Optical Particle Counter Research Articles

Measurements and calculations of enhanced side- and back-scattering of visible radiation by black carbon aggregates

Abstract. Aerosol particles have both natural and anthropogenic origins and are ubiquitous in the atmosphere. One particularly important type is carbonaceous aerosol, including a specific subset often termed “elemental carbon” chemically or “black carbon” (BC) radiatively. Carbonaceous aerosol particles have implications for atmospheric chemistry, human health, and climate, both directly and via their ability to act as sites of cloud droplet or ice crystal formation. Laboratory experiments and theory are needed to better understand these particles, specifically their radiative impact. Here we present laboratory measurements of scattering of visible radiation by analogs of atmospheric BC aggregates at scattering angles of 135±20∘ obtained using a depolarizing optical particle counter and accompanying theoretical calculations of scattering by compact and fractal theoretical BC aggregates. We show that, with random orientation, the theoretical calculations reproduce the qualitative behavior of the measurements but are unable to reproduce the highest values of the linear depolarization ratio; we are only able to obtain high values of the linear depolarization ratio using fixed orientation. Both our measurements and our theoretical calculations point to the possibility that fresh, unaged, bare, or uncoated BC aggregates, as opposed to the aged or coated BC or soot that was investigated in previous studies, can exhibit a higher back-scattering linear depolarization than previously assumed.

Comparison of virus aerosol concentrations across a face shield worn on a healthcare personnel during a simulated patient cough.

Patients diagnosed with coronavirus disease 2019 (COVID-19) aerosolize severe acute respiratory coronavirus virus 2 (SARS-CoV-2) via respiratory efforts, expose, and possibly infect healthcare personnel (HCP). To prevent transmission of SARS-CoV-2 HCP have been required to wear personal protective equipment (PPE) during patient care. Early in the COVID-19 pandemic, face shields were used as an approach to control HCP exposure to SARS-CoV-2, including eye protection. An MS2 bacteriophage was used as a surrogate for SARS-CoV-2 and was aerosolized using a coughing machine. A simulated HCP wearing a disposable plastic face shield was placed 0.41 m (16 inches) away from the coughing machine. The aerosolized virus was sampled using SKC biosamplers on the inside (near the mouth of the simulated HCP) and the outside of the face shield. The aerosolized virus collected by the SKC Biosampler was analyzed using a viability assay. Optical particle counters (OPCs) were placed next to the biosamplers to measure the particle concentration. There was a statistically significant reduction (P < .0006) in viable virus concentration on the inside of the face shield compared to the outside of the face shield. The particle concentration was significantly lower on the inside of the face shield compared to the outside of the face shield for 12 of the 16 particle sizes measured (P < .05). Reductions in virus and particle concentrations were observed on the inside of the face shield; however, viable virus was measured on the inside of the face shield, in the breathing zone of the HCP. Therefore, other exposure control methods need to be used to prevent transmission from virus aerosol.

Occupational exposure to nanomaterials and biomarkers in exhaled air and urine: Insights from the NanoExplore international cohort

The current evidence on nanomaterial toxicity is mostly derived from experimental studies making it challenging to translate it into human health risks. We established an international cohort (N = 141 workers) within the EU-LIFE project “NanoExplore” to address possible health effects from occupational exposures to nanomaterials. We used a handheld direct-reading optical particle counter to measure airborne nanoparticle number concentrations (PNC) and lung-deposited surface areas (LDSAs). Airborne particles were characterized by TEM and SEM-EDAX. We assessed oxidative/nitrosative stress with a panel of biomarkers in exhaled breath condensate (EBC) (8-isoprostane, malondialdehyde, nitrotyrosine), inflammation (high-sensitivity C reactive protein (hs-CRP), IL-1β, TNF-α, IL-10) and KL-6 (considered as biomarker of interstitial lung fibrosis) and urine (total antioxidant power (TAP), 8-isoprostane, and malondialdehyde). Exhaled breath sampled in gas-sampling bags were assessed for oxidative potential. These biomarkers were quantified pre-shift at the beginning of the workweek and post-shift the 4th day. Relationships between airborne nanoparticle concentration and biomarkers were assessed by multiple linear regression with log-transformed exposure and biomarker concentrations adjusted for potential confounders. We found a positive dose–response relationship for three inflammation biomarkers (IL-10, IL-1β and TNF-α) in EBC with both PNC and LDSA. A negative dose–response relationship was observed between PNC and TAP. This study suggests that occupational exposures to nanoparticles can affect the oxidative balance and the innate immunity in occupationally exposed workers. However, owing to the intrinsic variability of biomarkers, the observed changes along with their health significance should be assessed in a long-term perspective study.

