1
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Liu Z, Li H, Chu J, Huang Z, Xiao X, Wang Y, He J. The impact of high background particle concentration on the spatiotemporal distribution of Serratia marcescens bioaerosol. JOURNAL OF HAZARDOUS MATERIALS 2023; 458:131863. [PMID: 37354722 DOI: 10.1016/j.jhazmat.2023.131863] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2023] [Revised: 06/07/2023] [Accepted: 06/13/2023] [Indexed: 06/26/2023]
Abstract
Airborne transmission is a well-established mode of dissemination for infectious diseases, particularly in closed environments. However, previous research has often overlooked the potential impact of background particle concentration on bioaerosol characteristics. We compared the spatial and temporal distributions of bioaerosols under two levels of background particle concentration: heavily polluted (150-250 μg/m3) and excellent (0-35 μg/m3) in a typical ward. Serratia marcescens bioaerosol was adopted as a bioaerosol tracer, and the bioaerosol concentrations were quantified using six-stage Andersen cascade impactors. The results showed a significant reduction (over at least 62.9%) in bioaerosol concentration under heavily polluted levels compared to excellent levels at all sampling points. The temporal analysis also revealed that the decay rate of bioaerosols was higher (at least 0.654 min-1) under heavily polluted levels compared to excellent levels. These findings suggest that background particles can facilitate bioaerosol removal, contradicting the assumption made in previous research that background particle has no effect on bioaerosol characteristics. Furthermore, we observed differences in the size distribution of bioaerosols between the two levels of background particle concentration. The average bioaerosols size under heavily polluted levels was found to be higher than that under excellent levels, and the average particle size under heavily polluted levels gradually increased with time. In conclusion, these results highlight the importance of considering background particle concentration in future research on bioaerosol characteristics.
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Affiliation(s)
- Zhijian Liu
- School of Energy and Power Engineering, North China Electric Power University, Baoding 071003, China
| | - Haochuan Li
- School of Energy and Power Engineering, North China Electric Power University, Baoding 071003, China
| | - Jiaqi Chu
- School of Energy and Power Engineering, North China Electric Power University, Baoding 071003, China
| | - Zhenzhe Huang
- School of Energy and Power Engineering, North China Electric Power University, Baoding 071003, China
| | - Xia Xiao
- School of Energy and Power Engineering, North China Electric Power University, Baoding 071003, China
| | - Yongxin Wang
- School of Energy and Power Engineering, North China Electric Power University, Baoding 071003, China
| | - Junzhou He
- School of Energy and Power Engineering, North China Electric Power University, Baoding 071003, China.
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2
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Moravek A, VandenBoer TC, Finewax Z, Pagonis D, Nault BA, Brown WL, Day DA, Handschy AV, Stark H, Ziemann P, Jimenez JL, de Gouw JA, Young CJ. Reactive Chlorine Emissions from Cleaning and Reactive Nitrogen Chemistry in an Indoor Athletic Facility. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:15408-15416. [PMID: 36326040 DOI: 10.1021/acs.est.2c04622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Indoor gas-phase radical sources are poorly understood but expected to be much different from outdoors. Several potential radical sources were measured in a windowless, light-emitting diode (LED)-lit room in a college athletic facility over a 2 week period. Alternating measurements between the room air and the supply air of the heating, ventilation, and air-conditioning system allowed an assessment of sources. Use of a chlorine-based cleaner was a source of several photolabile reactive chlorine compounds, including ClNO2 and Cl2. During cleaning events, photolysis rates for these two compounds were up to 0.0023 pptv min-1, acting as a source of chlorine atoms even in this low-light indoor environment. Unrelated to cleaning events, elevated ClNO2 was often observed during daytime and lost to ventilation. The nitrate radical (NO3), which is rapidly photolyzed outdoors during daytime, may persist in low-light indoor environments. With negligible photolysis, loss rates of NO3 indoors were dominated by bimolecular reactions. At times with high NO2 and O3 ventilated from outdoors, N2O5 was observed. Elevated ClNO2 measured concurrently suggests the formation through heterogeneous reactions, acting as an additional source of reactive chlorine within the athletic facility and outdoors.
