Cleaning up our toxic air

Is there a pollution problem?

Air pollution in Europe costs more than £1.5trn a year roughly equivalent to a tenth of the continent's GDP, according to a 2015 study by the World Health Organisation. The study, covering EU and non-EU states, is the first attempt of its kind to calculate the monetary costs of polluted air. These costs come in the form of 600,000 premature deaths a year, as well as non-fatal illnesses.

Overall, the study found that pollution is a factor in the deaths or illnesses of at least one in four Europeans; that air pollution is the single biggest environmental health risk; and that in 2012 outdoor pollution, such as that from diesel car exhausts, accounted for 482,000 premature deaths Europe-wide.

How much of this is due to transport?

It depends on the type of pollution, but overall, road transport is the biggest single source of air pollution in cities. According to the World Atlas of Atmospheric Pollution (from 2011), road transport accounts for 88% of the carbon monoxide in London's atmosphere, 62% of particulate matter, and 53% of nitrogen dioxides (NOx).

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London, like Milan and Stockholm, has tried to tackle this via congestion charging and a low-emissions zone, and from 2020 an "ultra-low-emissions zone" will be created, meaning all pre-2007 motorcycles, pre-2006 petrol cars and pre-2015 diesel cars will pay an extra £12.50 on top of the existing £11.50 a day rate.

In Paris, meanwhile, new rules that come into effect next Friday (1 July) will ban pre-1997 cars and pre-1999 motorbikes from the streets on weekdays, in effect removing about 5% of polluting elements linked to cancers, heart disease and respiratory problems such as asthma.

Has diesel made it worse?

The UK has had a stop-start attitude to diesel. When he was chancellor in the early 2000s, Gordon Brown overhauled vehicle excise duty so that diesel cars, which are about 20% more efficient and emit less carbon dioxide (but up to twice as much NOx), cost less in tax than those with petrol engines. Brown also cut duty on low-sulphur diesel and reduced company-car taxes.

This all boosted diesel sales, encouraging 11 million cars on the roads but also boosted emissions of NOx and particulates. According to data cited by The Sunday Times, at least 7,000 deaths a year can be linked to diesel pollution. Many expect the VW emissions scandals (and others) to push drivers away from the fuel.

Are electric cars the answer?

At the point of use, in terms of NOx and hydrocarbon emissions, all-electric cars (such as the Nissan Leaf and the forthcoming Tesla Model 3) and plug-in hybrid vehicles (like the Toyota Prius) are obviously less polluting. But, sceptics say, you can't just consider the car you have to consider how its electricity is produced.

Given that a significant proportion of electricity is produced by coal-driven power stations (the global proportion is 41%, according to the World Coal Association), it is to some extent true that, as the green venture capitalist Vinod Khosla has noted, "electric cars are coal-powered". Also, while electric cars emit less carbon dioxide, the production of their batteries creates vast quantities of the greenhouse gas, meaning that over an electric car's lifetime the advantage is marginal. That's before you get into particulate matter.

What's that?

Particulate (or "PM") pollution is made up of tiny particles created by brake and tyre wear, and the road surface itself, and is produced by all cars. But because eco-vehicles are heavier (typically 24% heavier, due to the batteries and other extra parts), their non-exhaust emissions are far larger. Research published in the journal Atmospheric Environment found that eco-friendly cars produce far more non-exhaust "PM" pollution than the diesels and petrol engines they are slated to replace.

That's significant because, says the study's co-author Peter Achten, non-exhaust particulate emissions account for more pollution than exhaust emissions do, in all modern cars they surveyed. Moreover, these kinds of emissions are "more toxic than emissions from modern engines so they are likely to be key factors in the extra heart attacks, strokes and asthma attacks seen when air pollution levels surge".

What does the future hold?

The car industry has to make eco-friendly cars much lighter. The lithium-ion battery is the dominant electric-car technology, but it's so chunky the car base needs to be built around it. It's also flammable, adding to the complexity of integrating them into the design. A key challenge for policymakers is to focus not just on engines but on pollution overall. Either way, most analysts expect sales of hybrids, in the first instance, to rocket once the typical electric-only range exceeds 50 miles and prices fall to those of a similarly specified diesel or petrol model.

In ten years' time it's entirely possible that breakthroughs in technology will mean that after a century of cars driven by pollution-heavy combustion engines we'll be driving very different machines and breathing more easily.

How to build a better battery

Alternatives to the existing lithium-ion model are "jostlingon the starting line", says Peter Campbell in the FinancialTimes. Lithium-air batteries are considerably behindlithium-ion batteries in development, but have a higherenergy density and don't catch fire. Solid state batteries(the "holy grail" of battery technology) can be muchsmaller than liquid-based batteries, making them mucheasier to integrate into existing car designs.

Dyson isreportedly working on its own electric car on this basis.Toyota, meanwhile, a pioneer of hybrids, has alreadylaunched its first hydrogen-powered car (the Mirai). Ratherthan using a battery, hydrogen mixes with oxygen to createa fuel cell that runs the electric motor.