SACRAMENTO - The state Air Resources Board (ARB) has approved a new agricultural burning plan for the Sacramento Valley that will eliminate burning on days with marginal air quality and cut rice straw burning by up to 20 percent during the peak harvest season.

The plan was resubmitted by the air pollution control officers of the 10 valley counties after the ARB requested changes from the original proposal and it outlines how they will administer special restrictions on ag burning from mid-September to the end of October.

The changes in the plan are based on ARB recommendations, in which burning allocations will be reduced when weather conditions are most conducive to the build-up of air pollution or when air quality is poor.

Based on 1989 weather patterns, the ARB recommendations would have cut the acreage burning during the critical 75-day harvest season by 12 to 20 percent and would have eliminated it on 16 to 20 days with marginal weather and air pollution conditions.

The changes refine a new approach to managing Sacramento Valley agricultural burning that has been in place since 1980, and that balances an usually high demand for burning with seasonal weather conditions that are most likely to create air pollution problems.

Prior to 1980, as many 10,000 acres of rice straw were burned at a time, during a few days when weather and air quality allowed. The burning approval was based on weather predictions, however, during a transition from late summer to early fall, wind patterns and upper atmosphere temperature inversions can change suddenly, increasing pollution levels.

Since 1980, the ARB, local air pollution control officials, and the Rice Growers Association have changed how the burning is managed, matching the daily acreage allotments to daily weather and pollution conditions, sometimes allowing as little as 2,000 acres to be burned at a time. Instead of burning massive amounts of rice straw on a few days, growers burn a smaller amount each day to prevent creating more pollution than the atmosphere can accommodate.

In addition, county air pollution control officials can cut the ARB allocation if local weather conditions dictate it and are responsible for determining where the burning will take place to prevent the buildup of pollution over populated areas.

The new approach of daily allocations has reduced pollution during the peak rice harvest season by 68 percent since 1980, with excessive smoke measured at Sacramento Executive Airport an average 4.5 percent of the time, compared to 14.1 percent between 1970 and 1980. Prior to any regulation, excessive smoke at the same location was measured an average 24.4 percent of the time between 1961-70.

James D. Boyd, ARB executive officer, characterized the most recent changes as fine-tuning of a successful pollution control program. "The ag burning program has already cut pollution significantly and that performance was rewarded with a Clean Air Award from the Sacramento area Lung Association in 1985.

"The changes we approved for 1990 are the result of our experience with this new approach over the last 10 years and will make a good program work even better to protect public health," he said. "We will continue to review the program's performance and make future changes to upgrade it as we see the need."

The Sacramento Valley is one of the nation's largest rice growing regions, with up to 500,000 acres planted each year. Approximately 40 percent of the acreage is burned during the fall, with the remainder burned in the spring, when weather conditions are more helpful in dispersing the smoke and pollution.