Scientists have found electric, hybrid and other supposedly eco-friendly cars produce as much toxic particulate pollution as the “deadly diesels” they are meant to be replacing.
The tiny particles are produced by tyre and brake wear. This happens in
all cars, including diesel and petrol, but eco-vehicles produce more
because they are heavier, owing to the batteries and other parts needed
to propel them. The extra emissions are roughly equal to the
particulates saved by reduced engine use.
The added weight of eco-cars means that when they accelerate or slow
down, the tyres and brakes wear faster, producing more particulates. The
weight also whips up more particles from the road surface.
“We found that non-exhaust emissions, from brakes, tyres and the road,
are far larger than exhaust emissions in all modern cars,” said Peter
Achten, whose research is published in the journal Atmospheric
“These 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.”
Achten, who runs a scientific consultancy in Holland, and his co-author
Victor Timmers, of Edinburgh University, used technical data from the
motor industry and government research agencies, including direct tests
of brake, tyre and road wear rates, to show that the non-exhaust
emissions produced by a vehicle are directly related to its weight. They
also built a database of vehicle weights.
“We found that electric and eco-friendly cars typically weigh 24% more than conventional cars,” said Achten.
The findings fit with anecdotal complaints from electric and hybrid car
owners that their tyres wear out faster than on conventional vehicles.
The impact of non-exhaust emissions has long been suspected but is hard
to measure. Scientists at Hertfordshire University overcame this problem
by installing particulate air pollution monitors in the southbound
Hatfield tunnel on the A1(M), which carries up to 49,000 vehicles a day.
They found each vehicle produced 34-39 micrograms of particles per kilometre but only a third came from the engine.
The rest comprised mainly tiny pieces of bitumen whipped up from the
road, rubber from tyres and brake dust. In towns — where cars brake and
accelerate more often — this proportion may reach 90%.
Such findings are a problem for policy-makers whose anti-pollution
efforts have been focused on regulating engines. Professor Ranjeet
Sokhi, of Hertfordshire University, who led the study, said: “This
highlights the significance of non-exhaust emissions and a need for
The Society of Motor Manufacturers and Traders said the industry was
working to make eco-friendly cars lighter. “Such vehicles have zero or
ultra-low tailpipe emissions and have energy recovery systems, which
limit the need for active braking, reducing brake and tyre friction that
may contribute to particulate emissions.”
Toyota, a market leader in hybrid, plug-in hybrid and fuel-cell cars,
said the firm had no data on particulate emissions from brakes and tyres
but added: “An advantage of hybrid cars over diesel is that nitrogen
dioxide and hydrocarbon emissions are incomparably better.”
Frank Kelly, professor of environmental health at King’s College London,
said one hope lay in changing the composition of tyres and road
surfaces. “Non-exhaust PM [particulate matter] emissions are greater
than exhaust and we do not have regulations to deal with these
A Department for Transport spokesman said eco-vehicles still had huge benefits in cutting CO2 emissions.
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