Low Relative Humidity Levels Research Articles

Carbonation under Varying Humidity Conditions: A 3D Micro-Scale Kinetic Monte Carlo Approach.

This paper investigates the impact of varying humidity conditions on the carbonation depth in hardened cement paste using a 3-dimensional microscale kinetic Monte Carlo (kMC) approach. The kMC algorithm effectively simulates the carbonation process by capturing the interplay between CO2 diffusion and relative humidity at the microscale, providing insights into macro trends that align with historical models. The study reveals that the maximum carbonation depth is achieved at relative humidity levels between 55 and 65%, where the balance between water and CO2 diffusion is optimized. At lower relative humidity levels (<55%), a lower carbonation depth is observed. Conversely, at higher relative humidity levels (>65%), increased water content impedes CO2 diffusion, resulting in reduced carbonation depth for cement paste. The kMC model demonstrates a parabolic relationship between relative humidity and carbonation depth. Time series analysis shows that Fick's law is consistently followed, with carbonation depth following the relationship x = k√t at constant relative humidity. The kMC also breaks down the event cycle which shows that after an equilibrium (in terms of rate of events) is achieved between CO2 and H2O at a relative humidity of 75%, a shift occurs in the dominance from reactive to transport processes at a relative humidity of 85%. These findings highlight the importance of humidity in influencing carbonation rates on the one hand and demonstrate the effectiveness of the kMC approach in simulating these complex interactions at the microscale on the other hand.

Low Evaporation Enthalpy Ionic Covalent Organic Frameworks for Efficient Atmospheric Water Harvesting at Low Humidity.

Herein, we introduce a series of ionic covalent organic frameworks (iCOFs) with a focus on addressing the challenge of water collection at low relative humidity levels below 25%. These iCOFs are characterized by numerous hydrophilic sites and high water stability, enabling efficient water vapor adsorption even at relatively low humidity levels. Through the use of various hygroscopic salt cations and precise control of ion concentration within the pores, the water state within the iCOFs pores can be effectively managed. Among the iCOFs, TB-COF-Li stands out with an impressive adsorption capacity of 0.24 g g-1 from 0 to 22% RH. Notably, due to its ionic porous structure, TB-COF-Li exhibits a significantly lower enthalpy of evaporation, measured at 967.04 J g-1, compared to bulk water with an enthalpy of 2387.4 J g-1. Moreover, under simulated conditions of 1.5 solar intensity at 60 °C, the majority of the adsorbed water can be rapidly desorbed without the need for additional energy input. This efficient desorption process contributes to a high water collection rate of 0.092 g g-1 h-1 in the final atmospheric water harvesting device. The development of these iCOFs offers a promising and cost-effective solution for obtaining fresh water in arid regions.

Low Evaporation Enthalpy Ionic Covalent Organic Frameworks for Efficient Atmospheric Water Harvesting at Low Humidity

Herein, we introduce a series of ionic covalent organic frameworks (iCOFs) with a focus on addressing the challenge of water collection at low relative humidity levels below 25%. These iCOFs are characterized by numerous hydrophilic sites and high water stability, enabling efficient water vapor adsorption even at relatively low humidity levels. Through the use of various hygroscopic salt cations and precise control of ion concentration within the pores, the water state within the iCOFs pores can be effectively managed. Among the iCOFs, TB‐COF‐Li stands out with an impressive adsorption capacity of 0.24 g g‐1 from 0 to 22% RH. Notably, due to its ionic porous structure, TB‐COF‐Li exhibits a significantly lower enthalpy of evaporation, measured at 967.04 J g‐1, compared to bulk water with an enthalpy of 2387.4 J g‐1. Moreover, under simulated conditions of 1.5 solar intensity at 60 °C, the majority of the adsorbed water can be rapidly desorbed without the need for additional energy input. This efficient desorption process contributes to a high water collection rate of 0.092 g g‐1 h‐1 in the final atmospheric water harvesting device. The development of these iCOFs offers a promising and cost‐effective solution for obtaining fresh water in arid regions.

