Catalytic Converters

    Our main strategy until now for reducing NO emissions (and, hence, ozone levels) has been to remove NO from post-combustion emissions gases.  Advances in catalytic converter technology have allowed steady progress on this front.  The EPA's emissions standards for vehicles manufactured in 1980 are 6 grams/mile of nitrogen oxides and 2 grams/mile of hydrocarbons.  Improved catalytic converters have made it possible to lower the maximum level of emissions for cars manufactured after 1996 to 2 grams/mile of nitrogen oxides and 0.8 grams/mile of hydrocarbons.    The catalytic converter provides a noble metal (platinum or iridium) catalyst surface that promotes oxidation of VOCs and reduction of nitrogen oxides to yield innocuous products.   For more detail about how catalytic converters work, click here.   

California: A Model For Successful Pollution Reduction

    Although improved catalytic converters are helping, the persistence of ozone levels that exceed the NAAQS indicate that they are not enough. What else needs to be done?   The answer depends on the particular situation. Different regions of the country have different air-quality challenges. California, for example, has already reduced its reliance on fossil fuels to provide electricity. In December 2000, none of the electricity produced in California came from burning coal or oil, and two thirds of the electricity produced was derived from hydroelectric, nuclear and renewable energy sources. The remaining third was produced by burning natural gas.  In California, cars cause more smog than does electricity generation, although some nitrogen oxides are produced when natural gas is burned. (See Box 1 for more details.)

    California's efforts to improve air quality have not been limited to changes in the way it produces electricity. Legislation sets maximum emission levels for motor vehicles and industry, and the state sponsors public education for voluntary consumer choices that promote clean air. These efforts have paid off:  in 1970 there were 148 air-quality alerts, but in 1997 there was only one. Nevertheless, the growing population of California, and the growing number of automobiles, continue to put pressure on air quality. In 1999, seven of the ten highest areas of ozone concentration in the U.S. were in the state of California.  

    Therefore, in response to the growing demand for automobiles, California is attempting to implement a second strategy to reduce NO emissions:  finding alternative methods to power cars.  The California legislature has required auto manufacturers to manufacture a mix of vehicles that meet progressively more stringent standards for emissions. In addition, legislation exists that requires a certain percentage of the vehicles manufactured to be zero-emission vehicles (ZEVs).The ZEV requirement was suspended for all years prior to model year 2003. It remains to be seen whether car manufacturers will be expected to comply with the existing targets for ZEVs in 2003.  The answer will depend, at least in part, on the technology that is available for ZEVs.  In the next section, we take a look at the current technology for ZEVs.