Spatiotemporal variations in the association between particulate matter and airborne bacteria based on the size-resolved respiratory tract deposition in concentrated layer feeding operations.

Bacterial loading aggravates the health and environmental hazards of particulate matter (PM), particularly in concentrated animal feeding operations. Understanding the association between PM and airborne bacteria is conducive to accurately assessing occupational exposure, providing fundamental data for exposure mitigation via engineering solutions, and providing information regarding the physical properties influencing the transmission of airborne microorganisms at emission sources. In this work, we conducted a joint study to systematically determine the concentrations and size distributions of PM and airborne bacteria, and establish the quantitative relationship between PM and airborne bacteria in laying hen houses. The association between PM and airborne bacteria was expressed as the load of airborne bacteria on PM in terms of the identical particle size interval based on the size-resolved respiratory tract deposition. The concentrations and size distributions of PM and airborne bacteria in laying hen houses were affected by the in-house space (upper and lower), chicken activity (day and night), and outside temperature. The size distributions of PM and airborne bacteria indicated that the mass concentration of large particles decreased with increasing outside temperature, while the concentration of airborne bacteria loaded on the small particles increased with increasing outside temperature. The results indicated that particles with diameters ranging from 2.1 to 4.7 μm carried the most airborne bacteria. Therefore, particles with diameters ranging from 2.1 to 4.7 μm should be the focus of future experimental research on occupational exposure, air quality improvement, and the airborne transmission of PM and airborne microorganisms originating from concentrated layer feeding operations.