Radar-Derived Convective Features and Atmospheric Environments of Hail-Producing Storms over the Contiguous United States

Abstract Hail smaller than 0.75 in. is known to cause economic impacts yet remains understudied due to report biases towards recording larger hail sizes (≤1 in.). In this study, we assembled ground hail reports during 2017–22 from the National Centers for Environmental Information (NCEI) Storm Data, Community Collaborative Rain, Hail and Snow Network (CoCoRaHS), and Meteorological Phenomena Identification Near the Ground (mPING) databases. Then, these reports are collocated with the attributes of radar-derived convective features from the Multi-Radar Multi-Sensor (MRMS) system and fifth major global reanalysis produced by European Centre for Medium-Range Weather Forecasts (ERA5) atmospheric vertical profiles to construct a dataset describing properties of a full spectrum of hailstorms. The characteristics of radar reflectivity and atmospheric profiles are examined for hail of different sizes reported within selected regions over the contiguous United States (CONUS). In addition to the seasonal and diurnal variations, the morphology of convective features shows apparent regional differences from west to east in CONUS. The maximum expected size of hail (MESH) performance against reported hail sizes shows underestimation of hail with significant sizes and overestimation of small hail sizes. ERA5 vertical atmospheric profiles are explored to form relationships between storm environment and hail sizes. In addition to the relationships between wind shear and hail sizes, the roles of low-level relative humidity and freezing level height in regard to hail melting are discussed.

Diagnosis of Atmospheric Processes from a Local Perspective for the Western North Pacific Summer Monsoon Onset

Abstract The climatological western North Pacific summer monsoon onset, a so-called convection jump, occurs around the 41st pentad, corresponding to an abrupt northeastward extension of strong convection. This study investigates the process of convection jump from a local perspective. Composite analyses are performed based on the onset dates that are identified in individual years. The results show that the convective inhibition (CIN) decreases dramatically around the onset dates, while the convective available potential energy (CAPE) reaches its maximum long before the onset, suggesting that the CIN, rather than CAPE, plays a dominant role in triggering convection. Further analysis indicates that the reduction of CIN is induced by the increased low-level relative humidity, which is the result of enhanced water vapor convergence. The moisture transportation is primarily contributed by the wind transfer from easterlies to southeasterlies or southerlies along the southern boundary of the convection jump region, in accordance with the monsoon trough establishment. The present observational results may be used to evaluate climate models in simulating the stepwise evolution of summer monsoon. Significance Statement The convection jump refers to rapid convection extension to the northeastern part of the Philippines Sea in late July and corresponds to the deepening of the monsoon trough and northward shift of the western North Pacific subtropical high. Therefore, the convection jump has important impacts on the East Asian summer monsoon. The crucial role of transient atmospheric adjustment in triggering the convection jump has been shown in previous studies. However, the reason for the temporal preference of convection jump remains unknown. This study further specifies the process of atmospheric adjustments around the convection jump from a local perspective and reveals that the transition from the easterlies to southeasterlies or southerlies decreases convective inhibition and thus favors the convection jump. The present results can be used to diagnose the ability of climate models to simulate the stepwise evolution of Asian–Pacific summer monsoon.

A Review of Recent Developments in Edible Films and Coatings-Focus on Whey-Based Materials.

