Respirable-dust production from agricultural operations in the Sacramento Valley, California

Air quality in California's intensively farmed Central Valley violates regulatory particulate matter limits nearly year-round. Little is known about the amount of fugitive dust produced by individual agronomic operations. This study measured the respirable fraction, covering particles less than or equal to 4 mu m in aerodynamic diameter and the influences of climate, soil, and implement conditions on dust production. Respirable dust was collected at the implement from 18 cultural operations for a complete annual crop cycle on 22, 4097-m(2) plots, 11 km west of Davis, CA. Plots included conventional and organic corn (Zea rnays L.) and tomato [Lycopersicon lycopersicum (L.) Karsten] fields as well as fields with a winter cover crop or fallow plots followed by wheat (Triticum aestivum L.). The 266 samples were collected with standard cyclone samplers mounted directly on each implement as the dust source (average height of 94 cm above ground). Sampling near the dust source measured the relative respirable-particulate-matter production from each operation. The highest average respirable-dust concentration was 10.3 mg/m(3) air from soil ripping and land planing, carried out on dry surface soil. The lowest dust concentration was from dishing of corn stubble (0.3 mg/m(3)) into soil during the wet season. Approximately 64% of all operations were performed during hot and dry weather, producing 83% of the annual respirable dust for this three-crop system. Among the measured environmental and implement conditions, air temperature, soil moisture, wind speed, and tractor speed were significantly correlated with the dust concentration in an exponential model.