Emissions scenarios under a hydrogen economy David Damm EAS 6410 April 23, 2007

Outline Motivation for Hydrogen economy Potential effects of molecular hydrogen emissions Effects of hydrogen economy on GHG emissions Effects of hydrogen economy on surface air quality Proposed study

The role of hydrogen Primary Sources Energy Carriers CO2 CO2 Renewable (Solar, Wind, Biomass) Fossil Energy (Oil, coal, gas) Nuclear Energy Carriers gasoline (distillates) Hydrogen Electricity (Grid) CO2 CO2 Stationary, industrial, residential Transportation, small-scale distributed Energy Utilization

Motivation Electrochemical conversion of hydrogen to work (fuel cell) higher theoretical efficiency than combustion no “pollutants” such as CO, NOx, SOx, HC Enables energy pathways for GHG mitigation via centralized carbon sequestration via utilization of carbon-free primary energy sources Would anthropogenic emissions of hydrogen pose an environmental threat?

Hydrogen emissions Tromp (2003); stratospheric ozone depletion and temperature decrease (greenhouse warming potential) requires unreasonably high increase in atmospheric H2 (Prather, 2003) stratospheric H2 remains constant as CH4 has increased dramatically (Rohs, 2006) Schultz (2003), Rhee (2006); most tropospheric hydrogen consumed by uptake in soils (82%) with tropospheric lifetime of only 1.4 yrs. could soil sink accommodate increased H2 emissions? How is tropospheric O3 affected by hydrogen economy (via changes in NOx, SOx, CO, HC emissions)?

Motivation Do the potential benefits of hydrogen outweigh its potential environmental risks?

Methane

Methane

Nitrous Oxide (N2O)

Nitrous Oxide (N2O) Industrial sources include: nylon and nitric acid production, power plants, and vehicular emissions (~0.11 TgN/yr)

Carbon Monoxide (CO)

Volatile organics (VOC)

Nitrogen oxides (NOx)

Emissions scenarios

CO2 emissions

CH4 Projections

Ozone precursor emissions

Warming potential of GHG Scenario A1FI (IPCC report)

Hydrogen Economy study Estimate effect (present – 2100) on: Greenhouse gas emissions (CO2, CH4, O3) surface ozone precursor emissions (CO, H2, NOx, SOx, VOC) 1. Reference case: business-as-usual 2. Complete transition to hydrogen-powered FCV over 15, 25, 50 yr timeframe Hydrogen produced using fossil energy initially, transition to renewable within 25, 50 yr No hydrogen-powered FCV 2x renewable energy capability as (2), but displaces coal power plants rather than gasoline-powered vehicles Where should our investment be focused in the near term (considering only emissions and air quality)?

References [1] Tromp TK, Shia RL, Allen M, Eiler JM, Yung YL. (2003) “Potential environmental impact of a hydrogen economy on the stratosphere”. Science 300 (5626)1740-2 [2] Prather MJ. (2003) “An environmental experiment with H-2”? Science 302 (5645) 581-2 [3] Rohs S, Schiller C, Riese M, Engel A, Schmidt U, Wetter T et al. (2006) “Long-term changes of methane and hydrogen in the stratosphere in the period 1978-2003 and their impact on the abundance of stratospheric water vapor”. Journal of Geophysical Research-Atmospheres 111 (D14) [4] Rhee TS, Brenninkmeijer CAM, Rockmann T. (2006) “The overwhelming role of soils in the global atmospheric hydrogen cycle”. Atmospheric Chemistry and Physics 6 1611-25 [5] Schultz MG, Diehl T, Brasseur GP, Zittel W. (2003) “Air pollution and climate-forcing impacts of a global hydrogen economy”. Science 302 (5645) 624-7 [6] Intergovernmental Panel on Climate Change, “Climate Change 2001: The Scientific Basis” [7] Intergovernmental Panel on Climate Change, “Climate Change 2001: Mitigation” [8] Prather M, Gauss M, Berntsen T, Isaksen I, Sundet J, Bey I et al. (2003) “Fresh air in the 21st century?” Geophysical Research Letters 30 (2)