London's breathtaking legacy

Andrea Lee and Tom Bogdanowicz explore the wider impacts of air pollution on the capital and consider solutions for the future

A quick glance at the King’s College London’s annual air quality map shows that on virtually every major road in London the levels of air quality are in the red danger zone. Switching from cars, buses and taxis to cycling is an obvious part of the solution, along with an extended Ultra Low Emission Zone (ULEZ), but cyclists, drivers and pedestrians need to know how to minimise the impact to themselves and to others. 

Andrea Lee, healthy air campaigner at ClientEarth (a group of activist lawyers committed to a healthy planet) looks at the wider impacts of air pollution and Tom Bogdanowicz looks specifically at the impacts on cyclists and how to mitigate them.

Just how bad is the air that we breathe?

Depending on where you live and work, how or when you travel, and your general health, your impression of the air quality that you breathe will vary - from not even giving it a second thought to being unable to leave your house on some days. 

Some of us will have been lulled into a false sense of security as our towns and cities are no longer shrouded in the thick black smogs which could reduce visibility to just a few metres, leaving an acrid taste in the back of your throat. This had serious consequences with thousands of deaths alone in the weeks following the Great Smog of 1952. 

Public outrage, fuelled by newspapers and a vocal medical community, and successful lobbying by backbench MPs, led to the adoption of the Clean Air Act 1956. This ground-breaking legislation tackled the main source of pollution, coal from domestic heating. Eventually it led to the closing of factories and power stations in urban areas.

Sixty years on we face a much different challenge. Now the main sources of air pollution are emissions from motor vehicles, and in particular diesel vehicles, that produce very different pollutants to the smoke churned out by burning coal. 

In the UK there are 40,000 estimated early deaths - almost 10,000 in London alone - caused by an invisible but toxic cocktail of pollutants. This includes particulate matter, which is less than a third of the width of a human hair (also referred to as PM10 and PM2.5 based on the diameter measured in microns), and nitrogen dioxide gas.

The impacts that air pollution has on people with respiratory problems are not surprising, though not many will appreciate that an asthma attack can lead to hospitalisation or worse. Even fewer people will realise that the main health impact is in fact through cardiovascular disease, triggering heart attacks, strokes and heart failure and reducing survival rates.

Professor Sir Malcolm Green, founder of the British Lung Foundation, has described breathing in PM2.5 pollutants as ‘like inhaling little particles of tar. They go right down into the lungs and can pass through the membrane into the bloodstream.’

Air pollution is also known to cause lung and bladder cancer. It’s linked to premature births and low birth weight. A study by King’s College London and Queen Mary University has shown that long-term exposure to air pollution is stunting the lungs of children in London, something that will continue to affect them into their adult lives. There is also increasing evidence of links with diabetes, impaired cognitive functions and autism among other conditions and illnesses.

Legal limits continually breached

It’s worrying, in the face of all of this, that legal limits of air pollution are being broken across the UK. In London, the Mayor identified 187 ‘Air Quality Focus Areas’ - places where legal limits are broken, in some cases by up to three times. Oxford Street, Putney High Street and Brixton Road are now infamous air pollution hotspots, breaching limits for the whole of 2016 in just the first week of January. 

These limits should have been met by 2010 but the government has admitted that much of the UK will not comply until 2020, and London not until 2025, 15 years after the deadline.

A generation of children will have grown up breathing dirty air that they should have been protected from.

There are serious questions about the ability of the government’s new air quality plans to meet legal limits, even by 2025. That’s why ClientEarth is pursuing its legal challenge against the government to force them to take action, and why more and more environment sectors are voicing their concerns.

The UK is not alone; few countries in Europe comply with legal limits. London has a monumental challenge to overcome. City comparisons are difficult but a study commissioned by the Mayor in 2014 ranked the capital 15th out of 36 selected world cities and 10th out of 18 European cities for air quality. That was below cities such as Berlin, Amsterdam, Paris and Budapest.

Reducing emissions from motor vehicles, diesel in particular, is crucial in wider transport network, construction and development, energy generation and use, industry and agriculture.

We need the Mayor and the UK government to back a range of ambitious and practical strategies to transform how and where people live, work and enjoy the city, in order to create a real clean air zone for a cleaner and healthier London.

Cycling impacts and how to avoid them

People cycling and walking don’t emit NO2, PM2.5 or PM10s but they aren’t able to avoid breathing them. While all Londoners, can’t avoid pollutants some face greater levels of pollution than others.

Dr James Woodcock and colleagues at Cambridge University looked at the risks and benefits of cycling to London hire bike users, including the impacts of pollution. They concluded that the benefits far outweighed the risks and pollution formed a very small part of the risk calculation.

