Aerial Drone-Based Monitoring of Particulate Emissions During Almond Nut-Picking Operations

Abstract

Using the Federal Reference Method (FRM) air sampling protocol, the total suspended particulates (TSP), PM10 and PM2.5 levels across four low-dust harvesters were found to be 40% to 70% lower compared to that of a conventional Flory 480 harvester. All harvesters were able to achieve lower dust emissions without sacrificing harvest collection efficiency. As an alternative to the FRM protocol, a novel drone particulate measurement system (DPMS) was developed and was able to detect changes in the dust concentrations as a function of harvester operational settings. Dust reduction estimates using the DPMS data validated the results of previous years with slight deviations due to difference in local meteorology and confounding effects of orchard soil structure and management practices. The proposed use of DPMS reduces logistical needs, complexity issues, and feedback times compared to the FRM protocol. However, the DPMS data are still unlikely to replace the accuracy and precision of the mass-based FRM data. At this stage, the DPMS field protocol should only be used as a rapid screening tool to complement the existing FRM for evaluating dust abatement strategies and not for regulatory purposes. Using AERMOD, the aerial TSP concentrations from operating an old harvester yielded mean TSP emission factors (EFs) which were comparable to the 2017 FRM-based study. The use of aerial TSP concentrations in dispersion modelling revealed variability issues with the TSP EF estimates at low wind speed conditions (<2.5 m/s). Dust plume folding over and “mushrooming” effects were observed resulting to false high TSP readings. In terms of their coefficient of variation (CV), the area model’s CV = 0.84 while the RLINE model’s CV = 0.57. The 2017 FRM study has an overall CV of 0.20. Based on the dust migration simulations, harvesting at high wind speeds (> 5 m/s) is discouraged when there are nearby habitation downwind of the orchard as dusts can travel > 3km, especially at low humidity conditions. Dust plumes under medium wind speeds (2 – 5 m/s) can travel up to 1.2 km in less than an hour. With these results, future works should include efforts to understand threats, manage risks, mitigate incidents, and develop capabilities of the almond industry to provide critical information, such as time-sensitive health advisories.