Size relationship between airborne viable bacteria and particles in a controlled indoor environment study

An attempt was made to determine the relationship between airborne viable bacteria (predominantly of human origin) and particle concentrations of different sizes in a controlled environmental chamber focusing on the effect of temperature setting. At temperature settings of 20 degrees and 26 degrees C, six subjects performed simulated office work for 2.5 h, and the particle and total bacteria concentrations at six aerodynamically corresponding size ranges were measured at 20-min intervals. The study revealed that the main contributor of viable bacteria was humans. Viable bacteria concentrations in the size range between 1 and 3 microm was higher at 20 degrees C than at 26 degrees C. Bacteria >7.5 microm showed good correlation with particles of similar minimum size, and it is postulated that this may be because of bacteria rafting on skin scales shed by the subjects. At sizes between 3 and 7.5 microm, the correlations indicated that bacteria exists as clumps, while at size ranges between 1.0 and 2 microm bacteria exists freely. At 26 degrees C, bacteria of size >7.5 microm correlated with exhaled carbon dioxide indicating nasal carriers. Viability of bacteria was shown to be affected by thermal effects. The percentages of particles that were viable bacteria at the different sizes were all found to be very low (<1%).

Due to their respiratory health effects, determining exposure to airborne viable bacteria and particles of different sizes requires the study of their behavior in relation to each other. This study attempts to characterize the relationships of bacteria and particles that are predominantly of human origin. Findings of this work will help researchers in understanding how bacteria levels co-exist with particles of corresponding aerodynamic size across different size ranges between 20 degrees and 26 degrees C.