Packaging for food products is particularly important to preserve product quality and shelf life. The most used materials for food packaging are plastic, glass, metal, and paper. Plastic films produced based on petroleum are widely used for packaging because they have good mechanical properties and help preserve the characteristics of food. However, environmental concerns are leading the trend towards biopolymers. Films and coatings based on biopolymers have been extensively studied in recent years, as they cause less impact on the environment, can be obtained from renewable sources or by-products, are relatively abundant, have a good coating and film-forming capacity, are biodegradable and have nutritional properties that can be beneficial to human health. Whey protein-based films have demonstrated good mechanical resistance and a good barrier to gases when at low relative humidity levels, in addition to demonstrating an excellent barrier to aromatic compounds and especially oils. The use of whey proteins for films or coatings has been extensively studied, as these proteins are edible, have high nutritional value, and are biodegradable. Thus, the main objective of this document was to review new methodologies to improve the physicochemical properties of whey protein films and coatings. Importance will also be given to the combinations of whey proteins with other polymers and the development of new techniques that allow the manipulation of structures at a molecular level. The controlled release and mass transfer of new biomaterials and the improvement of the design of films and packaging materials with the desired functional properties can increase the quality of the films and, consequently, broaden their applications.

Investigation of the free-base Zr-porphyrin MOFs as relative humidity sensors for an indoor setting

Maintaining optimal relative humidity is paramount for human comfort. Therefore, the utilization of quartz crystal microbalance (QCM) as a relative humidity sensor platform holds significant promise due to its cost-effectiveness and high sensitivity. This study explores the efficacy of three free-base Zr porphyrin metal-organic frameworks (MOFs) - namely MOF-525, MOF-545, and NU-902 - as sensitive materials for QCM-based relative humidity sensors. Our extended experimental findings reveal that these materials exhibit notable sensitivity, particularly within relative humidity ranges of 40–100 %. However, we observe potential irreversible adsorption sites within the MOF-545 framework, hindering its ability to revert to its initial state after prolonged exposure. In light of this observation, we conduct periodic cycling experiments at relative humidity levels of 40–70 % to evaluate the measurement repeatability and feasibility of these sensors for indoor applications. Interestingly, the periodic cycling study demonstrates that MOF-545 shows promising repeatability, positioning it as a strong contender for indoor relative humidity sensing. In contrast, MOF-525 may necessitate extended desorption time, and NU-902 displays diminished sensitivity at low relative humidity levels. Nevertheless, a preliminary treatment of the MOF-545 QCM sensor may be necessary to address irreversible adsorption sites and uphold measurement repeatability, as only reversible adsorption sites are currently accessible. This study underscores the potential of MOF-based QCM sensors for effective relative humidity monitoring in indoor environments, thus facilitating improved comfort and environmental control.

Bipolar ionization-mediated airborne virus inactivation and deposition rates

Bipolar ionization (BPI) of indoor air has emerged as a widely implemented bulk-air disinfection technology to reduce human exposure to airborne viruses. This study presents BPI-mediated decay rate constants for the inactivation and deposition of infectious viral aerosols. Rate constants are estimated for the enveloped bacteriophage Ф6, a common SARS-CoV-2 surrogate, at low (∼25 %), medium (∼50 %) and high (∼75 %) relative humidity (RH) levels under bipolar ion concentrations of 106 ions/cm3. Enhanced BPI-facilitated viral inactivation rate constants of 4.6, 6.9, and 7.6 h −1 under low, middle, and high RH, respectively, are reported. BPI-mediated infectious decay and deposition rates for aerosolized Ф6 were RH-dependent, with significant increases from low to high RH (p < 0.05). Calculated BPI susceptibility constants, that account for ion concentrations, reveal limited airborne viral inactivation (<0.1 h −1) at bipolar ion levels (103 ions/cm3) that are common in bulk air where BPI is applied.

Estimating Fire Radiative Energy Density with Repeat-Pass Aerial Thermal-Infrared Imaging of Actively Progressing Wildfires

