Reduction In Particle Concentration Research Articles

Indoor Environmental Quality and Effectiveness of Portable Air Cleaners in Reducing Levels of Airborne Particles during Schools’ Reopening in the COVID-19 Pandemic

Educational buildings tend to fail in the contagion containment of airborne infectious diseases because of the high number of children, for several hours a day, inside enclosed environments that often have inadequate indoor air quality (IAQ) conditions. This study aimed to assess indoor environmental quality and test the effectiveness of portable air cleaners (PACs) in alleviating airborne particle levels in schools of Central–Southern Spain during the period of reopening after the lockdown due to the COVID-19 outbreak. To accomplish this, three sampling campaigns were organized from September to December 2020 to consistently monitor temperature and relative humidity, carbon dioxide, and particulate matter in nineteen classrooms (seven school buildings). Results showed that although the recommendation of maintaining the windows open throughout the day seemed to be effective in promoting, in general, proper ventilation conditions (based on CO2 levels). For the colder campaigns, this practice caused notorious thermal comfort impairment. In addition, a great number of the surveyed classrooms presented levels of PM2.5 and PM10, attributable to outdoor and indoor sources, which exceeded the current WHO guideline values. Moreover, considering the practice of having the windows opened, the installation of 1 unit of PACs per classroom was insufficient to ensure a reduction in particle concentration to safe levels. Importantly, it was also found that children of different ages at different education levels can be exposed to significantly different environmental conditions in their classrooms; thus, the corrective measures to employ in each individual educational setting should reflect the features and needs of the target space/building.

Impact of medical staff movement, airflow rate difference, and door leakage area on particle outflow in an airborne infection isolation room

Airborne Infection Isolation (AII) room are utilized to prevent the spread of infectious diseases such as the coronavirus disease 2019 (COVID-19) in 2020. However, the challenge of mitigating contaminant leaks from the AII room due to medical staff's entry still needs to be solved. This study aims to analyze the impact of airflow rate difference on contaminant outflow by conducting particle outflow experiments in a full-scale AII room chamber. The airflow rate difference was controlled by adjusting the pressure difference and door undercut height. Nine experimental cases were conducted, repeating five times for each case. Additionally, the Air Change Rate (ACR) in the AII room and the Equivalent Air Change Rate (EACR) in the anteroom were calculated using the concentration decay method to assess particle concentration reduction rate. The results indicate that the airflow rate difference did not significantly affect the particle outflow in this study. The particle concentration was 1.7–13.0 times higher when entering the AII room (“IN”) than when exiting the AII (“OUT”). During “IN”, the particle concentration at the upper part (1.5 m) was 1.3–3.8 times higher than at the lower part (0.5 m). In contrast, during “OUT”, the upper part concentration was 0.2–0.9 times the lower part. With increases in the airflow rate difference, the EACR of the anteroom increased. These findings underscore the importance of considering airflow rate difference, medical staff's entering and exiting, and vertical concentration difference to efficiently control contaminant outflow in the AII room.

Efficient preparation of high-purity and intact mesenchymal stem cell-derived extracellular vesicles.

Mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) have shown great promise for regeneration and immunomodulation. However, efficient and scalable methods for their preparation are still lacking. In this study, we present the adoption of a label-free technique known as "EXODUS" to isolate and purify MSC-EVs from the conditioned medium. Our findings indicate that EXODUS can rapidly isolate EVs from 10 mL of conditioned medium with a 5-fold higher yield compared to conventional approaches, including ultracentrifugation (UC) and polyethylene glycol precipitation (PEG) methods. Additionally, pre-storing the conditioned medium at 4°C for 1 week resulted in a ~2-fold higher yield of MSC-EVs compared to the freshly prepared medium. However, storing the purified EV particles at 4°C for 1 month led to a 2-fold reduction in particle concentration. Furthermore, we found that MSC-EVs isolated using EXODUS exhibit higher expression levels of EV markers such as Alix, Flotillin1, CD81, and TSG101 in comparison to PEG and UC methods. We also discovered that MSC-EVs isolated using EXODUS are enriched in response to cytokine, collagen-containing extracellular matrix, and calcium ion binding compared to PEG method and enriched in extracellular structure organization, extracellular matrix, and extracellular matrix structure constituents compared to UC. Finally, we demonstrated that MSC-EVs isolated using EXODUS exhibit greater potential in animal organ development, tissue development, and anatomical structure morphogenesis compared to the UC. These findings suggest that EXODUS is a suitable method for the large-scale preparation of high-quality MSC-EVs for various clinical applications.