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Affiliation(s)
- Alexander Moravek
- Department of Chemistry, York University, Toronto, OntarioM3J 1P3, Canada
| | | | - Zachary Finewax
- Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado80309, United States
- Department of Chemistry, University of Colorado, Boulder, Colorado80309, United States
| | - Demetrios Pagonis
- Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado80309, United States
- Department of Chemistry, University of Colorado, Boulder, Colorado80309, United States
| | - Benjamin A Nault
- Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado80309, United States
- Department of Chemistry, University of Colorado, Boulder, Colorado80309, United States
| | - Wyatt L Brown
- Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado80309, United States
- Department of Chemistry, University of Colorado, Boulder, Colorado80309, United States
| | - Douglas A Day
- Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado80309, United States
- Department of Chemistry, University of Colorado, Boulder, Colorado80309, United States
| | - Anne V Handschy
- Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado80309, United States
- Department of Chemistry, University of Colorado, Boulder, Colorado80309, United States
| | - Harald Stark
- Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado80309, United States
- Aerodyne Research, Inc., Billerica, Massachusetts01821, United States
| | - Paul Ziemann
- Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado80309, United States
- Department of Chemistry, University of Colorado, Boulder, Colorado80309, United States
| | - Jose L Jimenez
- Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado80309, United States
- Department of Chemistry, University of Colorado, Boulder, Colorado80309, United States
| | - Joost A de Gouw
- Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado80309, United States
- Department of Chemistry, University of Colorado, Boulder, Colorado80309, United States
| | - Cora J Young
- Department of Chemistry, York University, Toronto, OntarioM3J 1P3, Canada
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3
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Aydin M, Evrendilek F, Aydin IE, Savas SA, Evrendilek DE. Transport dynamics of SARS-CoV-2 under outdoor conditions. AIR QUALITY, ATMOSPHERE & HEALTH 2022; 15:893-899. [PMID: 35401876 PMCID: PMC8976539 DOI: 10.1007/s11869-022-01196-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/01/2022] [Accepted: 03/28/2022] [Indexed: 11/30/2022]
Affiliation(s)
- Mehmet Aydin
- Department of Soil Science (Soil Physics), Mustafa Kemal University, Hatay, Turkey
| | - Fatih Evrendilek
- Department of Environmental Engineering, Bolu Abant Izzet Baysal University, Bolu, Turkey
| | - Ismail Erkan Aydin
- Department of Emergency Medicine, Faculty of Medicine, Alanya Alaaddin Keykubat University, Alanya/Antalya, Turkey
| | - Seckin Aydin Savas
- Department of Plastic and Reconstructive Surgery, Faculty of Medicine, Alanya Alaaddin Keykubat University, Alanya/Antalya, Turkey
| | - Deniz Eren Evrendilek
- Department of Computing Science, Simon Fraser University, Burnaby, BC V5A 1S6 Canada
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4
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Kong M, Li L, Eilts SM, Li L, Hogan CJ, Pope ZC. Localized and Whole-Room Effects of Portable Air Filtration Units on Aerosol Particle Deposition and Concentration in a Classroom Environment. ACS ES&T ENGINEERING 2022; 2:653-669. [PMID: 37552723 PMCID: PMC8864773 DOI: 10.1021/acsestengg.1c00321] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Revised: 01/05/2022] [Accepted: 01/06/2022] [Indexed: 05/14/2023]
Abstract
In indoor environments with limited ventilation, recirculating portable air filtration (PAF) units may reduce COVID-19 infection risk via not only the direct aerosol route (i.e., inhalation) but also via an indirect aerosol route (i.e., contact with the surface where aerosol particles deposited). We systematically investigated the impact of PAF units in a mock classroom, as a supplement to background ventilation, on localized and whole-room surface deposition and particle concentration. Fluorescently tagged particles with a volumetric mean diameter near 2 μm were continuously introduced into the classroom environment via a breathing simulator with a prescribed inhalation-exhalation waveform. Deposition velocities were inferred on >50 horizontal and vertical surfaces throughout the classroom, while aerosol concentrations were spatially monitored via optical particle spectrometry. Results revealed a particle decay rate consistent with expectations based upon the reported clean air delivery rates of the PAF units. Additionally, the PAF units reduced peak concentrations by a factor of around 2.5 compared to the highest concentrations observed and led to a statistically significant reduction in deposition velocities for horizontal surfaces >2.5 m from the aerosol source. Our results not only confirm that PAF units can reduce particle concentrations but also demonstrate that they may lead to reduced particle deposition throughout an indoor environment when properly positioned with respect to the location of the particle source(s) within the room (e.g., where the largest group of students sit) and the predominant air distribution profile of the room.