Studies on estimating cumulative fire intensity from spreading wildland fires based on fire radiative energy density (FRED) have primarily been conducted through controlled experiments. The objective of this study was to assess the potential for estimating FRED for freely-burning wildfires at landscape scales. Airborne thermal infrared image sequences collected 8 and 9 December 2017 during the Thomas Fire were used for surface temperature derivation and FRED estimation. Sensitivity of varying ambient temperatures, and a newly developed method that adjusts for ash radiances on fire radiative flux density (FRFD) and FRED estimates were tested. Pixel-level image classification was run to identify FRFD time sequences that were complete or incomplete because of cloud obscuration and provided the basis for an obscuration gap filling technique. Variations in estimated ambient temperature used to estimate FRFD had little impact on FRED estimates, while our ash adjustment led to notable differences. An exponential decay model characterized FRFD time sequences well, providing a basis for gap filling irregular sequences caused by atmospheric obscuration. FRED estimates were regressed on rate of spread (ROS) magnitudes and found to be positively and significantly correlated. FRED magnitudes were higher on 9 December when the Thomas Fire burned under higher wind speeds and lower relative humidity levels (Santa Ana weather conditions) than on 8 December.

Enso influence on water vapor transport and thermodynamics over Northwestern South America

The interannual variability of hydroclimatic conditions in Northwestern South America, especially precipitation, is mainly influenced by the El Niño–Southern Oscillation (ENSO). We explore potential mechanisms that affect precipitation occurrence in Northwestern South America during El Niño and La Niña events over the period 1980–2019, using data from the ERA5 reanalysis. We look at the atmospheric moisture contribution from different sources using the Dynamic Recycling Model to track water vapor trajectories. Interestingly, conditions with reduced precipitation during El Niño events can take place along with increased precipitable water. To understand this, we analyze thermodynamic conditions in the atmosphere that are necessary for precipitation to occur over the region, such as convective available potential energy, convective inhibition, lifting condensation level, and low-level relative humidity. With this approach, we find more favorable thermodynamic conditions for the occurrence of precipitation during La Niña events, even if the content of water vapor is equal or even less than during El Niño events. We also look at the structure of the regional Hadley and Walker circulation in both types of events and find that a weaker ascending motion during El Niño events also inhibits convection. This study provides an integral picture of how precipitation anomalies over Northwestern South America during ENSO events are related to dynamic and thermodynamic conditions and sources of atmospheric moisture.

Association Between Nitrogen Dioxide Pollution and Cause-Specific Mortality in China: Cross-Sectional Time Series Study.

Nitrogen dioxide (NO2) has been frequently linked to a range of diseases and associated with high rates of mortality and morbidity worldwide. However, there is limited evidence regarding the risk of NO2 on a spectrum of causes of mortality. Moreover, adjustment for potential confounders in NO2 analysis has been insufficient, and the spatial resolution of exposure assessment has been limited. This study aimed to quantitatively assess the relationship between short-term NO2 exposure and death from a range of causes by adjusting for potential confounders in Guangzhou, China, and determine the modifying effect of gender and age. A time series study was conducted on 413,703 deaths that occurred in Guangzhou during the period of 2010 to 2018. The causes of death were classified into 10 categories and 26 subcategories. We utilized a generalized additive model with quasi-Poisson regression analysis using a natural cubic splines function with lag structure of 0 to 4 days to estimate the potential lag effect of NO2 on cause-specific mortality. We estimated the percentage change in cause-specific mortality rates per 10 μg/m3 increase in NO2 levels. We stratified meteorological factors such as temperature, humidity, wind speed, and air pressure into high and low levels with the median as the critical value and analyzed the effects of NO2 on various death-causing diseases at those high and low levels. To further identify potentially vulnerable subpopulations, we analyzed groups stratified by gender and age. A significant association existed between NO2 exposure and deaths from multiple causes. Each 10 μg/m3 increment in NO2 density at a lag of 0 to 4 days increased the risks of all-cause mortality by 1.73% (95% CI 1.36%-2.09%) and mortality due to nonaccidental causes, cardiovascular disease, respiratory disease, endocrine disease, and neoplasms by 1.75% (95% CI 1.38%-2.12%), 2.06% (95% CI 1.54%-2.59%), 2.32% (95% CI 1.51%-3.13%), 2.40% (95% CI 0.84%-3.98%), and 1.18% (95% CI 0.59%-1.78%), respectively. Among the 26 subcategories, mortality risk was associated with 16, including intentional self-harm, hypertensive disease, and ischemic stroke disease. Relatively higher effect estimates of NO2 on mortality existed for low levels of temperature, relative humidity, wind speed, and air pressure than with high levels, except a relatively higher effect estimate was present for endocrine disease at a high air pressure level. Most of the differences between subgroups were not statistically significant. The effect estimates for NO2 were similar by gender. There were significant differences between the age groups for mortality due to all causes, nonaccidental causes, and cardiovascular disease. Short-term NO2 exposure may increase the risk of mortality due to a spectrum of causes, especially in potentially vulnerable populations. These findings may be important for predicting and modifying guidelines for NO2 exposure in China.

