WIAC2025 - 6th Workplace and Indoor Aerosols Conference

May 6, 2025, 8:00 AM → May 8, 2025, 6:00 PM Europe/Rome

Angevin Aragonese Castle (Gaeta, Italy)

Andre Henriques (CERN), Giorgio Buonanno (Università di Cassino e del Lazio Meridionale), Luca Fontana (WHO)

Welcome to the WIAC2025 Indico portal which will serve as a central hub for two key functions: Participant Registration and Abstract Submission.

To start your registration process click register icon down below.

 

WIAC2025 Conference Home Page

Tue, May 6

8:30 AM → 9:00 AM REGISTRATION

Attendees Registration at desk

9:00 AM → 9:30 AM Opening remarks: Giorgio Buonanno (University of Cassino and Southern Lazio), Maria Neira (WHO), Maria Van Kerkhove (WHO), Enrica Porcari (CERN)

Giorgio Buonanno

9:30 AM → 10:30 AM SESSION 1a - Particles Emission: Understanding sources, estimation and measurements, Keynote Speakers

Moderators: Donald Milton and Lidia Morawska

9:30 AM Studying airborne disease transmission in indoor settings: an epidemiologist's perspective

Speaker: Nancy Leung (University of Hong Kong)

10:00 AM Airborne particle emission from indoor combustion sources

Speaker: Luca Stabile (University of Cassino and Southern Lazio)

10:30 AM → 11:00 AM Coffee Break

11:00 AM → 12:00 PM SESSION 1b - Particles Emission: Understanding sources, estimation and measurements, Oral presentation

Moderators: Donald Milton and Lidia Morawska

11:00 AM Evaluation of the Naneos Partector 2 Pro ultrafine particle monitor to support WHO’s 2021 good practice statements

Introduction
The 2021 WHO Air Quality Guidelines[1] included four good practice statements to help guide actions to decrease concentrations of ultrafine particles (UFP) and ultimately reduce population exposure to UFP. The good practice statements included recommendations to expand common air quality monitoring to include size-segregated and real-time measurements of UFP along with particulate matter (PM) mass measurements and to advance UFP monitoring technologies and approaches. Although instrumentation to monitor UFP has been developed and such instruments are active worldwide, their extensive space, controlled operating environments, and expertise requirements make them unsuitable for large-scale deployment into established air quality monitoring networks. A small, handheld UFP device called the Naneos Partector 2 Pro[2] (hereafter referred to as the P2 pro) based on a measurement technique involving unipolar diffusion chargers has shown promise as an alternative candidate monitor to be deployed at scale.

Objectives
This study’s primary objectives are: (i) to test and evaluate the P2 pro’s ability to monitor continuously in ambient conditions for 12 months, and (ii) to evaluate the P2 pro’s measurement performance with a focus on total particle number concentration (PNC) and particle size distributions. The UFP size range and size bins that will be evaluated correspond to the eight size bins the P2 pro reports, specifically, bins with 10, 16.3, 26.4, 43, 69.8, 113.5, 184.6, and 300 nm midpoints.

Methods
At the time of writing, twelve research groups based in Australasia, Asia, North America, and Europe have deployed P2 pro devices during, or before January 2025 and will monitor UFP for at least 12 months. The devices are installed in established air quality monitoring sites that generally include PM mass measurements. The devices will also (at least periodically) be colocated with mobility particle size spectrometers (MPSS) and/or condensation particle counters (CPC) which will be used as reference instrumentation for the evaluation of measurement performance of the UFP metrics. The monitoring sites cover a range of environments ensuring a diverse range of UFP characteristics and climatic zones. Monitoring is occurring within and outside urban areas with variable proximity to primary UFP emission sources. The 12 monitoring teams will monitor the P2 pro to identify potential malfunctions or failures quickly and intervene when necessary to maximise data capture rates. Observations will be uploaded monthly to allow for central storage and management to ensure consistent data analysis approaches. Furthermore, the Partector will be evaluated with the performance and uncertainty metrics contained within the CEN/TS 17434:20203 technical specification to allow for comparison among other UFP monitors and offer insight on what monitoring applications the P2 pro is most suited to.

Results
The P2 pro is being tested in 12 locations across the world and the evaluation period will run from January 2025 to December 2025. There have been no major failures or issues that have led to significant data loss. The P2 pro devices are performing well and are reporting observations reliably. The digital infrastructure is being developed to enable harmonised and consistent data analysis across all monitoring sites and devices. The exact procedures for the intercomparisons between the device under test and reference instruments (generally, MPSS) in the scope of CEN/TS 17434:2020 are under development. Comparisons will also be made with previous studies which have tested the Partector for shorter durations[4] or in specific conditions.[5]

Conclusions
The 2021 WHO Air Quality Guidelines delivered good practice statements relating to UFP. To support these statements, the handheld Naneos Partector 2 Pro UFP device is currently under test in 12 locations around the world. The evaluation of the device and the study’s outlined objectives are the first steps towards generating the required datasets to robustly calculate UFP’s exposure-response functions in the future.

References
[1] World Health Organization (2021). WHO global air quality guidelines: particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. https://www.who.int/publications/i/item/9789240034228
[2] Naneos particle solutions (2024). Partector 2 Pro. https://www.naneos.ch/partector2pro.html
[3] CEN/TS 17434:2020: Ambient air – Determination of the particle number size distribution of atmospheric aerosol using a mobility particle size spectrometer (MPSS).
[4] Asbach, C., Todea, A. M., and Kaminski, H. (2024). Evaluation of a Partector pro for atmospheric particle number size distribution and number concentration measurements at an urban background site. Aerosol Research, 2(1):1–12.
[5] Bezantakos, S., Varnava, C. K., Papaconstantinou, R., and Biskos, G. (2024). Performance of the Naneos Partector 2 multi-metric nanoparticle detector at reduced temperature and pressure conditions. Aerosol Science and Technology, 58(5):584–593.

Speaker: Lidia Morawska (Queensland University of Technology (QUT))

11:12 AM Infectivity of exhaled SARS-CoV-2 aerosols is sufficient to transmit covid-19 within minutes

Background
Exhaled SARS-CoV-2-containing aerosols contributed significantly to the rapid and vast spread of covid-19. However, quantitative experimental data on the infectivity of such aerosols is missing. Knowing the emission rates of infectious viruses from normal respiratory activities enables more accurate modelling of disease transmission in indoor environments.
Method
We collected the exhaled aerosols from breathing, talking and singing, respectively, from 38 individuals with covid-19 using a BioSpot (Aerosol Devices), and cultured the aerosol samples that contained detectable levels of SARS-CoV-2 RNA. In another setting we collected exhaled aerosols from one individual with covid-19 using a cascade impactor to determine the size distribution of SARS-CoV-2 RNA in aerosol. Then, we used the size distribution and the emission rates in an indoor air inhalation model to calculate the time needed to inhale one infectious dose.
Results
50% of the 38 individuals had detectable levels of SARS-CoV-2 RNA in the exhaled aerosol samples. From three individuals, six aerosol samples were culturable, of which five were successfully quantified using TCID50. The source strength of the three individuals was highest during singing, when they exhaled 4, 36, or 127 TCID50/s, respectively. Calculations with an indoor air transmission model showed that if an infected individual with this emission rate entered a room, a susceptible person would inhale an infectious dose within 6 to 37 min in a room with normal ventilation.
Conclusion
Our data show that exhaled aerosols from a single person can transmit covid-19 to others within minutes at normal indoor conditions.

