Particulate matter emission factors for almond harvest as a function of harvester speed

Almond harvest accounts for substantial particulate matter less than 10 microm in aerodynamic diameter (PM10) emissions in California each harvest season. This paper addresses the reduction of harvester ground speed from a standard 8 km/hr (5 mph) to 4 km/hr (2.5 mph) as a possible mitigation measure for reducing PM10 emissions. Ambient total suspended particulate (TSP) and PM10 sampling was conducted during harvest with alternating control (8 km/hr [5 mph]) and experimental (4 km/hr [2.5 mph]) treatments. On-site meteorological data were used in conjunction with both Industrial Source Complex-Short Term version 3 (ISCST3) and the American Meteorological Society/U.S. Environmental Protection Agency Regulatory Model (AERMOD) dispersion models to back-calculate emission rates from the measured concentrations. Baseline annual emission factors for nut pickup of 381 +/- 122 and 361 +/- 123 kg PM10/km2 x yr were determined using ISCST3 and AERMOD, respectively. Both of these values are substantially lower than the current PMIo emission factor for almond pickup of 4120 kg PM10/ km2 x yr. The particulate matter less than 2.5 microm in aerodynamic diameter (PM2.5) emission factors for nut pickup developed from this study were 25 +/- 8 kg PM2.5/km2 x yr and 24 +/- 8 kg PM10/km2 x yr were determined using ISCST3 and AERMOD, respectively. Reducing harvester speed resulted in an emissions reduction of 42% for TSP, but no differences were detected in emissions of PM10 and PM2.5. Differences detected in the emission factors developed using ISCST3 and AERMOD were not statistically significant, indicating that almond harvest emission factors previously developed using ISCST3 may be applied appropriately in AERMOD.