Aerosol and surface contamination assessment of a novel ventilated infectious aerosol containment device.

Healthcare personnels (HCPs) are at risk of respiratory infectious diseases during patient care activities. HCPs rely primarily on personal protective equipment to prevent pathogen exposures, but there is a need to develop alternative, or complementary control strategies, including engineering controls. The objective of this study was to evaluate the ability of the 3 designs (denoted D1A, D1B, and D2) of the University of Utah Containment Ventilation for Exposure Reduction (U-COVER), a protective barrier enclosure device to contain respirable aerosols when placed over a simulated patient. The 2 primary performance metrics were the percent reduction in: (i) the concentration of respirable aerosols in the simulated breathing zone of an HCP, and (ii) surface contamination outside the device, which were tested using salt aerosols and fluorescein aerosols, respectively. Briefly, salt or fluorescein aerosols were generated as though expelled by a prone patient under 3 conditions: (i) no device (control), (ii) with the device but without exhaust ventilation, and (iii) with the device with exhaust ventilation. Device D2 was also tested under simulated use conditions, in which cardboard "arms" were placed inside the device ports. All 3 device designs showed the ability to reduce particle concentrations in the simulated HCP breathing zone and on surfaces by >99% with exhaust ventilation compared to the control condition. Without exhaust ventilation, device performance was lower and highly variable. Under simulated use conditions, device D2 reduced particle concentrations in the simulated HCP breathing zone by ≥91% and on surfaces by >99% relative to control for all combinations of "arms" tested. The U-COVER device demonstrates excellent aerosol containment and warrants further testing with dynamic simulated or actual use conditions.

The mechanism of viscosity reduction of waxy oils induced by the electric field: A correlation between the viscosity reduction and the charged particle accumulation on wax particles

Wax molecules crystallize at ambient temperature, causing the crude oil to become a dispersed system, which poses challenges in the flow assurance of pipelines. Improving the cold flowability of crude oil is the fundamental solution to tackle these problems. Applying an electric field to waxy oil may markedly improve its cold flowability. The adhesion of charged particles on wax particles’ surface under the electric field has been demonstrated as the essential mechanism of the electrorheological effect. However, the correlation between the accumulated charged particles and the induced viscosity reduction has not been explored quantitatively. In this study, the viscosity and impedance of four crude oils before and after electric treatment were measured. The conductivity changes of the oils’ continuous phase were obtained by an equivalent circuit model. And then, the charged particles’ concentration before and after electric treatment was calculated by the Stokes equation. The results showed there is a positive correlation between viscosity reduction and charged particle concentration reduction in the continuous phase. Importantly, this correlation is also quantitatively applicable to the results of ten different waxy oils which has been published. This study provides a quantitative basis for the mechanism of electrorheological behavior of waxy oils.

The effect of clinical face shields on aerosolized particle exposure.

Face shields protect healthcare workers (HCWs) from fluid and large droplet contamination. Their effect on smaller aerosolized particles is unknown. An ultrasonic atomizer was used to simulate particle sizes equivalent to human breathing and forceful cough. Particles were measured at positions correlating to anesthetic personnel in relation to a patient inside an operating theatre environment. The effect of the application of face shields on HCW exposure was measured. Significant reductions in particle concentrations were measured after the application of vented and enclosed face shields. Face shields appear to reduce the concentration of aerosolized particles that HCWs are exposed to, thereby potentially conferring further protection against exposure to aerosolized particles in an operating theatre environment.