Speaker: Malin Alsved (Lund university)

11:24 AM Online particulate matter monitoring to track and control air quality in public transport

Objective: As an indoor environment, public transport is subject to special conditions with many passengers in a comparatively small space. Therefore, both an efficient control of the climatic parameters and a good air exchange are necessary to avoid transmission and spread of respiratory diseases. However, in such a dynamic system it is practically impossible to determine pathogenic substances with high temporal and spatial resolution, but easy-to-measure parameters like airborne particulate matter and carbon dioxide allow the air quality to be assessed in a passenger compartment online, which is useful for controlling the ventilation system.
Methods: Hand-held devices were used to measure temperature, relative humidity RH and carbon dioxide. An optical particle sizer was used to measure the particle concentration. The conversion to mass-related concentrations was based on the assumption of spherical particles and a density of 1 g/cm³. A portable monitoring system was also used for the recording of environmental parameters. The system consisted of a carbon dioxide sensor, an optical particle sensor and a temperature/humidity/pressure sensor. The measurement program focused on regional bus, tram and train traffic in Braunschweig and Hannover, or between the two cities. The occupancy of the passenger area was recorded for all route sections. In addition, measurements were carried out on the tram platform of the underground station at Hannover Central.
Results: In the case of the particles, the concentration peaks did not correspond to the occupancy density of the passengers, but often to their dynamics when the doors were regularly opened, combined with getting on and off. Some of the particles were brought in through the ambient air, some through clothing and the movement of passengers. As a result, the particle concentration in the cabin increased significantly at the bus stops. It was also noticeable that in various measurements the highest particle concentrations were recorded when several passengers boarded at the same time at the starting point. It is known that moving people are relevant particle sources or resuspend particles, but it is certain that the passengers' breathing is not the source of the particles. The maxima occurred only for a short time and reached the base level again within a few seconds. For each measurement run, ambient air measurements were carried out on $\rm PM_{10}$, but only at the respective start and final stations. These concentrations were mostly in the range of 10 µg/m³. However, there were bus and train platforms with significantly higher ambient air concentrations of $\rm PM_{10}$. For example, the values in the metro station at Hannover central station were consistently around 50 µg/m³. At other stations in Braunschweig and Hannover, smoking areas on the platforms, traffic or construction sites influenced the $\rm PM_{10}$ concentration in the passenger cabins when the doors were open. Therefore, the $\rm PM_{10}$ peaks did not always coincide with entry and exit of many people. As expected, the carbon dioxide concentration in the transport cabin was directly linked to the density of passengers.
The parameters $\rm PM_{1}$ and $\rm PM_{2.5}$, which were also measured with the sensors, did not provide any additional information for the issue of efficient ventilation, which is relevant here. There were also some deviations from the OPC data, which is due to the different measurement technologies.
Conclusion: The investigations carried out and the results presented do not claim to assess the risk of persons for an infection by pathogenic bioaerosols in passenger cabins in public transport. It is also explicitly warned against using this methodology for such purposes. However, it was demonstrated that the online measurement of simple parameters like $\rm PM_{10}$ and carbon dioxide is a valuable tool for assessing air quality as a function of time, location, number and dynamics of people and for controlling the ventilation in public transport.

Speaker: Prof. Tunga Salthammer (Fraunhofer WKI)

11:36 AM Mitigating airborne pathogen transmission in indoor environments: Inactivation effects of environmental factors

Objective: Urbanization and rising energy demand in buildings challenge public health by increasing airborne disease transmission risks in crowded indoor spaces. While improved ventilation has been recommended during the COVID-19 pandemic to lower infection risks, it also raises energy consumption, creating a trade-off between energy use and health protection. Current strategies like ventilation and portable air cleaners (PACs) are used to reduce indoor pathogens. However, factors like relative humidity (RH) and air composition have been studied in less detail, and they significantly affect pathogen inactivation by altering aerosol salinity and pH, to which pathogens are sensitive. Despite extensive biological research on the inactivation in droplets, their integration into indoor air studies remains limited. This study explores pathogen inactivation and removal through experiments examining how RH, air composition – particularly volatile ammonia, ventilation rates, and PACs impact pathogen survival. This abstract focuses on the inactivation effects of RH and air composition to develop sustainable infection control strategies.
Methods: In a biosafety level 1 chamber, experiments used E. coli as a surrogate for respiratory pathogens. Artificial saliva (AS) was aerosolized using a coughing machine to simulate respiratory emissions with 10 coughs per series. A factorial design was employed to study pathogen inactivation across three RH levels (30%, 50%, 70%) and distances (1m, 2m, 4m). Air temperature and air change rate were fixed at 23℃ and 1, respectively. Subsequent experiments will assess the effect of ammonia concentrations (3.65 ppb, 36.5 ppb, 365 ppb) on pathogen inactivation. Additional surrogates such as Staphylococcus epidermidis, Φ6, and MS2 will also be included. Pathogen removal experiments will vary ventilation rates, PAC placements (near the source, midway in the cough jet, and at certain distances), and source distances. Bioaerosol sampling occurred immediately after emission and after a decay period, using 6-stage Andersen impactors. GRIMM 11-D aerosol spectrometers and MetOne HHPC+ optical particle counters continuously monitored size-resolved particle concentrations at the center of the cough jet, positioned at designated distances from the source. Particle concentrations at three locations, 1 m from the bioaerosol sampling point and outside the cough jet, were measured using Graywolf PC-3500 optical particle counters. Environmental parameters such as chamber relative humidity, CO₂, and ammonia levels were continuously recorded by an Onset HOBO Max CO₂ logger and a Picarro NH₃ analyzer, at locations unaffected by the cough jet.
Results: Over 90% of particles were below 2 μm, with only AS being expelled. When E. coli was present, 85% of the particles remained in that same size range. Adding E. coli reduced particle concentrations compared to pure AS due to viscosity changes. Coughing caused particle concentrations in the jet to spike, but they quickly decreased, indicating significant immediate exposure to pathogen-laden particles during coughing. In pathogen inactivation experiments, RH could affect pathogen survival by altering aerosol particle salinity and size. At low RH, particle evaporation accelerated, shifting size distribution toward smaller particles. Mid-range RH would promote supersaturation, enhancing pathogen inactivation, while salt efflorescence hinders further inactivation at low RH. As for volatile ammonia, high ammonia levels are expected to raise aerosol pH indoors, reducing acidity and potentially slowing inactivation. Unlike RH, ammonia does not directly affect particle sizes. As distance from the coughing machine increases, exposure to pathogen-laden aerosols decreases as the cough jet dissipates, becoming more susceptible to airflow disruption. This study emphasizes the distinct effects of RH and ammonia on the sensitivities of four pathogens. Optimizing RH and ammonia to establish aerosol pH and salinity that promotes pathogen die-off could yield energy-efficient inactivation strategies. Future experiments will further optimize ventilation rates and PAC usage to decrease airborne pathogens pathogens further.
Conclusion: Incorporating insights from indoor air science and biological studies offers a comprehensive approach to optimizing infection control strategies. This research addresses significant knowledge gaps by investigating the effects of RH, ammonia concentrations, ventilation rates, and PAC placements. The ongoing data analysis will yield findings that may inform energy-efficient strategies, thereby balancing health protection with sustainability. This research aims to promote sustainable indoor air quality management by providing practical, evidence-based recommendations supporting public health and energy conservation.

