Fuming biofuels

Biofuels may be promoted for their green credentials, even though those credentials are often disputed, but what’s not disputed is that burning biofuels in engines still generates emissions that can add to atmospheric pollution. The question is whether the growing use of biofuels is changing the nature of that pollution, and a new study now reports that they are, and faster than envisaged.

This study, conducted by a team of US scientists led by Joan Willey at the University of North Carolina at Wilmington, monitored the concentration of ethanol in samples of rainwater and air collected at the university campus between 2010 and 2017. This ethanol would have come from many different sources, some of which would have been biological, but they would also have come from the growing use of bioethanol as a fuel.

This is because bioethanol is not completely burnt in an automobile engine, with the unburnt portion being emitted in the exhaust fumes. In addition, the production of bioethanol can release ethanol to the atmosphere. With the use of ethanol as a fuel generally growing, both because it is making up a greater proportion of the fuel supply and because the amount of automobile travel is steadily increasing, ethanol emissions in the US have been predicted to double by 2022.

In fact, Willey and her team found that the ethanol concentrations in their rainwater and air samples increased fourfold between 2010 and 2017. They were able to attribute much of this increase to the growing use of bioethanol by analyzing the carbon isotopes in the rainwater ethanol, which revealed that the majority (almost 60%) was derived from bioethanol rather than biological sources.

As the scientists report in a paper in Climate and Atmospheric Science, extra travelling seemed to be responsible for most of the increased use of bioethanol. When Willey and her team plotted the increase in ethanol emissions over time against the number of kilometers (km) travelled by automobiles in North Carolina each year, which rose from around 165 billion km in 2010 to 190 billion km in 2017, they found a linear relationship.

The main concern over rising ethanol emissions is that ethanol tends to react with hydroxyl radicals in the atmosphere to produce acetaldehyde, which is an important pollutant, contributing to the formation of smog and ozone. On the other hand, ethanol combustion also produces lower amounts of acetaldehyde precursors such as aromatics and alkenes compared to gasoline. So the overall effect of increased ethanol emissions on atmospheric pollution is still rather unclear.

As is the effect of biofuel emissions on health. But a new paper in Environmental Toxicology and Pharmacology, by a team of scientists from Norway and Poland, led by Oddvar Myhre at the Norwegian Institute of Public Health, adds to growing evidence that this effect is fairly minimal, as least for biodiesel emissions. Myhre and his team exposed rats to the emissions produced by a normal car burning two types of diesel, one containing 7% biodiesel and the other containing 7% biodiesel and 13% synthetic diesel made from hydrogenated vegetable oil.

They exposed the rats to the exhaust fumes regularly for either seven days or 28 days and then studied their lungs. While they detected slight differences in gene expression in the lung tissue of the rats exposed to the two diesels, they did not detect any major adverse effects, whether the rats were exposed for seven days or 28 days. Other studies on the health effects of biodiesel exhaust fumes have reported conflicting results, but many have failed to find any adverse effects on lung tissue.

So while biofuels are undoubtedly polluting, they don’t seem to be too bad for our health, which is good for their credentials.

The views represented here are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd. or of the SCI.