Air Change Research Articles

<sec><title>BACKGROUND</title>Due to rising temperatures, individuals are predicted to spend more time in under-ventilated indoor spaces, increasing TB transmission risk. We studied the impact of indoor ventilation on TB transmission risk in homes of persons with TB and in health care facilities in Puducherry, India.</sec><sec><title>METHODS</title>We measured ventilation in air changes per hour (ACH) under different ventilation conditions using a carbon dioxide decay method. We estimated transmission risk using the Wells–Riley equation.</sec><sec><title>RESULTS</title>Forty-five measurements were taken in 13 homes and 7 health care spaces. In the closed condition (doors and windows closed, fans off), ACH was low (mean 2.23, standard deviation [SD] 2.27) and TB transmission risk was high at 62% (SD 31%). When air conditioning (AC) was on, ACH reduced to 0.75 (SD 0.51), and TB transmission was highest at 76% (SD 13%). Natural ventilation significantly improved ACH (mean 9.46, SD 3.90; P < 0.001) and TB transmission risk to mean 20% (SD 14%; P < 0.001) compared with the closed condition.</sec><sec><title>CONCLUSION</title>TB transmission risk in homes and health care spaces is high, especially with AC on. Adapting to rising temperatures using novel methods of ventilation, cooling, and air purification is critical to TB infection control in the era of climate change.</sec>

Indoor Air Quality (IAQ) in gyms is a concern for both athletic performance and for reducing airborne transmission of viruses, particularly during peak usage hours. To reduce the build-up of breath exhalate and other bodily emissions, facilities typically force outside fresh air through the indoor space, but building operators often limit this air flow to minimize air conditioning costs. Small enterprises and non-profits often lack affordable ways to test fresh air ventilation. Grounded in first principles, this study presents a low-cost monitoring approach for evaluating fresh air adequacy by using the carbon dioxide (CO<sub>2</sub>) tracer gas decay method to estimate Air Change Rates (ACR), translate them into occupancy thresholds, and assess Particulate Matter (PM). Monitoring was performed in the American University of Beirut weight room over two weeks in July–August 2025. A low-cost sensor system was designed and built to measure CO<sub>2</sub> and particulate matter (PM₁.₀, PM₂.₅, PM₁₀). ACR was estimated by fitting nighttime CO<sub>2</sub> decay after gym closure to a mass-balance model. Compliance with the standards of the American Society for Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) was assessed, and CO<sub>2</sub>–PM associations were tested with Spearman’s correlation. Across 10 valid nights, ACR ranged from 1.00–1.94 h⁻¹ (mean 1.51 ± 0.37 h⁻¹), a value that would accommodate ~17 occupants according to ASHRAE 62.1. The weight room frequently hosts more than double that number during the evening hours of the Fall and Spring semesters, indicating insufficient fresh air flow for the number of users. The mean indoor CO<sub>2</sub> during open hours was ~792 ppm and tracked gym occupancy patterns. PM concentrations did not correlate with occupancy, and peaked during the hours the gym was closed, indicating a different mechanism for PM build-up. This work demonstrates that public facilities can assess ventilation with inexpensive monitoring, offering a practical alternative to costly HVAC engineering services. The approach enables resource-constrained operators to identify ventilation gaps and pursue evidence-based improvements to IAQ without disrupting normal operations.

ABSTRACTThe sensory systems of animals are essential for them to respond to environmental cues and signals. However, their functionality might be altered by climate change. Most bats, for example, rely on acoustic signal emission to acquire food, but their high-frequency echolocation calls are strongly attenuated in the air. Attenuation in air changes with changing weather conditions, which can lead to shifts in echo-based prey detection distance. However, bats can adjust call parameters to the task and environment, and this behavioural plasticity may help them to counteract potential increases in sound attenuation to keep echo detectability constant. We explored this ability in a community of insectivorous bats in a montane forest of Costa Rica. We recorded bat echolocation calls in response to experimentally increased temperatures, simulating intermediate and arguably realistic projected climate change scenarios. We calculated atmospheric attenuation and detection distance for each temperature and echolocation call. We found some changes in source level and call duration, yet not in peak frequency, and responses to increasing atmospheric attenuation were not consistent across species. This might be explained by several non-mutually exclusive reasons, including that the experimental increase in temperature and change of atmospheric attenuation were not sufficient to affect close-range prey detection. Ultimately, this study contributes to our understanding of sensory system adaptation under the pressure imposed by climate change.