Speaker: Hui Dong

11:48 AM Indoor Air Quality of Offices: Beyond CO2 to Chemical Pollutants

Objective
Poor indoor air quality (IAQ) can impact health, a concern emphasized during the COVID-19 pandemic. Belgium’s Federal Public Services (FPS) of Health launched the Indoor Air Quality Platform to address this. This platform unites public agencies, academics, and industry representatives to enhance IAQ in public enclosed spaces (e.g., restaurants, hotels, cultural and sports venues) through knowledge-sharing, research, and policy support. Sciensano, Belgium's national public health institute, supports the FPS and the Platform by conducting IAQ studies in office environments and publicly accessible enclosed spaces.
Methods
Low-cost sensors measured the indoor and outdoor air quality in both office spaces and publicly accessible areas inside these office buildings across public entities. Monitoring the publicly accessible areas ensures a focus on environments with significant public interaction, while including office spaces added valuable data points thanks to their controlled conditions, extensive existing literature, and ease of comparison. Pollutants like carbon dioxide (CO2), carbon monoxide (CO), nitrogen dioxide (NO2), ozone, particulate matter (PM10, PM2.5), and total volatile organic compounds (TVOC) (more specifically formaldehyde), alongside temperature, relative humidity, and sound were monitored over periods ranging from two weeks to one month at various times throughout the year.
Results
These indoor air quality measurements conducted at various times throughout the year revealed a first view of differences in pollutant trends between buildings with and without HVAC systems and the influence of outdoor air on indoor levels.
Key findings included indoor CO2 levels often below 1000ppm, thanks to effective ventilation and low occupancy. Outdoor pollutant peaks, notably NO2, PM, and ozone, directly impacted indoor air quality, especially in HVAC-equipped spaces. At night, VOC and formaldehyde levels increased, probably due to the emission from building materials and furniture. Offices with HVAC systems often had reduced humidity (30%-40%) and, in the more recent buildings with large glass windows, summer temperature sometimes reached 30°C.
Conclusion
This monitoring campaign provided valuable insights into pollutant tendencies, HVAC system performance, and the interaction between outdoor and indoor air quality inside the office buildings across public entities. This research underscores the importance of well-maintained HVAC systems and highlights the role of sensors in detecting and identifying aberrant situations or events.
Future long-term measuring campaigns will soon expand to public enclosed spaces like sports and cultural centers and will allow us to create a mapping of the pollutants present in these different spaces and to develop an ‘indoor barometer’. These efforts aim to improve IAQ in shared environments, benefiting public health and well-being.

Speaker: Dr Sarah J.D. Nauwelaerts

12:00 PM → 12:30 PM Discussion panel

Moderators: Donald Milton and Lidia Morawska - Panelists: speakers of session 1a and session 1b

12:30 PM → 1:30 PM Lunch

1:30 PM → 2:30 PM SESSION 2a - Exposure and Dose: Assessing the human health implications

Moderators: Nancy Leung and Aneta Wierbizcka

1:30 PM Aspects of host immunity that can impact transmission and susceptibility to airborne infections

Speaker: Julian Tang (University Hospitals of Leicester)

2:00 PM Human health and ambient air pollution: patterns of exposure and health effects

Speaker: Heather Adair-Rohani (World Health Organization)

2:30 PM → 3:00 PM Coffee Break

3:00 PM → 4:00 PM SESSION 2b - Exposure and Dose: Assessing the human health implications, Oral Presentations

Moderators: Nancy Leung and Aneta Wierbizcka

3:00 PM Evaluating air cleaning in Dutch primary schools: study design and preliminary results of the Clean Air for Everyone (CLAIRE) project

Introduction
Children in Europe spend a substantial amount of their time in classrooms, where indoor air quality (IAQ) guidelines are often not met. Poor IAQ — shaped by factors such as bioaerosols (including bacteria, viruses), particulate matter (PM), and volatile organic compounds — has been associated with respiratory morbidity and infectious disease transmission. While ventilation plays a key role in improving IAQ, since the COVID-19 pandemic, mobile air cleaners equipped with high-efficiency particulate air (HEPA) filters or alternative technologies, such as ionizers, are increasingly considered as a supplementary measure to protect against acute respiratory infections.

To date, air cleaner efficiency has been predominantly assessed in controlled environments using artificial aerosols, with limited real-world evidence of their effectiveness in occupied classrooms. Moreover, feasibility of integrating air cleaners into school settings remains unclear. This study aims to address these gaps by evaluating the impact of air cleaners on airborne bioaerosols and general IAQ indicators in primary school classrooms through a large-scale randomized controlled trial (RCT).

Methods
The RCT utilizes classrooms within a school as the randomization unit. At each school, sets of three classrooms with similar building characteristics are selected and randomly assigned to one of the three study regimes: 1) intervention with HEPA filter air cleaners, 2) intervention with air cleaners using an alternative technology, and 3) no intervention (control).

Bioaerosol samples from classrooms are passively collected using electrostatic dust fall collectors (EDCs), suspended 30 centimeters from the ceiling for a three-week sampling duration. A baseline (pre-intervention) measurement is followed by three repeated measurements during intervention. After DNA and RNA extraction of EDCs, levels of total 16S rRNA, S. aureus, S. epidermis, S. salivarius, M. catarrhalis, Influenza A/B and RSV are quantified by qPCR.

Concurrently, PM10, PM2.5, PM1, CO2, temperature, and relative humidity are continuously monitored in each classroom at one-minute intervals using IAQ sensors. Additionally, student absenteeism is recorded, and respiratory health of the pupils is assessed via a parental survey before and after intervention.

Results
From December 2023 to April 2024, a total of 12 schools were enrolled in the study. Data collection continues from October 2024 through April 2025, expanding the study to a total of 26 schools. The implementation of air cleaners in school environments presents practical challenges, including issues related to device size and sound levels.

Preliminary analysis of bioaerosol markers from the initial measurement period (December 2023–April 2024) showed the following bioaerosol detection rates: Influenza A (0%), Influenza B (1.5%), RSV (8%), 16S rRNA (97%), S. epidermidis (40%), M. catarrhalis (55%), S. aureus (49%), and S. salivarius (55%). Upon completion of data collection in April 2025, the study will assess the impact of air cleaners on bioaerosol concentrations and PM levels.

