A hydrogen economy s potential environmental impacts
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A Hydrogen Economy’s Potential Environmental Impacts. Chun Zhao Evan Cobb. A Hydrogen Economy. www.gii.com.hk. Hydrogen characteristics in the atm. Observed global hydrogen burden: 182 Tg Global sink: 74.4 Tg/yr Lifetime : 2.5 years Rahn etc. 2003

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A Hydrogen Economy’s Potential Environmental Impacts

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A hydrogen economy s potential environmental impacts

A Hydrogen Economy’s Potential Environmental Impacts

Chun Zhao

Evan Cobb

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


A hydrogen economy

A Hydrogen Economy

www.gii.com.hk

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Hydrogen characteristics in the atm

Hydrogen characteristics in the atm.

  • Observed global hydrogen burden: 182 Tg

  • Global sink: 74.4 Tg/yr

  • Lifetime : 2.5 years Rahn etc. 2003

  • Current Mixing Ratio of H2: 510ppbv

  • Tropospheric hydrogen

  • Stratospheric hydrogen

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Hydrogen in troposphere

Hydrogen in troposphere

The sources and sinks of hydrogen in troposphere

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Note for table of sources and sinks

Main source of Hydrogen: oxidation of organic compounds

Main sink of Hydrogen: soil uptake

Man-made sources: fossil fuel combustion

CO + H2O H2 + CO2

Main chemical sink:

OH + H2 H + H2O

Debate: How is H2 lost?

What portion of H2 is consumed by soil/microbial activity?

Note for table of sources and sinks

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Hydrogen production from oxidation of organic compounds

Hydrogen production from oxidation of organic compounds

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Reduction in oh

Reduction in OH

  • H2 behaves like CO (takes up one OH and releases one HO2 radical + H20)

    Michael Prather, 2003.

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Reduction in oh by no x

Reduction in OH by ↓NOx

Shultz et al. 2003

  • Decrease in OH is largely driven by the reduction in NOx emissions

  • Importance of HOx/NOx coupling leads to non-linear dependence of OH on NOx levels

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Hydrogen in the stratosphere

Hydrogen in the Stratosphere

The main hydrogen reservoirs in Stratosphere:

Molecular hydrogen (H2)

Water vapor (H2O)

Methane ( CH4)

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


H 2 sources in the stratosphere

H2 Sources in the Stratosphere

CH4

OH, O(1D), Cl

CH3

O2HHO,OH,HCl

CH3O2

NO NO2

CH3O

O2 HO2

CH2O

hv OH

CO+H2HCO+HHCO+H2O

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H 2 sinks the in stratosphere

H2 sinks the in stratosphere

Reaction with OH, O(1D), Cl:

  • H2 + OH H2O + H

  • H2 + O(1D) OH + H

  • H2 + Cl HCl + H

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The fate of hydrogen in stratosphere

The fate of Hydrogen in stratosphere

  • The H2 mixing ratio in the lower and middle stratosphere is nearly constant, the net hydrogen cycling in the stratosphere can be regarded as a loss in methane and a production of water.

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Main reactions of h 2 in the stratosphere

Main reactions of H2 in the stratosphere

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Potential chemical changes in the stratosphere

Potential chemical changes in the stratosphere

  • H2 + OH → H2O + H

  • “[H2O]…would result in cooling of the lower stratosphere, and the disturbance of ozone chemistry, which depends on heterogeneous reactions involving hydrochloric acid and chlorine nitrate on ices of H2O.” Tromp et al. 2003 pg. 1740

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Environmental impact overview

Tropospheric Effects

Reduced oxidative capacity of atm. (OH)

Reductions in NOx, soot, sulfates, CO2, O3

Increased surface H2 concentrations

Change in atmosphere-biosphere reactions

Global warming

Stratospheric Effects

Increase of water vapor

Cooling in lower layers

Enhanced ozone destruction chemistry

Increase in noctilucent clouds

Global warming

Environmental Impact Overview

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Impacts all hinge upon

Impacts ALL hinge upon…

  • Production methods of H2

    • “Clean” or “dirty”

  • Leak rates from system

    • Current networks in Germany achieve 0.1%

    • Natural gas pipelines: 0.5-1.5%

    • 10-20% losses possible from uncontrolled evaporation from liquid storage tanks

    • Complete fossil fuel replacement and 3% leak rate would ↑ H2 emissions 1.35-2 times.

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Increased surface h 2

Increased Surface H2

  • H2 source is from system leaks

  • H2 burden could increase by 30%-120%

  • Increased partial pressures of H2 could affect microbial colonies

  • More pronounced changes in N.H. than S.H.

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Environmental impacts schultz et al 2003

Environmental ImpactsSchultz et al. 2003

  • Increased H2 concentrations lead to a reduction in OH and an increased lifetime of CH4 and without reductions in NOx, increases in tropospheric O3

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Global warming impacts

Global Warming Impacts

  • Increased lifetime of CH4

  • Changes of tropospheric and stratospheric ozone levels

  • Noctilucent cloud formation (albedo change)

  • Dependent on generation processes

  • Dependent on level of fuel cell replacement

    • Massive reductions in CO, CO2, NOx, and other combustion emission if made cleanly

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Gwp increase for ch 4

Schultz et al.

In some models, ΤCH4 would increase by 26%

Radiative forcing of 0.5 W*m-2

Prather

Doesn’t take NOx reductions into account

Increases lifetime of CH4

0.60 ppm H2 increase

GWP of ~0.026 W*m-2

GWP Increase for CH4

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Gwp of h 2 production

GWP of H2 Production

  • Reductions of greenhouse gas emissions

    • How much?

  • Increase of greenhouse emissions

    • Emissions of CO2: ↑34%, CH4: ↑19%

    • H2 made by:

      • Hydrolysis after electricity from coal power

      • Gasification of coal

      • Natural gas reforming

Shultz et al. 2003

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Reduction of tropospheric o 3

Reduction of Tropospheric O3

  • Up to 50% reductions of NOx and CO by 100% fuel cell replacement of surface fleet reduces tropospheric ozone

  • Assumes all H2 is produced using emission-free processes

  • Reduction of 1-8 ppbv in surface ozone throughout N.H.

    Shultz et al. 2003

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Reduction of stratospheric ozone

Reduction of Stratospheric Ozone

  • Increases of H2 to stratosphere result in

    • Increase of H20

    • Decrease of columnar O3

    • Tromp et al. 2003

Increase of H20

Decrease of O3

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Noctilucent clouds

Noctilucent Clouds

  • Clouds at extremely high altitude, about 85 km, that literally shine at night. They form in the cold, summer polar mesopause and are believed to be ice crystals. (http://lasp.colorado.edu/noctilucent_clouds/)

  • “An increase in the mesosphere of H2O derived from H2 could lead to an increase in noctilucent clouds, with potential impact on Earth’s albedo and mesopheric chemistry.” –Tromp et al. 2003

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Summary

Summary

  • An H2 economy could provide substantial improvements in local, regional, global air quality and lower greenhouse gas emissions depending upon production processes.

  • Large uncertainties remain

    • NOx, CH4, CO2 emission changes

    • H2 lifetime

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


Questions

Questions?

Ga Tech - EAS 6410 - Air Chemistry Group Presentation


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