Machine learning methods for low-cost pollen monitoring – Model optimisation and interpretability

Pollen is a major issue globally, causing as much as 40 % of the population to suffer from hay fever and other allergic conditions. Current techniques for monitoring pollen are either laborious and slow, or expensive, thus alternative methods are needed to provide timely and more localised information on airborne pollen concentrations. We have demonstrated previously that low-cost Optical Particle Counter (OPC) sensors can be used to estimate pollen concentrations when machine learning methods are used to process the data and learn the relationships between OPC output data and conventionally measured pollen concentrations.This study demonstrates how methodical hyperparameter tuning can be employed to significantly improve model performance. We present the results of a range of models based on tuned hyperparameter configurations trained to predict Poaceae (Barnhart), Quercus (L.), Betula (L.), Pinus (L.) and total pollen concentrations. The results achieved here are a significant improvement on results we previously reported: the average R2 scores for the total pollen models have at least doubled compared to using previous parameter settings.Furthermore, we employ the explainable Artificial Intelligence (XAI) technique, SHAP, to interpret the models and understand how each of the input features (i.e. particle sizes) affect the estimated output concentration for each pollen type. In particular, we found that Quercus pollen has a strong positive correlation with particles of optical diameter 1.7–2.3 μm, which distinguishes it from other pollen types such as Poaceae and may suggest that type-specific subpollen particles are present in this size range.There is much further work to be done, especially in training and testing models on data obtained across different environments to evaluate the extent of generalisability. Nevertheless, this work demonstrates the potential this method can offer for low-cost monitoring of pollen and the valuable insight we can gain from what the model has learned.

Characterization of Particle Size Distributions and Water-Soluble Ions in Particulate Matter Measured at a Broiler Farm

The chemical composition and size distribution of particulate matter produced at broiler poultry houses is not well understood, so this is a novel study to understand the particulate size distributions at a poultry house as well as the ionic composition of the particulate matter using real-time methods. Two optical particle counters provided particle size distributions inside and outside the house. An ambient ion monitor and a particle-in-liquid sampler analyzed the ionic chemical composition of the particulate matter in the house while a scanning mobility particle sizer provided size information in the nanoparticle range. Ammonia concentrations in the house were measured using a chemical sensor. Ammonia concentrations in the house were consistently in the lower part of the per million range 2–20 ppm. The optical particle counter and ion chromatography measurements both showed a strong diurnal variation of particulate matter concentration in the house throughout the study, associated with the lights being on and animal activity. Particulate mass concentration inside the house was dominated by coarse mode particles as opposed to the outdoor sampler which showed much smaller sizes. A few new particle formation and growth events were observed in the house. Ionic constituents detected by chromatography made up a small fraction of the overall mass concentration. The composition of the ionic constituents was similar for most of the study with typical ions being ammonium, sodium, potassium, chloride, sulfate, nitrate, nitrite, phosphate, and several carboxylates (formate, acetate, propionate, and butyrate.) At the end of the study, bromide was also detected during the last several days. Overall, we determined that the ionic components of the particulate matter formed through secondary particle formation was small, but also that some ionic constituents can be associated with management practices.

