NO2), and ozone formed as a secondary pollutant from chemical reactions in the atmosphere. Although various suggestions have been made that some particles, such as those in diesel exhaust, could be more harmful than others, the particles present at any location are a combined mixture from multiple sources and relative toxicities have not been established.
Information from the epidemiolocal studies can be used to derive response functions that enable the impacts of exposure to be estimated when combined with data on pollutant concentrations and population. The UK’s Committee on the Medical Effects of Air Pollutants (COMEAP) has estimated the mortality burden of air pollution in the UK from exposure to fine particles PM2.5 and nitrogen dioxide, NO2, in 2013, indicating a mortality burden of between 328,000 and 416,000 years of life lost across the population every year. This translates to between 28,000 and 36,000 equivalent attributable deaths. A study by the Royal College of Physicians provides a higher estimate of 40,000 equivalent attributable deaths per year, but includes ozone as well as NO2 and PM2.5 (www.rcplondon.ac.uk/projects/outputs/every-breath-we-take-lifelong-impact-air-pollution). The RCP report highlighted a wide range of health impacts affecting all stages of human life from the womb to old age. These include links between air pollution and cancer, asthma, stroke and heart disease, diabetes, obesity and changes linked to dementia – all of them being illnesses of high concern for the NHS.
What is being done about it
Recognition of these problems has led to international and national steps to improve the situation; which is illustrated below by a map of annual average PM2.5 concentrations in 2016, and indicates around 15 million people in the UK are exposed above the WHO standard of 10 micrograms per cubic metre (µg.m-3). The worst areas in red are clearly correlated with cities and urban populations, where effects of local sources are superimposed on a background from national sources, long-range contributions imported from other countries and shipping, and including secondary particles formed by chemical reactions in the atmosphere. International action under the UNECE Air Convention and the European Commission has led to the setting of ceilings for emissions from each country to control the transboundary imported pollution including PM2.5 and ozone. The distribution of nitrogen dioxide is even more concentrated in urban areas, but is mainly due to local sources, particularly traffic.
Annual average PM2.5 concentrations in 2016 (UKIAM model)
Reduction of air pollution at the national level is being addressed in Defra’s “Clean Air Strategy” as published in January 2019, and covering pollutant emissions from transport, at home, from farming and from industry (www.gov.uk/government/publications/clean-air-strategy-2019). An announcement by Michael Gove while still Environment Minister set a commitment to work towards attainment of the WHO standard of 10µg.m-3 for PM2.5, which is very much tighter than the current legal limit value of 25 µg.m-3 set by EU legislation; and will require substantial reduction in emissions of both primary particles and gaseous precursors of secondary particles. Action at the city level is also focused on reducing pollution, particularly NO2 concentrations; with measures like low emission zones and encouraging travel by walking, cycling or public transport. Changes in individual behaviour to help improve health are also needed to complement regulatory measures, and this requires wider awareness of the sources of air pollution and their consequences. It is also important to take a broader perspective, where for example the benefits of improved physical fitness from cycling or walking for short journeys can outweigh any disbenefits of exposure to air pollution, especially if there are suitable routes available. The medical profession can play an important role here in recognising connections between air pollution and health; and disseminating information to patients and the public.
The role of the NHS
As one of the world’s largest organisations (in terms of staff, behind only the US and Chinese military, McDonalds and Walmart), and costing the equivalent of around 6% of the UK’s GDP, it is not surprising that the NHS uses a significant quantity of energy for space and water heating, lighting and running equipment, and transport. For some years, the NHS Sustainable Development Unit (SDU) has investigated the carbon footprint of the health service. Recognising the NHS’ responsibility for health protection, SDU launched HOTT (Health Outcomes of Travel Tool) in 2017, which quantifies the health burden of air pollution and noise from transport linked to the NHS, along with accidents and greenhouse gas emissions. Version 3 of the tool has recently been released (www.sduhealth.org.uk/delivery/measure/health-outcomes-travel-tool.aspx). A future extension to HOTT will also quantify the air pollution impacts and GHG emissions of energy use by NHS Trusts.
HOTT provides analysis for NHS organisations at the level of individual CCGs, Ambulance Trusts and non-ambulance Providers such as hospital Foundation Trusts. The model uses up to date information on patient and staff numbers, travel distances, pollutant emissions and pollutant damage costs derived by Defra that cover the following outcomes for the two major transport pollutants:
- PM2.5: mortality, respiratory and cardiovascular hospital admissions, stroke, chronic heart disease, asthma and productivity
- NO2: mortality, respiratory hospital admissions, asthma, diabetes, productivity
As an illustration, results indicate 12.4 billion miles a year of travel linked to the activities of ambulance trusts, primary care and CCGs, and other providers in the NHS, with an associated estimate of health damage costs from air pollution of £162 million in 2018.
The HOTT tool allows users to develop their own future scenarios for transport provision, for example promotion of active travel, modal shift from cars to public transport and increasing the rate of electrification for the vehicle fleet, to see how these will affect future performance. Results can be used to assist in developing the business case for investment in cleaner and safer travel. There is also the potential for the NHS to use HOTT more widely, considering the travel burdens linked to other major organisations, such as universities, local authorities and private enterprises, and collaborating to increase the shift to more sustainable travel.
Content provided by Professor Helen ApSimon – Imperial College London, and Dr Mike Holland – Imperial College & EMRC