Dr Audrey de Nazelle and her colleagues at Imperial College compared pollutants inhaled using different transport modes in Barcelona. They found that car users experienced higher concentrations compared to active commuters, but it evened out because of the greater ventilation rates of active travellers.

Other researchers have observed that journey time (often shorter by bike than by car in London) also affects exposure, as does ‘distance from the tailpipe’. So riding in a wide cycle track separated from a busy road may reduce your pollutant intake compared to riding in the traffic stream. Using a side street will reduce it even further.

Dr Ben Barratt of King’s College compared inhalation of black carbon by ambulance drivers, office workers, children and cycle couriers. The cycle couriers emerged with the second lowest intake and the ambulance drivers with the highest. Barratt suggests that the pollutants in an enclosed box (the ambulance) led to greater intake than that of couriers in the open air.

Of London road users, taxi drivers are perhaps the worst off, spending all day on busy roads inhaling some of the diesel fumes their own engines emit. It is not surprising that their union favours stronger legislation on air quality (black cabs will be switching to hybrid electric-petrol vehicles from 2018).

The academic literature consistently says the health benefits of cycling far outweigh the potential risks. So far there is little evidence that short-term exposure to pollutants has a marked impact on healthy individuals but there is no reason to inhale particles if you can avoid them.

The solutions?

The most obvious solution is to encourage others to cycle and minimise your own car use. If you can afford to, switch to an electric car if you need to drive.

The campaign to make all of inner London (not just central London) an ULEZ could dramatically improve air quality. Woodcock found that if most trips were walked or cycled (as is the case in parts of Holland) particulate matter would be reduced by a third.

Route choice

At the individual level, the most obvious, zero cost solution to poor air quality is to avoid the roads where it’s worst. Several studies confirm that route choice influences exposure to pollutants.

The difference in air quality between the worst and best streets in London is enormous, ranging from ‘unhealthy’ to ‘good’ on the same day at the same time. You can check the relative ratings of routes and streets on the King’s College London air quality map ( or AQI international map ( on a ‘live’ or annual basis. While London rates poorly in the European context, look up Delhi or Beijing on the AQI map to see how unchecked traffic growth can reduce air quality to levels that are often described as ‘hazardous’.

In London you can assume that most A-roads will be over the EU limit (annual mean objective) for pollutants, as will some inner city B-roads. Even minor streets in the Square Mile exceed the limits for NO2, but minor roads in the rest of inner London are at, or close to, meeting the annual objectives. Beyond inner London generally you are cycling on roads marked in green (below EU limits) on the King’s College map.

Using routes through parks obviously helps reduce your pollutant intake and avoiding roads with HGVs and buses helps avoids the worst of the diesel emissions. If you can’t avoid major roads, choose those with cycle tracks away from the traffic stream. The King’s College map takes into account factors such as topography and building design as well as vehicle volumes.

Timing of your rides

Timing can also minimise exposure. If you have the opportunity to avoid rush hours you can miss the worst of the exhaust fumes.

There are also specific days when pollution levels are higher in London. They don’t reach the Beijing ‘airpocalypse’ levels of AQIs beyond 400, but can still reach an AQI of 150 - three times recommended levels.

Taking a longer but ‘cleaner’ route on such days could reduce your exposure.

Cycling masks

Face masks of various types are used by some cyclists. Better masks are usually certified to a standard such as N95 indicating the percentage of particles (whether PM10 or PM 2.5) they eliminate. But how effective are they?

An academic study in Beijing (Langrish et al) found that, under test conditions, a single-use 3M industrial dust respirator mask did reduce the intake of particle pollutants (not gases like N02) when used by walkers and helped reduce negative effects of pollution on blood pressure and heart rate variability. However the researchers’ initial testing of a range of masks also found that the four cycling masks they tested (% penetrance of 11 and above) did not provide the same level of protection as the single-use industrial dust mask (% penetrance of 3.4). We are not aware of academic studies that fully test cycle-specific masks.

What is clear is that poorly-fitting masks reduce their effectiveness. ‘They’re better than nothing, but they’re hard to breathe through during vigorous exercise,’ says Mandy Dryer, a respiratory physiotherapist at the Manchester Royal Infirmary. ‘All too often the seal around your mouth and nose isn’t air-tight, so you end up sucking in unfiltered air through a gap and don’t push yourself as hard, so you don’t get the fitness benefits of cycling.

Getting a secure and comfortable fit is no easy matter. Any facial hair or stubble can create extra gaps, as can a mask in the wrong size or without secure coverage of the nose. So always follow manufacturer instructions and try as many as you can.

Image: David Holt, under Creative Commons license