Gaussian optics optimization of an optical particle counter for measurement in high-pressure gas.

An optimization model for the parameters of the pressure-resistant lens of an optical particle counter, based on Gaussian optics theory, was established to increase the measurement accuracy of the counter for high-pressure natural gas. Comparing the experimental and calculated values of the calibrated model, when the pressure-resistant lens is displaced by 2mm under atmospheric pressure, the relative error of the measured body deformation is 0.15%. When the air pressure varies in the range 0.10-5.09MPa, the maximum relative error of optical measurement volume deformation with the change of refractive index is 0.13%, which shows that the model has high reliability and accuracy.

A newly developed dilution system for optical particle size and concentration measurements in oil-injected screw compressors

Oil mist coalescence separators are widely used downstream of screw compressors. Unfortunately, due to high concentration most of the available literature reporting particle sizes in raw or clean gas of screw compressors is on model systems at atmospheric pressure and room temperature. To study oil mist coalescence separators under real-world conditions, the pressurized aerosol needs to be diluted.In this work, two newly developed isobaric and isothermal dilution systems for particle size measurements using an optical particle counter (200 nm–10 µm) in the application scenario are presented. For both systems, one a single-stage and the other a triple-stage system, transfer functions were determined in the laboratory using a pressurized oil atomizer.As a proof of concept, the triple-stage dilution system was used on a compressor test bench to study the influence of operating conditions (varying pressure and volume flow) on the particle size distribution and concentration in raw and clean gas. Both raw and clean gas particle size distributions showed most particles in the size range below 500 nm. The achievable dilution factor of 1000 was sufficient for measuring the raw gas concentration.On a second compressor test bench, the single-stage dilution system was used to study the influence of different coalescence separators on clean gas particle size distribution and concentration. Three separators were used for experiments: one industry-typical reference separator, one with less layers, and one with a weakened entrainment separation fleece. As expected, the particle size distributions showed clear differences, i.e., higher penetration or increased entrainment.Copyright © 2023 American Association for Aerosol Research

Applicability of the low-cost OPC-N3 optical particle counter for microphysical measurements of fog

Abstract. Low-cost devices for particulate matter measurements are characterised by small dimensions and a light weight. This advantage makes them ideal for UAV measurements, where those parameters are crucial. However, they also have some issues. The values of particulate matter from low-cost optical particle counters can be biased by high ambient humidity. In this article, we evaluate the low-cost Alphasense OPC-N3 optical particle counter for measuring the microphysical properties of fog. This study aimed to show that OPC-N3 not only registers aerosols or humidified aerosols but also registers fog droplets. The study was carried out on the rooftop of the Institute of Geophysics, University of Warsaw, Poland, during autumn–winter 2021. To validate the results, the data from OPC-N3 were compared with the data obtained from the reference instrument, the Oxford Lasers VisiSize D30. VisiSize D30 is a shadowgraph device able to register photos of individual droplets. Considering the effective radius of droplets, it is possible to differentiate low-visibility situations between fog conditions (which are not hazardous for people) from haze events, when highly polluted air can cause health risks to people. The compared microphysical properties were liquid water content (LWC), number concentration (Nc), effective radius reff and statistical moments of radius. The Pearson correlation coefficient between both devices for LWC was 0.92, Nc was 0.95 and reff was 0.63. Overall, these results suggest good compliance between instruments. However, the OPC-N3 has to be corrected regarding professional equipment.