Conclusion
This large-scale RCT will address a critical knowledge gap, providing real-world evidence on the efficacy of air cleaning technologies in reducing airborne microbial, viral, and PM levels in primary school classrooms. Ultimately, findings from this study will offer crucial insights into the feasibility and public health implications of air cleaners in school environments, informing future evidence-based public health strategies to enhance IAQ and mitigate airborne disease transmission in educational settings.

Speaker: Esmée Janssen (Utrecht University, Institute for Risk Assessment Sciences)

3:15 PM ENVIRONMENTAL MONITORING OF RESPIRATORY VIRUSES (SARS-CoV-2, RESPIRATORY SYNCYTIAL VIRUS, AND INFLUENZA A) IN A HEALTHCARE SETTING

Background/Objective
The growing concern about the rapid spread of respiratory diseases has reinforced the importance of environmental monitoring of infectious diseases as an indispensable tool for public health. In particular, monitoring respiratory viruses in air samples is essential for early detection, prevention, and control of epidemic outbreaks, providing a more comprehensive understanding of transmission dynamics. Environmental monitoring not only helps identify the presence of pathogens but also enables for the assessment of their concentration in high-risk areas, contributing to more informed decision-making for preventive measures.
In the context of healthcare facilities, which are frequented by vulnerable population and where the presence of viruses might be more prevalent, such monitoring becomes even more essential. The ability to detect respiratory viruses such as SARS-CoV-2, Influenza A, and Respiratory Syncytial Virus (RSV) in hospital environments is crucial for assessing the risk of airborne transmission and evaluating the effectiveness of infection control measures. By identifying virus hotspots, targeted interventions can be implemented to reduce transmission, thereby ensuring the safety of patients, healthcare workers, and visitors.

This study aims to analyse the presence of respiratory viruses, including SARS-CoV-2, Influenza A, and RSV, in air samples collected from different areas within a hospital. Additionally, the study seeks to characterize the viral load in identified peaks to gain a deeper understanding of the concentration of these viruses in hospital settings, which could be useful to assess their potential contribution to hospital-associated outbreaks.

Methods
Between December 17, 2021, and January 19, 2023, air samples were collected in sterile 47 mm quartz fibre filters using Derenda low-volume samplers (2.3 m³/h) equipped with PM2.5 inlets in a hospital located in Castelló de la Plana, Valencian Community, Spain. Samples were collected in consecutive 24-hour sampling cycles during weekdays.
RNA was extracted from the filters, which had been previously spiked with Mengovirus (MgV) as an internal extraction control. Subsequently, RT-qPCR analysis was conducted, targeting the E fragment of the SARS-CoV-2 envelope protein (E); the matrix (M) gene of Influenza A; and the matrix (M) gene of RSV. Clinical data from the hospital's emergency department was inspected to identify peaks in emergency cases associated with infections caused by these viruses. The medians and interquartile ranges (IQR) of viral concentrations during the identified peaks were calculated and expressed as genomic copies per cubic meter (gc/m³).

Results
The mean recovery rate for the internal control MgV was 27 % ± 24 %. The analysis revealed an increase in emergency cases associated with infections caused by the three studied viruses as follows. There was peak of SARS-CoV-2 from December 17, 2021, to April 30, 2022. Two peaks of Influenza A were identified. A first peak in March and April 2022, and a second peak in December 2022. The peak of RSV occurred in November 2022. During the months when an increase in emergency cases associated with these viruses was observed, the median (IQR) number of emergency cases recorded were 8 (17), 3 (5), and 2 (2) for SARS-CoV-2, Influenza A, and RSV, respectively. The median (IQR) viral concentrations during the months with increased emergency cases associated with these viruses were 3.2 (6.2), 0.81 (1.5), and 3.3 (3.9) gc/m³ for SARS-CoV-2, Influenza A, and RSV, respectively.

Conclusion
An increase in the genetic load corresponding to SARS-CoV-2, Influenza A, and RSV viruses has been detected in aerosols collected during the months that recorded a rise in emergency cases associated with these viruses at the reference hospital in Castelló. Future studies should explore the potential of measuring viral traces in aerosols as a tool for environmental surveillance of viruses.

Speaker: Juana Maria Delgado-Saborit (Universitat Jaume I)

3:30 PM Indoor clean air for kitchens and other living spaces

Speaker: Prashant Kumar (Global Centre for Clean Air Research (GCARE), University of Surrey)

3:45 PM Outdoor Concentration versus Personal Exposure in Urban Residents: Which PM2.5 Metric Is Associated with Respiratory Pathophysiology?

Objective: Contemporary outdoor PM2.5 levels are generally low in Western cities, which may make indoor contributions to personal exposure more significant. We aim to compare acute effects of PM2.5 measured as outdoor concentration versus personal exposure on respiratory pathophysiologic indicators in adults with or without asthma.
Methods: From 2021-2023, we conducted a panel study in 42 adults (17 with and 25 without asthma) residing in London, UK. Each participant was measured in a summer month and a winter month for airway resistance (R5, R20, and R5–R20), lung function (FEV1), and pulmonary inflammation (FeNO). Outdoor PM2.5 concentration was estimated hourly over the 48 hours preceding each health assessment using the inverse distance weighting (IDW) method using the data measured at 3 nearby monitoring stations. Personal PM2.5 exposure was measured over the same period using Airspeck-P wearable sensor attached to participants. Mixed-effects models combined with distributed lag models (DLMs), including an interaction term for asthma status, were applied to evaluate the effects of 4-hour averaged outdoor and personal PM2.5 exposure, respectively.
Results: Outdoor PM2.5 concentrations were higher than personal concentrations, with median (IQR) being 6.03 (6.21) μg/m³ and 2.71 (4.36) μg/m³, respectively. We observed significant associations of increasing outdoor PM2.5 concentrations with increased airway resistance (effect lagged by 8-19 hours) and with decreased lung function (effect lagged by 8-31 hours) only in asthmatic participants (not in healthy participants). In contrast, personal PM2.5 exposure was not significantly associated with any of the respiratory pathophysiology indicators.
Conclusion: Individuals with asthma showed worsened respiratory pathophysiology 8 – 31 hours after an increase in 4-hour averaged outdoor PM2.5 concentration. Substantially lower personal PM2.5 exposure compared to outdoor PM2.5 concentration suggests that indoor PM2.5 levels were lower. Sources and factors associated with indoor PM2.5 exposure may have attenuated the respiratory effects of outdoor PM2.5 under contemporary air quality conditions in London.

Speaker: Jim Zhang (Duke University)

4:00 PM → 4:30 PM Discussion panel

Moderators: Nancy Leung and Aneta Wierbizcka - Panelists: speakers of session 2a and session 2b

4:30 PM → 6:00 PM POSTER SESSION: Poster & Exhibitor social hour: networking with drinks and researchers

Poster Session and Reception

Wed, May 7

9:30 AM → 10:30 AM SESSION 3a - Mitigation Measures and Strategies: Exploring environmentally sustainable solutions such as indoor ventilation and beyond,Keynote Speakers

Moderators: Richard Corsi and Luca Fontana

9:30 AM Ventilation (huh, yeah). What is it good for?

