California Driving Cycle

Tables 1 and 2 sununarize the development of the legislation in the United States from the time when serious attention was paid to reducing emissions from automobiles. From 1977 in California, where there were some particularly pressing air-quality problems [3], they were allowed to legislate lower levels of emissions than in the rest of the United States. The emission numbers are generated by driving the vehicle on a chassis dynamometer (rolling road) to a well-defined test drive cycle (see Fig. 1). This cycle represents conditions typical on a U.S. freeway and has a maximum speed of 55 mph. The emissions are collected from the tailpipe as soon as the ignition is switched on, analyzed, and the pollutant concentrations calculated. It can be seen from the table that emission limits are decreasing steadily, especially from 1993 onward, and that over the period there has been a major reduction in the emission levels. With the introduction of each successive emissions band, a small percentage of vehicles are required to meet the next band. This culminates in a requirement for a small number of vehicles to emit zero emissions in the year 2000, which can be achieved currently only by electric vehicles.

The spectral content of alkenone record has only been assessed in a few records. In one noteworthy example, Schneider et al. (1999) provide evidence that tropical Atlantic SST has a strong imprint from the precessional (—21 kyr) cycle of insolation. Precessional variability drives contrasts in summer and winter heating, particularly at low latitudes. An expected result is that precession regulates the monsoonal cycle of the tropics. This result is consistent with the strength of precession and the weakness of obliquity (41 kyr) components in the spectra of equatorial U f7 records. Both Schneider et al. (1999) and our own unpublished work off the California margin also show that the 41 kyr component in SST is larger at higher latitudes in late Pleistocene time series than it is in low-latitude records. 

It is not easy to compare the emissions values obtained during the two cycles. In addition to the obvious differences between the driving protocols, the total amount of all the hydrocarbons are measured in Europe, whereas methane is not included in the United States. Also, all new production vehicles have to meet every new European legislative mandate as soon as it is introduced, compared to a phasing in strategy in California. However, it is generally considered that future legislation will require similar technical solutions for both markets. 

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