126 A Laboratory Procedure and a Recording System for the Maintenance of Personal, Hand-Held and Benchtop Time-Resolved Aerosol Instruments

Abstract The HSE Science and Research Centre use time-resolved instruments to collect aerosol data for research and to support the sampling of aerosols in workplace environments. The performance of these instruments (traditional and low cost sensor devices) is dependent on regular maintenance and calibration. However, it can deteriorate within the recommended manufacturer calibration period, particularly if they have been exposed to high concentration of dust, or exposed for extended periods. This poster will describe the practical strategy developed at HSE for the maintenance of time-resolved devices and the lessons learnt. HSE owns a range of hand-held or compact time-resolved instruments, which are optical particle counters (OPCs), condensation particle counters (CPCs), diffusion chargers as well as photometers measuring particle number, surface area and mass concentrations. Some of the instruments are size-resolved devices. Photometers and OPCs were benchmarked using SPHERIGLASS ® A- 5000 in a calm-air chamber for a wide range of concentrations against a dedicated reference photometer or OPC, not necessarily of the same model or size range characteristic. For devices, measuring in the nanometre size range (CPCs and Diffusion Chargers), a salt nanoparticle aerosol was generated using a Collison nebulizer and a CPC used as the reference. Acceptable tolerances from the reference concentration were established for the CPCs and Diffusion Chargers. For each photometer model, an average ratio of the evaluated photometers concentrations by the reference photometers concentrations was calculated and a linearity plot of the photometer concentration versus the reference photometer concentration was established. © Crown Copyright (2022)

124 Laboratory Evaluation of Low-Cost Optical Particle Counters for Occupational Respirable Exposure Measurements

Abstract Direct-reading, time-resolved devices, such as optical particle counters (OPCs) and photometers, offer a unique insight into the temporal and spatial distribution of airborne particles. They can provide a comprehensive picture of changes in concentration of airborne particles in occupational settings and therefore can be used to investigate failures in engineering control systems as well as identify exposures driven by working procedures and methods. In recent years, new developments have led to the commercialisation of low- cost optical-based sensors, which provide particle matter (PM) mass concentrations including PM2.5 and PM10 for environmental monitoring. TNO, NIOSH, and HSE are investigating their application to occupational settings with the aim to produce guidelines for calibration and use. This study evaluated the performance and accuracy of six commercially available low-cost sensors (Airbeam 2, Airveda, Omni Awair, OPC-N3, OPC-R1 and PATS+), in calm air test chambers, against reference devices including an Aerodynamic Particle Sizer (APS 3320), GK2.69 respirable cyclones, and pDR-1500 photometers. Several factors were considered: type of dust (particles having different size distribution, shape and refractive index), within- and between-device variations and exposure pattern (peak and constant concentrations). The devices were subjected to relatively high respirable concentrations (greater than 1 mg/m3) in addition to low concentrations. This presentation will present the results of the laboratory testing with particular focus on their accuracy, response, and calibration for quantitative exposure measurements. The low-cost sensor devices are also being deployed in the workplace for further evaluation and practicality of use.

39 Investigation of Workplace Silica Exposures Using Novel Samplers and Methods

Abstract Scientists from the Health and Safety Executive visited a range of workplaces where there was the potential for exposure to silica. The aim of the visits was to determine potential worker exposures to dust and respirable crystalline silica by static air monitoring and exhaled breath condensate (EBC). To evaluate potential airborne exposures low-cost particle monitors were deployed alongside more established scientific equipment. On site airborne dust concentrations were measured at different locations using two photometers, an optical particle counter (OPC) and a respirable cyclone. The size distribution was measured in real-time using a low-cost OPC and by offline analysis of a polycarbonate membrane filter housed inside an inhalable sampler using a Coulter Counter III. Pre and post shift samples of EBC were taken from 29 workers, with samples analysed by single particle inductively coupled plasma tandem mass spectrometry to measure Si-containing particles. The real-time air monitoring data showed sustained increased concentrations or peaks corresponding to specific areas or activities, therefore indicating the tasks and/or locations most likely to contribute to worker exposure. The low-cost instruments were also effective in highlighting site locations and tasks most likely to contribute to worker exposure. An approach combining multiple sampling techniques provided a good characterisation of airborne, silica containing dusts. The EBC results consistently showed increased numbers of silicon containing particles post-shift compared with pre-shift.