ABSTARCT Honeycomb pests, bacteria, parasites, fungi, viruses, unconscious pesticide use, water, air, environmental pollution and severe climate change cause significant colony losses. The aim of this study was to see how locally isolated Bacillus strains and proteins isolated from different locations affect bee diseases and pests. In this study, Bacillus sp. strains isolated from soil (TB1), bee (AB1), wax moth (GB1) (Galleria mellonella), boxwood pest (CB1) (Cydalima perspectalis) and Varroa destructor were analyzed. In addition, the effects of Cry 1, Cry 3 and Cry 4 proteins obtained from Cry protein screening on Bacillus sp. strains were also examined. It was observed that a total of four Bacillus sp. strains were effective against both wax moth and Varroa destructor. Since bacteria and proteins are applied through food in each application, they are given to their food and transferred to the pests. According to the results obtained as a result of the application, the effect of GB1 bacteria on wax moth was 83.3% and the effect of AB1 bacteria on Varroa destructor was 66.6%. Cry1 protein was found to cause 73.66% mortality, especially in wax moth and was significantly different from the other groups (F (2,6) = 68.83; p < 0.05). It was determined that the mortality values of GB1 isolate and Cry4 protein on Varroa destructor were equal at the end of the experiment (p > 0.05). According to the data obtained in this context, the strain with the highest results has the potential to be used for future formulation studies.

The effects of environmental and climatic factors on the prevalence of allergic rhinitis (AR) in Changchun, China, have not been reported. This study aimed to investigate the relationship between meteorological factors, air pollution, and the number of AR outpatient visits in Changchun, and determine whether different temperature and humidity conditions would influence the effect of air pollution on the number of AR outpatient visits. Generalized additive and distributional lag non-linear models were used to assess the relationship between meteorological factors, air pollution, and the number of AR outpatient visits. Using different temperatures and relative humidities, we determined whether the effects of air pollution on the number of AR outpatients would change under different meteorological conditions. In total, 15,338 AR outpatient records were collected during the study period. Except for O3, other pollutants were positively correlated with AR outpatient visits overall. Results found that each 10 µg/m3 increase in PM2.5, PM10 and NO2, and per 1 µg/m3 increase in the daily average concentration of SO2, the number of AR outpatient visits increased by 1.45% (95% CI: 0.23%-2.70%), 1.03% (95% CI: 0.06%-2.00%), 3.98% (95% CI: 1.25%-6.78%), and 1.68% (95% CI: 0.78%-2.59%), respectively. Air pollution has immediate and cumulative lagged effects on these visits. There was a non-linear correlation between meteorological factors and the number of AR outpatient visits. Low and high temperatures, low RH and low barometric pressure may affect the number of AR outpatient visits. Compared with the minimum risk of each respective meteorological factor, their Relative Risk (RR) values are 1.65(95%CI: 0.80–3.40), 1.05(95%CI: 1.03–1.08), 1.53(95%CI: 1.21–1.93), and 1.75(95%CI: 1.25–2.43), respectively. The impact of low temperature is more pronounced. The hazardous effect of extreme meteorological factors was stronger in the < 15 years age group. In addition, The effect of air pollution on the number of AR outpatient visits increased at low temperature (< 33.3% percentile) and low relative humidity (< 33.3% percentile). Increased air pollution and changes in meteorological factors are associated with an increased risk of AR outpatient visits. Children < 15 years old are the most vulnerable to extreme weather factors. Low temperature and low RH could positively modify the effects of air pollution on AR outpatient visits.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-16265-1.

Balancing sustainability and safety: Reducing HVAC air exchange rates in operating rooms without increasing infection risk.

Intensive care units (ICUs) are high-risk areas for hospital-acquired infections. Although impinging jet ventilation (IJV) shows great potential in cooling conditions, its ventilation efficiency in heating conditions remains questionable. This study numerically investigates the performance of IJV in a four-bed ICU, examining key factors such as air inlet position, outdoor temperature and air change rate. The interaction between the warm supply air current and cold air currents from exterior walls and windows determines airflow characteristics and respiratory droplet dispersion. Positioning the air inlet near the window promotes early mixing of warm and cold air currents, resulting in a more uniform temperature distribution (vertical gradients: &lt; 0.2°C/m vs. 0.83°C/m). Lower outdoor thermal loads (e.g. 20°C vs. −10°C) enhance air mixing and droplet removal efficiency. Increasing the air change rate (ACH) from 4 to 12 ACH reduces the intake fraction of fine droplets (&lt;5 μm) by adjacent susceptible patients from 0.48% to &lt;0.05%. Temperature differences between patient-level air and outlet air remain within 1.0°C if ACH ≥8, ensuring thermal comfort. This study has validated IJV's potential for ICU applications and has provided theoretical guidance for its design.