Applying negative ions to reduce surgical smoke in operation room

Long-term exposure to surgical smoke generated from electrocautery can increase health risks for medical personnel. Surgical smoke contains high concentrations of nanoparticles (NP, diameter ≤200 nm) and particulate matters with diameter less than 2.5 μm (PM 2.5 ), which can cause respiratory illnesses in medical personnel. Currently, local exhaust ventilation (LEV) is often used to reduce particles levels. However, LEV generates extra noise and can be easily blocked by blood clots formed during surgery. In this study, we added an ionizer to an electrosurgical pencil to help increase NP removal efficiency and compared the removal efficiency with that of a smoke evacuation pencil. The experiments were performed in an animal surgical facility in which air change rate, relative humidity, and temperature were controlled. We measured the PM 2.5 and NP concentrations near the source and in the breathing zone. The ionizer alone, wall suction, smoke evacuation pencil, and wall suction plus ionizer reduce NP number concentrations by 80.1%, 84.5%, 90.3%, and 92.4%, respectively in the breathing zone. The respective reductions in PM 2.5 were 86.5%, 92.9%, 93.0%, and 97.2%. Similar PM 2.5 and NP removal efficiency was seen near the source. Wall suction plus ionizer shows the highest removal efficiency for NP and PM 2.5 , but the removal efficiency is not significantly higher ( p > 0.05) than the commercial smoke evacuation pencil and wall suction. Moreover, excess lifetime carcinogenic risk also decreased by 79.1%, 90.7%, 93.0%, and 95.6% for the negative ions (NI), wall suction, smoke evacuation pencil, and NI + wall suction, respectively. The newly developed surgical smoke removal devices help reduce particle concentrations and thus can help protect the health of medical personnel. • Negative ions can help reduce surgical smoke concentrations without generating additional noise. • Adding negative ions to wall suction proves to be the most efficient method for reducing the particle number and mass concentrations in surgical smoke. • Negative ions can be used in clinical practice or other workplaces that requires silence and efficient removal rates of nanoparticles.

Identification of Recombinant Chimpanzee Adenovirus C68 Degradation Products Detected by AEX-HPLC.

Physicochemical tests represent important tools for the analytical control strategy of biotherapeutics. For adenoviral modalities, anion-exchange high performance liquid chromatography (AEX-HPLC) represents an important methodology, as it is able to simultaneously provide information on viral particle concentration, product purity and surface charge in a high-throughput manner. During product development of an adenoviral-based therapeutic, an accelerated stability study was performed and showed changes in each of the AEX-HPLC reportable attributes. These changes also correlated with a decrease in product infectivity prompting a detailed characterization of the impurity and mechanism of the surface charge change. Characterization experiments identified the impurity to be free hexon trimer, suggesting that capsid degradation could be contributing to both the impurity and reduced particle concentration. Additional mass spectrometry characterization identified deamidation of specific hexon residues to be associated with the external surface charge modification observed upon thermal stress conditions. To demonstrate a causal relationship between deamidation and surface charge changes observed by AEX-HPLC, site-directed mutagenesis experiments were performed. Through this effort, it was concluded that deamidation of asparagine 414 was responsible for the surface charge alteration observed in the AEX-HPLC profile but was not associated with the reduction in infectivity. Overall, this manuscript details critical characterization efforts conducted to enable understanding of a pivotal physicochemical test for adenoviral based therapeutics.

Localized and Whole-Room Effects of Portable Air Filtration Units on Aerosol Particle Deposition and Concentration in a Classroom Environment.

In indoor environments with limited ventilation, recirculating portable air filtration (PAF) units may reduce COVID-19 infection risk via not only the direct aerosol route (i.e., inhalation) but also via an indirect aerosol route (i.e., contact with the surface where aerosol particles deposited). We systematically investigated the impact of PAF units in a mock classroom, as a supplement to background ventilation, on localized and whole-room surface deposition and particle concentration. Fluorescently tagged particles with a volumetric mean diameter near 2 μm were continuously introduced into the classroom environment via a breathing simulator with a prescribed inhalation–exhalation waveform. Deposition velocities were inferred on >50 horizontal and vertical surfaces throughout the classroom, while aerosol concentrations were spatially monitored via optical particle spectrometry. Results revealed a particle decay rate consistent with expectations based upon the reported clean air delivery rates of the PAF units. Additionally, the PAF units reduced peak concentrations by a factor of around 2.5 compared to the highest concentrations observed and led to a statistically significant reduction in deposition velocities for horizontal surfaces >2.5 m from the aerosol source. Our results not only confirm that PAF units can reduce particle concentrations but also demonstrate that they may lead to reduced particle deposition throughout an indoor environment when properly positioned with respect to the location of the particle source(s) within the room (e.g., where the largest group of students sit) and the predominant air distribution profile of the room.

