A breath of fresh air

3rd May 2019

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  • Pollution & Waste Management



Tim Smedley talks to Kathryn Manning about the harmful impact air pollution has on our health and environment, and the action we can take

When did you become interested in air pollution as a health issue?

It was 2015, I had just become a dad, and a headline in the Evening Standard grabbed my attention: “Oxford Street has worst diesel pollution on Earth“. I was suddenly confronted with a jarring reality: London is a wealthy capital city known for its tree-lined streets and plentiful parks, and yet it has some of the worst diesel pollution in the world. I discovered that air pollution killed tens of thousands of people in the UK, and millions across the world, every year. Despite being a sustainability journalist, I felt blindsided by this issue. What is air pollution? Why is it bad for our health? And – most importantly – what can we do about it? My journey for the answers took me further afield than London, incorporating Delhi, Beijing, Paris, Helsinki...and Milton Keynes. While shocked by the impact extreme air pollution has on health and societies, I also found an optimistic vision for how cities can start clearing the air.

What are the most common delusions about air pollution?

The two big ones are: “I can't see it, so it can't be that bad“, and “this is just a big city problem“. Modern pollution gases and particles are often invisible. Whereas London in the 1950s was swathed in thick black coal smoke, today's road vehicles churn out smogs of much smaller particles. When we breathe in PM2.5 (pollution particles 2.5 micrometres or less) and nitrogen dioxide (NO2), the health effects are felt at every stage of life – from reduced birth weights and reduced lung growth in children, to cancers in adults and dementia in the elderly. The smallest particles (nanoparticles) can pass through the lungs and into our bloodstream, where they can raise blood pressure and cause blockages, leading to strokes and heart attacks.

“We should think about air pollution more in terms of exposure, and less in terms of percentages“

This isn't exclusive to large cities. Small port cities such as Southampton often find themselves with pollution levels exceeding those of central London due to the fuel burned by the shipping industry. The French Alpine resort of Chamonix – once famed for its fresh mountain air – is now often enveloped in smog from the line of lorries at the Mont Blanc Tunnel.

How localised is this pollution, and how far can it travel?

A good question. We should think about air pollution more in terms of exposure, and less in terms of percentages. In London, the background percentage of PM2.5 can be up to 75% 'transboundary' – meaning it has blown in from the surrounding area, or from the Continent. However, peaks of pollution are always local to the source – and the source is transport fumes on the roads where we live, work and breathe. If you look at a 'heatmap' of pollution of any city, the roads glow red like veins (see Figure 1). Nanoparticles and NO2 only exist within metres of their source. Nanoparticles are too small to register on mass-based PM2.5 averages. And it is the number that we breathe in, not the mass, that we should be most concerned about.

Where is the world's worst air pollution?

In the WHO air quality database, all of the top 15 most polluted cities, and 25 of the top 27, are in India or China. Varanasi, India, currently tops the chart at 217 micrograms of PM2.5 per cubic metre (µg/m³) , compared to London's 15µg/m³.

The worst I experienced was Delhi (currently number 11 in the WHO chart, and the world's most polluted capital city, with an average 143¬µg/m¬≥). In the cab from the airport, my portable pollution monitor registered PM2.5 above 300¬µg/m¬≥: levels I had never experienced before. When I arrived at my B&B, my host exclaimed: “What a great day to have arrived – the smog has gone!“. She told me the levels the week before were up at 1,000¬µg/m¬≥, and street dogs were dying in the roads. November 2017 is now known as the 'Great Smog of Delhi', and PM levels peaked at 1,486¬µg/m¬≥ – among the highest ever recorded anywhere, let alone a city of more than 20 million people.

Is there a 'safe' level of pollution that our bodies are equipped to deal with?

The short answer is: no. The longer answer is that the WHO has health-based 'guideline values' or safe limits. For PM2.5, it recommends an annual mean limit of 10μg/m3, and a 24-hour mean of 25μg/m3. For NO2 it's 40μg/m3 (annual mean), sulphur dioxide 20μg/m3 (24-hour mean), and ozone 100μg/m3 (eight-hour mean). Countries also set their own 'safe' levels. The EU has legal limit values for NO2 of 40μg/m3 (annual mean) and an hourly mean of 200 µg/m3 that cannot be exceeded more than 18 times in a year (London breached its annual air pollution limits just five days into 2017).

However, in terms of health, there is currently no known 'safe level' for most of these pollutants. The WHO's 10μg/m3 for PM2.5 still wouldn't be good for us Рjust as one cigarette a week is better than a packet, but we still need to quit. That said, an annual mean of zero would be impossible Рthere will always be dust and dirt in the air, and this registers as PM2.5. The current toxicological evidence suggests that our bodies can deal with such natural particles Рit's the ones from combustion, especially from carbon-rich petroleum and solid fuels, that damage our health the most.

Are we measuring pollution correctly?

Another important question. I believe the focus is currently too much on average PM2.5 levels by mass, and too little on exposure and nanoparticles. Average PM2.5 figures offer a useful litmus test for a city, but a focus shift towards exposure to nanoparticles would concentrate policy on hyper-local actions, such as closing the roads outside schools to cars during drop-off and pick-up times. It would also shift local authorities away from measuring pollution with a handful of fixed, blunt-instrument air pollution sensors such as diffusion tubes, which can only measure average NO2 levels and give us no data for peak pollution times or episodes.

What are the links between climate change and air pollution?

This is the best bit. While the focus on air pollution is more on PM2.5 and NO2 than CO2 and methane, action taken toreduce one almost always reduces the other. We need to rapidly replace urban transport modes that burn fossil fuels with electric vehicles, walking and cycling. In so doing, we can halt the release of CO2 trapped within petrol and diesel. Particles from coal and gas are also bad news, so we need to shift our heating and electricity generation to renewable sources.

A shocking statistic I came across is that a third of all shipping is simply transporting barrels of oil around the world. If we stopped using oil, a third of shipping (and shipping emissions, which are among the worst) would disappear. Tackling air pollution and climate change, therefore, run hand-in-hand. However, unlike climate change, urban air pollution is local and short-lived, and can be stopped at the source.

What are some of the best ideas to counter pollution in cities around the world?

The great thing about reducing air pollution is that we know how to do it: electrification of transport and heating, and making walking and cycling the easy option. When I visited Helsinki, a new transport bridge connecting the centre to an island suburb had been designated for public transport, bicycles and pedestrians only, making the right choice the easy choice. London is trying to achieve the same with cycle superhighways and the Ultra Low Emissions Zone (ULEZ), and Madrid has plans to go one further with a Zero Emissions Zone by 2020. China is electrifying public transport: every one of Shenzhen's 16,000 buses is now electric. Other cities, such as Singapore, are adding to their urban greenery: planting vegetation in cities can reduce street-level concentrations of NO2 by 40% and PM by 60%. California's cap-and-trade scheme earns $900m a year by charging the worst industrial emitters, and spends this money on clean air schemes, including trees, electric car grants and high-speed rail, ring-fenced for the areas that are most exposed to air pollution. There are numerous policies that I spell out in more detail in my book, but it all comes down to removing combustion from our streets.

Tim Smedley is a sustainability journalist and author of Clearing The Air: the Beginning and the End of Air Pollution, published by Bloomsbury

Image credit: iStock


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