Aerosol particles and airborne microorganisms are crucial factors of indoor air quality. The purpose of the present study was to evaluate the interrelationships among aerosol numbers, various types of airborne bacteria, temperature, and relative humidity (RH) to decide which parameters have more significant relationships among them. The concentrations of aerosol numbers, airborne total aerobic bacteria, Staphylococcus aureus (S. aureus), and Escherichia coli (E. coli) in the indoor air, as well as indoor and outdoor temperatures and RH, were assessed each week for a total of 20 days in a tie-stall dairy barn during the summer season in Tochigi, Japan. The mean concentrations of the fine aerosol numbers (0.3-2.0 µm) were greater than the mean concentrations of coarse aerosol numbers (5.0-10.0 µm). Among the airborne total aerobic bacteria, the mean concentration of airborne S. aureus was higher compared with airborne E. coli. More significant positive associations were found between outdoor environmental temperatures and aerosol numbers rather than indoor temperatures and aerosol numbers. All three types of airborne bacteria were associated with both outdoor and indoor environmental temperatures. These findings are crucial in the mitigation of aerosol numbers and airborne bacteria in the indoor air of dairy barns.
Keywords: aerosol numbers; airborne bacteria; dairy cows; relative humidity; summer season; temperature; tie-stall barn.