Air purifier location and position are key in reducing transmission of coronavirus aerosol

Purifier configuration can significantly reduce particle concentrations in lecture halls.

Simultaneous temporal, spatial and size-resolved measurements of aerosol particles in closed indoor environments applying mobile filters in various use-cases

This paper focuses on simultaneous, time- and space-resolved measurements of particle size distributions in three different closed indoor environments (small office room, elementary-school classroom, and seminar room) applying mobile air filters in four scenarios (decay curves, filtration while people are present, a temporal strong point source, impact of filter orientation & cross-flow ventilation). The experiments reveal, that mobile indoor air filters, equipped with high-performance filter media (HEPA - quality), remove particles in the investigated rooms in relevant submicron size classes (x < 1 μm) efficiently and uniformly over time.For the description of the local decrease in particle concentration a simple mathematical model based on a transient continuous stirred tank reactor was applied. The local decay curves obtained in the different room-types were compared to simulated ones assuming ideal mixing of the indoor air. The real-room scenarios show a slower particle decay than the predicted ones assuming ideal mixing of the indoor air. The experiments reported in this contribution demonstrate, that indoor air filters, operated with a filtration rate of 3.5 h−1 and positioned correctly, are capable of lowering the particle concentration in all relevant size classes in real-world closed indoor environments slowly over time (e.g. a reduction in particle concentration of 50 % after 30 min in a classroom w/o particle sources). In the investigated set-ups, at filtration rates above 9 h−1, the filters’ performance is close to cross-flow window-ventilation. The experiments reveal, that mobile air filters cannot avoid close distance transmission of submicron aerosol particles from one person to another. Therefore, they do not replace any of the well-known methods to avoid aerosol-driven infection (like wearing an efficient face mask correctly, limiting the number of people and time of stay in closed indoor environments, frequent ventilation). Mobile air filter devices may represent an additional component in an entire prevention strategy, especially when rooms cannot be ventilated regularly, efficiently or the constellation of people in groups changes frequently (e.g. waiting areas).

Numerical investigation of particle cloud sedimentation in power-law shear-thinning fluids for moderate Reynolds number

A series of numerical simulations are performed for the sedimentation process of a particle cloud in shear-thinning fluids using lattice Boltzmann and discrete element methods. The initial particle concentration, c0, and the power-law index of the fluid, n, and Reynolds number, Re, are varied in these simulations. For 1.0⩽Re⩽10.9, the particle cloud size grows in the longitudinal direction as the cloud settles, leading to reduced particle concentration and a quasi-steady settling velocity, w¯∞. The velocity ratio, w¯∞/w∞, where w∞ is the corresponding single-particle terminal velocity, is found to decrease with both n and Re. This velocity ratio is only weakly dependent on the initial concentration (0.05⩽c0⩽0.20) due to particle dispersion. For 0.071⩽Re<1.0, the cloud loses its initial shape and disintegrates while settling, with particles escaping from the cloud due to differential particle settling velocities.