Insights into mechanism and modelling of dynamic moisture sorption in dual-porous insulation materials with micro- and nano-scale pores

HypothesisUnderstanding moisture sorption in porous insulation materials is challenging due to the influence of multiscale pore structures on phase behavior and transport properties. Dynamic moisture sorption in dual-porous materials is likely co-determined by interior micro- and nano-scale pores, and an accurate physical model for predicting moisture evolution can be developed by clarifying the sorption mechanisms. ExperimentsMoisture behavior during the dynamic sorption of dual-porous insulation material is measured by low-field nuclear magnetic resonance (NMR) experiments. The contributions of micro- and nano-scale pores to the adsorbed moisture are differentiated using NMR relaxometry, and the evolution of moisture morphology is quantitatively analyzed. FindingsAnalysis of T2 evolution reveals that the moisture in nano-scale pores alters from adsorption layers to liquid with increasing relative humidity (RH), while minimal sorption occurs in micro-scale pores. Moisture is mainly transferred as vapor molecules at low RH levels, with the dynamic sorption enhanced by molecular diffusion in micro-scale pores. Capillary flow in nano-scale pores dominates moisture transport when RH rises above a threshold, leading to a significant increase in apparent moisture diffusivity. According to the elucidated mechanism, a physical model is further developed to predict moisture sorption inside dual-porous insulation materials, and it may serve as a basis for evaluating and optimizing the performance of dual-porous systems in different environments.

Enhancing indoor air quality in office buildings: Insight from a field study

Building tight for minimizing building energy consumption and related carbon emissions might negatively affect indoor air quality (IAQ) if this is not correctly designed and evaluated during operation. To address this concern, a post occupancy evaluation study was conducted in a recent large office building in the Autonomous Province of Bolzano (Italy). The aim of the study was to collect evidence from a relevant case study and use it as a basis to define a standardized strategy for continuous monitoring of a larger portfolio of office buildings. Additionally, carbon dioxide (CO2), particulate matter (PM2.5, PM10), total volatile organic compounds (TVOC), air temperature, and relative humidity were recorded 24/7 for a 5-week period in winter 2023. Detailed spot measurements of VOCs and aldehydes were also carried out. Perceived air quality (PAQ) was evaluated through satisfaction surveys which covered various factors influencing PAQ including 14 potential sources of dissatisfaction. A cross-modal approach allowed for a comprehensive examination of the different domains (thermal, visual, acoustic, and IAQ) on PAQ. Measured contaminants’ levels were below recommended limits. Overall, participants were neither satisfied nor dissatisfied with PAQ, and possible related sources of dissatisfaction were elements such as the relative humidity. Sick building syndrome (SBS) selfreported symptoms such as dry skin and itchy eyes confirmed potentially too low relative humidity levels.