Speaker: Pawel Wargocki (Technical University of Denmark)

10:00 AM Designing the Air: Maximizing Viral Decay to Limit Disease Transmission

Speaker: Allen Haddrell (University of Bristol)

10:30 AM → 11:00 AM Coffee Break

11:00 AM → 12:00 PM SESSION 3b - Mitigation Measures and Strategies: Exploring environmentally sustainable solutions such as indoor ventilation and beyond, Oral Presentations

Moderators: Richard Corsi and Luca Fontana

11:00 AM Crowd-Data Collection of Indoor CO₂-Levels using Portable CO2-Sensors and a Mobile App

High CO₂ levels in indoor spaces not only have direct adverse affects on human wellbeing but are also, in most cases, a reliable indicator of the amount of rebreathed air and thus for the risk of spread of airborne diseases. Despite its importance, large-scale datasets on indoor CO₂ levels across diverse, publicly accessible spaces remain scarce.

Existing research on indoor CO₂ levels so far focuses mostly on a narrow range of environments such as hospitals, schools, or residential homes. While these studies provide valuable insights, they are frequently constrained by limited sample sizes, narrow geographic coverage, or short observation periods. This leaves a substantial knowledge gap regarding CO₂ levels in a broader range of public indoor spaces, such as restaurants, shops, museums, public transport, and other high-traffic areas, which the IndoorCO₂Map project attempts to close.

IndoorCO2Map.com is an open source and open data citizen data collection project that enables individuals to measure and share CO₂ concentration data using portable sensors. Participants can contribute data from all kinds of publicly accessible indoor locations, creating a comprehensive and diverse dataset of real-world indoor CO₂ levels. This crowd-sourced approach is designed to scale geographically and temporally, overcoming many resource constraints of traditional studies.

The project combines accessible technology, including low-cost CO₂ sensors, with an intuitive and privacy respecting mobile app where users can record and upload their measurements. Each data point is timestamped, and annotated with geodata about the location type using OpenStreetMap, facilitating detailed analysis of spatial and temporal trends in indoor air quality.

The project is currently still in beta testing and little effort has been taken to increase the user base. Nevertheless around 7000 measurements, ranging from the minimum 5 minutes to hour long recordings, have been already taken as of January 10th, making it the largest publicly available dataset. Currently around 30 to 50 measurements per day are taken in average, with around 80% of them being in Germany so far.
Preliminary results from the dataset will be discussed, highlighting patterns of CO₂ concentrations across various public indoor spaces. For instance, Variation of CO₂ levels by venue type, time of day, week of day and season.

Key challenges will also be addressed, such as ensuring data quality and reliability in a crowd-sourced dataset, addressing privacy concerns, and fostering sustained engagement from contributors. Biases resulting from differences between the general population and app users will also be discussed.

Furthermore, it will be discussed how this data can complement other studies, inform public health initiatives, urban planning, and provide guidance for policy-making. For example, insights from IndoorCO₂Map.com could guide ventilation standards, identify high-risk locations and provide guidance for individual decision-making of visitors/customers. It can also be used for hypothesis generation for scientific studies.

By leveraging citizen data collection, IndoorCO2Map.com already demonstrates a scalable, community-driven approach to tackling data gaps in regards to indoor air quality. The project not only fills an important data gap, but also raises public awareness about the significance of ventilation in maintaining safe and healthy indoor environments. Because the data and code is open source, it can also be adapted by others for specific research questions, be expanded in the future to other indoor pollutants or, if necessary, a stricter approach to user verification can be implemented.

Speaker: Aurel Wünsch

11:15 AM Carbon Dioxide Measurements at Multiple Points in an Elementary School Classroom And Risk Estimation of Airborne Transmission: A Two-Month Field Campaign

Introduction:
The concentration of carbon dioxide (CO2) is commonly used as a proxy for indoor air quality, particularly for assessing ventilation in indoor environments and estimating the risk of airborne transmission. Ventilation rates are commonly estimated using the mass balance equation under the assumption of a well-mixed environment. To estimate transmission risk, the Wells-Riley models are frequently employed as a balance between accuracy and computational efficiency. These models account for the estimated ventilation rate or utilize the rebreathing fraction of air, which is derived from CO2 concentration (Rudnick & Milton, 2003). However, in most cases, a single CO2 measurement point is used for both purposes.

Motivated by the COVID-19 pandemic, recent studies have explored the use of multiple measurement points in school classrooms, although these efforts have typically been limited to periods shorter than a week.

Aim:
The objective of this study is to evaluate, over a relatively long measurement campaign, the spatial variability of CO2 concentration within a naturally ventilated elementary school classroom and assess their impact on estimating the risk of airborne transmission.

Methodology:
The study was conducted in a naturally ventilated classroom in Montevideo, Uruguay, measuring 8 m × 6 m × 3.5 m (length × width × height). The classroom features four windows on one wall, a door, and an upper window on the opposite wall. It operates in two shifts: a morning session (8:00 a.m. – 12:00 p.m. with a 30-minute break at 10:00 a.m.) and an afternoon session (1:00 p.m. – 5:00 p.m. with a 30-minute break at 3:00 p.m.), hosting fifth-grade students aged 10–11 years (25 students in the morning, 30 in the afternoon).
Over two months, 13 monitoring devices were deployed in the classroom. Four devices were installed on each of the side walls at two different heights (1 m and 2.2 m), one on the front wall at a height of 2 m, one on the back wall at a height of 2.2 m, and three along the classroom axis at a height of 2.4 m. Each device recorded data every 30 seconds, measuring CO2 concentration using an NDIR sensor (Senseair Sunrise 006-0-0008), air temperature, and relative humidity (Sensirion SHT40-AD1B-R2).
The differences in CO2 concentration, based on daily averages for each occupancy period, were analyzed. Additionally, the daily risk of airborne transmission, estimated from the rebreathed fraction of air measured by each device, was evaluated for different quanta emission rates, ranging from 1 quanta/h to 100 quanta/h.

Results:
When comparing the daily averages of each device, there is greater variability in the morning shift than in the afternoon shift. In contrast, the minimum and maximum daily CO2 concentrations are similar for both shifts. The ratio between the maximum and minimum daily averages across the different devices ranges from 1.05 to 1.47. The minimum daily average is most frequently measured by one of the devices installed on the side wall with windows (100% and 89% of the days for the morning and afternoon shifts, respectively), as expected. Meanwhile, the maximum daily average is typically recorded by the devices installed at higher positions, particularly those along the classroom axis (60% of the days).
Regarding the risk of airborne transmission, the variation in estimated risk across devices for each day is greater than the variation in daily average CO2 concentration. The ratio of the minimum to maximum estimated risk can reach as high as 2.7. Interestingly, this difference in estimated risk is not observed on the day with the largest variation in daily average CO2 concentration across devices; instead, it occurs on the day with the lowest average CO2 concentration. This is consistent with the model equation, which shows that for the same ratio of mean CO2 concentrations measured by two sensors, the corresponding ratio of estimated risks is larger at lower CO2 concentrations.