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Affiliation(s)
- Meng Kong
- Well Living Lab, Rochester,
Minnesota 55902, United States
| | - Linhao Li
- Well Living Lab, Rochester,
Minnesota 55902, United States
| | - Stephanie M. Eilts
- Department of Mechanical Engineering,
University of Minnesota, Minneapolis, Minnesota 55455,
United States
| | - Li Li
- Department of Mechanical Engineering,
University of Minnesota, Minneapolis, Minnesota 55455,
United States
| | - Christopher J. Hogan
- Department of Mechanical Engineering,
University of Minnesota, Minneapolis, Minnesota 55455,
United States
| | - Zachary C. Pope
- Well Living Lab, Rochester,
Minnesota 55902, United States
- Mayo Clinic, Department of Physiology and
Biomedical Engineering, Rochester, Minnesota 55905, United
States
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5
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Peng Z, Rojas ALP, Kropff E, Bahnfleth W, Buonanno G, Dancer SJ, Kurnitski J, Li Y, Loomans MGLC, Marr LC, Morawska L, Nazaroff W, Noakes C, Querol X, Sekhar C, Tellier R, Greenhalgh T, Bourouiba L, Boerstra A, Tang JW, Miller SL, Jimenez JL. Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:1125-1137. [PMID: 34985868 DOI: 10.1021/acs.est.1c06531] [Citation(s) in RCA: 60] [Impact Index Per Article: 30.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Some infectious diseases, including COVID-19, can undergo airborne transmission. This may happen at close proximity, but as time indoors increases, infections can occur in shared room air despite distancing. We propose two indicators of infection risk for this situation, that is, relative risk parameter (Hr) and risk parameter (H). They combine the key factors that control airborne disease transmission indoors: virus-containing aerosol generation rate, breathing flow rate, masking and its quality, ventilation and aerosol-removal rates, number of occupants, and duration of exposure. COVID-19 outbreaks show a clear trend that is consistent with airborne infection and enable recommendations to minimize transmission risk. Transmission in typical prepandemic indoor spaces is highly sensitive to mitigation efforts. Previous outbreaks of measles, influenza, and tuberculosis were also assessed. Measles outbreaks occur at much lower risk parameter values than COVID-19, while tuberculosis outbreaks are observed at higher risk parameter values. Because both diseases are accepted as airborne, the fact that COVID-19 is less contagious than measles does not rule out airborne transmission. It is important that future outbreak reports include information on masking, ventilation and aerosol-removal rates, number of occupants, and duration of exposure, to investigate airborne transmission.
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Affiliation(s)
- Z Peng
- Dept. of Chemistry and CIRES, University of Colorado, Boulder, Colorado 80309, United States
| | - A L Pineda Rojas
- CIMA, UMI-IFAECI/CNRS, FCEyN, Universidad de Buenos Aires─UBA/CONICET, Buenos Aires C1428EGA, Argentina
| | - E Kropff
- Leloir Institute─IIBBA/CONICET, CBA, Buenos Aires C1405BWE, Argentina
| | - W Bahnfleth
- Dept. of Architectural Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - G Buonanno
- Dept. of Civil and Mechanical Engineering, University of Cassino and Southern Lazio, Cassino 03043, Italy
| | - S J Dancer
- Dept. of Microbiology, NHS Lanarkshire, Glasgow, Scotland G75 8RG, U.K
- School of Applied Sciences, Edinburgh Napier University, Edinburgh, Scotland EH11 4BN, U.K
| | - J Kurnitski
- REHVA Technology and Research Committee, Tallinn University of Technology, Tallinn 19086, Estonia
| | - Y Li
- Dept. of Mechanical Engineering, The University of Hong Kong, Hong Kong 999077, China
| | - M G L C Loomans
- Dept. of the Built Environment, Eindhoven University of Technology, Eindhoven 5612 AZ, The Netherlands
| | - L C Marr
- Dept. of Civil and Environmental Engineering, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - L Morawska
- International Laboratory for Air Quality and Health, Queensland University of Technology, Brisbane, Queensland 4001, Australia
| | - W Nazaroff
- Dept. of Civil and Environmental Engineering, University of California, Berkeley, California 94720, United States
| | - C Noakes
- School of Civil Engineering, University of Leeds, Leeds LS2 9JT, U.K
| | - X Querol
- Institute of Environmental Assessment and Water Research, IDAEA, Spanish Research Council, CSIC, Barcelona 08034, Spain
| | - C Sekhar
- Dept. of the Built Environment, National University of Singapore , 117566 Singapore
| | - R Tellier
- Dept. of Medicine, McGill University and McGill University Health Centre, Montreal, Québec H4A 3J1, Canada