The present investigation provides a comparative six-month analysis of atmospheric pollution by polycyclic aromatic hydrocarbons (PAHs) in the urban region of Opole, Poland. The study employs dual monitoring methods: traditional quartz filter-based active air sampling and active moss biomonitoring using Pleurozium schreberi, Sphagnum fallax, and Dicranum polysetum mosses. The experimental campaign took place from August 2021 to February 2022, spanning the autumn and winter seasons. PAH concentrations were measured using gas chromatography–mass spectrometry (GC-MS) following methodical sample extraction protocols. Filters documented transient air changes in PAHs, particularly high-molecular-weight (HMW) components such as benzo[a]pyrene (BaP), which exhibited considerable increases during the colder months due to heightened heating activities and less dispersion. The size of particles deposited on the filters varied from 0.16 to 73.6 μm, with an average size of 0.71 μm. Mosses exhibited cumulative uptake trends, with D. polysetum showing the greatest bioaccumulation efficiency, particularly for low- and medium-molecular-weight PAHs, followed by P. schreberi and S. fallax. Meteorological indices, including sun radiation and air temperature, demonstrated significant negative relationships with PAH buildup in mosses. Diagnostic ratio analysis verified primarily pyrogenic sources (e.g., fossil fuel burning), although petrogenic contributions were detected in D. polysetum, indicating its increased sensitivity to evaporative emissions. The study shows that the integration of moss biomonitoring with traditional filter samples provides a strong, complementary framework for assessing air quality, particularly in fluctuating meteorological settings. The results advocate for the integration of moss-based methodologies into environmental monitoring initiatives and provide significant insights into contaminant dynamics influenced by seasonal and meteorological factors.

Airborne bioaerosol transmission in hospital waiting corridor: Characteristic, exposure risk and evaluation of prevention strategies.

Portable air cleaners with HEPA filtration and UV-C irradiation to reduce air contamination in a multi-patient dental environment.

Numerical analysis of surface temperature growth for various chemistry 26,650 Li-ion cell utilizing air and biobased phase change material cooling

The National Cookstove Program has been launched by the Federal Government of Mexico, attempting to reach one million rural homes by the year 2030. Voluntary ISO emission standards for fine particulate matter (PM2.5) and carbon monoxide (CO) relate emission rates from stoves to indoor air concentrations using a single zone box model (SZM) to derive performance tiers. Region-specific emission benchmarks for cookstove performance that are linked to estimated benefits in reduced indoor air concentrations and resultant health impacts will be important in product selection. Here we compare the SZM to measured indoor PM2.5 and CO concentrations for five stove stacking combinations using controlled cooking tests of typical foods from the Purepecha region of Mexico to derive region-specific benchmarks. The results demonstrate that the SZM systematically overpredicted PM2.5 emissions based on thermal plume effects and ventilation which can be adjusted based on strong relationships (Adjusted r2 = 0.96, p &lt; 0.001) with emission rates and air changes per hour. Adjustment of PM2.5 ISO voluntary standards for systematic bias caused by plume buoyancy and ventilation is important in ensuring that the ISO benchmarks reflect the actual indoor concentrations measured in homes. The ISO benchmarks for CO should be revisited as the indoor concentrations from traditional stoves met the most stringent benchmarks but were in the range of concentrations associated with adverse health impacts in adults and psychosocial impacts in children.

Recent experimental and epidemiologic data have strongly associated air pollution in the pathogenesis of insulin resistance and type 2 diabetes mellitus. We explored the effect of inhalational exposure to concentrated ambient particulate matter smaller than 2.5 μm (PM2.5), or filtered air, using a whole-body inhalation system (6 hours/day, 5 days/week) for 24 weeks on metabolism and brown adipose tissue (BAT) function. Mechanistic evaluation of insulin resistance, glucose uptake with 18F-fluorodeoxyglucose positron emission tomography, alongside evaluation for differentially methylated regions, chromatin accessibility, and differential expression of genes was performed. PM2.5 exposure impaired metabolism through changes in key BAT transcriptional programs involved in redox stress, lipid deposition, fibrosis, and altered thermogenesis. Significant differential methylation and widespread chromatin remodeling was noted in BAT with PM2.5. Integrated analysis uncovered a role for the histone deacetylase HDAC9 and histone demethylase KDM2B. The latter demethylates Lys-4 and Lys-36 of histone H3. Specifically, studies using ChIP combined with quantitative PCR confirmed HDAC9 and KDM2B occupancy and reduced H3K36me2 on the promoter of target BAT genes in PM2.5 mice, while Hdac9/Kdm2b knockdown and overexpression increased and reduced BAT metabolism, respectively. Collectively, our results provide insights into air pollution exposure and changes in BAT and metabolism.

