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Converting all U.S. onroad vehicles to hydrogen fuel-cell vehicles (HFCVs) may improve air quality, health, and climate significantly, whether the hydrogen is produced by steam reforming of natural gas, wind electrolysis, or coal gasification. Most benefits would result from eliminating current vehicle exhaust. Wind and natural gas HFCVs offer the greatest potential health benefits and could save 3700 to 6400 U.S. lives annually. Wind HFCVs should benefit climate most. An all-HFCV fleet would hardly affect tropospheric water vapor concentrations. Conversion to coal HFCVs may improve health but would damage climate more than fossil/electric hybrids. The real cost of hydrogen from wind electrolysis may be below that of U.S. gasoline.

Laboratory studies of heterogeneous reactions important for ozone depletion over Antarctica are reported. The reaction of chlorine nitrate (ClONO(2)) with H(2)0 and hydrogen chloride (HCl) on surfaces that simulate polar stratospheric clouds [ice and nitric acid (HNO(3))-ice and sulfuric acid] are studied at temperatures relevant to the Antarctic stratosphere. The reaction of ClONO(2) on ice and certain mixtures of HNO(3) and ice proceeded readily. The sticking coefficient of ClONO(2) on ice of 0.009 +/- 0.002 was observed. A reaction produced gas-phase hypochlorous acid (HOCl) and condensed-phase HNO(3); HOC1 underwent a secondary reaction on ice producing dichlorine monoxide (Cl(2)O). In addition to the reaction with H(2)0, ClONO(2) reacted with HCl on ice to form gas-phase chlorine (Cl(2)) and condensed-phase HNO(3.) Essentially all of the HCl in the bulk of the ice can react with ClONO(2) on the ice surface. The gaseous products of the above reactions, HOCl, Cl(2)0, and Cl(2), could readily photolyze in the Antarctic spring to produce active chlorine for ozone depletion. Furthermore, the formation of condensed-phase HNO(3) could serve as a sink for odd nitrogen species that would otherwise scavenge the active chlorine.

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