A survey of particulate matter on california dairy farms.

Over the past 30 yr, individual California dairy operations have grown in size; however, little is known about the distribution and determinants of particulate matter (PM) concentrations on these dairies. Elevated exposure to PM is associated with respiratory and cardiovascular health effects, particularly in occupational settings. The purpose of this study was to quantify the concentrations of PM and all inhalable PM (0-100 µm) on California dairies. Samplers were placed at various locations (e.g., milking parlor, grain storage area, drylot corral, and freestall barns) on 13 different dairies to collect PM and all inhalable PM during the 2008 summer months. The PM and all inhalable PM concentrations varied between different areas on a dairy and from dairy to dairy. Geometric mean concentrations for PM and inhalable PM were 24 µg m (range, 2-116 µg m) and 332 μg m (range, 74-1690 µg m). A key variable for explaining variation in PM concentrations with a mixed effects model was regional background ambient concentrations of PM No significant differences were observed in mean concentrations between upwind and downwind fence line concentrations (adjusted geometric mean ratio [AGMR] = 0.7; 95% CI, 0.4-1.3), although significant differences were found between upwind and central location mean values (AGMR = 0.5; 95% CI, 0.3-0.8; < 0.01). These results indicate dairy PM sources and, thus, elevated occupational exposure. Covariates, such as the age of the dairy and number of cows in the freestall barn and drylot corral, were important variables in explaining PM concentration variability. Levels of PM were lower compared with dairies in other U.S. states and other countries.