Numerical simulation of a pulse hailstorm in the plateau region in southwestern China

Pulse hailstorms over southwestern China generally produce small hailstones with diameters <20 mm, causing nonnegligible damage to crops. This study examines the mechanisms behind the typical pulse hailstorms which frequently occur in plateau regions in southwestern China. Utilizing radar observations and the Cloud Model 1 (CM1) numerical model developed by George Bryan, the influence of environmental factors on pulse hailstorms and the associated small hailstones is investigated. The results indicate that: firstly, hailstones are primarily generated from frozen droplets, which further grow through collecting supercooled liquid water; secondly, a higher convective available potential energy (CAPE) and lower low-level relative humidity (RH) lead to the raising of convection initiation height; and lastly, higher CAPE values result in smaller hailstones on the surface due to the intensified hailstone melting process caused by higher melting layer and warmer temperatures within the warm layer (>0 °C) in this situation.

Tailoring titanosilicate molecular sieves by vanadium substitution for humidity sensing applications

There is a great interest in developing humidity sensors with enhanced sensitivity at all relative humidity (RH) ranges. To explore this, vanadium (V)-incorporated titanosilicate microporous thin films were successfully fabricated to investigate their performances as humidity sensors. The V-precursor was directly added to obtain V/V+Ti atomic of 0.1 (V0.1ETS-10) to 0.2 (V0.2ETS-10) and 0.3 (V0.3ETS-10), and characterized by FE-SEM, XRD, Raman, UV-Vis, and XPS analyses. The ETS-10 sensor displayed high sensitivity (1.11 × 104) and linearity (R2=0.9818) at room temperature across medium (32–67 %) and high (>67 %) relative humidity (RH), with rapid response (∼8 s) and recovery times (∼35 s). The sensor with an optimized amount of vanadium doping (V0.2ETS-10), showed a significant improvement in the performance in the low RH region (8–32 %) with enhanced sensitivity (1.75 × 104) and linearity (R2=0.9914). The results of our study indicate that the formation of Ti3+ with the emergence of V4+ and V5+ states resulted in enhanced sensitivity at low RH levels. Based on the obtained results, a plausible shift in the humidity sensing mechanism evolves from chemisorbed intracrystalline water to physisorbed intercrytalline and surface water with increasing RH. However, higher vanadium content led to structural alteration and impurities resulting in a notable reduction in sensitivity (1.17 × 103) and linearity (R2=0.8927).

Revisiting integrating nephelometer measurements

Integrating nephelometers are designed to measure the scattering coefficient, bsp, of an aerosol introduced into its sampling chamber. They have been and are used extensively in laboratory studies and short-term intensive aerosol characterization studies to validate and improve optical aerosol models. They are used to measure long-term temporal and spatial trends of the particle scattering coefficient, and to measure trends in the scattering enhancement factor, f(RH). The National Park Service (NPS) has operated Optec NGN nephelometers with an open sampling chamber, referred to as NGNambient, designed to measure total (coarse plus fine) particle scattering at near ambient relative humidity (RH). However, the NGN is no longer manufactured and will be replaced with Ambilabs 2WIN nephelometers. An intercomparison study was initiated to compare the NGNambient, an enclosed heated NGN, two 2WIN nephelometers, one held at RH ≤ 40% and another modified to sample at near ambient RH, and a TSI (Shoreview, MN, USA).The objective of the study was to evaluate the suitability of the 2WIN to replace the NGNambient and more generally to assess the suitability of the 2WIN instrument to be used to track long term trends in bsp and f(RH) values. The two 2WIN's, TSI and the heated NGN have enclosed sampling chambers with PM2.5 inlets. Measurements of particle physical and chemical properties and sampling chamber RH allowed for an assessment of the inter-comparability of relationships between optical models and nephelometer measurements. Heating of the sampling chamber to reduce RH to less than 40% did not significantly volatilize particle nitrate but heating to reduce the RH to near 20% did. It was also determined that measurement of the scattering enhancement function, f(RH), was underestimated in this study, by about 20% for RH levels of 70% or greater, when the reference RH nephelometer was held at RH ≤ 40% compared to when the RH ≤ 10%. The study highlighted the importance of careful calibration of the instrument and careful documentation of the sampling chamber environment in which the measurement is made. Knowing precisely the RH in the sensor volume is critical to the interpretation of measured bsp levels. Monitoring of long-term temporal and spatial trends should be done either with the sampling chamber at or near ambient RH to track changes in ambient bsp or at RH ≤ 10% to understand changes in particulate mass concentrations contributing to bsp. Understanding changes in f(RH) over time and space should be done with the reference bsp at RH ≤ 10%. The lower RH levels should be achieved by some method other than heating the chamber to avoid volatilization of the aerosol species such as ammonium nitrate.

