Well-to-wheel emission factors for future cars in Germany with a focus on fleet composition, new technologies and emissions from energy supplies

Until today road transport remains largely fossil fuel driven and therefore significantly contributes to emissions of greenhouse gases and air pollutants, particularly nitrogen oxides and particulate matter (EEA 2015). On the other hand, new vehicle technologies are emerging and existing technologies are being improved regarding fuel efficiency and transport emissions. The assessment of technologies and their implementation with the aid of scenario analysis is an appropriate tool to evaluate effects of different development pathways. The assessment of future emissions to air needs to consider not only tailpipe emissions from engines, but also emissions associated with the generation of electricity, since transport will increasingly be electrified. In this context and with regard to the requirement to provide robust environmental assessment of transport activities this contribution addresses some of the major gaps in prospective emission estimation from future cars and vehicle fleets. The aim of this work is to provide emission factors for future cars and fleets that allow the calculation of comprehensive emission effects in scenario analysis. This work is motivated by the project Transport and the Environment (Henning et al., 2015), in which twelve institutes of the German Aerospace Center (DLR) developed three explorative scenarios of the German transport system up to 2040, in order to analyse their environmental impact. The scenarios were named Reference, Free Play and Regulated Shift, and Table 1 characterizes the main storylines of these long-term pathways. The scenario definitions provide consistent context settings, and societal levers were identified that affect both, the transport and the energy system. Emissions and environmental effects were calculated using a network of models, established at the DLR. Both, the transport and the energy system are included in the scenarios. The derivation of the scenarios including the setting of model parameter can be found in Seum et al. (forthcoming). The calculation of new car and fleet-wide emission factors, which explicitly take into account factors stemming from the electricity supply, is necessary for transport scenario analysis. It goes thereby beyond scenario approaches, where improvements in technologies are only considered as relative changes. Conventional tank-to-wheel emission factors are expanded by including well-to-tank emissions derived from defined energy scenarios. This allows a non-bias comparison of different technologies. This integrated approach to develop new emission factors is presented in this article, using the example of passenger cars. The focus is on four main pollutants of road transportation, namely carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOx), and fine particulate matter (PM10). In a first step, we modified existing tank-to-wheel emission factors to reflect the vehicle composition of future scenario fleets. Since new propulsion technologies, particularly electric drives, are swiftly appearing, we developed new tailpipe emission factors for hybrid technologies, based on own measurements on the DLR test-bed and literature reviews. Furthermore, for plug-in-hybrid, battery-electric, and fuel cell technologies energy consumption factors are calculated using an advanced model-based approach. The generation of electricity and the resulting emissions were considered based on long-term energy scenarios. We enhanced for this purpose a bottom-up normative energy scenario by a calibrated top-down emission forecast. The final results are well-to-wheel emission factors that include raw material processing to provide the energy for transportation. The extraction and transport of raw materials is omitted, but could be added through life cycle assessment data