Biodiesel (Fatty Acid Methyl Ester, FAME) is being blended into fossil diesel as a common strategy for implementing renewable energy into motorized transport, in Europe, US and Canada. From the precautionary principle it follows that knowledge of unintended effects from this strategy should be obtained. We have elucidated a theory for how the blending can increase the exhaust toxicity. It is based on the aggregation of uncombusted FAME and PAH (Polynuclear Aromatic Hydrocarbons, from the fossil diesel) into nanoparticles after the time of combustion, during the cooling of the exhaust on its travel through the exhaust pipe and out into the ambient air. These nanoparticles have polar moieties, from the methyl ester head if the FAMEs, thus increase the ability of PAHs to be transported with moisture drops into the lungs and eventually across cell membranes. Molecular Dynamics Simulations on the super computing facilities at the Biomedical Research Centre at Uppsala University have demonstrated that such nanoparticles are likely to be formed, with diameters of less than 10 nm. This work-in-progress will be supplemented with assessment of the toxic properties of these nanoparticles in lung cell exposure studies.