RN CB ems filter 30117Robin Nyström (left) and Christoffer Boman of Bio4Energy are checking the soot content of diesel exhaust by analysing what got caught in an emission filter. Photo by Bio4Energy.Despite the European Union transport target for its 28 countries to reach a ten per cent share of renewable energy in the overall fuel mix by 2020—and estimates by consultants CE Delft and TNO in a 2013 study ordered by the European Commission, showing that biodiesel will contribute 6.6 per cent the target—there is only relatively little science available on how best to assess emissions from biodiesel combustion, and notably of the part that is particulate matter, for the results to be relevant for human health and the environment.

Domestic wood burning and combustion of diesel fuel in automotive engines are considered to be the two main sources of emissions of particulate matter globally. Whether these latter impact negatively on human health depends on the size, shape and composition of the particles, as well as how well the body of a person who is exposed to such emissions is able to resist their impact, for how long the exposure goes on and with which intensity. According to the authors of a 2015 Review of the Health Impact of Airborne Particulate Matter, published in Environment International, "small" particles of concern include inhalable coarse particles with a diameter of 2.5 to 10 micrometre (μm) and fine particles smaller than 2.5 μm in diameter.

Biodiesel vs standard diesel RobinNystromTo complicate matters further, the authors of Bringing Biofuels on the Market point out that: “Raising the blending limits for biodiesel is more difficult because of the more complex diesel emission control technology and the possible presence of impurities in biodiesel. For most passenger car manufacturers substantial time would be needed to adapt the regeneration strategy for diesel particulate filters to the higher biodiesel blend”.

 The research environment Bio4Energy of Sweden has a team of scientists dedicated to delivering knowledge on the properties of particulate matter formed as a result of biofuel combustion. The researchers collaborate closely with colleagues at Northern Sweden’s largest hospital, the University Hospital of Umeå, to map the effects on human health of exposure to biofuel, and notably biodiesel emissions. In fact, last month PhD student This email address is being protected from spambots. You need JavaScript enabled to view it. of the Bio4Energy team presented an encompassing package of work on Particle Emissions from Residential Wood and Biodiesel Combustion.

In his thesis, Nyström and his advisors take the seemingly much needed step of discussing how well current methods for checking emissions from car exhaust are adapted to fuels based on renewable oil-based feedstock—biodiesel made from rapeseed oil methyl ester, RME, in this case. They do this starting from results collected over a decade showing the emission profile of RME biodiesel and focusing on the formation of particulate matter.

Always running parallel tests of emissions from fossil diesel and RME biodiesel, the studies confirm that emissions to air of particulate matter in the form of soot and organic compounds such as polycyclic aromatic hydrocarbons (PAH), were substantially less voluminous, and the size of individual particles smaller, in the biodiesel trials. In the environment, PAH molecules are found in coal and tar deposits and may form on the incomplete combustion of organic matter. As such they may be carcinogenic.

However, the researchers also show that the formation of very small particles either remained the same, in the biodiesel trials as compared with standard diesel, or increased substantially in number, depending on the climatic conditions mimicked in the trials. To mimic real-life conditions, the scientists used dilution of the emissions with varying amounts of air, which were allowed to sit in a mixing chamber at a fixed residence time. This meant the emissions could be tested at different levels of cooling.  

“The results vary between the same amount of particles to a tripling of the amount of [fine] particles”, said This email address is being protected from spambots. You need JavaScript enabled to view it., associate professor at Umeå University (UmU) and Nyström’s chief academic advisor.

“In other words there is a potential to spur the formation in abundance of these very small particles. The question is, how important is this for human health and the climate?”, Boman said.

He added that the results would feed into a large collaboration project, started in spring 2016, to assess the health effects of a range of biofuels. Led by professor Thomas Sandström of UmU and NUS, the project’s chief focus was on RME biodiesel, but other oil-based types of biodiesel would be added for study down the line. 

The aim of this work is to deliver new knowledge which can help scientists and policy makers better to understand the characteristics and effects of emission of particulate matter from biodiesel exhaust. In a more long-term perspective the researchers hope to contribute to recommendations in view of setting emission standards or giving input to biofuel certification schemes. 

In Bio4Energy, the group of researchers investigating the effects on human health and the environment of biofuel emissions in the form of vehicle exhaust belong to the research and development platforms Bio4Energy Environment and Nutrient Recycling and Bio4Energy Thermochemical Conversion Technologies.

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