Conclusions:
A two-month measurement campaign was conducted in an elementary school classroom, recording CO2 concentration, air temperature, and relative humidity at 13 points. The daily average CO2 concentration during occupied hours was analyzed, and its spatial and temporal distribution was evaluated. The estimated risk of airborne transmission and its variability across devices were assessed. The results show that daily CO2 averages can differ by up to 47%, while the estimated risk can vary by as much as 170%. The variation in risk across devices depends on the CO2 concentration, decreasing as the concentration increases. Consequently the influence of the measurement point on the estimated risk decreases with higher CO2 concentrations. Additionally, the observed variability is relatively low compared to the uncertainty associated with other factors, like quanta emission rate.

Speaker: Dr Mariana Mendina (Instituto de Mecánica de los Fluidos e Ingeniería Ambiental, Facultad de Ingeniería, Universidad de la República, Uruguay.)

11:30 AM FAR-UV Technology and Germicidal Ultraviolet (GUV): A Policy and Research Review for Indoor Air Quality and Disease Transmission Control

The COVID-19 pandemic underscored the vital role of indoor air quality (IAQ) in reducing airborne disease transmission indoors. Far-Ultraviolet (FAR-UV) technology, emitting light between 200-235 nm, emerges as a promising alternative to traditional wavelengths of Germicidal Ultraviolet (GUV), promoting airborne disinfection without many of the safety concerns related to improperly installed upper-room GUV systems. Studies indicate that FAR-UV effectively inactivates various pathogens, though questions remained around its safety, appropriate use cases, and the regulatory environment associated with this new technology. To understand these issues Johns Hopkins University Center for Health Security (CHS) recently convened a high-level working group to discuss the potential of FAR-UV technology as a public health tool. The meeting brought together interdisciplinary experts, including engineers, public health specialists, and policymakers, to evaluate current research findings and strategize on implementation pathways. Discussions emphasized the importance of FAR-UV as a scalable solution to enhance IAQ and reduce indoor disease transmission.

Findings from this working group demonstrate that FAR-UV has high efficacy and low energy requirements compared to other disinfection methods or other engineering controls. FAR-UV could be a promising tool to combat disease transmission in high-risk indoor environments and improve IAQ, particularly when coupled with ventilation systems. Further research is necessary, however, to ensure the safe use of FAR-UV technology, including the development a clearer understanding of the chemical interactions between FAR-UV light, ozone, and volatile organic compounds, as well as the need to identify best practices to mitigate secondary organic aerosols generated by FAR-UV use. Further studies highlighting the best use cases and appropriate venues for FAR-UV deployment are also recommended. Finally, the regulatory landscape for FAR-UV technology remains underdeveloped. Establishing standardized guidelines and conducting comprehensive human health risk assessments are crucial steps for informing policy toward ensuring safe and effective implementation. Regulatory clarity for this novel technology would foster public trust and encourage more widespread adoption.

FAR-UV technology holds significant promise as an engineering solution to enhance indoor air quality and control disease spread. Its high efficacy in pathogen inactivation, coupled with a favorable safety profile, positions it as a valuable tool in public health strategies. Implementation of FAR-UV, as well as GUV, technology should be considered for locations that have high infection potential. However, we must address environmental concerns and establish robust regulatory frameworks to realize its full potential in diverse indoor environments.

Speakers: Dr Gigi Gronvall (Johns Hopkins Center for Health Security), Paula Olsiewski (Johns Hopkins Center for Health Security)

11:45 AM Is the usual social distance sufficient to avoid airborne infection of expiratory droplets in indoor environments?

As airborne transmission of expiratory droplets is one of the important pathways for viral respiratory diseases including the recent pandemic COVID-19 to infect healthy people, it is extremely important to explore and understand the detailed mechanisms of virus spread through airborne expiratory droplets. To reduce the risk of exposure to viral respiratory diseases, the World Health Organization recommends main measures, namely hand hygiene, social distancing, and wearing masks. Among the recommended measures, there is a hot debate about social distancing related to the exposure risk, especially in indoor environments. Through expiratory activities, airborne virus-laden droplets may spread over long distances, such as tens of meters in indoor environments, and remain in the air for a long time, making it an important route of exposure. Unfortunately, the scientific evidence on many public health policies regarding social distancing is still fragmentary. The public has only a rudimentary understanding of airborne transmission of viral respiratory diseases and proper social distancing. To address the concern of “whether the usual social distance is sufficient to avoid airborne infection of expiratory droplets in indoor environments”, this project uses systematic, multidisciplinary experimental, theoretical and modelling approaches. The spatiotemporal variations of size distributions, velocity vector fields and airborne dynamics of expiratory droplets generated from people infected with Influenza A or B, and the quantities of influenza virus at different distances from the test subjects are firstly measured using a suite of the state-of-the-art instruments and methods. Bacteriophage phi 6 is then used as a surrogate of coronavirus and other human pathogenic enveloped viruses to investigate the survivability and number of viruses in size-resolved droplets at different time and locations from the release point under different environmental conditions (e.g. temperature and relative humidity) with the aid of cultivation method and RT-qPCR technique. The outcomes of the project are the knowledge necessary to determine proper social distancing in various indoor environments, which will contribute to the control of respiratory infectious diseases.

Speaker: Hai Guo (Hong Kong Polytechnic University)

12:00 PM → 12:30 PM Discussion panel

Moderators: Richard Corsi and Luca Fontana - Panelists: speakers of session 3a and session 3b

12:30 PM → 1:30 PM Lunch

1:30 PM → 2:30 PM SESSION 4a - Mathematical Modeling and Risk Assessment, Keynote Speakers

Moderators: Allen Haddrell and Prashant Kumar

1:30 PM Building Performance Standards & Risk Assessment Tools: Perspectives from Facilities Management

Speaker: Alexander Mikszewski (Queensland University of Technology)

2:00 PM Modelling Natural Processes: A Multidisciplinary Advantage or Burden

Speaker: Andre Henriques (Conseil Européen pour la Recherche Nucléaire (CERN))

2:30 PM → 3:00 PM Coffee Break

3:00 PM → 4:00 PM SESSION 4b - Mathematical Modeling and Risk Assessment, Oral Presentations

Moderators: Allen Haddrell and Prashant Kumar

3:00 PM Dynamics of Airborne Epidemics Are Strongly Determined by Heterogeneity in Ventilation: Insights from Hybrid Air-Dynamic Disease Models

Background: While the areas of study of indoor air and infectious disease epidemiology both emphasize the use of modeling for understanding disease transmission systems, siloing of disciplines, different model assumptions, and different vocabulary have limited the emergence of transdisciplinary science around airborne infectious diseases. Here we show that integration of simple air and epidemic models provides useful and policy-relevant insights that can be used to protect population health.

