The computer model calculates the annual costs to society from the deleterious effects of urban air pollution over the century.  The following graph shows that either hydrogen-powered fuel cell electric vehicles or battery EVs would be required to eliminate most urban air pollution costs:

To summarize:

• Business as usual--100% gasoline vehicles: the costs of urban air pollution rise rapidly over the century
• Gasoline hybrid electric vehicle scenario: hybrids help cut pollution slightly
• Gasoline plug-in hybrid electric vehicle scenario: plugging in gasoline cars does not help to reduce urban air pollution much until after 2040, since more than half the nation’s electricity comes from burning coal, frequently inside the urban airsheds around large cities; once the grid becomes greener after 2040, plugging in hybrids does help to cut air pollution, although emissions rise again after 2070 due to increased vehicle miles traveled
• Biofuel (cellulosic ethanol) plug-in hybrid electric vehicle scenario: replacing gasoline with cellulosic ethanol or other biofuels has relatively little impact on overall urban air pollution, since liquid hydrocarbon fuels are still being burned inside the internal combustion engine.
• Hydrogen internal combustion engine (ICE) hybrid scenario: replacing gasoline with hydrogen in a conventional hybrid does decrease pollution cost significantly by the last half of the century
• Fuel cell electric vehicle scenario: hydrogen-powered fuel cell EVs would substantially reduce urban air pollution. We expected that pollution would be reduced close to zero by the end of the century, but the Argonne National Laboratory GREET model used to calculate emissions includes the particulate matter (PM) generated by brake and tire wear.  As shown in the graph, the FCEV scenario does reduce air pollution close to the PM limit from brake and tire wear.
• Battery electric vehicle scenario: Battery EVs, if accepted by almost all drivers of light duty cars and trucks, would reduce urban air pollution to almost the same level as the fuel cell electric vehicle. However, we do not expect most drivers to accept the charging time and range limitations of full-function BEVs.

ANother interesting topic is the local air pollution of gasoline HEVs like the Toyota Prius vs local air pollution from PHEVS like the Chevy Volt.  The California Air Resources Board has determined that the PHEV Volt will generate more local pollution than the HEV Prius, including more than 20 times more CO, more NMOG and more NOx:

 (source: see this link)

As a result, the Prius is certified by CARB as an SULEV (super Ultra low emitting vehicle), while the Volt is rated as the higher emitting ULEV (Ultra low emitting vehicle.)

For the full technical details of our computer simulation results, see the August 2009 International Journal of Hydrogen Energy article.  For a detailed description of the input assumptions for these models, see another article published in December of 2009.