SACRAMENTO - The California Resources Board (ARB) has tightened emission standards for new cars and trucks that will significantly reduce the amount of pollution they generate on hot summer days.

The new standard, adopted at a public hearing that ended late Thursday, August 9, while much of the state baked in over 100 degree temperatures, will be phased in over the 1995-98 model years, and will reduce by about 80 percent the emissions of smog-forming hydrocarbons that are created by evaporating gasoline.

While the ARB retained the emissions limit of 2 grams, measured over a test that manufacturers perform on prototype vehicles, it made major improvements in the test itself to make it stricter and to better reflect typical California summer weather conditions.

Among the significant changes, car makers must limit this evaporation in temperatures as high as 105 degrees, common summertime temperatures in many of California's inland cities and desert areas on days when smog formation is greatest. The old standard covered emissions only up to 84 degrees.

Manufacturers also must meet this emission limit 100,000 miles for cars and 120,000 miles for trucks, double the mileage limit of the past and equal to durability required for tailpipe emission limits adopted in the last year.

ARB research shows that these emissions are generated as gasoline heats, up to 130 degrees in some cases, either from engine temperatures while the car is being driven, or while cooling down after a trip, as well as while parked during hot weather.

ARB Chairwoman Jananne Sharpless noted that, as California continues to set the nation's strictest tailpipe standards, evaporative hydrocarbons are becoming a larger part of a vehicle's overall pollution. "Evaporative gasoline can account for as much as one-third of the pollution generated by a new car," she said during a public hearing in San Diego. "As our emission limits further reduce tailpipe emissions, evaporative could account for half of all the smog-forming hydrocarbon that a car produces if we did not adopt these new standards."

By adopting the new standards, she said, "We are telling car makers to build a car that virtually eliminates emissions from evaporating gasoline."

These emissions have been controlled on cars since 1970, with charcoal filled canisters that absorb this evaporation from fuel lines and gas tanks and route the vapors into the engine, where they are burned. To comply with the new ARB limits, manufacturers are expected to increase the size of these canisters to absorb more vapors. They also may take measures to cool the fuel, such as insulating fuel systems and the use of air exchangers. The ARB estimates the cost of these changes will be low, about $18 per car.

In addition to reducing smog-forming hydrocarbon, the new standard is expected to also cut highly toxic benzene, a natural component of crude of crude oil and gasoline by about 25 percent.

 Board member Roberta Hughan, who is also a mayor of Gilroy and a director of the Bay Area Air Quality Management District, noted that the new ARB rule is a bargain compared to anti-smog measures that the Bay area agency is considered for industrial facilities. "When we can control this much pollution at this little cost, we're really accomplishing something."