Measuring Cattle Feedlot Dust Using Laser Diffraction Analysis

Considerable amounts of particulate matter (PM), including total suspended particulates (TSP), particulates with equivalent aerodynamic diameter less than or equal to 10 µm (PM10), and particulates with equivalent aerodynamic diameter less than or equal to 2.5 µm (PM2.5), are emitted from large beef cattle feedlots. Particle size distribution and concentrations of TSP, PM10, and PM2.5 at a commercial cattle feedlot in Kansas were measured over a two-year period. The feedlot had a capacity of 30,000 head with a total pen area of 50 ha and was equipped with a sprinkler system for dust control. Collocated low-volume samplers for TSP, PM10, and PM2.5 were used to measure concentrations of TSP, PM10, and PM2.5 at the upwind and downwind edges of the feedlot. A laser diffraction (LD) analyzer (Beckman Coulter LS 13 320) was utilized to determine the particle size distribution of dust samples collected by TSP samplers. A micro-orifice uniform deposit impactor (MOUDI) was also used to measure particle size distribution at the downwind edge of the feedlot. Considering the same effective size range, the LD analyzer and MOUDI did not differ significantly in mean geometric mean diameter (GMD) (11.6 vs. 13.0 µm) and in mean geometric standard deviation (2.3 vs. 2.3). Wind speed and period of sampling significantly affected the mean GMD of the particles. The PM10 and PM2.5 concentrations that were calculated from the LD method and TSP data were not significantly different from those measured by low-volume PM10 and PM2.5 samplers (122 vs. 131 µg m-3 for PM10 and 26 vs. 35 µg m-3 for PM2.5). Both PM10 and PM2.5 fractions decreased as pen surface water content increased, but the PM2.5/PM10 ratio showed little change as pen surface water content increased.