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Surface tension influences the fraction of atmospheric particles that become cloud droplets. Although surfactants are an important component of aerosol mass, the surface tension of activating aerosol particles is still unresolved, with most climate models assuming activating particles have a surface tension equal to that of water. By studying picoliter droplet coalescence, we demonstrate that surfactants can significantly reduce the surface tension of finite-sized droplets below the value for water, consistent with recent field measurements. Significantly, this surface tension reduction is droplet size-dependent and does not correspond exactly to the macroscopic solution value. A fully independent monolayer partitioning model confirms the observed finite-size-dependent surface tension arises from the high surface-to-volume ratio in finite-sized droplets and enables predictions of aerosol hygroscopic growth. This model, constrained by the laboratory measurements, is consistent with a reduction in critical supersaturation for activation, potentially substantially increasing cloud droplet number concentration and modifying radiative cooling relative to current estimates assuming a water surface tension. The results highlight the need for improved constraints on the identities, properties, and concentrations of atmospheric aerosol surfactants inmultiple environments and are broadly applicable to any discipline where finite volume effects are operative, such as studies of the competition between reaction rates within the bulk and at the surface of confined volumes and explorations of the influence of surfactants on dried particle morphology from spray driers.

Simultaneous indoor and outdoor PM₁₀ and PM₂.₅ concentration measurements were conducted in seven primary schools in the Athens area. Both gravimetric samplers and continuous monitors were used. Filters were subsequently analyzed for anion species. Moreover ultrafine particles number concentration was monitored continuously indoors and outdoors. Mean 8-hr PM₁₀ concentration was measured equal to 229 ± 182 μg/m³ indoors and 166 ± 133 μg/m³ outdoors. The respective PM₂.₅ concentrations were 82 ± 56 μg/m³ indoors and 56 ± 26 μg/m³ outdoors. Ultrafine particles 8-h mean number concentration was measured equal to 24,000 ± 17,900 particles/cm³ indoors and 32,000 ± 14,200 particles/cm³ outdoors. PM₁₀ outdoor concentrations exhibited a greater spatial variability than the corresponding PM₂.₅ ones. I/O ratios were close or above 1.00 for PM₁₀ and PM₂.₅ and smaller than 1.00 for ultrafine particles. Very high I/O ratios were observed when intense activities took place. The initial results of the chemical analysis showed that [graphic removed] accounts for the 6.6 ± 3.5% of the PM₁₀ and [graphic removed] for the 3.1 ± 1.4%.The corresponding results for PM₂.₅ are 12.0 ± 7.7% for [graphic removed] and 3.1 ± 1.9% for [graphic removed] . PM₂.₅ [graphic removed] indoor concentrations were highly correlated with outdoor ones and the regression line had the largest slope and a very low intercept, indicative of no indoor sources of fine particulate [graphic removed] . The results of the statistical analysis of indoor and outdoor concentration data support the use of [graphic removed] as a proper surrogate for indoor PM of outdoor origin.

The change in planetary albedo due to aerosol–cloud interactions during the industrial era is the leading source of uncertainty in inferring Earth’s climate sensitivity to increased greenhouse gases from the historical record. The variable that controls aerosol–cloud interactions in warm clouds is droplet number concentration. Global climate models demonstrate that the present-day hemispheric contrast in cloud droplet number concentration between the pristine Southern Hemisphere and the polluted Northern Hemisphere oceans can be used as a proxy for anthropogenically driven change in cloud droplet number concentration. Remotely sensed estimates constrain this change in droplet number concentration to be between 8 cm−3 and 24 cm−3. By extension, the radiative forcing since 1850 from aerosol–cloud interactions is constrained to be −1.2 W·m−2 to −0.6 W·m−2. The robustness of this constraint depends upon the assumption that pristine Southern Ocean droplet number concentration is a suitable proxy for preindustrial concentrations. Droplet number concentrations calculated from satellite data over the Southern Ocean are high in austral summer. Near Antarctica, they reach values typical of Northern Hemisphere polluted outflows. These concentrations are found to agree with several in situ datasets. In contrast, climate models show systematic underpredictions of cloud droplet number concentration across the Southern Ocean. Near Antarctica, where precipitation sinks of aerosol are small, the underestimation by climate models is particularly large. This motivates the need for detailed process studies of aerosol production and aerosol–cloud interactions in pristine environments. The hemispheric difference in satellite estimated cloud droplet number concentration implies preindustrial aerosol concentrations were higher than estimated by most models.

