Study questions health impact of green fuels

The rush to reduce vehicles’ CO2 emissions could have unwelcome effects on human health, scientists have warned. Recent studies have highlighted the need for more research into the air quality implications of biodiesel and ethanol use.

The most eye-catching of the studies suggests the US will see 4% more smog-related illnesses and deaths by 2020 if ethanol becomes the main transport fuel.1 This would mean 185 extra deaths and 1,200 more asthma-related hospital visits.

The study, led by Professor Mark Jacobson of Stanford University, is based around a scenario in which the use of E85 - a petrol-ethanol blend with 85% ethanol - becomes widespread.

E85-fuelled vehicles produce fewer nitrogen oxides (NOx) than petrol engines but more volatile organic compounds (VOCs), particularly formaldehyde and acetaldehyde.

The emissions of E85-fuelled vehicles were fed into a computer model simulating the complex reactions that produce ground-level ozone - the primary constituent of summer smog. Ozone forms from NOx and VOCs when they are exposed to sunlight. Paradoxically, high NOx levels destroy ozone by reacting with it to release oxygen.

The results predicted bioethanol substitution would lead on average to higher ozone and photochemical smog levels. Professor Jacobson thinks this impact on air quality, and ethanol’s limited carbon reductions (ENDS Report 382, pp 26-29 ), means the idea should be dropped entirely.

"Biofuels do not benefit air quality or climate… so I’m not sure what benefit they are providing except to divert resources from cleaner solutions to climate and air pollution problems," he says.

A preferable solution, he believes, would be battery-powered cars recharged using wind turbines - a system estimated to require 70,000-120,000 5-megawatt turbines across the US. He claims this would need 15-30 times less land than to produce ethanol.

The study only looked at the US but the impacts in the UK could be worse, says Professor Jacobson. Any increase in VOCs would exacerbate higher smog levels expected as a result of rising air temperatures (ENDS Report 385, p 29 ).

Very little research on the health implications of ethanol fuel emissions in the UK appears to have been carried out.

Ethanol-powered vehicles have generally been assumed to be slightly cleaner than those running on petrol, says Clare Wenner, head of transport biofuels at the Renewable Energy Association. Research has tended to focus on climate impacts and sustainability.

The same gap seems to exist for biodiesel. Researchers from the University of North Carolina and the US Environmental Protection Agency in a recent review of the topic discovered only a handful of studies.2

These suggested biodiesel’s exhaust emissions are "less likely to present any risk to human health relative to petroleum diesel emissions". But they noted the "speculative nature" of these finding and recommended they be backed up by research on biological systems.

Biodiesel exhaust has lower levels of carbon monoxide and polycyclic aromatic hydrocarbons but more NOx, which may have implications for smog formation. For particulates, the picture is complex: biodiesel produces less particulate matter than normal diesel but more of it is soluble, potentially affecting its toxicity.

Further factors that should be considered include the effects of fuel additives and pesticides used to grow biodiesel crops.

These warnings follow a study published earlier this year which predicted that the growing popularity of diesel cars in the UK will result in an extra 90 deaths from air pollution-related illnesses each year by 2020 (ENDS Report 385, pp 28-29 ).

The Department for Transport said it was unaware of any UK research on biofuels’ air quality effects. But a spokeswoman pointed out that the UK’s renewable transport fuel obligation (RTFO) is set at only 5% rather than 85% (ENDS Report 386, p 40 ).

"Government has consistently said that before we increase the level of the RTFO above 5% we want to consider a wide range of factors," she says. "We are not claiming any air quality benefits for biofuels - we are supporting them for climate change reasons."

  • German researchers have also raised concerns about hydrogen fuels. Thomas Feck of the Jülich Research Centre told the European Geosciences Union conference that he feared hydrogen leaks could deplete the stratospheric ozone layer. A very leaky hydrogen economy would cause a 9% depletion, while a more careful application of the technology would result in losses of below 3%, he said.

    Previous studies have suggested leaked hydrogen would act as a minor greenhouse gas by increasing methane and ozone levels in the lower atmosphere (ENDS Report 382, pp 24-25 ).

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