Far-ultraviolet-C (far-UVC) irradiation has emerged as a breakthrough disinfection technology for the treatment of indoor air. Far-UVC wavelengths (222 nm) from filtered krypton-chloride excimer lamps are effective at inactivating airborne viruses and are safe for human exposure, thus enabling the continuous treatment of bulk air in occupied settings. This study quantifies the susceptibility of airborne SARS-CoV-2, aerosolized in human saliva, to far-UVC radiation. We measured fluence rate-based Z-value susceptibility constants (±standard error) of 4.4 ± 0.6 and 6.8 ± 0.7 cm2 mJ-1 for airborne SARS-CoV-2 under 40% and 65% relative humidity (RH) levels, respectively. At modeled far-UVC irradiation levels corresponding to 25% of the maximum safe human exposure limit, the resulting far-UVC equivalent air changes per hour (eACH) exceeded 62 h-1 at 65% RH and were significantly greater than the corresponding airborne SARS-CoV-2 natural decay rate (±standard error) of 5.4 ± 1.1 h-1, measured in the absence of far-UVC. These results define first-order loss rates for airborne SARS-CoV-2 under far-UVC exposure and support quantitative risk assessments and rational disinfection system implementation.

Symbiotic nitrogen fixation (SNF) is an effective strategy for legumes and actinorhizal plants to acquire atmospheric nitrogen (N2) for their growth and development. Like other enzymatic processes in roots, the efficiency of SNF is highly dependent on soil temperature. Since global atmospheric temperature change also affects soil temperature, it is essential to know the temperature response of different types of plant-microbial symbioses capable of SNF at the molecular, physiological, and ecosystem levels on air and soil temperature changes. This is of particular significance, because the ability of nitrogen-fixing microbial symbionts to deal with temperature changes in the soil can affect growth and development of legumes and actinorhizal plants and, hence, the sustainability of ecosystems in a changing climate. However, temperature response may differ between different groups of nitrogen-fixing microbial symbionts (e.g., rhizobia vs. Frankia) and between different strains of the same microbial symbiont. In the present review, we summarize current knowledge on the temperature response of SNF, describe unexplored research topics, and propose future basic and applied research avenues under controlled conditions and in field studies. It provides a holistic view on the subject to encourage interdisciplinary research on this subject which has been largely neglected during the last decades, but of increasing significance due to global climate change.

Admission to shared hospital rooms are a risk factor of healthcare-associated (HA) SARS-CoV-2. Quantifying the impact of engineering controls such as ventilation and filtration is essential to informing resource utilization and infection prevention guidelines. Multicenter test-negative study of patients exposed to SARS-CoV-2 in shared rooms across five hospitals between January and October, 2022. Independent variables tested were measured air changes per hour (ACH), presence of any room mechanical ventilation (RMV), or portable high-efficiency particulate air (HEPA) filter. Covariates included facility (number of beds in room, outbreak status of unit), source patient (presence of symptoms, RT-PCR cycle threshold (Ct) value), and exposed patient factors (age, sex, time from last SARS-CoV-2 vaccine, previous SARS-CoV-2 infection, exposure duration). Multilevel logistic mixed models used to estimate the impact of engineering controls on transmission. Among 468 exposed patients, secondary attack rate was 26.3% (range 7.5-33.3% across hospitals). In multivariable analysis, increased ACH was associated with decreased odds of infection (adjusted odds ratio (aOR) 0.88, 95% CI 0.78-1.00; p=.046) as were exposure duration and Ct value of source patient. Presence of RMV was also associated with decreased odds of infection (aOR 0.51, 95% CI 0.27-0.95; p=.034) while use of portable HEPA filter was not significant (aOR 0.58, 95% CI 0.26-1.31; p=.18). Improved ventilation was independently associated with lower odds of SARS-CoV-2 infection among exposed roommates. Ensuring RMV is present and optimizing ACH may significantly mitigate the risk of HA-SARS-CoV-2. Future prospective studies should assess optimal ACH thresholds and the impact of portable HEPA filters.

