NEWS
ENVIRONMENT Ozone from EVs ANTHONY KING
A new study suggests that electric cars can create almost twice as much ozone per kilometre as cars powered by conventional fossil fuels. The study compared ozone emitted from LPG, petrol, diesel and electric versions of the Ford Focus family car, using an inventory that covered vehicle tailpipe emissions and fuel production. Emissions for electric vehicles (EVs) were based on electricity generation in the UK. When only tailpipe emissions were
considered, the per kilometre ozone impact of petrol and LPG cars is 44 to 88% of diesel’s, while electric cars have no tailpipe emissions of ozone precursors. However, if fuel production and tailpipe emissions are added together, the electric car has highest for ozone, the analysis found (Eur. Transp. Res. Rev, doi: 10.1007/s12544-017-0263-7). ‘The main result was that electric cars in
the UK at least are higher in ozone generation than conventional fossil fuel cars, which is not how most people would see it,’ says study author Eric Johnson at Atlantic Consulting. ‘These battery EVs don’t have emissions while driving, which is great. But if you look at the entire fuel cycle, starting from the coal mine or gas field or oil well, where the fuel is coming from to feed the power plant, then they create more ozone.’
MATERIALS TECHNOLOGY Data storage forever ANTHONY KING
A new printing technique may allow huge amounts of data to be stored on surfaces without fear of it degrading. Conventional pigments or dyes used to print and store information tend to fade and gradually disappear over time, but the new technique relies instead on ‘structural colour’ that results when light is shone on indented metal. Structural colour is ideal for
long-term data archival, since the images produced in this way ‘last quite literally forever,’ says Alasdair Clark, senior author and physicist at the University of Glasgow, UK. ‘When you start thinking about data storage
strategies over the long term, over decades or hundreds of years, this has the possibility of being really useful. You don’t need any special reading strategy to read the data again, just a microscope.’ The researchers took a 150nm thick film of aluminium and punched cross-shaped holes in it (Adv. Funct. Mater., doi: 10.1002/ adfm.201701866). The crosses are asymmetric, so that light shone on them goes through either the long arm or short arm - depending on the plane of light polarisation. A different image is projected when the plane of polarisation switches. ‘By changing the shape and the size of the crosses we can
dictate the colour of the light going through,’ explains Clark. ‘We can create detailed nano- images, codes or any sort of visual information whereby we can essentially print two sets of visual information in that unit area using the same pixel.’ The researchers created
images with a resolution of 100,000 dots per inch (DPI), whereas quality printing is 300 DPI. They generated pieces of QR codes, with the smallest readable units 370nm X 370nm, and calculated that a single A4 sheet of aluminium could hold more than 900Gb of data. The fragiliy of the aluminum
could be overcome by embedding it in a protective
plastic casing, according to Clark. However, material scientist
Rahesh Menon at the University of Utah, UK, says the etching technique would be slow, challenging and expensive to scale up for data storage. He thinks it may be more useful as, for example, in anti- counterfeiting applications. ‘These are really small features and the process, though relatively standard, would be difficult for someone who is not an expert,’ he says. ‘Two images on one device adds to its security potential.’ Meanwhile, another possible application could be for colour filters for cameras, say the researchers.
He advises that the energy mix of
power stations should be considered when thinking about mass switchover to EVs. Countries such as France should be seen as being fairly ‘clean’ on ozone emissions, since around 70% of its electricity generation relies on nuclear power. However, China and India are more reliant on coal. ‘They would tend to be significantly dirtier sources than the UK,’ says Johnson. However, atmospheric chemist John
Wenger at University College Cork, Ireland, notes that the pollution from power stations will be dispersed around the country. ‘For electric vehicle usage, these pollutants will not be released in urban areas and there will be a huge drop in NOx levels and ozone formation downwind of cities,’ he says, adding: ‘It is expected that coal will be phased out in the UK and renewables will be used in greater amounts. This means that, as the percentage of EVs increase over time, the emissions from power sources will also drop.’ ‘This paper addresses an interesting
and important topic: how different motor vehicle fuels compare in terms of their role in ground-level ozone formation,’ notes Nick Hewitt, atmospheric chemist at Lancaster University, UK. However, he adds that the atmospheric chemistry involved is ‘highly non-linear’ and requires sophisticated modelling that takes spatial distribution of
oxides of nitrogen (NOx) and volatile organic compounds (VOCs) into account. ‘A spreadsheet based impact assessment model such as the one used in the paper is simply not suitable for comparing the relative importance of distributed primary emissions from vehicle tailpipes with localised emissions from power stations,’ Hewitt concludes. Ground level ozone is not emitted directly
into the air, but is created by chemical reactions between NOx, VOCs and other minor reactants in the presence of sunlight. It is mainly released by vehicles, power plants and industrial activities. Breathing ozone can trigger health problems, particularly for children, the elderly and people who have lung conditions such as asthma.
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