Evaluation of Particulate Matter Abatement Strategies for Almond Harvest

ABSTRACT

Almond harvest accounts for substantial PM₁₀ (particulate matter [PM] ≤10 μm in nominal aerodynamic diameter) emissions in California each harvest season. This paper evaluates the effects of using reduced-pass sweepers and lower harvester separation fan speeds (930 rpm) on lowering PM emissions from almond harvesting operations. In-canopy measurements of PM concentrations were collected along with PM concentration measurements at the orchard boundary; these were used in conjunction with on-site meteorological data and inverse dispersion modeling to back-calculate emission rates from the measured concentrations. The harvester discharge plume was measured as a function of visible plume opacity during conditioning operations. Reduced-pass sweeping showed the potential for reducing PM emissions, but results were confounded because of differences in orchard maturity and irrigation methods. Fuel consumption and sweeping time per unit area were reduced when comparing a reduced-pass sweeper to a conventional sweeper. Reducing the separation fan speed from 1080 to 930 rpm led to reductions in PM emissions. In general, foreign matter levels within harvested product were nominally affected by separation fan speed in the south (less mature) orchard; however, in samples conditioned using the lower fan speed from the north (more mature) orchard, these levels were unacceptable.

IMPLICATIONS

The results of this research indicate that PM emissions from almond sweeping operations may be reduced by use of reduced-pass sweepers. Additionally, increased efficiencies in fuel consumption and time required for sweeping may be realized by use of reduced-pass sweepers. Reducing harvester separation fan speeds results in lower emissions from nut conditioning, but foreign matter levels in conditioned samples from more mature orchards were unacceptable.

ACKNOWLEDGMENTS

The researchers acknowledge the Almond Board of California and the National Research Initiative Competitive Grant no. 2009-55112-05217 from the U.S. Department of Agriculture Cooperative State Research, Education, and Extension Service Air Quality Program for support of this project.