Relationship between Indoor and Outdoor Fluorescent Biological Aerosol Particles

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1 M. A. Schnabel (ed.), Back to the Future: The Next 50 Years, (51 st International Conference of the Architectural Science Association (ANZAScA)), 2017, Architectural Science Association (ANZAScA), pp Relationship between Indoor and Outdoor Fluorescent Biological Aerosol Particles Jin Zhou 1, Ye Kang 2, and Dominique Hes 3 1, 3 University of Melbourne, Victoria, Australia {Jin.zhou, dhe}@unimelb.edu.au 2 Tongji University, Shanghai, P.R.China kangyecn@163.com Abstract: This study aims i) to characterize the ratios of bioaerosol levels in a meeting room to outdoor levels and ii) to investigate the impact of two factors, air conditioning and mechanical ventilation (ACMV) operation status and human occupancy, on time resolved relationship between indoor and outdoor bioaerosols. Using an ultraviolet light induced fluorescence (UV LIF) technique, we measured number concentrations of total aerosol particulate matter (tpm) and fluorescent biological aerosol particles (biopm) ( µm and µm diameter) in an office and outdoors, sampling with 1 min resolution. The air conditioning and mechanical ventilation (ACMV) system equipped with high grade filters was effective in controlling both tpm and biopm indoors. As expected, removal efficiencies were found to be size dependent. One human subject walking on the carpet was found to be a strong contributor to biopm, resulting in 2 3 times higher concentration than that outdoors. Compared to the times when the room is vacant, the biological proportion of total airborne particles increased by an order of magnitude during the light walking period. Consequently, indoor to outdoor ratios depend on the ACMV operating conditions and on human activities. This pilot study provides preliminary data concerning the biopm levels in an indoor environment equipped with an ACMV system. Ongoing investigations using this approach promise to improve our understanding of the processes that influence indoor bioaerosol levels and the effectiveness of control alternatives. Keywords: Bioaerosol; real time; indoor to outdoor ratio; human occupancy. 1. Introduction Bioaerosols are airborne particles that contain living organisms or were released from living organisms. They contain biologically active bacteria, spores, viruses, toxins, and other similar material. As summarized in a review work (Nazaroff, 2016), there are many reasons to be interested in indoor bioaerosols: (i) Humans spend most of their time indoors, and bioaerosols are abundant in the built environment, (ii) bioaerosols play important roles influencing public health, and (iii) the goal of improving bioaerosol management can influence building operation strategies. Quantification of bioaerosol

2 608 J. Zhou, Y. Kang and D. Hes concentrations and the influencing processes is valuable for multiple applications within the indoor environmental sciences. Several recent studies have employed DNA based approaches to examine airborne biological particles in a variety of indoor spaces (Hewitt et al., 2012; Hospodsky et al., 2015; Yamamoto et al., 2015). These studies have revealed that human occupancy and activities increase the abundance of bioaerosols and also leave human associated taxa in the built environment. However, this approach is not well suited for studying short term dynamic processes that might influence the concentrations and fates of bioaerosols indoors. Compared to DNA based method, new developments in ultraviolet light induced fluorescence (UV LIF) measurement technique provide the capability of real time detection of biological aerosol particles. This UV LIF technique provides opportunities in various applications, such as in laboratory studies (Healy et al., 2012; Toprak and Schnaiter, 2013) and in outdoor areas (Gabey et al., 2010; Huffman et al., 2010; Crawford et al., 2014). The studies that using UV LIF measurement to investigate bioaerosols in indoor environments are limited. Two examples, Bhangar et al. (2014) and Handorean et al. (2015) characterized fluorescent biological aerosol particle levels in a mechanical ventilated classroom and a hospital, respectively. Office is an environment where working adults spend