| | - T Greenhalgh
- Nuffield Dept. of Primary Care Health Sciences, University of Oxford, Oxford OX2 6GG, U.K
| | - L Bourouiba
- The Fluid Dynamics of Disease Transmission Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - A Boerstra
- REHVA (Federation of European Heating, Ventilation and Air Conditioning Associations), BBA Binnenmilieu, The Hague 2501 CJ, The Netherlands
| | - J W Tang
- Dept. of Respiratory Sciences, University of Leicester, Leicester LE1 7RH, U.K
| | - S L Miller
- Dept. of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309, United States
| | - J L Jimenez
- Dept. of Chemistry and CIRES, University of Colorado, Boulder, Colorado 80309, United States
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6
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Peng Z, Rojas ALP, Kropff E, Bahnfleth W, Buonanno G, Dancer SJ, Kurnitski J, Li Y, Loomans MGLC, Marr LC, Morawska L, Nazaroff W, Noakes C, Querol X, Sekhar C, Tellier R, Greenhalgh T, Bourouiba L, Boerstra A, Tang JW, Miller SL, Jimenez JL. Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022. [PMID: 34985868 DOI: 10.1101/2021.04.21.21255898] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Some infectious diseases, including COVID-19, can undergo airborne transmission. This may happen at close proximity, but as time indoors increases, infections can occur in shared room air despite distancing. We propose two indicators of infection risk for this situation, that is, relative risk parameter (Hr) and risk parameter (H). They combine the key factors that control airborne disease transmission indoors: virus-containing aerosol generation rate, breathing flow rate, masking and its quality, ventilation and aerosol-removal rates, number of occupants, and duration of exposure. COVID-19 outbreaks show a clear trend that is consistent with airborne infection and enable recommendations to minimize transmission risk. Transmission in typical prepandemic indoor spaces is highly sensitive to mitigation efforts. Previous outbreaks of measles, influenza, and tuberculosis were also assessed. Measles outbreaks occur at much lower risk parameter values than COVID-19, while tuberculosis outbreaks are observed at higher risk parameter values. Because both diseases are accepted as airborne, the fact that COVID-19 is less contagious than measles does not rule out airborne transmission. It is important that future outbreak reports include information on masking, ventilation and aerosol-removal rates, number of occupants, and duration of exposure, to investigate airborne transmission.
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Affiliation(s)
- Z Peng
- Dept. of Chemistry and CIRES, University of Colorado, Boulder, Colorado 80309, United States
| | - A L Pineda Rojas
- CIMA, UMI-IFAECI/CNRS, FCEyN, Universidad de Buenos Aires─UBA/CONICET, Buenos Aires C1428EGA, Argentina
| | - E Kropff
- Leloir Institute─IIBBA/CONICET, CBA, Buenos Aires C1405BWE, Argentina
| | - W Bahnfleth
- Dept. of Architectural Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - G Buonanno
- Dept. of Civil and Mechanical Engineering, University of Cassino and Southern Lazio, Cassino 03043, Italy
| | - S J Dancer
- Dept. of Microbiology, NHS Lanarkshire, Glasgow, Scotland G75 8RG, U.K
- School of Applied Sciences, Edinburgh Napier University, Edinburgh, Scotland EH11 4BN, U.K
| | - J Kurnitski
- REHVA Technology and Research Committee, Tallinn University of Technology, Tallinn 19086, Estonia
| | - Y Li
- Dept. of Mechanical Engineering, The University of Hong Kong, Hong Kong 999077, China
| | - M G L C Loomans
- Dept. of the Built Environment, Eindhoven University of Technology, Eindhoven 5612 AZ, The Netherlands
| | - L C Marr
- Dept. of Civil and Environmental Engineering, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - L Morawska
- International Laboratory for Air Quality and Health, Queensland University of Technology, Brisbane, Queensland 4001, Australia
| | - W Nazaroff
- Dept. of Civil and Environmental Engineering, University of California, Berkeley, California 94720, United States
| | - C Noakes
- School of Civil Engineering, University of Leeds, Leeds LS2 9JT, U.K
| | - X Querol
- Institute of Environmental Assessment and Water Research, IDAEA, Spanish Research Council, CSIC, Barcelona 08034, Spain
| | - C Sekhar
- Dept. of the Built Environment, National University of Singapore , 117566 Singapore
| | - R Tellier
- Dept. of Medicine, McGill University and McGill University Health Centre, Montreal, Québec H4A 3J1, Canada
| | - T Greenhalgh
- Nuffield Dept. of Primary Care Health Sciences, University of Oxford, Oxford OX2 6GG, U.K
| | - L Bourouiba