Chemical composition-dependent hygroscopic behavior of individual ambient aerosol particles collected at a coastal site

Abstract. This study investigated the hygroscopic behavior of individual ambient aerosol particles collected at a coastal site of Jeju Island, South Korea. The size of the particles changes along with the phase transitions during humidification and dehydration processes, and the chemical compositions of the particles were determined by optical microscopy and scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDX), respectively. Of the 39 particles analyzed, 24 were aged sea spray aerosols (SSAs), with diverse mixing ratios of Cl− and NO3-. The ambient SSAs exhibited multiple deliquescence and efflorescence transitions that were dominantly influenced by NaCl, NaNO3, MgCl2, Mg(NO3)2, and organic species covering the surface of the aged SSAs. For Cl-rich SSAs with X(Na,Mg)Cl&gt;0.4, although some particles showed very slow water uptake at low relative humidity levels (RH ≃30 %), two major transitions were observed during the humidification process. The first was at RH ≃63.8 %, regardless of their chemical compositions, which is the mutual deliquescence relative humidity (MDRH) level; and the second was at RH 67.5 % to 73.5 %, depending on their chemical compositions, which are the final deliquescence relative humidity (DRH) levels. During the dehydration process, the Cl-rich SSAs showed single-stage efflorescence at RH 33.0 % to 50.5 %, due to simultaneous heterogeneous crystallization of inorganic salts. For Cl-depleted SSAs with X(Na,Mg)Cl&lt;0.4, two prompt deliquescence transitions were observed during the humidification process. The first was at MDRH 63.8 %, and the second was at RH 65.4 % to 72.9 %. The mutual deliquescence transition was more distinguishable for Cl-depleted SSAs. During the dehydration process, step-wise transitions were observed at efflorescence RH levels (ERH 24.6 % to 46.0 % and 17.9 % to 30.5 %), depending on their chemical compositions. Additionally, aged mineral particles showed partial or complete phase changes with varying RH due to the presence of SSAs and/or NO3- species. In contrast, non-reacted mineral and Fe-rich particles maintained their size during the entire hygroscopic process. The mixture particles of organic and ammonium sulfate (AS) exhibited lower deliquescence and efflorescence RH levels compared to pure AS salt, highlighting the impact of organic species on the hygroscopic behavior of AS. These findings emphasize the complexity of atmospheric aerosols and the importance of considering their composition and mixing state when modeling their hygroscopic behavior and subsequent atmospheric impacts.

Acute and subchronic exposure to urban atmospheric pollutants aggravate acute respiratory failure in infants

Urban air pollution is a major factor that affects the respiratory health of children and adolescents. Less studied is exposure during the first two years of life. This study analyzed the influence of acute and subchronic exposure to urban air pollutants on the severity of acute respiratory failure (ARF) in the first two years of life. This population-based study included 7364 infants hospitalized with ARF. Acute exposure was considered to have occurred 1, 3 and 7 days before hospitalization and subchronic exposure was considered the mean of the last 30 and 60 days. We found that for acute exposure, significant increases in days of hospitalization (LOS) occurred at lag 1 day for NO2 (0.24), SO2 (6.64), and CO (1.86); lag 3 days for PM10 (0.30), PM2.5 (0.37), SO2 (10.8), and CO (0.71); and lag 7 days for NO2 (0.16), SO2 (5.07) and CO (0.87). Increases in the risk of death occurred at lag 1 day for NO2 (1.06), SO2 (3.64), and CO (1.28); and lag 3 days for NO2 (1.04), SO2 (2.04), and CO (1.19). Subchronic exposures at 30 and 60 days occurred for SO2 (9.18, 3.77) and CO (6.53, 2.97), respectively. The associations were more pronounced with higher temperatures and lower relative humidity levels. We concluded that acute and subchronic exposure to higher atmospheric concentrations of all the pollutants studied were associated with greater severity of ARF. The greatest increases in LOS and risk of death occurred with hot and dry weather.