106 Investigation of Workplace Silica Exposures Using Novel Samplers and Methods

Abstract Scientists from the Health and Safety Executive visited a manufacturing workplace where coatings are prepared by loading powders, frit and water into various sized mills. The aim of the visit was to determine potential worker exposures to dust and respirable crystalline silica by static air monitoring and exhaled breath condensate. Low-cost particle monitors were deployed alongside more established scientific equipment. Airborne dust concentrations were measured at three site locations using two photometers, an optical particle counter (OPC) and a respirable cyclone. The size distribution was measured in real-time using a low-cost OPC and by offline analysis of a polycarbonate membrane filter housed inside an inhalable sampler. Pre and post shift samples of exhaled breath condensate were collected from 6 workers, with samples analysed by single particle inductively coupled plasma mass spectrometry to measure the number and size of silicon containing particles present. The real-time air monitoring data at all three locations showed peaks in airborne concentrations corresponding to the loading activities and indicating the tasks most likely to contribute to worker exposure. The average concentration of respirable dust measured closest to the process was 0.13 mg.m-3 for the 8-hour shift. The low-cost monitors provided good information about the changes in concentration over time relating to worker activities.

94 Reducing Exposure to Respirable Crystalline Silica in the Construction and Minerals Industry by Using Wearable Real Time Respirable Dust Monitors

Abstract Real time monitoring of respirable dust (as a surrogate for RCS) opens the opportunity to warn workers when entering work areas with increased dust levels to provide them the information to fit RPE properly or exit the area. However in the past, the adoption of such monitoring approaches has been limited due to the bulkiness and price of devices. This paper reflects on how the miniaturisation of Optical Particle Counters has enabled light weight (&amp;lt;150g) wearable devices to be developed which are convenient for workers in the construction and minerals industry to wear on all working days. It provides an overview of the Optical particle counter. its performance in measuring respirable dust and how it has been integrated into a battery powered ' DustCanary; wearable device. Due to its size and convenience the DustCanary provides protection to both those at first line risk due to the areas they work (eg stone cutters, plant operatives) who by wearing such can devices can help identify changes in performance of Local Exhaust Ventilation (LEV). or controls so that remedial action can be taken secondary risk on a plant who are not necessarily wearing RPE (such as delivery drivers) who can be warned when they enter an area where there are elevated respirable dust levels Case study data and examples will be shared.

Development and evaluation of an online monitoring single-particle optical particle counter with polarization detection

We developed a single-particle optical particle counter with polarization detection (SOPC) for the real-time measurement of the optical size and depolarization ratio (defined as the ratio of the vertical component to the parallel component of backward scattering) of atmospheric particles, the polarization ratio (DR) value can reflect the irregularity of the particles. The SOPC can detect aerosol particles with size larger than 500 nm and the maximum particle count rate reaches ∼1.8 × 105 particles per liter. The SOPC uses a modulated polarization laser to measure the optical size of particles according to forward scattering signal and the DR value of the particles by backward S and P signal components. The sampling rate of the SOPC was 106 #/(sec·channel), and all the raw data were processed online. The calibration curve was obtained by polystyrene latex spheres with sizes of 0.5-10 µm, and the average relative deviation of measurement was 3.96% for sub 3 µm particles. T-matrix method calculations showed that the DR value of backscatter light at 120° could describe the variations in the aspect ratio of particles in the above size range. We performed insitu observations for the evaluation of the SOPC, the mass concentration constructed by the SOPC showed good agreement with the PM2.5 measurements in a nearby state-controlled monitoring site. This instrument could provide useful data for source appointment and regulations against air pollution.

