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Collision-induced fragmentation of atmospheric ice particles is a crucially important but understudied secondary ice production mechanism in clouds. We present a laboratory study dedicated to fragmentation due to graupel–graupel and frozen drop–frozen drop collisions and the role of these collisions in augmenting the ice particle concentration in clouds. For this, graupel particles of different sizes and densities were created utilizing dry growth conditions in a cold chamber at −7 and −15 °C using a setup that simulates the natural rotation and tumbling motion of freely falling graupel. Ice spheres, as proxies for frozen drops and ice pellets, were generated by freezing purified water in 3D-printed spherical molds. We conducted collision experiments inside the cold chamber utilizing a fall tube that ensures the central and repeatable collision of ice particles at different collision kinetic energies. The number of fragments generated in the collisions was analyzed, following a theoretical framework, as a function of the collision kinetic energy. The detection limit of our experiments was 30 µm; thus, fragments with sizes lower than 30 µm could not be detected. The observed number of fragments varied between 1 and 20 and was, thus, comparable to or higher than the number of fragments resulting from drop freezing experiments. Our results revealed a strong dependency of the fragment number on the density of the colliding ice particles, which can be attributed to the particles' structure. The sizes of the fragments that we detected were in the submillimeter range for graupel and up to 3 mm for ice spheres. Another set of experiments, focusing on the multiple collision of graupel revealed that the number of fragments generated decreases significantly and approaches zero when a particle undergoes more than three collisions in a row.

Properties of frozen hydrometeors in clouds remain difficult to sense remotely. Estimates of number concentration, distribution shape, ice particle density, and ice water content are essential for connecting cloud processes to surface precipitation. Progress has been made with dual-frequency radars, but validation has been difficult because of lack of particle imaging and sizing observations collocated with the radar measurements. Here, data are used from two airborne profiling (up and down) radars, the W-band Wyoming Cloud Radar and the Ka-band Profiling Radar, allowing for Ka–W-band dual-wavelength ratio (DWR) profiles. The aircraft (the University of Wyoming King Air) also carried a suite of in situ cloud and precipitation probes. This arrangement is optimal for relating the “flight-level” DWR (an average from radar gates below and above flight level) to ice particle size distributions measured by in situ optical array probes, as well as bulk properties such as minimum snow particle density and ice water content. This comparison reveals a strong relationship between DWR and the ice particle median-volume diameter. An optimal range of DWR values ensures the highest retrieval confidence, bounded by the radars’ relative calibration and DWR saturation, found here to be about 2.5–7.5 dB. The DWR-defined size distribution shape is used with a Mie scattering model and an experimental mass–diameter relationship to test retrievals of ice particle concentration and ice water content. Comparison with flight-level cloud-probe data indicate good performance, allowing microphysical interpretations for the rest of the vertical radar transects.

To investigate the causative component for certain health outcomes, the associations between the properties of ambient particles and cause-specific mortality (all-cause, cardiovascular, and respiratory-related mortality) measured in Seoul, Korea, from January 1, 2013, to December 31, 2016, were evaluated with a quasi-Poisson generalized additive model (GAM). The total mass of PM 10 and PM 2.5 moderately affected respiratory-related mortality but had almost no impact on all-cause and cardiovascular-related mortality. Among PM 2.5 mass compositions, ammonium sulfate, which is in generally 300–500 nm as a secondary species, showed the most statistically significant effect on respiratory-related mortality at lag 4 ( p  < 0.1) but not for other mortalities. However, from the size-selective investigations, cardiovascular-related mortality was impacted by particle number concentrations (PNCs), particle surface concentrations (PSCs), and particle volume concentrations (PVCs) in the size range from 50 to 200 nm with a statistically significant association, particularly at lag 1, suggesting that mass is not the only way to examine mortality, which is likely because mass and chemical composition concentrations are generally controlled by larger-sized particles. Our study suggests that the size-specific mortality and/or impacts of size-resolved properties on mortalities need to be evaluated since smaller particles get into the body more efficiently, and therefore, more diverse size-dependent causes and effects can occur.