- The Fluid Dynamics of Disease Transmission Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - A Boerstra
- REHVA (Federation of European Heating, Ventilation and Air Conditioning Associations), BBA Binnenmilieu, The Hague 2501 CJ, The Netherlands
| | - J W Tang
- Dept. of Respiratory Sciences, University of Leicester, Leicester LE1 7RH, U.K
| | - S L Miller
- Dept. of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309, United States
| | - J L Jimenez
- Dept. of Chemistry and CIRES, University of Colorado, Boulder, Colorado 80309, United States
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7
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Vlachokostas A, Burns CA, Salsbury TI, Daniel RC, James DP, Flaherty JE, Wang N, Underhill RM, Kulkarni G, Pease LF. Experimental evaluation of respiratory droplet spread to rooms connected by a central ventilation system. INDOOR AIR 2022; 32:e12940. [PMID: 35048430 DOI: 10.1111/ina.12940] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 09/20/2021] [Accepted: 09/24/2021] [Indexed: 06/14/2023]
Abstract
This article presents results from an experimental study to ascertain the transmissibility of the SARS-CoV-2 virus between rooms in a building that are connected by a central ventilation system. Respiratory droplet surrogates made of mucus and virus mimics were released in one room in a test building, and measurements of concentration levels were made in other rooms connected via the ventilation system. The paper presents experimental results for different ventilation system configurations, including ventilation rate, filtration level (up to MERV-13), and fractional outdoor air intake. The most important finding is that respiratory droplets can and do transit through central ventilation systems, suggesting a mechanism for viral transmission (and COVID-19 specifically) within the built environment in reasonable agreement with well-mixed models. We also find the deposition of small droplets (0.5-4 μm) on room walls to be negligibly small.
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Affiliation(s)
- Alex Vlachokostas
- Pacific Northwest National Laboratory (PNNL), Richland, Washington, USA
| | - Carolyn A Burns
- Pacific Northwest National Laboratory (PNNL), Richland, Washington, USA
| | | | - Richard C Daniel
- Pacific Northwest National Laboratory (PNNL), Richland, Washington, USA
| | - Daniel P James
- Pacific Northwest National Laboratory (PNNL), Richland, Washington, USA
| | - Julia E Flaherty
- Pacific Northwest National Laboratory (PNNL), Richland, Washington, USA
| | - Na Wang
- Pacific Northwest National Laboratory (PNNL), Richland, Washington, USA
| | | | - Gourihar Kulkarni
- Pacific Northwest National Laboratory (PNNL), Richland, Washington, USA
| | - Leonard F Pease
- Pacific Northwest National Laboratory (PNNL), Richland, Washington, USA
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8
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Nazaroff WW. Indoor aerosol science aspects of SARS-CoV-2 transmission. INDOOR AIR 2022; 32:e12970. [PMID: 34873752 DOI: 10.1111/ina.12970] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Revised: 11/17/2021] [Accepted: 11/26/2021] [Indexed: 05/04/2023]
Abstract
Knowledge about person-to-person transmission of SARS-CoV-2 is reviewed, emphasizing three components: emission of virus-containing particles and drops from infectious persons; transport and fate of such emissions indoors; and inhalation of viral particles by susceptible persons. Emissions are usefully clustered into three groups: small particles (diameter 0.1-5 µm), large particles (5-100 µm), and ballistic drops (>100 µm). Speaking generates particles and drops across the size spectrum. Small particles are removed from indoor air at room scale by ventilation, filtration, and deposition; large particles mainly deposit onto indoor surfaces. Proximate exposure enhancements are associated with large particles with contributions from ballistic drops. Masking and social distancing are effective in mitigating transmission from proximate exposures. At room scale, masking, ventilation, and filtration can contribute to limit exposures. Important information gaps prevent a quantitative reconciliation of the high overall global spread of COVID-19 with known transmission pathways. Available information supports several findings with moderate-to-high confidence: transmission occurs predominantly indoors; inhalation of airborne particles (up to 50 µm in diameter) contributes substantially to viral spread; transmission occurs in near proximity and at room scale; speaking is a major source of airborne SARS-CoV-2 virus; and emissions can occur without strong illness symptoms.
