|Ag Burning Program-91
The fall 1991 agricultural burning season got under way September 16 and ran
for 76 days through November 30. Just under 158,000 acres were burned, a
7,000 acre decrease from the previous season and the second lowest total
ever. Of the total burned acreage, 126,000 acres was rice ground.
Air quality remained relatively good and significantly fewer complaints about smoke were received by the state Air Resources Board and local air pollution control districts. Burning program personnel note that it is difficult to determine whether this sharp reduction was the result of improved program management, less citizen opposition now that burning will be phased out, or perhaps a combination of both.
The dominant weather feature affecting agricultural burning was again the persistent high pressure system and associated dry; stagnant atmospheric conditions. Persistent air inversions limited ventilation and consequently reduced burning, leading to 23 no burn days -10 more than the previous season.
Data collected during the fall 1991 burning season illustrate vividly that the Sacramento Valley's air pollution problems have many causes. Even with minimal burning during September, for instance, PM 10 (particulate matter of less than 10 microns) air quality standards were often exceeded and sometimes by a large margin. Interestingly, when burning increased in late October, PM 10 levels exceeded the standard less frequently and by a smaller margin. On two no burn days - October 15 and 18 - at monitoring sites in Colusa and Yuba City, PM 10 levels exceeded 100 micrograms per cubic meter (50 micrograms is the state standard).
The burning of rice stubble has been a politically easy and visible target for clean air activists. However, data gathered from individual locations or valleywide on a monthly or seasonal basis show that the coefficient of haze (COH), one of the standard measures of air pollution, peaks during morning commute hours and again overnight. This strongly suggests that the valley's problem with excessive particulate material is due more to urban generated pollution sources, such as car exhaust and wood smoke than rice field burning.
Program personnel also report two procedural changes leading to a significant increase in the amount of data received from the system of automated meteorological observing stations (AMOS). Last summer an investigation into the use of a new radio frequency began in hopes of improving reception at valley monitoring stations. After a period of testing, however, this proved not to be an available option. Tests revealed that the most favorable path to the Sutter Buttes, which serves the south Sacramento Valley portion of the AMOS network, was through repeaters at Cohasset and Biggs from the signal generated at Chico State Farm. Improvements were also made in recalling stations that were initially missed.
Recommendations for improvements in the agricultural burning program will be heavily influenced by AB 1378, the rice burning phase-down bill enacted during the 1991 legislative session. Program personnel expect both the Air Resources Board and many public groups will want to propose changes in the 1992 season's burning plan and suggest that these proposals be addressed early enough to allow for adequate evaluation and incorporation into the program as necessary.
Educating the public about how the program operates, the controls it places on the rice industry, and the success it has demonstrated in the past should continue to be an important part of the agricultural burning program. This educational process is critical if the fall burn program is to survive as a viable option should economically feasible alternatives to burning not be found by the turn of the century deadline.