Air quality data collection near pollution sources is difficult, particularly when sites are complex, have physical barriers, or are themselves moving. Small Unmanned Aerial Vehicles (UAVs) offer new approaches to air pollution and atmospheric studies. However, there are a number of critical design decisions which need to be made to enable representative data collection, in particular the location of the air sampler or air sensor intake. The aim of this research was to establish the best mounting point for four gas sensors and a Particle Number Concentration (PNC) monitor, onboard a hexacopter, so to develop a UAV system capable of measuring point source emissions. The research included two different tests: (1) evaluate the air flow behavior of a hexacopter, its downwash and upwash effect, by measuring air speed along three axes to determine the location where the sensors should be mounted; (2) evaluate the use of gas sensors for CO2, CO, NO2 and NO, and the PNC monitor (DISCmini) to assess the efficiency and performance of the UAV based system by measuring emissions from a diesel engine. The air speed behavior map produced by test 1 shows the best mounting point for the sensors to be alongside the UAV. This position is less affected by the propeller downwash effect. Test 2 results demonstrated that the UAV propellers cause a dispersion effect shown by the decrease of gas and PN concentration measured in real time. A Linear Regression model was used to estimate how the sensor position, relative to the UAV center, affects pollutant concentration measurements when the propellers are turned on. This research establishes guidelines on how to develop a UAV system to measure point source emissions. Such research should be undertaken before any UAV system is developed for real world data collection.

Brass bands that include wind instruments are heavily affected by rules established during the pandemic. The aim of this experimental work was to assess the aerosols emitted through different wind instruments. The Aerodynamic Particle Sizer (APS) was used to measure the aerosols emitted and transmit those characteristics to a database. The results revealed that the dynamic level at which a note is produced, regardless of whether it is a clarinet, trumpet, or bassoon, significantly changes in aerosol concentrations emitted. Specifically, if there is a higher dynamic level, an increase in emissions of particle concentration will occur by comparing the levels piano , mezzo forte , and forte . These aerosols are produced with a diameter of approximately 0.8 μm, except for the Navarra bagpipe, which has a diameter of 1.8 μm. In addition, this last instrument is the one that emits more particles every second, reaching a value five times larger than that with two reeds, such as the bassoon. Staccato and legato are two well-known techniques among musicians that help in articulating a musical piece. The difference between the two methods in terms of the concentration of the number of particles is not remarkable and is almost negligible.

Low-cost sensors (LCSs) for particulate matter (PM) concentrations have attracted the interest of researchers, supplementing their efforts to quantify PM in higher spatiotemporal resolution. The precision of PM mass concentration measurements from PMS 5003 sensors has been widely documented, though limited information is available regarding their size selectivity and number concentration measurement accuracy. In this work, PMS 5003 sensors, along with a Federal Referral Methods (FRM) sampler (Grimm spectrometer), were deployed across three sites with different atmospheric profiles, an urban (Germanou) and a background (UPat) site in Patras (Greece), and a semi-arid site in Almería (Spain, PSA). The LCSs particle number concentration measurements were investigated for different size bins. Findings for particles with diameter between 0.3 and 10 μm suggest that particle size significantly affected the LCSs’ response. The LCSs could accurately detect number concentrations for particles smaller than 1 μm in the urban (R2 = 0.9) and background sites (R2 = 0.92), while a modest correlation was found with the reference instrument in the semi-arid area (R2 = 0.69). However, their performance was rather poor (R2

Increasing demand for size-resolved identification and quantification of microplastic particles in drinking water and environmental samples requires the adequate validation of methods and techniques that can be used for this purpose. In turn, the feasibility of such validation depends on the existence of suitable certified reference materials (CRM). A new candidate reference material (RM), consisting of polyethylene terephthalate (PET) particles and a water matrix, has been developed. Here, we examine its suitability with respect to a homogeneous and stable microplastic particle number concentration across its individual units. A measurement series employing tailor-made software for automated counting and analysis of particles (TUM-ParticleTyper 2) coupled with Raman microspectroscopy showed evidence of the candidate RM homogeneity with a relative standard deviation of 12% of PET particle counts involving particle sizes >30 µm. Both the total particle count and the respective sums within distinct size classes were comparable in all selected candidate RM units. We demonstrate the feasibility of production of a reference material that is sufficiently homogeneous and stable with respect to the particle number concentration.