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Affiliation(s)
- William W Nazaroff
- Department of Civil and Environmental Engineering, University of California, Berkeley, California, USA
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9
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Bueno de Mesquita PJ, Delp WW, Chan WR, Bahnfleth WP, Singer BC. Control of airborne infectious disease in buildings: Evidence and research priorities. INDOOR AIR 2022; 32:e12965. [PMID: 34816493 DOI: 10.1111/ina.12965] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Revised: 10/07/2021] [Accepted: 11/11/2021] [Indexed: 06/13/2023]
Abstract
The evolution of SARS-CoV-2 virus has resulted in variants likely to be more readily transmitted through respiratory aerosols, underscoring the increased potential for indoor environmental controls to mitigate risk. Use of tight-fitting face masks to trap infectious aerosol in exhaled breath and reduce inhalation exposure to contaminated air is of critical importance for disease control. Administrative controls including the regulation of occupancy and interpersonal spacing are also important, while presenting social and economic challenges. Indoor engineering controls including ventilation, exhaust, air flow control, filtration, and disinfection by germicidal ultraviolet irradiation can reduce reliance on stringent occupancy restrictions. However, the effects of controls-individually and in combination-on reducing infectious aerosol transfer indoors remain to be clearly characterized to the extent needed to support widespread implementation by building operators. We review aerobiologic and epidemiologic evidence of indoor environmental controls against transmission and present a quantitative aerosol transfer scenario illustrating relative differences in exposure at close-interactive, room, and building scales. We identify an overarching need for investment to implement building controls and evaluate their effectiveness on infection in well-characterized and real-world settings, supported by specific, methodological advances. Improved understanding of engineering control effectiveness guides implementation at scale while considering occupant comfort, operational challenges, and energy costs.
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Affiliation(s)
| | - William W Delp
- Indoor Environment Group, Lawrence Berkeley National Laboratory, Berkeley, California, USA
| | - Wanyu R Chan
- Indoor Environment Group, Lawrence Berkeley National Laboratory, Berkeley, California, USA
| | - William P Bahnfleth
- Department of Architectural Engineering, Pennsylvania State University, State College, Pennsylvania, USA
| | - Brett C Singer
- Indoor Environment Group, Lawrence Berkeley National Laboratory, Berkeley, California, USA
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10
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Wagner J, Sparks TL, Miller S, Chen W, Macher JM, Waldman JM. Modeling the impacts of physical distancing and other exposure determinants on aerosol transmission. JOURNAL OF OCCUPATIONAL AND ENVIRONMENTAL HYGIENE 2021; 18:495-509. [PMID: 34515602 DOI: 10.1080/15459624.2021.1963445] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Minimization of airborne virus transmission has become increasingly important due to pandemic and endemic infectious respiratory diseases. Physical distancing is a frequently advocated control measure, but the proximity-based transmission it is intended to control is challenging to incorporate into generalized, ventilation-based models. We utilize a size-dependent aerosol release model with turbulent dispersion to assess the impact of direct, near-field transport in conjunction with changes in ventilation, exposure duration, exhalation/inhalation rates, and masks. We demonstrate this model on indoor and outdoor scenarios to estimate the relative impacts on infection risk. The model can be expressed as a product of six multiplicative factors that may be used to identify opportunities for risk reduction. The additive nature of the short-range (proximity) and long-range (background) transmission components of the aerosol transport factor implies that they must be minimized simultaneously. Indoor simulations showed that close physical distances attenuated the impact of most other risk reduction factors. Increasing ventilation resulted in a 17-fold risk decrease at further physical distances but only a 6-fold decrease at shorter distances. Distance, emission rate, and duration also had large impacts on risk (11-65-fold), while air direction and inhalation rate had lower risk impacts (3-4-fold range). Surgical mask and respirator models predicted higher maximum risk impacts (33- and 280-fold, respectively) than cloth masks (4-fold). Most simulations showed decreasing risk at distances > 1-2 m (3-6 ft). The risk benefit of maintaining 2-m distance vs. 1 m depended substantially on the environmental turbulence and ventilation rate. Outdoors, long-range transmission was negligible and short-range transmission was the primary determinant of risk. Temporary passing events increased risk by up to 50 times at very slow walking speeds and close passing distances, but the relative risks outdoors were still much lower than indoors. The current model assumes turbulent dispersion typical of a given room size and ventilation rate. However, calm environments or confined airflows may increase transmission risks beyond levels predicted with this turbulent model.