most of their daytimes, yet its concentrations of biological aerosol particles are not well characterized. In addition, to date, there are no studies utilizing UV LIF to investigate the time resolved relationship between indoor and outdoor bioaerosols. Previous research (Toprak and Schnaiter, 2013; Healy et al., 2014; Hernandez et al., 2016) has demonstrated that airborne spores, bacteria, pollen, and their fragments are detected by the UV LIF technique. It is worthwhile to note that it possesses some inherent limitations. The fluorescent particle concentrations represent the lower limit estimate of the abundance of primary biological aerosol particles (Huffman et al., 2010; Pöhlker et al., 2012; 2013). The UV LIF technique may support discrimination between broad bioaerosol categories (spores, bacteria, pollen) (Healy et al., 2012; Hernandez et al., 2016); however, it cannot provide information at level of genus or specie as can DNA based analysis methods. The design of the present study was motivated by the context summarised above. Specifically, i) efforts on quantifying bioaerosol concentrations in built environment is warranted owning to the increased concern on indoor bioaerosol and its associated health impacts; ii) the new development of UV LIF technique offers the opportunity to capture the temporal pattern of bioaerosol dynamics; and iii) the factors influencing indoor bioaerosol concentrations are not well characterised. To contribute new knowledge and inform building operations, the specific aim of this investigation is i) to characterize the ratios of bioaerosol levels in a meeting room to outdoor levels and ii) to investigate the impact of two factors, air conditioning and mechanical ventilation (ACMV) operation status and human occupancy, on time resolved relationship between indoor and outdoor bioaerosols. The results of this work are of potential use to improve the prediction of bioaerosol concentrations in built environment. The work also contributes to a better understanding of the human activities and ACMV system as influential factors to indoor bioaerosols, which could improve the building design and operation. 2. Methods A meeting room with carpeted flooring and a central air conditioning and mechanical ventilation (ACMV) system in a university building in western Singapore was selected as the study site. The room volume was ~150 m 3 based on physical dimensions (length width height = 7.52 m 6.95 m 2.75 m). It shared ACMV ducts with nearby offices and labs. The ACMV system was a central forced air system with integration of outdoor air intake and indoor air recirculation. The ACMV system operated from 8:00 to

3 Relationship between Indoor and Outdoor Fluorescent Biological Aerosol Particles :00 every day. The room air exchange rate (AER) was 2.6±0.3 (mean ± sd) per hour when the mechanical ventilation system was on. The supply air to the room, which comprised about 90% recirculated air and 10% outdoor air (according to ACMV design), was filtered with MERV 13 filters that were replaced every 3 6 months. When the mechanical ventilation system was off, the infiltration and leakage caused the room AER to be 0.7±0.03 per hour. The AER was evaluated through sulphur hexafluoride (SF6) tracer decay tests. The mean value and standard deviation of AER was determined from analysing three SF6 decay tests (5 hours of data for each test when the ACMV system was on, 12 hours of data for each test when the ACMV system was off). Observational monitoring was conducted for 6 days (labelled D1 D6). The room was unoccupied during the monitoring period except 13:00 to 16:00 on D3 D6. One human subject performed light walking during the occupied period. The human subject was doing typical office work in another indoor space before the scripted experiment. Biotrak (Model 9510 BD; TSI, Inc.) was used to measure time resolved number concentrations of tpm and biopm in two particle size ranges ( µm and µm). The device was configured to sample air during 40 s out of every 1 min. The sampling flow rate was 28 L/min. We took measurements indoors and outdoors by using tubing and an auto switch device. The frequency of switching between indoor and outdoor samples was once per four minutes. The indoor sampling inlet (S1) was placed at the centre