A case study of weather impact on air pollution during the COVID-19 pandemic in South Africa

This study investigates climate, weather characteristics, and air pollution during the third COVID-19 wave in South Africa. During this time, a decrease in of SO2 and NO2 column mass was observed. The investigation displays a positive trend in for tropospheric Ozone (O3) mass mixing in winter over the last two decades with a fitted slope of 1.0005. Despite the negative trend for the daily changes (for all 12 months) of the total column mass density for PM2.5 during the year before the pandemic and two years after for pandemic years, they have slightly increased specifically during winter COVID-19 third wave time. The temporal seasonal yearly time changes (1961–2021) of different meteorological parameters such as surface temperature, low-level vertical pressure velocity, low-level relative humidity, and precipitation rate over South Africa show sharp changes from 2020 to 2021. This analysis indicates rather colder surface temperatures, smaller but positive low-level vertical velocity, slightly higher low-level relative humidity, and higher total country precipitation rate in the study area during the COVID-19 pandemic years. Weather chart analysis displays a very stable atmospheric condition during the third wave of COVID-19 peak time. This is correlated with the extension of the atmospheric ridge associated with a blocking high pressure, downward motion, positive vorticity, and rather weak winds specific in the north, west, and central areas causing atmospheric stability and possible accumulation of the atmospheric pollution corresponding to the higher COVID-19 cases during the South Africa third wave.

Short-term impact of extreme temperatures, relative humidity and air pollution on emergency hospital admissions due to kidney disease and kidney-related conditions in the Greater Madrid area (Spain)

While some studies report a possible association between heat waves and kidney disease and kidney-related conditions, there still is no consistent scientific consensus on the matter or on the role played by other variables, such as air pollution and relative humidity.Ecological retrospective time series study 01-01-2013 to 31-12-2018). Dependent variables: daily emergency hospitalisations due to kidney disease (KD), acute kidney injury (AKI), lithiasis (L), dysnatraemia (DY) and hypovolaemia (HPV). Independent variables: maximum and minimum daily temperature (Tmax, Tmin, °C), and daily relative humidity (RH, %). Other variables were also calculated, such as the daily temperature for risk of kidney disease (Theat, °C) and low daily hazardous relative humidity (HRH%).As variables of air pollution, we used the daily mean concentrations of PM10, PM2.5, NO2 and O3 in μg/m3. Based on these, we then calculated their daily excesses over World Health Organisation (WHO) guideline levels (hPM10, hPM2.5, hNO2 and hO3 respectively). Poisson family generalised linear models (GLMs) (link = log) were used to calculate relative risks (RRs), and attributable risks and attributable admissions. In the models, we controlled for the covariates included: seasonalities, trend, autoregressive component, day of the week, month and year.A statistically significant association was found between Theat and all the dependent variables analysed. The greatest AKI disease burden was attributable to Theat (2.2 % (1.7, 2.6) of attributable hospital admissions), followed by hNO2 (1.7 % (0.9, 3.4)) and HRH (0.8 (0.6, 1.1)). In the case of hypovolaemia and dysnatraemia, the greatest disease burden again corresponded to Theat, with 6.9 % (6.2, 7.6) and 5.7 (4.8, 6.6) of attributable hospital admissions respectively.Episodes of extreme heat exacerbate daily emergency hospital admissions due to kidney disease and kidney-related conditions; and attributable risks are likewise seen for low relative humidity and high ozone levels.