The effect of portable air-purifiers in improving indoor air quality in pediatric intensive care units at two tertiary hospitals in Riyadh, Saudi Arabia

Background: A set of environmental preventive measures involving ventilation control within healthcare facilities is well established. Portable air purifiers have been introduced in recent years as one of alternative technologies used to prevent infection and other respiratory complications in indoor environment. Objective: To asses indoor air quality in pediatric intensive care units at two tertiary hospitals in Riyadh, Saudi Arabia in the presence and absence of portable air purifiers.Method: Fine particles (PM 2.5) and coarse particles (PM10) were obtained using optical particle counter and microbial counts were obtained using Andersen air sampler from outdoor and two patient rooms in pediatric intensive care units. Pollutants levels reduction between outdoor and indoor were calculated and compared using Statistical Package for the Social Sciences software (SPSS Version 27.0. Armonk, NY: IBM Corp) were utilized for statistical analysis. Results: In hospital A and B, non-protective environment room (NPE) had a significantly higher number of fine particles and total bacterial count (TBC) respectively than semi-protective environment room (SPE). Meanwhile, there was significantly higher reductions of fine particles (hospital A) and coarse particles, fine particles and TBC (hospital B) in SPE rooms compared with NPE room. Hospital-A had significantly higher reduction efficacy compared with matched rooms in hospital-B for fine particles, coarse particles, and TBC. Conclusion: This study demonstrated that portable air purifiers have a great impact in the reduction of indoor air pollutants in PICUs including fine particulate matters and TBC in particular. Furthermore, ventilation systems equipped with HEPA filters along with portable air purifiers significantly reduce the levels indoor air pollutants of outdoor sources. Moreover, this study showed that newer and well-maintained HVAC systems play a significant role in controlling the levels of airborne pollutants.

Evaluation of aerosols in a simulated orthodontic debanding procedure

Dental practitioners may be at risk for exposure to severe acute respiratory syndrome corona virus 2 when performing aerosol generating procedures. Though recent evidence suggests that coronavirus may be transmitted through aerosol generating procedures, it is unknown whether common procedures performed in dental clinics generate aerosol. The aim of this study was to simultaneously quantify airborne concentrations of the bacteriophage MS2 near the oral cavity of a dental mannequin and behind personal protective equipment (i.e., face shield) of the practitioner during a simulated orthodontic debanding procedure. A deband was performed eight times on a dental mannequin. Optical particle counters and SKC Biosamplers were used to measure particle concentration and to collect virus aerosol generated during the procedure, both near the oral cavity and behind the orthodontists face shield. A plaque assay was used to determine the viable virus airborne concentration. When comparing the two measuring locations, near the oral cavity and behind the clinician’s face shield, there was no statistically significant difference of virus concentrations or particle size distribution. This study suggests that debanding under these conditions generates live virus aerosol and a face shield does not provide increased protection from virus aerosol, but does provide some protection against splatter during the procedure.

Releasing high positive end-expiratory pressure to a low level generates a pronounced increase in particle flow from the airways

ObjectivesDetecting particle flow from the airways by a non-invasive analyzing technique might serve as an additional tool to monitor mechanical ventilation. In the present study, we used a customized particles in exhaled air (PExA) technique, which is an optical particle counter for the monitoring of particle flow in exhaled air. We studied particle flow while increasing and releasing positive end-expiratory pressure (PEEP). The aim of this study was to investigate the impact of different levels of PEEP on particle flow in exhaled air in an experimental setting. We hypothesized that gradually increasing PEEP will reduce the particle flow from the airways and releasing PEEP from a high level to a low level will result in increased particle flow.MethodsFive fully anesthetized domestic pigs received a gradual increase of PEEP from 5 cmH2O to a maximum of 25 cmH2O during volume-controlled ventilation. The particle count along with vital parameters and ventilator settings were collected continuously and measurements were taken after every increase in PEEP. The particle sizes measured were between 0.41 µm and 4.55 µm.ResultsA significant increase in particle count was seen going from all levels of PEEP to release of PEEP. At a PEEP level of 15 cmH2O, there was a median particle count of 282 (154–710) compared to release of PEEP to a level of 5 cmH2O which led to a median particle count of 3754 (2437–10,606) (p < 0.009). A decrease in blood pressure was seen from baseline to all levels of PEEP and significantly so at a PEEP level of 20 cmH2O.ConclusionsIn the present study, a significant increase in particle count was seen on releasing PEEP back to baseline compared to all levels of PEEP, while no changes were seen when gradually increasing PEEP. These findings further explore the significance of changes in particle flow and their part in pathophysiological processes within the lung.

