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In Situ Transmissiometer Measurements for Real-Time Monitoring of Dust Discharge during Orchard Nut Harvesting

Biological and Agricultural Engineering, One Shields Ave, UC Davis, Davis, CA 95616

^* Corresponding author (ddowney{at}ucdavis.edu).

Received for publication August 20, 2006. Rapid assessments of operating conditions and field preparation on dust discharge from nut harvesters are needed to guide improved equipment design and grower practices for dust reduction. An industrial opacity sensor, typically used for industrial stack monitoring, was adapted for use on a nut harvester to measure relative dust intensity during nut pick-up operations in almond orchards. Due to the high volume of discharge air and the presence of large debris such as leaves, additional components were coupled with the sensor to enable subsampling of the air. Pre-harvest windrow preparation conditions were evaluated. Results indicated that relative dust intensity decreased by 32% during harvest activities after windrow preparation with proper nut sweeper adjustment. Conventional harvesting results indicated that under typical operating conditions, reducing the separation fan speed could reduce relative dust intensity by 54%. Ground speed also had a strong effect; reducing speed from 4.8 to 2.4 km h^–1 reduced opacity of discharged air by 50%. The measurement system was also mounted on a separate vehicle and used as a tool for comparing modifications in harvest machine designs where direct measurement of discharge may not be feasible due to mechanical constraints. A comparison between a conventional harvester and one modification in the harvester design found that the machine modification decreased relative dust intensity by 73%. The measurement tools described in this work can be used to provide rapid feedback on harvester operating conditions, orchard cultural practices, and machine design modifications.

Abbreviations: PM, particulate matter • PM2.5, particulate matter with aerodynamic diameter of 2.5 µm or less • PM10, particulate matter with aerodynamic diameter of 10 µm or less • PTO, power take-off • SJV, San Joaquin Valley