of the study room, at a height of 1.2 m. Outdoor air (S2) was sampled via an inlet protruding from a window to the outdoor corridor. Figure 1 illustrated the experimental design for the monitoring. The red arrows stand for the sampling point S1 and S2 through turbines. The black arrows illustrate the particle dynamics in indoor environment. They are i) particle gain due to air infiltration (Q L C O p), contribution from mechanical ventilation system [Q M (1 Ƞ M )] and emissions due to human activity (E); and ii) particle loss due to filter removal (Q R Ƞ R, Ƞ R = 0 in this work), deposition (, and air exfiltration Q L + Q M ) C]. The descriptions of abbreviations were noted in Figure 1. Figure 1: Schematic diagram for experimental design. The C and C O are indoor and outdoor particle concentrations, respectively. The Q stands for the air flow. Its subscripts L, M, and R correspond to infiltration, mechanical ventilation, and recirculation. The Ƞ M and Ƞ R are the particle removal rates of ventilation and recirculation filters, respectively. The p and are particle size dependent infiltration and deposition loss rates, respectively. The E is particle emission due to human activities. Calibration testing of aerosol losses in the tubing and auto switch device was conducted before the monitoring period. For this purpose, the sampling inlets were collocated for 5 hours in an outdoor

4 610 J. Zhou, Y. Kang and D. Hes environment at a height of 1.2 m. We added a third sampling inlet (S3), which didn t connect with any tubing or switch device. Sample S3 was designated as the reference case. The objective was to adjust data from S1 and S2 to match as closely as possible the response of the S3, so as to offset the aerosol losses during transport from the point of sampling and the point of measurement. Table 1 summarized the calibration factors specific to S1 and S2. 3. Results Table 1: Calibration factor (mean ± sd) for sampling point S1 (indoor) and S2 (outdoor). Particle size µm µm Particle type tpm biopm tpm biopm S1 0.95± ± ± ±0.12 S2 0.94± ± ± ±0.09 Figure 2 showed the time series plots of the tpm and biopm concentrations measured outdoors. Noting that the concentrations are plotted on different scale a larger scale (million particles per m 3 ) is applied to tpm compared to the scale (thousand particles per m 3 ) used for biopm we can observe high variation across monitoring days. The concentrations measured on D1 is about 2 the values recorded on D6. The significant variation is true for both tpm and biopm concentrations. Figure 2: Time series data for the number concentrations of total particles (tpm, top frames) and biological aerosol particles (biopm, bottom frames) in the diameter range µm measured outdoors on (a) day D1 and (b) day D2. The measurement date and sampling point were noted on the top left and top right of each frame, respectively. Figure 3 presented the time series concentrations measured in the selected office for total (top) and biological (bottom) aerosol particles. Similar to outdoor concentration plots, the scale for total aerosol

5 Relationship between Indoor and Outdoor Fluorescent Biological Aerosol Particles 611 particles is one magnitude larger than the scale used for bioaerosols. We can observe consistent pattern between tpm and biopm for both occupied and unoccupied period. The concentration reduction and peak can be associated with the operation of ACMV system and human activity, respectively. Figure 3: Time series data for the number concentrations of total particles (tpm, top frames) and biological aerosol particles (biopm, bottom frames) in the diameter range µm measured in (a) unoccupied office on D1 and (b) occupied office on D4. The measurement date and sampling point were noted on the top left and top right of each frame, respectively. 