Methods: The Wells-Riley (WR) model is a simple, widely used model for estimation of cross-sectional risk of transmission of infection from an infectious case. The Reed-Frost (RF) model is a disease transmission model used to simulate transmission over time as a discrete process in relatively small populations. Both models treat infection transmission as a binomial process, which allows hybridization whereby WR is used as the RF transmission coefficient (a “WRRF” model). We simulate disease dynamics for a disease similar to Wuhan-variant SARS-CoV-2 which dominated in the early months of the recent pandemic. Cases may either be a minority “aerosolizers”, who are highly infective in poorly ventilated environments, or “non-aerosolizers”, who are less infectious but equally infective in all environments, regardless of ventilation efficiency. We used a meta-population structure and modeled transmission both within and between three sub-populations with poor, intermediate, and good ventilation respectively. We performed both deterministic and stochastic model runs with the initial outbreak seeded with an “aerosolizer” in one of the three linked populations.

Results: Final total outbreak size was strongly influenced by which sub-population was seeded with the first case; final outbreak size was approximately 3-fold larger when initial seeding occurred in the poorly ventilated sub-population than when seeded in better-ventilated subpopulations due to large initial case numbers. For outbreaks seeded in the poorly ventilated population, improvement in ventilation in that population slowed epidemic emergence in the other two subpopulations more effectively than further improvements in ventilation in already well-ventilated environments. In stochastic model runs, the probability of stochastic extinction was inversely related to ventilation rate in the population in which the initial case was seeded.

Conclusions: Ventilation can easily be incorporated into epidemic models, and evaluation of heterogeneity in ventilation provides important insights into the dynamics of emerging infectious diseases. In particular, outbreak size, rapidity of spread between populations, and the likelihood of stochastic extinction in the population as a whole are driven by ventilation quality in the worst-ventilated environments. This supports the importance of universal ventilation standards as an important element of population health protection.

Speaker: David Fisman (University of Toronto)

3:15 PM The role of numerical modeling in improving indoor air quality

The COVID-19 pandemic significantly contributed to deepen our understanding of respiratory virus transmission, emphasizing the critical role of indoor environments and the necessity of effective ventilation. Historically, public health guidelines primarily addressed large droplet as transmission routes. It was not until the spring of 2021, due to the increasing scientific evidence, that major health organizations like the US CDC and WHO recognized airborne transmission as the predominant pathway for SARS-CoV-2. Environmental measures to disinfect and clean surfaces in public and semi-public places did not significantly reduce the spread of COVID-19. In contrast, the cancellation of small gatherings and the closure of educational institutions, i.e., activities characterized by high crowding in poorly ventilated indoor environments, had a significant impact on reducing the spread of the virus.
This shift underscored the importance of managing indoor air quality through improved ventilation and air cleaning strategies. Numerical modelling, from zero-dimensional (0D) to complex three dimensional (3D) Computational Fluid Dynamics (CFD) techniques, have proven essential in optimizing HVAC systems and designing effective airflow patterns to ensure safety and comfort in confined spaces. This work presents mathematical and numerical modelling activities conducted in various indoor environments, contributing to a better understanding of pollutant and viral aerosol transmission, with a particular emphasis on validating the results obtained.
The transmission of respiratory viruses occurs through three routes: large respiratory particles (spray) transmission, inhalation of airborne respiratory particles, and touch transmission. Historically, public health guidelines underestimated airborne transmission, but the pandemic highlighted its significance. Enhanced ventilation and air cleaning strategies, supported by numerical modeling, particularly CFD, are crucial for mitigating airborne transmission. In fact, CFD provides detailed insights into velocity, pressure, and temperature fields, as well as particle distribution, enabling the optimization of HVAC systems and airflow patterns in confined spaces.
This study employs a Eulerian-Lagrangian approach to model the dispersion of virus-laden respiratory particles in indoor environments. The model tracks individual particles using a force balance equation, considering forces such as drag, gravity, and virtual mass. The particle number emission rate (ERN) and volume distributions were estimated based on experimental data, focusing on airborne respiratory particles (<90 µm). The model was validated through experimental measurements, including Particle Image Velocimetry (PIV), and applied to various indoor settings, such as close-contact interactions, car cabins, and university lecture rooms.
CFD simulations demonstrated that large respiratory particles (>100 µm) significantly contribute to infection risk at distances less than 0.6 meters, while airborne respiratory particles dominate at greater distances. In car cabins, airflow patterns significantly influenced the spatial distribution of virus-laden particles, with higher exposure risks for passengers sitting behind an infected driver. In lecture rooms, the air change rate (ACH) alone was insufficient to assess exposure risk; local airflow patterns and the asymmetric disposition of seats relative to diffusers and exhaust grilles played crucial roles.

Speaker: Fausto Arpino (Università degli Studi di Cassino e del Lazio Meridionale)

3:30 PM Studying performance of mobile air cleaning devices in classrooms: a pilot study comparing two passive bio-aerosol sampling methods

Introduction:
Application of mobile air cleaning devices (MACs) in schools has been put forward as a potential control measure to limit and/or prevent respiratory virus outbreaks through reduction of viral concentrations in air. However, evidence on the effectiveness of air cleaning technologies on viral levels in general, and in schools specifically is lacking. Exploring airborne viral exposure levels is a challenging task which is further complicated by the realities of sampling in active and dynamic classrooms. .Therefore, we compared applicability of two passive bio-aerosol sampling methods in a pilot study on performance of air cleaning devices.
Methods:
Five Dutch primary schools were enrolled in a randomized cross-over study during October till end December 2023. The study included 45 classrooms equipped with three different types of MACs and included 15 control classrooms with no MACs installed. MACS were operational for three weeks and switched off for three weeks during the study period. In each classroom bio-aerosol air samples were passively collected during each of these three week periods. A regular sized electrostatic dustfall collector (EDC) and a smaller electrostatic cloth in a petridish (miniEDC) were applied. Both sample types were placed side by side into a box hung 30cm below the ceiling of the classroom. Human viruses (respiratory syncytial virus A (RSV A), influenza A and B) and bacterial markers representing various origin niches were determined by qPCR. The latter included total bacteria (16S rRNA), S. salivarius (oral), S. aureus (skin and upper respiratory tract), M. catarrhalis (upper respiratory tract) and S. epidermidis (skin). Differences in microbial levels between EDC and miniEDC, and associations between microbial levels and operational status of MACs (for classrooms equipped with MACs) or sampling order (for control classrooms) were explored.
Results:
Levels of viral and bacterial markers were generally low, often below the limit of quantification of the respective qPCRs, except for total bacteria which was measurable and quantifiable in all in EDC and miniEDC samples. Total bacterial (16SrRNA) yield was higher for EDCs than miniEDCs. Of the viral markers influenza A and B were not detected in any of the samples, whereas RSV A was detected in 60% and 65% of EDC and miniEDC samples, respectively. Detection levels of S. salivarius, S. epidermidis, S. aureus and M. catarrhalis ranged between 60-90% for EDC and between 40-80% for mini EDC samples, showing generally higher probability of detection in EDC samples. A trend of lower bacterial and viral detection was observed with MACs on compared to with MACs off. While these findings suggest a potential reduction in microbial load, the statistical significance of the observed differences remains uncertain due to the limited sample size. Also, detection of bacterial and viral markers in control classrooms varied between sampling periods.
Conclusion:
MiniEDCs take up less space and are more easy to handle in the laboratory, but showed to be less sensitive than regular EDCs. Passive bio-aerosol sampling with EDCs can be a useful tool to study the impact of MACs on microbial levels in future large-scale studies, as they are cost effective and easily implemented. Natural variation of bacterial and viral levels over time should be taken into consideration when designing such a study, favoring a randomized controlled trial with classroom as the randomization unit.

