Rice Straw Particulate



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Project Leader and Principal UC Investigators

B.M. Jenkins, Associate Professor Agncultural Engineering Department, UC Davis

S.Q. Turn, Graduate Research Assistant, Agricultural Engineering Department, UC Davis

R.B. Williams, Graduate Research Assistant Agricultural Engineering Department, UC Davis

D. Scales, Air and Idustrial Hygiene Laboratory (AIHL), Department of Health Services, Berkeley, CA

D. Scales, Air and Idustrial Hygiene Laboratory (AIHL), Department of Health Services, Berkeley, CA

J. McCormack, Air Resources Board, Sacramento, CA

J. McCormack, Air Resources Board, Sacramento, CA

J.F. Williams, Farm Advisor, Sutter/Yuba Counties

S.C. Scardaci, Farm Advisor, Colusa County


Growers commissioned this study in 1990 to create a body of factual information for discussions concerning the particulate matter in rice straw burning emissions. After two years of research, however, much of the information is still inconclusive.
Open field burning is the object of much scrutiny these days. Picture shows a silica fiber magnified thousands of times under an electron microscope.

In both field samples and wind tunnel experiments, researchers detected silica fibers, the substance which has led to considerable public debate. Additionally, researchers detected aluminum in fibers from field samples but not in the wind tunnel experiments, a finding which leads them to speculate that the source of alumina-silicate particles may be the soil. The silica fibers and also potassium chloride particles are believed to originate primarily from the straw.

Researchers also used the UC Davis wind tunnel to estimate silica particle emissions. A wide range of results shows the considerable uncertainty that exists concerning predictions of silica emissions from the approximately one million tons of rice straw burned in California.

An emission factor for alumina-silicate fibers cannot be derived because they weren't found in wind tunnel samples. They did appear in field area samples, including both upwind and downwind samples, but were not found in short duration samples taken just behind field flames.

Researchers caution that quantitative results are representative only of the conditions tested at that time. Results do not show, for example, whether fibers are emitted continuously or whether discrete processes may be involved in forming and transporting fibers. Nor do these results show whether all plant tissues contribute equally to silica fiber production.

Analyses of filters collected from municipal areas in the Sacramento Valley during permissible burn days have not been completed and estimated exposures, therefore, cannot yet be computed. Samples collected during rice harvesting have also not yet been analyzed. Results will be reported at a later date.

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