Wednesday, 9 July 2014
We present measurements of aerosol and cloud contrail microphysics measured in-situ behind the CFM56-2-C1 engines of the NASA DC-8 aircraft during the 2014 Alternative Fuel Effects on Contrails and Cruise Emissions (ACCESS) project. Aircraft engine emissions can have a disproportionately large climatic impact since they are emitted high in the troposphere and in remote regions with otherwise low aerosol concentrations. This has motivated numerous past ground-based studies focused on quantifying the emissions indices of non-volatile and semi-volatile aerosol species, however, it is unclear the extent to which emissions on the ground translate to emissions at cruise conditions. In addition, the ability of engine-emitted aerosols to nucleate ice crystals and form linear contrails or contrail cirrus clouds remains poorly understood.
To better understand these effects, the ACCESS-I project was conducted in 2013 to quantify aerosol emission indices for a number of petroleum-based and bio-based jet fuels at cruise conditions, while the 2014 ACCESS-II project focused on measuring the contrail microphysics. Three different fuel types are discussed: a low-sulfur JP-8 fuel, a 50:50 blend of JP-8 and a camelina-based HEFA fuel, and the JP-8 fuel doped with sulfur. Emissions were sampled using a large number of aerosol and gas instruments integrated on an HU-25 Falcon jet that was positioned in the DC-8 exhaust plume at approximately 50-500 m distance behind the engines. It was found that the biojet fuel blend substantially decreases the aerosol number and mass emissions indices, while the gas phase emission indices were similar across fuels. The effects of these fuel-induced changes of aerosol emissions on contrail properties will be discussed.
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