Speaker: Inge Wouters (Utrecht University)

3:45 PM Indoor air quality assessment through relationships between fungal and bacterial loads and physical parameters in primary school classrooms in Montevideo, Uruguay

Exposure to bacteria and fungi in enclosed spaces for long periods of time has been associated with adverse health effects. Airborne fungi can cause lung disease and irritation of the mucous membrane and airborne bacteria are possible catalysts for conditions such as asthma, rhinitis and bronchitis. The issue of healthy educational buildings is a global concern because children are particularly at risk not only of lung damage and infection but also present a decreased cognitive performance and reduced productivity caused by poor indoor air quality (IAQ). In this study, the relationships between bacterial and fungal loads and physical parameters are sought in order to have a better understanding and offer alternatives that improve the IAQ in classrooms.

Four bacterial and fungal culture campaigns were conducted in 11 classrooms distributed in four schools in a humid subtropical climate zone like Montevideo, Uruguay during 2023-2024. Environmental parameters (outdoor temperature, relative humidity, season), ventilation and comfort parameters (indoor CO2, temperature and humidity, fungal and bacterial cultures) and other parameters (occupancy, open windows and doors, air-conditioning operation, buildings, among others) were taken during biological data collection periods. Microbiological sampling was carried out biannually (winter and spring), using air filtration by CAPTUS system (AravanLabs). The CFU (colony-forming unit) count for both fungi and bacteria was performed on samples taken from five classrooms across two different school shifts.

The Spearman correlation matrix, along with the Mann-Whitney and Kruskal-Wallis tests, were used to assess the correlation between bacterial and fungal loads and physical parameters.

There were significant correlations between bacterial loads and mean CO2 (r = 0.30, p < 0.03), and mean outside temperature (r = -0.27, p < 0.05) values. A significant difference was found between the bacterial count and a CO2 value of 800 ppm (U = 196.0, p = 0.016), reported by Morawska et al. 2024 as a threshold to maintain a low infection risk under standard classroom conditions. There is an increase in the average bacterial count of 56% in the winter season while only an increase of 9% is observed in the average fungal count compared to the values reported in spring. No significant differences were found between the biological counts and parameters such as building, season, and schedule (morning/afternoon) based on the Kruskal-Wallis test (p>0.05). Results highlight the importance of continuous monitoring of CO2, temperature, and relative humidity in schools as a simple yet effective mechanism that can be used to make various decisions that promote better IAQ in classrooms.

Speaker: Dr Paola Scavone (Department of Microbiology, Instituto de Investigaciones Biológicas Clemente Estable, MEC, Montevideo, Uruguay)

4:00 PM → 4:30 PM Discussion panel

Moderators: Allen Haddrell and Prashant Kumar - Panelists: speakers of session 4a and session 4b

4:30 PM → 6:00 PM POSTER SESSION: Posters & Exhibitors social hour: Networking with drinks and researchers

Poster Session and Reception

Thu, May 8

8:45 AM → 11:00 AM SESSION 5a - Way Forward, Keynote Speakers

Introduction: Luca Fontana
Moderators: Alice Simniceanu and Paula Olsiewski

8:45 AM Setting the Stage for the Final Session -

Luca Fontana

9:00 AM Translating scientific knowledge into policies that ensure clean indoor air

Speaker: Lidia Morawska (Queensland University of Technology)

9:30 AM Indoor Airborne Pathogen Transmission and Mitigation, a Multidisciplinary Review, Remaining Gaps and Actionable Improvements

Improving indoor air quality (IAQ) can result in a range of measurable health benefits, including reduction of infectious disease risks, and cognitive performance improvements. Using engineering controls to minimize the indoor transmission of airborne pathogens saves lives and improves health cost-effectively. Despite a strong evidence base, gaps remain in understanding disease transmission. To understand these gaps, the Johns Hopkins Center for Health Security (CHS) recently convened an interdisciplinary group of experts, including engineers, public health specialists, and policymakers.

We assessed pathogen transmission mechanisms across engineering and health sciences considering how pathogens are emitted from different parts of the respiratory tract and how many pathogens are emitted in this way; how pathogens are transmitted from one person to another in the air; how long pathogens may remain infectious in the air; the quantity of pathogens produced; and the relationship between exposure dose and the likelihood of infection. Addressing knowledge gaps and how they inform practices is important for future advances in IAQ engineering interventions to reduce disease transmission.

Our convening resulted in several key findings: (1) While increasing air changes per hour and improving filtration can reduce disease transmission, these interventions alone may be insufficient, particularly for close-proximity transmission; (2) Layered interventions combining multiple strategies show promise but require further study; (3) Current mathematical models of airborne disease transmission face limitations and could benefit from further integration of biological, physical, and epidemiological factors; (4) Far-UVC technology shows potential as a safe air disinfection method but requires additional research regarding ozone generation and other air quality impacts; (5) Personal air filtration devices demonstrate early promise in computational fluid dynamics studies.

This research highlights the critical need for breaking down disciplinary silos to advance our understanding of indoor airborne pathogen transmission. We identified specific knowledge gaps that require interdisciplinary collaboration, particularly in understanding the complex interactions between pathogen biology, physical transmission mechanisms, and building systems. Future research should focus on developing integrated approaches that combine expertise from multiple disciplines to create more effective, evidence-based interventions for improving indoor air quality and reducing disease transmission. This work provides a foundation for future collaborative research efforts and highlights the importance of considering both engineering and health perspectives in developing practical solutions for indoor air quality challenges.

We provide actionable insights for policymakers and building designers, offering a roadmap to implement cost-effective, evidence-based strategies that enhance indoor air quality, reduce disease transmission, and improve public health outcomes.

Speaker: Gigi Gronvall (Johns Hopkins Center for Health Security)

10:00 AM Application to building policy, what is missing, needed to improve/implement and next steps

Speaker: Walt Vernon (Mazzetti)

10:30 AM Safe and scalable care in the context of respiratory pathogens

Speaker: Janet Diaz

11:00 AM → 11:30 AM Coffee Break

11:30 AM → 12:30 PM SESSION 5b - Way Forward, Keynote Speakers

Moderators: Alice Simniceanu and Paula Olsiewski

11:30 AM Public Empowerment in a Time of Crisis: The Effectiveness of Do-It-Yourself Air Cleaners

Speaker: Richard Corsi (University of California, Davis)

12:00 PM Data gaps, the precautionary principle, and the tragic consequences of type-II errors

Speaker: Donald Milton (University of Maryland)

12:30 PM → 1:30 PM Discussion panel & closing remarks

Moderators: Alice Simniceanu and - Panelists: speakers of session 5a and session 5b
Closing remarks: Luca Fontana, CERN, Giorgio Buonanno