The long read - Air Pollution

Burning Is Bad

Air pollution contributed to 6.5 million premature deaths worldwide in 2015 – similar to deaths from smoking [1].


Burning of carbon based fuels is one of the main sources of air pollution, especially when the fuels are impure and/or are burnt in a poorly controlled manner. So for example, smoke from domestic fires kills nearly two million people each year and sickens millions more, according to the World Health Organisation (WHO).


In low-income countries, such as those in Africa and Asia, indoor smoke from cooking has become the sixth biggest killer, globally killing more people than malaria. Forest fires and burning of agricultural and other wastes adds to the problem.


In industrialised regions, coal burnt in power stations, industry and homes is one of the main culprits, China and India being particularly badly affected. In China 1.6 million people die each year from heart, lung and stroke problems because of polluted air. Faced with this and the threat of climate change, the Chinese government has begun to invest heavily in renewable energy. In India, Delhi was blanketed by dense smog for most of November: chief minister, Arvind Kejriwal, called it a “gas chamber”; at its worst, pollution levels were nearly 40 times WHO limits. The pollution haze is even reducing India's solar power output by an estimated 17% to 25%.


Here in London 4,000 people are thought to have died in the immediate aftermath of the Great Smog of December 1952, and the government finally passed the Clean Air Act 1956 which created smokeless zones and shifted household heating towards cleaner coals, gas and electricity. Unfortunately post war London took a backwards step with transport, dismantling its electric tram and trolley bus network. Ealing's last 607 trolley bus ran in 1960 [2], and in the years since then, motor vehicles have become the main generator of air pollution in London










Delhi Smog 2017                                           


                                                    London Smog 1952














607 Electric Trolley Buses

Served Ealing until 1960







Dirty Vehicles

London's vehicles pollute not only with their engine exhausts but also with the dust from tyre & road surface wear and brake pad wear. The growth in pollution is due firstly to the enormous growth  in vehicle numbers, increasing from about 4 million in Great Britain in 1950 to over 34 million in 2010. The second factor is the growth of diesel.

The diesel engine is more efficient than petrol, especially in city start-stop driving, so although it is more expensive to buy, it has long been the engine of choice for lorries, buses and vans since the fuel savings make it worthwhile. Those fuel savings also mean that diesels produce 15% less CO2 than petrol, but unfortunately they emit four times more nitrogen oxide pollution (NOx) and 22 times more particulates - the tiny particles that penetrate the lungs, brain and heart.

Diesel engine manufacturers have long sought to change the engine's reputation for being noisier and smellier, and to minimise smoke and NOx, so that they could penetrate the car market. I first came to Acton in 1979 to work in Lucas CAV's diesel research centre where we measured emissions from engines under test. The number of diesel cars did grow slowly, but the real boom started towards the end of the 1990s when the European commission sought to reduce CO2 emissions because of climate change. The Commission was lobbied by big German car makers BMW, Volkswagen and Daimler, to incentivise diesel, a technology at which they excelled, rather than petrol-electric hybrids. The subsequent agreement with European car makers was backed by then EU transport commissioner Neil Kinnock and UK environment secretary John Prescott. As a result, diesel's UK market share rose from under 10% in 1995 to over 50% in 2012, and the European car fleet was transformed from being almost entirely petrol to predominantly diesel [3].

Breakdown of NOx Emissions in Greater London in 2010, by Source

(NRMM= Non Road Mobile Machinery)

Cleaning Up London

In 2016 the annual mean limit for NO2 pollution (40 ug/m3) was broken at 59 of 97 London sites [4]. This NO2 is mostly from diesel engines. Moving to electric or petrol-electric hybrids would greatly reduce it.

However every area in the capital also exceeds World Health Organisation (WHO) limits for damaging fine particles invisible to the naked eye known as PM2.5 (Particulate Matter with a diameter of less than 2.5 microns, 1 micron = one thousandth of a mm). Nearly 95% of the capital’s population live in areas that exceed the limit by 50% or more [5]. The main traffic sources of PM 2.5 are diesel exhaust, and tyre wear, brake wear and road surface abrasion from all vehicles [6].

As even electric vehicles will suffer tyre wear (especially if they have heavy batteries), reducing all vehicle use is the best way to avoid transport emissions. Electric trams and trains are the cleanest mass transport technology: they have steel wheels instead of rubber tyres, and with regenerative braking (the electric motors work in reverse when slowing, generating useful electricity) they can minimise brake dust.

We must also attend to non-traffic sources of PM2.5. Researchers at King’s College London have found that wood-burning accounts for up to 31% of the city’s particulate pollution, up from 10% in the past [7]. Sadly the environmentally minded should therefore avoid the lure of a wood stove and focus on insulating their house instead; likewise avoid disposing of garden or DIY waste via a bonfire. Gas is a fairly clean fuel, however gas combustion in homes and businesses accounts for a total of 21% of NOx emissions in London [8].

The Mayor's Plans

Under London's new Mayor Sadiq Khan, TfL will seek to ensure that from 2018, all new double-deck buses will be hybrid, electric or hydrogen. In central London, all double-deck buses will be hybrid by 2019 and all new single-deck buses will emit zero exhaust emissions by 2020. The whole bus fleet should emit zero exhaust emissions by 2037 at the latest. All new taxis are to be zero emission capable (hybrid?). [9]












An electric double-decker bus, built for TFL by Chinese manufacturers BYD.






Among plans to tackle pollution from diesel cars in the capital, the new T-Charge [5] was introduced in October which charges older, more polluting vehicles an extra £10 to drive in central London.

Regarding wood stoves, the mayor has asked the environment department to amend the Clean Air Act to allow for the creation of zero-emission zones where the burning of solid fuel is not allowed from 2025 onwards.


While there is much to welcome in the Mayor's plans, FoE may want to push for a greater reduction of overall vehicle use including for example the wasteful duplication of delivery vans. We will be conscious that heavy battery-electric vehicles are not problem free. Similarly pressing for the  minimising of building heating requirements can only help air quality as well as cutting carbon emissions.

Personal exposure can be reduced by avoiding busy streets and reducing exercise when pollution levels are at their highest. You can see detailed live air quality data for London's streets here: The worst areas are said to be as bad as smoking several cigarettes per day.


[1] Pollution has been linked to nine million deaths worldwide in 2015, a report in The Lancet has found. The WHO estimates 7 million deaths annually due to tobacco

[2]  Ealings 607 Trolly Bus.

[3] The rise of diesel in Europe: the impact on health and pollution


[5]  T Charge. Nearly 95% of the capital’s population live in areas that exceed the WHO PM2.5 limit by 50% or more.

[6 Sources of PM2.5 emissions in London are from tyre and brake wear, construction and wood burning.


[8] Gas boiler emissions. Policy Exchange is a centre-right think tank. 

[9] London Mayor's Draft Transport Strategy.

[10] Air pollution on busy roads as bad as passively smoking 10 a day.