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Affiliation(s)
- Jeff Wagner
- Environmental Health Laboratory, California Dept. of Public Health, Richmond, California
| | - Tamara L Sparks
- Environmental Health Laboratory, California Dept. of Public Health, Richmond, California
| | - Shelly Miller
- Department of Mechanical Engineering, University of Colorado, Boulder, Colorado
| | - Wenhao Chen
- Environmental Health Laboratory, California Dept. of Public Health, Richmond, California
| | - Janet M Macher
- Environmental Health Laboratory, California Dept. of Public Health, Richmond, California
| | - Jed M Waldman
- Environmental Health Laboratory, California Dept. of Public Health, Richmond, California
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11
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Ooi CC, Suwardi A, Ou Yang ZL, Xu G, Tan CKI, Daniel D, Li H, Ge Z, Leong FY, Marimuthu K, Ng OT, Lim SB, Lim P, Mak WS, Cheong WCD, Loh XJ, Kang CW, Lim KH. Risk assessment of airborne COVID-19 exposure in social settings. PHYSICS OF FLUIDS (WOODBURY, N.Y. : 1994) 2021; 33:087118. [PMID: 34552314 PMCID: PMC8450907 DOI: 10.1063/5.0055547] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Accepted: 08/09/2021] [Indexed: 05/04/2023]
Abstract
The COVID-19 pandemic has led to many countries oscillating between various states of lock-down as they seek to balance keeping the economy and essential services running and minimizing the risk of further transmission. Decisions are made about which activities to keep open across a range of social settings and venues guided only by ad hoc heuristics regarding social distancing and personal hygiene. Hence, we propose the dual use of computational fluid dynamic simulations and surrogate aerosol measurements for location-specific assessment of risk of infection across different real-world settings. We propose a 3-tiered risk assessment scheme to facilitate classification of scenarios into risk levels based on simulations and experiments. Threshold values of <54 and >840 viral copies and <5% and >40% of original aerosol concentration are chosen to stratify low, medium, and high risk. This can help prioritize allowable activities and guide implementation of phased lockdowns or re-opening. Using a public bus in Singapore as a case study, we evaluate the relative risk of infection across scenarios such as different activities and passenger positions and demonstrate the effectiveness of our risk assessment methodology as a simple and easily interpretable framework. For example, this study revealed that the bus's air-conditioning greatly influences dispersion and increases the risk of certain seats and that talking can result in similar relative risk to coughing for passengers around an infected person. Both numerical and experimental approaches show similar relative risk levels with a Spearman's correlation coefficient of 0.74 despite differing observables, demonstrating applicability of this risk assessment methodology to other scenarios.
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Affiliation(s)
- Chin Chun Ooi
- Institute of High Performance Computing, Agency for Science, Technology and Research, 1 Fusionopolis Way, Singapore 138632
| | - Ady Suwardi
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 2 Fusionopolis Way, Singapore 138634
| | - Zhong Liang Ou Yang
- Institute of High Performance Computing, Agency for Science, Technology and Research, 1 Fusionopolis Way, Singapore 138632
| | - George Xu
- Institute of High Performance Computing, Agency for Science, Technology and Research, 1 Fusionopolis Way, Singapore 138632
| | - Chee Kiang Ivan Tan
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 2 Fusionopolis Way, Singapore 138634
| | - Dan Daniel
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 2 Fusionopolis Way, Singapore 138634
| | - Hongying Li
- Institute of High Performance Computing, Agency for Science, Technology and Research, 1 Fusionopolis Way, Singapore 138632
| | - Zhengwei Ge
- Institute of High Performance Computing, Agency for Science, Technology and Research, 1 Fusionopolis Way, Singapore 138632
| | - Fong Yew Leong
- Institute of High Performance Computing, Agency for Science, Technology and Research, 1 Fusionopolis Way, Singapore 138632
| | - Kalisvar Marimuthu
- National Centre for Infectious Diseases, Tan Tock Seng Hospital, 16 Jalan Tan Tock Seng, Singapore 308443
| | - Oon Tek Ng
- National Centre for Infectious Diseases, Tan Tock Seng Hospital, 16 Jalan Tan Tock Seng, Singapore 308443
| | - Shin Bin Lim
- Ministry of Health Singapore, College of Medicine Building, 16 College Road, Singapore 169854
| | - Peter Lim
- Land Transport Authority, 1 Hampshire Road, Singapore 219428
| | - Wai Siong Mak
- Land Transport Authority, 1 Hampshire Road, Singapore 219428
| | - Wun Chet Davy Cheong