Household air pollution from, and fuel efficiency of, different coal types following local cooking practices in Xuanwei, China

The domestic combustion of smoky (bituminous) coal in the Chinese counties of Xuanwei and Fuyuan, are responsible for some of the highest rates of lung cancer in the world. Cancer rates vary between coal producing regions (deposits) in the area, with coals from Laibin exhibiting particularly high risks and smokeless (anthracite) coal exhibiting lower risks. However, little information is available on the specific burning characteristics of coals from throughout the area. We conducted an extensive controlled burning experiment using coal from multiple deposits in either a traditional firepit or ventilated stove, accompanied by a detailed examination of time-weighted and real-time size-aggregated particle concentrations. Smoky coal caused higher particle concentrations of all sizes than smokeless coal, with variations observed by geological source. Virtually all particle emissions were in the PM2.5 fraction (98% - mass based), and 75% and 46% were in the PM1 and PM0.3 fraction respectively. Real-time concentrations of PM1 and PM0.1 peaked after coal was added and declined afterwards. Ventilation reduced particle concentrations by up to 15-fold and increased the coal burning rate by 1.9-fold. These findings may provide valuable insight for reducing exposure and adverse health effects associated with domestic coal combustion.

In Reply to the Letter to the Editor Regarding “Novel Decompressive Hemicraniectomy Technique for Traumatic Brain Injury: Technical Note”

Present guidelines on reducing aerosol generation during neurosurgical procedures are futile. The aim of this article was to describe a novel device to contain aerosol within a small localized environment around the operative field—the negative pressure assisted microenvironment surgical hood (NEPA-MESH).This device can be assembled using easily available materials—steel wires, image intensifier cover, surgical drape, and three-dimensional–printed self-locking copolyester double hoops. Large-bore pipes in continuity with a high-volume suction apparatus create a constant negative pressure microenvironment around the operative field. The CEM DT-9880 particle counter was used to estimate particle concentration inside the NEPA-MESH during various stages of a neurosurgical procedure as well as outside. The NEPA-MESH was tested in different craniotomies and endoscopic procedures.Mean particle concentration inside the NEPA-MESH and outside during drilling in various procedures was calculated and compared using unpaired t test. Significant reduction in particle concentrations was recorded for particles sized 0.3 μm (t = 17.55, P < 0.0001), 0.5 μm (t = 11.39, P < 0.0001), 1 μm (t = 6.36, P = 0.0002), 2.5 μm (t = 2.04, P = 0.074), 5.0 μm (t = 7.026, P = 0.0008), and 10 μm (t = 4.39, P = 0.0023).As definitive evidence demonstrating the presence of coronavirus disease 2019 (COVID-19) in aerosol particles is awaited, we describe a cost-effective strategy to reduce aerosol contamination. Significant reduction in particle concentrations was seen outside the NEPA-MESH compared with inside it during various stages of neurosurgical procedures.

Letter to the Editor Regarding “Evolution of Minimally Invasive Lumbar Spine Surgery”

Present guidelines on reducing aerosol generation during neurosurgical procedures are futile. The aim of this article was to describe a novel device to contain aerosol within a small localized environment around the operative field—the negative pressure assisted microenvironment surgical hood (NEPA-MESH).This device can be assembled using easily available materials—steel wires, image intensifier cover, surgical drape, and three-dimensional–printed self-locking copolyester double hoops. Large-bore pipes in continuity with a high-volume suction apparatus create a constant negative pressure microenvironment around the operative field. The CEM DT-9880 particle counter was used to estimate particle concentration inside the NEPA-MESH during various stages of a neurosurgical procedure as well as outside. The NEPA-MESH was tested in different craniotomies and endoscopic procedures.Mean particle concentration inside the NEPA-MESH and outside during drilling in various procedures was calculated and compared using unpaired t test. Significant reduction in particle concentrations was recorded for particles sized 0.3 μm (t = 17.55, P < 0.0001), 0.5 μm (t = 11.39, P < 0.0001), 1 μm (t = 6.36, P = 0.0002), 2.5 μm (t = 2.04, P = 0.074), 5.0 μm (t = 7.026, P = 0.0008), and 10 μm (t = 4.39, P = 0.0023).As definitive evidence demonstrating the presence of coronavirus disease 2019 (COVID-19) in aerosol particles is awaited, we describe a cost-effective strategy to reduce aerosol contamination. Significant reduction in particle concentrations was seen outside the NEPA-MESH compared with inside it during various stages of neurosurgical procedures.

