Atmospheric reactivity of cyclic ethers of relevance to biofuel combustion

Abstract: Biofuels are considered to be an environmental friendly alternative to fossil fuels as they have the potential to reduce the global emissions of greenhouse gases. Studies have showed that an increased use of ethanol could alter the atmospheric chemical composition and enhance urban ozone concentrations resulting in higher human mortality rates. In recent years furanic compounds have been considered as second generation biofuels as they can be produced from non-food biomass. This project aims to improve the understanding of the impact of furanic biofuels in the atmosphere. Laboratory studies have been performed in smog chambers at Copenhagen Centre for Atmospheric Research and the University of Oslo, considering the reactions of furan, 2,3-dihydrofuran and 2,5-dihydrofuran with ozone and chlorine radicals. The furanic ozonolysis mechanism was further studied using computational methods. The results of the relative rate studies show that furan reacts slower with both ozone and Cl than the two DHF do, while the reactions of 2,3-DHF with ozone and Cl is faster than the corresponding reactions of 2,5-DHF. When comparing the results with literature data it was found that furans will mainly decompose due to tropospheric reactions with OH. The furanic Cl reaction may become important, close to local chlorine sources, in highly polluted areas were elevated VOC concentrations result in increased competition for the tropospheric OH reaction. Furthermore it was found that 2,3-DHF react immediately with Cl2, while furan and 2,5-DHF did not. The results of the product study propose that furanic ozonolysis produces shorter oxygenated organic compounds, such as aldehydes and carboxylic acids. This study shows that furanic biofuels mainly decompose into atmospheric compounds associated with elevated tropospheric ozone levels and urban air pollution. Emission of these compounds to the atmosphere can therefore be expected to result in elevated levels of ground level ozone.