10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Indoor-Outdoor (I/O) Exchange of Bioaerosols at Various Ventilation Modes
JURATE VIRKUTYTE, Christine Uebel, Kelechi Isiugo, Michael Benjamin, Andrew Maier, Mark T. Hernandez, Sergey A. Grinshpun, Tiina Reponen, University of Cincinnati
Abstract Number: 216 Working Group: Bioaerosols
Abstract People are exposed to bioaerosols both indoors and outdoors. Previous studies have typically focused on individual classes of airborne microbes. To simultaneously evaluate the indoor-outdoor exchange of bioaerosol particles, two direct Ultraviolet laser induced fluorescence instruments (UVLIF) were concomitantly deployed inside and outside of unoccupied home in summer, Cincinnati, OH. Three ventilation modes were studied: 1) windows closed, air conditioner off; 2) windows closed and air conditioner on (set at 70oF) and 3) windows opened and air conditioner off. As determined by CO2 decay, air exchange rates were 0.15, 0.24 and 1.03 for the above ventilation modes, respectively. As judged by UVLIF, of the fluorescent particles indoors, approximately 26% were bacteria, 38% were fungal spores, and 21% were pollens or their fragments. The respective values for outdoors were 31, 29, and 25%. The total concentrations of fluorescent bioaerosol particles indoors were 17,036, 16,725, 31,143 counts per m-3 for ventilation modes 1, 2 and 3, respectively. The corresponding outdoor values were 58,502, 51,372 and 40,050 counts per m-3. Average I/O ratios for total fluorescent particles were 0.64, 0.27 and 0.77 for ventilation modes 1, 2 and 3, respectively. Ventilation mode 2 had the lowest I/O ratios for all the bioaerosol types, except for bacteria. We hypothesize that larger I/O ratio for bacteria (0.69) in comparison to fungi (0.12) and pollen (0.08) during ventilation mode 2 can be attributed to particle size. Individual airborne bacteria cells are usually in the range between 0.5 to 1.5 µm in optical diameter, thus they remain in the air longer and are generally less efficiently filtered by the ventilation filter than their fungal and pollen counterparts. According to Spearman’s correlation analysis, the indoor total fluorescent particle concentration had a significant positive correlation with fungi (r = 0.94, P < 0.001). Meanwhile, the outdoor total particle concentration had a significant positive correlation with bacteria (r = 0.89, P = 0.02) and fungi (r = 0.83, P = 0.04). However, a negative correlation was found with pollen (r = -0.89, P = 0.02). In conclusion, this study emphasizes the need for more detailed research on I/O exchange mechanisms for various bioaerosol types.
This research study was supported by the National Institute for Occupational Safety and Health through the Targeted Research Training Program of the University of Cincinnati Education and Research Center Grant #T42OH008432.