Potential Environmental Impacts of Hydrogen-based Transportation and Power Systems

Hydrogen (H2) offers advantages as an energy carrier: minimal discharge of pollutants, production from multiple sources, increased thermodynamic efficiencies compared to fossil fuels, and reduced dependence on foreign oil. However, potential impacts from the H2 generation processes, transport and distribution of H2, and releases of H2 into the atmosphere have been proposed. The goal of this project was to analyze the effects of emissions of hydrogen, the six criteria pollutants and greenhouse gases on climate, human health, materials and structures. This project was part of a larger effort by DOE to assess the life-cycle costs and benefits and environmental impacts to inform decisions regarding future hydrogen research. Technical Approach: A modeling approach was developed and used to evaluate the potential environmental effects associated with the conversion of the on-road vehicle fleet from fossil-fuel vehicles to hydrogen fuel cell vehicles. GATOR-GCMOM was the primary tool used to predict atmospheric concentrations of gases and aerosols for selected scenarios. This model accounts for all feedbacks among major atmospheric processes based on first principles. The future scenarios and the emission rates selected for this analysis of hydrogen environmental effects are based on the scenarios developed by IPCC. The scenarios selected for the model simulations are a 2000 and 2050 A1B base cases, and a 2050 A1B case with hydrogen fuel cell vehicles (HFCVs). The hydrogen fuel cell scenario assumed conversion of 90% of fossil-fuel on-road vehicles (FFOV) in developed countries and 45% of FFOVs vehicles in other countries to HFCVs, with the H2 produced by steam-reforming of natural gas (SHFCVs). Simulations were conducted to examine the effect of converting the world’s FFOVs to HFCVs, where the H2 is produced by wind-powered electrolysis (WHFCVs). In all scenarios a 3% leakage of H2 consumed was assumed. Two new models were developed that provide the ability to evaluate a wider range of conditions and address some of the uncertainties that exist in the evaluation of hydrogen emissions. A simplified global hydrogen cycle model that simulates hydrogen dynamics in the troposphere and stratosphere was developed. A Monte Carlo framework was developed to address hydrogen uptake variability for different types of ecosystems. Findings 1.Converting vehicles worldwide in 2050 to SHFCVs at 90% penetration in developed countries and 45% penetration in other countries is expected to reduce NOx, CO, CO2, CH4, some other organic gases, ozone, PAN, black carbon, and other particle components in the troposphere, but may increase some other organic gases, depending on emissions. Conversion to SHFCVs is also expected to cool the troposphere and warm the stratosphere, but to a lesser extent than WHFCVs. Finally, SHFCVs are expected to increase UTLS ozone while decreasing upper stratospheric ozone, but to a lesser extent than WHFCVs. 2.The predicted criteria pollutant concentrations from the GATOR-GCMOM simulations indicated that near-surface annual mean concentrations in the US are likely to increase from the 2000 base case to the 2050 A1B base case for CO2 and ozone due to the increased economic activity, but to decrease for CO, NO2, SO2, and PM10 due to improved pollution control equipment and energy efficiencies. The shift to SHFCVs in 2050 was predicted to result in decreased concentrations for all the criteria pollutants, except for SO2 and PM10. The higher predicted concentrations for SO2 and PM10 were attributed to increased emissions using the steam-reforming method to generate H2. If renewable methods such as wind-based electrolysis were used to generate H2, the emissions of SO2 and PM10 would be lower. 3.The effects on air quality, human health, ecosystem, and building structures were quantified by comparing the GATOR-GCMOM model output and accepted health and ecosystem effects levels and ambient air quality criteria. Shifting to HFCVs is expected to result in improved air quality and benefits to human health. Shifting to HFCVs is unlikely to result in damage to buildings. 4.Results are thought to be robust for larger leakage rates of H2 and for greater penetrations of HFCVs, since the controlling factor for stratospheric ozone impacts is the reduction in fossil-fuel greenhouse gases and the resulting surface cooling, which reduces water vapor emissions and stratospheric warming, which increases tropopause stability reducing water vapor transport to the stratosphere. 5.The supplemental modeling results were generally supportive of the results from the GATOR-GCMOM simulations, and recommendations for additional analyses were made. Extending the duration of the simulation to coincide with the time required for hydrogen mixing ratios to attain a steady state condition was recommended. Further evaluation of algorithms to describe hydrogen uptake in the model was also recommended