The school environment is crucial for the child’s health and well-being. On the other hand, the data about the role of school’s aerosol pollution on the etiology of chronic non-communicable diseases remain scarce. This study aims to evaluate the level of indoor aerosol pollution in primary schools and its relation to the incidence of doctor’s diagnosed asthma among younger school-age children. The cross-sectional study was carried out in 11 primary schools of Vilnius during 1 year of education from autumn 2017 to spring 2018. Particle number (PNC) and mass (PMC) concentrations in the size range of 0.3–10 µm were measured using an Optical Particle Sizer (OPS, TSI model 3330). The annual incidence of doctor’s diagnosed asthma in each school was calculated retrospectively from the data of medical records. The total number of 6–11 years old children who participated in the study was 3638. The incidence of asthma per school ranged from 1.8 to 6.0%. Mean indoor air pollution based on measurements in classrooms during the lessons was calculated for each school. Levels of PNC and PMC in schools ranged between 33.0 and 168.0 particles/cm 3 and 1.7–6.8 µg/m 3 , respectively. There was a statistically significant correlation between the incidence of asthma and PNC as well as asthma and PMC in the particle size range of 0.3–1 µm ( r  = 0.66, p  = 0.028) and ( r  = 0.71, p  = 0.017) respectively. No significant correlation was found between asthma incidence and indoor air pollution in the particle size range of 0.3–2.5 and 0.3–10 µm.    Conclusion : We concluded that the number and mass concentrations of indoor air aerosol pollution in primary schools in the particle size range of 0.3–1 µm are primarily associated with the incidence of doctor’s diagnosed asthma among younger school-age children. What is Known: • Both indoor and outdoor aerosol pollution is associated with bronchial asthma in children. What is New: • The incidence of bronchial asthma among younger school age children is related to indoor air quality in primary schools. • Aerosol pollutants in the size range of 0.3–1 µm in contrast to larger size range particles can play major role in the etiology of bronchial asthma in children.

The dispersion of solid particles in zones of turbulent recirculation flow is of interest in various technological applications. Many experimental studies have been developed in order to know the contribution of Stokes numbers and mean drift parameter on the entering and dispersion of particles in the recirculation zone however to our knowledge there are not numerical studies reported about it. In this work, we made a numerical study of the incompressible turbulent flow laden with solid particles in sudden expansion pipes with different expansion ratios and different Reynolds number upstream of the pipe, using LES and Germano dynamic model with JetCode program for the continuous phase (air). The solid particles movement (different diameters were considered) was solved by using a Lagrangian tracking algorithm coupled to JetCode taking into account only drag and gravity forces supposing one way coupling. Finally, we calculated Stokes numbers based on the different fluid time scales and the mean drift parameter for all the solved cases and studied their isolated effect on the solid particle dispersion in the recirculation zones by computing the concentration by means of the particle number within the recirculation zones. Our results coincided with the experimental findings reported by others authors: the particle concentration exhibits a maximum value as the Reynolds number upstream in the pipe is decreased, the pipe expansion ratio is increased and particle size is decreased. Regarding the results obtained numerically about the solid particle dispersion within turbulent recirculation zones in terms of Stokes numbers and the mean drift parameters, coincided adequately with the experimental results.

A correlation between the mass concentration of particulate matter (PM) and the occurrence of health-related problems or diseases has been confirmed by several studies. However, little is known about indoor PM concentrations, their associated risks or their impact on health. In this work, the PM1, PM2.5 and PM10 produced by different indoor aerosol sources (candles, cooking, electronic cigarettes, tobacco cigarettes, mosquito coils and incense) are studied. The purpose is to quantify the emission characteristics of different indoor particle sources. The mass concentration, the numerical concentration, and the size distribution of PM from various sources were determined in an examination room 65 m3 in volume. Sub-micrometer particles and approximations of PM1, PM2.5 and PM10 concentrations were measured simultaneously using a diffusion aerosol spectrometer (DAS). The ultrafine particle concentration for the studied indoor aerosol sources was approximately 7 × 104 particles/cm3 (incense, mosquito coils and electronic cigarettes), 1.2 × 105 particles/cm3 for candles and cooking and 2.7 × 105 particles/cm3 for tobacco cigarettes. The results indicate that electronic cigarettes can raise indoor PM2.5 levels more than 100 times. PM1 concentrations can be nearly 55 and 30 times higher than the background level during electronic cigarette usage and tobacco cigarette burning, respectively. It is necessary to study the evaluation of indoor PM, assess the toxic potential of internal molecules and develop and test strategies to ensure the improvement of indoor air quality.