Negative Pressure Assisted Microenvironment Surgical Hood: A Novel Cost-Effective Device to Minimize Aerosol Contamination During Neurosurgical Procedures in Times of COVID-19

ObjectivePresent guidelines on reducing aerosol generation during neurosurgical procedures are futile. The aim of this article was to describe a novel device to contain aerosol within a small localized environment around the operative field—the negative pressure assisted microenvironment surgical hood (NEPA-MESH).MethodsThis device can be assembled using easily available materials—steel wires, image intensifier cover, surgical drape, and three-dimensional–printed self-locking copolyester double hoops. Large-bore pipes in continuity with a high-volume suction apparatus create a constant negative pressure microenvironment around the operative field. The CEM DT-9880 particle counter was used to estimate particle concentration inside the NEPA-MESH during various stages of a neurosurgical procedure as well as outside. The NEPA-MESH was tested in different craniotomies and endoscopic procedures.ResultsMean particle concentration inside the NEPA-MESH and outside during drilling in various procedures was calculated and compared using unpaired t test. Significant reduction in particle concentrations was recorded for particles sized 0.3 μm (t = 17.55, P < 0.0001), 0.5 μm (t = 11.39, P < 0.0001), 1 μm (t = 6.36, P = 0.0002), 2.5 μm (t = 2.04, P = 0.074), 5.0 μm (t = 7.026, P = 0.0008), and 10 μm (t = 4.39, P = 0.0023).ConclusionsAs definitive evidence demonstrating the presence of coronavirus disease 2019 (COVID-19) in aerosol particles is awaited, we describe a cost-effective strategy to reduce aerosol contamination. Significant reduction in particle concentrations was seen outside the NEPA-MESH compared with inside it during various stages of neurosurgical procedures.

Effects of roadside green infrastructure on particle exposure: A focus on cyclists and pedestrians on pathways between urban roads and vegetative barriers

Roadside green infrastructure (GI) has attracted worldwide attention for its potentials to alleviate local air pollution. However, previous studies have not clearly characterized the effects of roadside GI on personal exposure levels to vehicular emissions, particularly for cyclists and pedestrians on the pathways between urban roads and vegetative barriers. In this study, field experiments were implemented to measure and compare the concentration levels of particulate matter (PM) and black carbon (BC) on pathways (e.g., bike lanes and sidewalks) and near residential buildings with and without roadside GI. Results show that the presence of GI significantly elevated the particle concentrations over bike lanes and sidewalks. Compared with the GI-free case, an increase of up to 20% and 28% was separately observed for BC and PM on the pathways before GI. This is strongly associated with the impact of GI on local wind fields that impedes the dispersion of traffic-emitted particles on the roadways. However, roadside GI brought a significant reduction of particle concentrations near residential buildings, separately decreasing by about 8% for BC and 6% for PM. Then Computational Fluid Dynamics software was adopted to simulate the diffusion process of traffic-emitted particles in the typical urban scenarios of roadways, pathways, GI, and residential buildings, and further analyze the particle distribution patterns under six roadside GI configurations. Simulation results suggest that tall vegetative barriers can lead to the accumulation of particles on the pathways and increase cyclists' and pedestrians’ exposure to local particulate pollution. The GI case of “tree canopy only” can be a potentially viable choice to reduce particle concentrations on the pathways due to the fact that its better ventilation conditions are more favorable for particle diffusion than other GI configurations. However, compared with the complex GI configurations, the scenario with no roadside GI exhibits more positive effects on decreasing particulate exposure on the pathways. These findings could provide practical insights into roadside GI design and important implications in near-road air quality improvements.

SARS-CoV-2: characterisation and mitigation of risks associated with aerosol generating procedures in dental practices.