Warm-sector rainstorms (WSR) are among the main weather events that cause significant casualties in the Sichuan Basin (SCB). These events are challenging to predict accurately using numerical models, partly due to the locally high air pollution that complicates WSR microphysical and precipitation processes. Aerosols affect the initial cloud droplet number concentration (CDNC) directly, and the CDNC is a key parameter in microphysical schemes that directly influences precipitation prediction. However, how and to what extent the CDNC affects WSR predictions in the SCB remains unclear. In this study, sensitivity experiments were conducted using a cloud-resolving model to investigate how the CDNC affects WSRs in the SCB. The study showed that when the CDNC is high, warm rainfall is reduced, while the cold rainfall is increased, which changes with convection development. First, a higher initial CDNC inhibits warm rainfall during the initial stage of convection. Second, during convection development, a higher initial CDNC accelerates graupel growth and its transformation into rainwater. The cold rainfall process plays a dominant role in this process, leading to an increase in rainfall intensity. Finally, during the convection mature stage, the promoting effect of the CDNC on the cold rainfall process weakens, leading to a decreased rainfall intensity in the higher initial CDNC. In the “initial-development-mature” stage, a higher initial CDNC distinctly affects the precipitation intensity in the form of \"suppression-promotion-suppression.\" The findings of this study contribute to the ability to anticipate the development of WSRs based on pollution conditions in the SCB.

A long‐term, consistent satellite record of cloud droplet number concentration (Nd) is essential for understanding aerosol‐cloud interactions and their climate effects. However, the Aqua MODIS‐retrieved Nd exhibits an unexpected and substantial increase over the near‐global oceans after 2022, contradicting the expected decline from continued emission reduction efforts. Here we demonstrate that this surge is not physical but largely an artifact of sensor orbital drift, which alters viewing geometry and solar illumination. By leveraging concurrent Suomi‐NPP VIIRS observations unaffected by drift, we developed an empirical correction that removes this artificial signal and quantified global mean Nd artificial biases of +2.4 cm−3 in 2023 and +5.0 cm−3 in 2024. These biases substantially distort the Nd trends, reversing the previously decreasing global Nd trend into an apparent strong rise after 2022. These findings highlight the critical need to correct for such artifacts when constructing satellite‐based climate data records.

Investigating the vertical distribution of mineral dust masses and their microphysical properties is crucial for accurately assessing the climate effects of dust. However, there are limited studies related to relevant in situ observations over dust source areas. In this study, the near-surface vertical characteristics (within 500 m a.g.l) of dust mass concentrations in five size fractions (PMs: TSP, PM10, PM4, PM2.5, and PM1) were investigated using an unmanned aerial vehicle (UAV) in Tazhong (TZ) in the Taklimakan Desert (TD) in July 2021. To the best of our knowledge, the vertical profiles of particle number concentration (PNC), effective radius (Reff), and volume concentration (Cv) were obtained for the first time by UAV over the TD. Four scenarios of clear sky, floating dust, blowing sand, and dust storm were selected based on the classification criteria for PMs. The PMs, PNC, Reff, and Cv decreased with height for all scenarios. From clear-sky to dust-storm scenarios PMs, PNC, Reff, and Cv in the column gradually increased. Reff (Cv) increased from 1.15 μm (0.08 μm3/μm2) to 4.53 μm (0.74 μm3/μm2). The diurnal variations of PMs, PNC, and Reff (Cv) revealed a unimodal pattern, with the peak occurring between 13:00 and 16:00, due to the evolution of wind speed and the atmospheric boundary layer in TZ. Unexpectedly, among the three postprecipitation scenarios (P1, P2, and P3), the PNC of P2 was smaller than those of P1 and P3. The Reff (Cv) for P2 was similar to or greater than that for dust storms, which may be associated with moist dust particles on the ground surface being carried into the air by wind. These investigations add to our understanding of the mineral dust vertical characteristics over the source area, and provide a meaningful reference for colocated lidar inversion and dust simulations.