Comparing Two Methods of Reducing Hospital Toilet Aerosols.

When flushed, uncovered hospital toilets have been shown to generate aerosols potentially containing bacteria, viruses, and hazardous drugs, which can be inhaled by healthcare workers and contaminate surfaces. Guidelines recommend placing a plastic-backed absorbent pad (PBP) over the toilet, although no studies have evaluated the effectiveness of this intervention. The purpose of this study was to evaluate the effectiveness of using a PBP versus the Splashblocker®, a solid, reusable engineering barrier control, to reduce post-flush aerosol particles. Aerosol measurements were taken with an optical particle counter in a bathroom testing chamber equipped with a commercial hospital toilet and flushometer valve. Three tests were performed at a height of 16 inches above the floor and 40 inches above the floor. Both the PBP and the Splashblocker significantly reduced the number of post-flush particles by more than 99% at 16 inches above the floor and 40 inches above the floor. The results indicate that both interventions are equally beneficial in reducing aerosols after flushing a hospital toilet.

Size distribution and relationship of airborne SARS-CoV-2 RNA to indoor aerosol in hospital ward environments

Aerosol particles proved to play a key role in airborne transmission of SARS-CoV-2 viruses. Therefore, their size-fractionated collection and analysis is invaluable. However, aerosol sampling in COVID departments is not straightforward, especially in the sub-500-nm size range. In this study, particle number concentrations were measured with high temporal resolution using an optical particle counter, and several 8 h daytime sample sets were collected simultaneously on gelatin filters with cascade impactors in two different hospital wards during both alpha and delta variants of concern periods. Due to the large number (152) of size-fractionated samples, SARS-CoV-2 RNA copies could be statistically analyzed over a wide range of aerosol particle diameters (70–10 µm). Our results revealed that SARS-CoV-2 RNA is most likely to exist in particles with 0.5–4 µm aerodynamic diameter, but also in ultrafine particles. Correlation analysis of particulate matter (PM) and RNA copies highlighted the importance of indoor medical activity. It was found that the daily maximum increment of PM mass concentration correlated the most with the number concentration of SARS-CoV-2 RNA in the corresponding size fractions. Our results suggest that particle resuspension from surrounding surfaces is an important source of SARS-CoV-2 RNA present in the air of hospital rooms.

Interaction of a droplet spray with a turbulent plane air jet impacting a wall: Application to the confinement of atmospheres contaminated with particles by air curtain.

Experiments are carried out to study the interaction of a spray of spherical micronic oil droplets with a turbulent plane air jet impacting a wall. The context is the separation of a contaminated atmosphere with passive particles from a clean atmosphere by using a dynamical air curtain. A spinning disk is used to produce the spray of oil droplets close to the air jet. The diameter of the produced droplets varies between 0.3 and m. The jet and particulate Reynolds numbers and the jet and Kolmogorov-Stokes numbers are, respectively, equal to Re , , and . The ratio of the jet height to nozzle width is . The flow properties in the experiments are measured by particle image velocimetry and are in good agreement with large eddy simulation results. The droplet/particle passing rate (PPR) through the air jet is measured by an optical particle counter. The PPR decreases with the increase in the droplet diameter for the studied droplet size range. Whatever the droplet size is, the PPR increases with time due to the presence of two large vortices on each side of the air jet that bring the droplets back to the jet. The accuracy and repeatability of the measurements are verified. The present results can be used to validate Eulerian/Lagrangian numerical simulations on the interaction of micronic droplets with a turbulent air jet.