"The Department of Energy says that replacing gasoline with propane in small engines like lawn equipment leads to substantial reductions in emissions, though the full impact has yet to be quantified in studies. Lehr Inc. offers propane-powered lawn equipment such as the Eco Trimmer and the new Eco Blower. The Eco Trimmer meets new EPA standards that will take effect in 2010 and 2011, the company says."

Source:"Lawn Equipment Future Use" is an easily defendable qualitative factor, so competing institutions will have a difficult time overcoming it.