4. Discussion Comparing outdoor tpm with outdoor biopm in Figure 2, the concentration profile for biopm didn t always follow the broad trends of the tpm, implying that their sources were time dependent and the composition of tpm was changing at different times of the day. The biological proportion of total airborne particles (BPTP) of outdoor particles in the µm and µm diameter range were 0.14±0.12% (mean ± sd) and 0.82±0.68%, respectively, during the monitoring period. The ACMV system served as an important indoor/outdoor air exchange pathway. The ACMV system equipped with high grade filters effectively reduced the indoor aerosol concentrations. As shown in the concentrations plots for indoor environment (Figure 3), the concentrations for both tpm and biopm dropped significantly as soon as the ACMV system was turned on at 8:00, indicating the effectiveness of this removal mechanism. The presence of a human occupant is an important factor for both indoor tpm and biopm. Figure 3(b) shows a significantly higher indoor concentration occurring at 13:00 16:00 on D4, which coincides with a designated light walking period. The probable causes of the observed peaks are resuspension of tpm and biopm from the carpet and shedding from the clothing, hair or skin of the occupant. The indoor/outdoor (I/O) ratios for biopm (2.1 for µm particles, 3.3 for µm particles) were significantly higher than the values for tpm (0.10 for µm particles, 0.33 for µm particles) (Table 2), which

6 612 J. Zhou, Y. Kang and D. Hes indicates that walking on the carpet makes a stronger contribution to biopm than to tpm. The timeaveraged BPTP indoors was 1.9% and 5.6% for the particles in the size range µm and µm, respectively, higher than the BPTP estimated for unoccupied periods by one order of magnitude. This result further substantiates the important role of human activities contributing to bioaerosols indoors. Table 2 and Table 3 summarized the results for µm and µm particles, respectively. Overall, across the six monitoring days, the time averaged outdoor concentration of total airborne particles in the µm (and µm) diameter range was 4000k/m3 (150k/m 3 ); the value for biological aerosol particles was 3.2k/m 3 (1.1k/m 3 ). The indoor concentrations were less than a quarter of the outdoor concentrations when the room was vacant. During occupied times, the average indooroutdoor (I/O) ratios for biopm were higher than the value for tpm by a factor of 20 for µm particles and by a factor of 10 for µm particles. These higher ratios indicate that the particles resuspended from carpet and/or shed from occupants were strong determinants of indoor biopm levels. Table 2: Time averaged particle number concentrations (PNC) of total airborne particles (tpm, 1000 particles per m3), biological aerosol particles (biopm, particles per m3), and indoor to outdoor concentration ratios (I/O) in the diameter range µm. Condition ACMV off, unoccupied ACMV on, unoccupied ACMV on, occupied tpm biopm tpm biopm tpm biopm Indoor PNC I/O t(h) Outdoor PNC t(h) Table 3: Time averaged particle number concentrations (PNC) of total airborne particles (tpm, 1000 particles per m3), biological aerosol particles (biopm, particles per m3), and indoor to outdoor concentration ratios (I/O) in the diameter range µm. Condition ACMV off, unoccupied ACMV on, unoccupied ACMV on, occupied tpm biopm tpm biopm tpm biopm Indoor PNC I/O t(h) Outdoor PNC t(h) Conclusions The real time tpm and biopm monitoring instrument is a useful tool, with the potential to provide important insights linking indoor environments with building operation. The number concentrations of

7 Relationship between Indoor and Outdoor Fluorescent Biological Aerosol Particles 613 tpm and biopm of the particles in size range µm and µm in an unoccupied meeting room was lower than the outdoor level by one to two orders of magnitude. It is also worth noted that the I/O ratios in the unoccupied room reduced significantly when ACMV system was operating. The reduction can be attributable to particle removal effect provided by high grade filters and reduced outdoor particle penetration due to pressurization of indoor environment. Activity of human occupants was an important source for tpm and biopm. Light walking resulted in a 2 3 times higher indoor biopm concentration than that outdoors. Data indicate that the biological proportion of total airborne particles was one order ofmagnitude higher during light walking, compared to times when the room was vacant. Further investigations with real time UV LIF instruments have the potential to inform deeper understanding of indoor bioaerosol dynamics. The experimental procedure undertaken here could fruitfully be applied to explore additional aspects of indoor bioaerosol dynamics: