Chemists at Ludwig Maximilians Universität München report that 20% of the gases produced by the combustion of R1234yf—the approved low global warming potential refrigerant for mobile air conditioning (MAC) systems, the adoption of which has met with resistance from German automakers —consist of the highly toxic chemical carbonyl fluoride.Carbonyl fluoride is structurally related to phosgene (which contains chlorine in place of fluorine), which was used as a chemical weapon during the First World War. Kornath and his co-workers have just published the results of their investigation in the journal Zeitschrift für Naturforschung B.