Winter, 1992 (v5n2)
Jenkins, B.M., S.Q. Turn and R.B. Williams
Agric. Ecosystems Environ.
38:313-330. 1992
State legislation enacted
in 1983 stipulates that new energy producing facilities that rely on biomass
fuels should not result in an increase in the total pollutant emissions
for the district in which the facility is constructed. The legislation
requires that new facilities reduce or offset pollution levels elsewhere
in the region. Since the burning of agricultural wastes in power plants
reduces certain types of air pollutants compared to field burning, crop
residues could be considered offset fuels. This allowance establishes
an economic incentive for using agricultural wastes as fuels.
In 1984, the California Air
Resources Board, which has primary responsibility for regulating atmospheric
emissions, developed a procedure to determine the magnitude of the offset
credits, that is, the incremental emissions permitted in a given period
of time because facilities use offset fuels. The offset credit for a particular
pollutant (in kg per day) takes into account: 1) the quantity of biomass
used by the facility, 2) the mass of pollutant emitted per mass of biomass
burned, and 3) the fraction of the total crop residue that is burned in
the field during a specified period (winter, spring, summer, fall).
The purpose of this study was to determine with greater accuracy the third factor listed, i.e., the proportion of the crop residue burned in a given season of the year. This information would be used to refine the procedure for calculating allowable atmospheric emissions from power-generating facilities using fuel that would otherwise be burned in the field.
Methods
The authors attempted to use two sources for their study: 1) a compilation of agricultural burn reports, and 2) direct survey (interviews) of growers. Because the burn reports were shown to be highly inaccurate, only the interview method was used. Interviews were conducted with 609 growers in Fresno, Kern, Merced, and Stanislaus Counties. Sixteen crops were represented, including 6 field crops and 10 orchard and vine crops. In addition to the survey results, existing information on emission factors and crop residue yields statewide were used.
Results
The proportion of crop residue
burned in the San Joaquin Valley was high for almonds, apricots, cherries,
walnuts, and rice (table 1).
| Table 1. Burn fractions (proportion of crop residue that is burned) for sixteen crops surveyed in the San Joaquin Valley. | |
| Crop | Burn Fraction (%) |
| Almonds | 84 |
| Apricots | 60 |
| Cherries | 56 |
| Walnuts | 95 |
| Rice | 99 |
The total emissions from
agricultural burning were highest for almonds, walnuts, rice, and wheat.
Statewide, orchard and vine crops account for 27 percent of the agricultural
biomass that is burned; for the San Joaquin Valley alone, this figure
increases to 75 percent of the total biomass burned. The difference between
the statewide percentage and that for the San Joaquin Valley alone is
due primarily to rice straw burning in the Sacramento Valley. Statewide,
rice and almonds together make up 82 percent of the agricultural biomass
that is burned (table 2).
Emissions of particulate
matter into the atmosphere from agricultural burning are over 3.5 million
tons annually in California. This figure, however, represents less than
1 percent of the total particulate matter emissions from various sources.
The contribution of agricultural burning to emissions of carbon
monoxide, hydrocarbons, oxides of nitrogen, and sulfur is also quite low,
both statewide and in the San Joaquin Valley.
While the authors found some
inconsistencies in the quarterly distribution of emissions, the very high
value obtained by the survey for the fall season was consistent with rice
straw burning in the Sacramento Valley. On an annual basis, power plants
would have full emission offsets available. On a quarterly basis, however,
they are likely to lose offsets in the spring and summer when power plant
emissions exceed field burning emissions. To protect ambient air quality,
therefore, the facilities will be required to: 1) install additional pollution
control equipment, 2) reduce non-agricultural source emissions to obtain
sufficient offset credits, or 3) defer the burning of some fuel sources
to different seasons than would have been the case if field burned.
For more information write
to: B. Jenkins, Agricultural Engineering Department, University of California,
Davis, CA 95616.
(DEC.344)
Contributed by Chuck Ingels
| Table 2. Crop residue burned in California for four of the sixteen crops surveyed. | ||||||
| Crop | Winter | Spring | Summer | Fall | Total | % of Total
(all crops) |
| Almonds | 242,407 | 5,155 | 0 | 28,020 | 275,582 | 18 |
| Walnuts | 46,564 | 57,406 | 0 | 5,451 | 109,420 | 7 |
| Rice | 267,004 | 0 | 0 | 727,318 | 994,321 | 64 |
| Wheat | 0 | 0 | 86,144 | 2,674 | 88,817 | 6 |
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