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 2 Fusionopolis Way, Singapore 138634
| | - Xian Jun Loh
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 2 Fusionopolis Way, Singapore 138634
| | - Chang Wei Kang
- Institute of High Performance Computing, Agency for Science, Technology and Research, 1 Fusionopolis Way, Singapore 138632
| | - Keng Hui Lim
- Institute of High Performance Computing, Agency for Science, Technology and Research, 1 Fusionopolis Way, Singapore 138632
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12
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Boedicker EK, Emerson EW, McMeeking GR, Patel S, Vance ME, Farmer DK. Fates and spatial variations of accumulation mode particles in a multi-zone indoor environment during the HOMEChem campaign. ENVIRONMENTAL SCIENCE. PROCESSES & IMPACTS 2021; 23:1029-1039. [PMID: 34142692 DOI: 10.1039/d1em00087j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Studying the indoor dynamics that impact particles is crucial in order to understand indoor air chemistry and assess overall human exposure to particles. This work investigates spatial gradients in particle concentration, caused by indoor transport and loss mechanisms. We conducted a variety of cooking experiments during the House Observations of Microbial and Environmental Chemistry (HOMEChem) campaign in June 2018 that allowed us to probe these mechanisms. We measured size-resolved (0.06-1 μm and 0.13-3 μm) particle number concentrations from cooking experiments using optical instruments at four locations throughout the house simultaneously. The particle number concentration in the kitchen was 40 ± 10% and 70 ± 10% higher than the concentrations in the living room and the bedroom, respectively. There was a minor size dependence, with larger differences in the smaller sizes of the accumulation mode (0.1-2.5 μm) than the larger end of the range. Dilution accounts for the majority of these concentration differences. Surface deposition was the dominant fate of particles within a zone, with observed deposition velocities ranging from 0.1 to 0.6 m h-1.
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Affiliation(s)
- Erin K Boedicker
- Department of Chemistry, Colorado State University, 200 W Lake St., Fort Collins, CO 80523, USA.
| | - Ethan W Emerson
- Handix Scientific LLC, 5485 Conestoga Court, Suite 104B, Boulder, CO 80301, USA
| | - Gavin R McMeeking
- Handix Scientific LLC, 5485 Conestoga Court, Suite 104B, Boulder, CO 80301, USA
| | - Sameer Patel
- Department of Civil Engineering, Indian Institute of Technology Gandhinagar, Palaj, Gandhinagar, Gujarat 382355, India
| | - Marina E Vance
- Department of Mechanical Engineering, University of Colorado Boulder, 111 Engineering Drive, 427 UCB, Boulder, CO 80309, USA
| | - Delphine K Farmer
- Department of Chemistry, Colorado State University, 200 W Lake St., Fort Collins, CO 80523, USA.
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13
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Peng Z, Jimenez JL. Exhaled CO 2 as a COVID-19 Infection Risk Proxy for Different Indoor Environments and Activities. ENVIRONMENTAL SCIENCE & TECHNOLOGY LETTERS 2021; 8:392-397. [PMID: 37566374 PMCID: PMC8043197 DOI: 10.1021/acs.estlett.1c00183] [Citation(s) in RCA: 94] [Impact Index Per Article: 31.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Revised: 04/01/2021] [Accepted: 04/02/2021] [Indexed: 05/21/2023]
Abstract
CO2 is co-exhaled with aerosols containing SARS-CoV-2 by COVID-19-infected people and can be used as a proxy of SARS-CoV-2 concentrations indoors. Indoor CO2 measurements by low-cost sensors hold promise for mass monitoring of indoor aerosol transmission risk for COVID-19 and other respiratory diseases. We derive analytical expressions of CO2-based risk proxies and apply them to various typical indoor environments. The relative infection risk in a given environment scales with excess CO2 level, and thus, keeping CO2 as low as feasible in a space allows optimization of the protection provided by ventilation. We show that the CO2 level corresponding to a given absolute infection risk varies by >2 orders of magnitude for different environments and activities. Although large uncertainties, mainly from virus exhalation rates, are still associated with infection risk estimates, our study provides more specific and practical recommendations for low-cost CO2-based indoor infection risk monitoring.
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Affiliation(s)
- Zhe Peng
- Cooperative Institute for Research in Environmental Sciences and Department
of Chemistry, University of Colorado, Boulder, Colorado 80309,
United States
| | - Jose L. Jimenez
- Cooperative Institute for Research in Environmental Sciences and Department
of Chemistry, University of Colorado, Boulder, Colorado 80309,
United States
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