Introduction The objectives were to characterise the particle size distribution of aerosols generated by standard dental aerosol generating procedures (AGPs) and to assess the impact of aerosol-management interventions on 'fallow time'. Interventions included combinations of high-volume intraoral suction (HVS[IO]), high-volume extraoral suction (HVS[EO]) and an air cleaning system (ACS).Method A sequence of six AGPs were performed on a phantom head. Real-time aerosol measurements (particle size range 0.0062-9.6 μm) were acquired from six locations within a typical dental treatment room (35 m3).Results The majority (>99%) of AGP particles were <0.3 μm diameter and remained at elevated levels around the dental team during the AGPs. With no active aerosol-management interventions, AGP particles were estimated to remain above the baseline range for up to 30 minutes from the end of the sequence of procedures.Conclusions The results emphasise the importance of personal protection equipment, particularly respiratory protection. Use of HVS(IO), either alone or in combination with the ACS, reduced particle concentrations to baseline levels on completion of AGPs. These data indicate potential to eliminate fallow time. The study was performed using a phantom head so confirmatory studies with patients are required.Zusatzmaterial online: Zu diesem Beitrag sind unter 10.1038/s41415-020-2504-8 für autorisierte Leser zusätzliche Dateien abrufbar.

Development of Measurement Methodology for Sub 23 nm Particle Number (PN) Measurements

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;A proposal for sub-23 nm Solid Particle Number (SPN) measurement method was developed by the Particle Measurement Programme (PMP) group, based on the current SPN measurement method. In the proposal, a Particle Number Counter (PNC) having (65 ± 15)% counting efficiency at 10 nm and &amp;gt;90% at 15 nm (PNC10) replaces the current regulation PNC efficiency of 50±12% at 23 nm and &amp;gt;90% at 41 nm. Additionally, a catalytically active evaporation tube (CS) is required for sub-23 nm measurement method instead of the non-reactive evaporation tube (ET) of the current regulation. Here experimental work carried out at the JRC to address the issues of sub-23 nm SPN-measurement method is presented. The PNC10 was shown to be less dependent on the particle material than the PNC23, thus soot-like particles are still allowed for PNC-calibration. The high charging probability of soot-like particles was shown to have a low effect on PNC calibration uncertainties. The new proposed linearity test which requires that the PNC readings need to be within ±5% of the slope was here shown to be applicable. The proposal requires that Particle Concentration Reduction Factor (PCRF) at 15 nm shall be at most 100% higher than the 100 nm PCRF for the Volatile Particle Remover (VPR). The allowed variability in VPR-losses and PNC10-efficiencies of the new proposal could cause differences up to 36% when a distribution with Geometric Mean Diameter at 15 nm was simulated. Yet, for the commercial CS and ET systems with experimentally determined PCRF 15 nm to 100 nm ratios of 80% and 50% respectively, the maximum difference was 19% using PNC10. The average PCRF in the proposal is calculated as in the current regulation, with an average of PCRFs at 30 nm, 50 nm and 100 nm in order to keep the comparability with the 23 nm regulation and because the addition of the PCRF at 15 nm did not improve the accuracy.&lt;/div&gt;&lt;/div&gt;

A study of the effect of regenerated CCN on marine stratocumulus cloud development using the WRF-LES model with spectral bin microphysics scheme

Impacts of regenerated cloud condensation nuclei (CCN) on daytime marine stratocumulus clouds (MSC) and stratocumulus-topped boundary layer (STBL) are investigated, by implementing five different CCN regeneration methods in the spectral bin microphysics (SBM) scheme of the Weather Research and Forecasting (WRF) large eddy simulation (LES) model. Without the CCN regeneration process, the model shows unrealistic reduction of total (cloud drops + CCN) particle concentrations but produces very large cloud drops, compared to observations. Such reduction of particle concentrations is remedied when CCN regeneration process is implemented in the model. Evaluation of the model performance with aircraft measurement data confirms that CCN regeneration is critical for realistic simulation of MSC development. However, depending on the selected CCN regeneration method, results vary significantly especially at a later hour of simulation time (5 h). Such variabilities of the microphysical properties and dynamical structures are caused mainly by the different ways of regenerating CCN particles after entrainment of warm and dry air and subsequent evaporation of cloud drops near cloud top, which, in turn, affects cloud radiative properties such as SW heating and LW cooling that drives STBL convection. We are confident that this study can provide a guidance for simulating more realistic three-dimensional MSC cloud development by including the crucial process of CCN regeneration in the SBM scheme. All in all, we recommend the methods, which primarily replenish the depleted CCN with large CCN.