A fast-growing area of research is the development of low-cost sensors for measuring air pollutants. The affordability and size of low-cost particle sensors makes them an attractive option for use in experiments requiring a number of instruments such as high-density spatial mapping. However, for these low-cost sensors to be useful for these types of studies their accuracy and precision need to be quantified. We evaluated the Alphasense OPC-N2, a promising low-cost miniature optical particle counter, for monitoring ambient airborne particles at typical urban background sites in the UK. The precision of the OPC-N2 was assessed by co-locating 14 instruments at a site to investigate the variation in measured concentrations. Comparison to two different reference optical particle counters as well as a TEOM-FDMS enabled the accuracy of the OPC-N2 to be evaluated. Comparison of the OPC-N2 to the reference optical instruments shows some limitations for measuring mass concentrations of PM1, PM2.5 and PM10. The OPC-N2 demonstrated a significant positive artefact in measured particle mass during times of high ambient RH (> 85 %) and a calibration factor was developed based upon κ-Köhler theory, using average bulk particle aerosol hygroscopicity. Application of this RH correction factor resulted in the OPC-N2 measurements being within 33 % of the TEOM-FDMS, comparable to the agreement between a reference optical particle counter and the TEOM-FDMS (20 %). Inter-unit precision for the 14 OPC-N2 sensors of 22 ± 13 % for PM10 mass concentrations was observed. Overall, the OPC-N2 was found to accurately measure ambient airborne particle mass concentration provided they are (i) correctly calibrated and (ii) corrected for ambient RH. The level of precision demonstrated between multiple OPC-N2s suggests that they would be suitable devices for applications where the spatial variability in particle concentration was to be determined.

Fil: Carreras, Hebe Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina

Many airborne pathogens such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are transmitted indoors via aerosol particles. During exercise, pulmonary ventilation can increase over 10-fold, and therefore, exercisers will exhale a greater volume of aerosol-containing air. However, we currently do not know how exercise affects the concentration of aerosol particles in exhaled air and the overall emission of aerosol particles. Consequently, we developed a method to measure in parallel the concentration of aerosol particles in expired air, pulmonary ventilation, and aerosol particle emission at rest and during a graded exercise test to exhaustion. We used this method to test eight women and eight men in a descriptive study. We found that the aerosol particle concentration in expired air increased significantly from 56 ± 53 particles/liter at rest to 633 ± 422 particles/liter at maximal intensity. Aerosol particle emission per subject increased significantly by a factor of 132 from 580 ± 489 particles/min at rest to a super emission of 76,200 ± 48,000 particles/min during maximal exercise. There were no sex differences in aerosol particle emission, but endurance-training subjects emitted significantly more aerosol particles during maximal exercise than untrained subjects. Overall, aerosol particle emission increased moderately up to an exercise intensity of ∼2 W/kg and exponentially thereafter. Together, these data might partly explain superspreader events especially during high-intensity group exercise indoors and suggest that strong infection prevention measures are needed especially during exercise at an intensity that exceeds ∼2 W/kg. Investigations of influencing factors like airway and whole-body hydration status during exercise on aerosol particle generation are needed.

We investigate the transport of size-selected particles suspended in turbulent boundary layers at friction Reynolds numbers up to $Re_\\tau = 19\\,000$. We use microscopic glass spheres in air, spanning a wide range of viscous Stokes numbers, $St^+ = 18\\text {--}870$. These are imaged simultaneously with the flow tracers, and particle image and tracking velocimetry are used to measure the two-phase flow along a wall-normal plane in the logarithmic region. The air flow statistics are not altered by the particles at the present mass loading. In comparison to the classic equilibrium solution, the particle concentration profiles display weaker wall-normal gradients. This is shown to be an effect of particle inertia: this manifests itself through different mechanisms in different strata of the flow, and the effects on the concentration are captured by a three-layer parameterization of the profile. The particles lag the fluid across the boundary layer, with a mean slip velocity of the order of the friction velocity and increasing with particle inertia. Near the wall this lag is mainly due to the instantaneous slip of the particles relative to the surrounding fluid, while away from the wall the leading cause is the preferential sampling of low-speed fluid regions. Larger particles (in the size range of sand, as opposed to dust) display a qualitatively different behaviour, likely because of nonlinear drag effects. All considered particles oversample specific regions of the fluid flow: they favour regions of negative streamwise fluctuations, especially ejection events, and are likely to be found about the centre of strain cells with backward-leaning compressive axis and forward-leaning extensive axis. This pattern is visible for a wide range of Stokes numbers, underscoring the multi-scale nature of preferential concentration. The present findings highlight how high-Reynolds-number features of turbulent boundary layers impact the transport of suspended inertial particles, and thus are especially relevant to environmental and geophysical flows.