i) other factors that are expected to influence indoor concentrations (e.g. air exchange rate, human activity intensity, etc.) and ii) the efficiency of control strategies (e.g. building air filters, air purifier, etc.). Given the limitation of the UV LIF technique specified in introduction, it is also valuable to explore the collaborative work with DNA based methods. Coupling two measurement approach can usefully evaluate to what extent and what type the UV LIF technique captures the biological components in the air of built environments. Acknowledgements This work was funded by Thrive Research Hub, the Faculty of Architecture, Building and Planning, The University of Melbourne. The research data were provided by the Berkeley Education Alliance for Research in Singapore (BEARS) for the Singapore Berkeley Building Efficiency and Sustainability in the Tropics (SinBerBEST) Program. References Bhangar, S., Huffman, J. A. and Nazaroff, W. W. (2014) Size resolved fluorescent biological aerosol particle concentrations and occupant emissions in a university classroom, Indoor Air, 24(6), Crawford, I., Robinson, N. H., Flynn, M. J., Foot, V. E., Gallagher, M. W., Huffman, J. A., Stanley, W. R. and Kaye, P. H. (2014) Characterisation of bioaerosol emissions from a Colorado pine forest: Results from the beachon rombas experiment, Atmospheric Chemistry and Physics, 14(16), Gabey, A. M., Gallagher, M. W., Whitehead, J., Dorsey, J. R., Kaye, P. H. and Stanley, W. R. (2010) Measurements and comparison of primary biological aerosol above and below a tropical forest canopy using a dual channel fluorescence spectrometer, Atmospheric Chemistry and Physics, 10(10), Handorean, A., Robertson, C. E., Harris, J. K., Frank, D., Hull, N., Kotter, C., Stevens, M. J., Baumgardner, D., Pace, N. R. and Hernandez, M. (2015) Microbial aerosol liberation from soiled textiles isolated during routine residuals handling in a modern health care setting, Microbiome, 3, 72. Healy, D. A., Huffman, J. A., O'Connor, D. J., Pöhlker, C., Pöschl, U. and Sodeau, J. R. (2014) Ambient measurements of biological aerosol particles near Killarney, Ireland: A comparison between real time fluorescence and microscopy techniques, Atmospheric Chemistry and Physics, 14(15), Healy, D. A., O'Connor, D. J., Burke, A. M. and Sodeau, J. R. (2012) A laboratory assessment of the Waveband Integrated Bioaerosol Sensor (WIBS 4) using individual samples of pollen and fungal spore material, Atmospheric Environment, 60, Hernandez, M., Perring, A. E., McCabe, K., Kok, G., Granger, G. and Baumgardner, D. (2016) Chamber catalogues of optical and fluorescent signatures distinguish bioaerosol classes, Atmospheric Measurement Techniques, 9(7),

8 614 J. Zhou, Y. Kang and D. Hes Hewitt, K. M., Gerba, C. P., Maxwell, S. L. and Kelley, S. T. (2012) Office space bacterial abundance and diversity in three metropolitan areas, PLoS ONE, 7(5). Hospodsky, D., Yamamoto, N., Nazaroff, W. W., Miller, D., Gorthala, S. and Peccia, J. (2015) Characterizing airborne fungal and bacterial concentrations and emission rates in six occupied children's classrooms, Indoor Air, 25(6), Huffman, J. A., Treutlein, B. and Pöschl, U. (2010) Fluorescent biological aerosol particle concentrations and size distributions measured with an Ultraviolet Aerodynamic Particle Sizer (UV APS) in Central Europe, Atmospheric Chemistry and Physics, 10(7), Nazaroff, W. W. (2016) Indoor bioaerosol dynamics, Indoor Air, 26(1), Pöhlker, C., Huffman, J. A. and Pöschl, U. (2012) Autofluorescence of atmospheric bioaerosols Fluorescent biomolecules and potential interferences, Atmospheric Measurement Techniques, 5(1), Pöhlker, C., Huffman, J. A. and Pöschl, U. (2013) Autofluorescence of atmospheric bioaerosols: Spectral fingerprints and taxonomic trends of pollen, Atmospheric Measurement Techniques, 6(12), Toprak, E. and Schnaiter, M. (2013) Fluorescent biological aerosol particles measured with the Waveband Integrated Bioaerosol Sensor WIBS 4: Laboratory tests combined with a one year field study, Atmospheric Chemistry and Physics, 13(1), Yamamoto, N., Hospodsky, D., Dannemiller, K. C., Nazaroff, W. W. and Peccia, J. (2015) Indoor emissions as a primary source of airborne allergenic fungal particles in classrooms, Environmental Science and Technology, 49(8),