In high-density urban environments, single-sided ventilation in multi-storey residential buildings often proves inadequate, leading to poor indoor air quality and increased reliance on mechanical systems. This study investigates the effectiveness of wing wall configurations as passive strategies to enhance wind-driven natural ventilation in a multi-unit, two-storey building model. Using validated computational fluid dynamics (CFD) simulations, five wing wall layouts were evaluated under five prevailing wind directions, with results benchmarked against boundary-layer wind tunnel experiments. Key performance indicators included indoor air speed and air change rate (ACH). The findings reveal that the addition of wing walls can increase indoor air speeds and ACH by 50% to 200% compared to baseline conditions, with the greatest improvements observed on upper floors. Among the configurations tested, the arrangement with two inner fins perpendicular to the window (Case 2) achieved the highest ventilation performance, particularly at a wind angle of 67.5°. These results underscore the influence of both building geometry and wind direction on natural ventilation efficacy in complex, multi-unit settings.

Dose variation due to changes in bowel air poses significant challenges for carbon radiotherapy in pancreatic cancer. This retrospective study evaluated adensity-override optimization technique to mitigate dosimetric uncertainties caused by bowel air changes. Planning CT and cone-beam CT data from 8patients with locally advanced pancreatic cancer undergoing stereotactic ablative radiotherapy were analyzed. Treatment simulations used adose of 55.2GyE in 12fractions with afour-field setup (anterior, lateral, posterior, posterior oblique). Four density-override patterns were compared: pattern0 (no override), pattern1 (replacing bowel gas with water), pattern2 (replacing the entire bowel with mean bowel HU), and pattern3 (replacing bowel gas with mean bowel HU). Dose evaluations included fraction-wise and accumulated dose analyses, focusing on target coverage, homogeneity index, and organs at risk doses. Pattern2 achieved the largest clinical tumor volume coverage and the fewest fractions with > 5% coverage loss for the anterior beam, followed by pattern3. However, pattern2 demonstrated poorer homogeneity for the lateral beam compared to patterns1 and3 and ahigher gastrointestinal (GI) dose for the anterior beam. This study evaluated the importance of density overrides to address bowel air variations. For patients where amore uniform dose is desirable or whose tumor is adjacent to the GI tract, apattern3 density-override should be considered.

ABSTRACTDentin hypersensitivity is characterized by transient, sharp pain resulting from dentin exposure due to enamel or cementum loss. Current treatments, which primarily focus on superficial tubule occlusion or nerve desensitization, provide only temporary relief. Copine7 (CPNE7) induces odontoblast differentiation and physiologic dentin regeneration, enabling biological dentin sealing and presenting a novel therapeutic approach. This study reports the first‐in‐human results of a randomized, double‐blind, dose‐escalation phase 1/2a clinical trial evaluating the safety, tolerability, preliminary efficacy, and pharmacokinetics of the CPNE7‐derived functional peptide (selcopintide) in patients with dentin hypersensitivity. In Part A (Single Ascending Dose, SAD), 24 participants received a single topical application of selcopintide at ascending doses (2.5, 5, and 10 μg/tooth) in a 6:2 randomization ratio (treatment: placebo). In Part B (Multiple Ascending Dose, MAD), 16 participants received three topical applications (5 and 10 μg/tooth) over 15 days (day 1, 8, and 15; visits 2–4) with the same randomization ratio. Efficacy endpoints were assessed by changes in cold water, evaporative air, and tactile sensitivity. In Part B, the 10 μg selcopintide group demonstrated statistically significant reductions from the baseline across all three measures (p < 0.05), with a mean decrease of −23.2 ± 19.4 mm in VAS, the primary efficacy endpoint. All doses were well tolerated, with no serious adverse events and no detectable systemic absorption of selcopintide. These findings support the safety, tolerability, and preliminary efficacy of selcopintide as a novel therapeutic candidate for the treatment of dentin hypersensitivity.

Hybrid ventilation is indicated as one of the effective methods of maintaining thermal comfort and indoor air quality and reducing energy consumption in buildings. It assumes the capacity to switch between natural and mechanical ventilation, allowing the most efficient use of the outdoor air potential. This article aims to quantify the impact of changing ventilation system, from natural to hybrid, on indoor air parameters and air change rates in a bedroom of a single-family house. The distinct aspects of this study include longitudinal measurement over three years, natural ventilation substituted by hybrid ventilation halfway into the monitoring period, and unaltered building and user characteristics. The analysis is based on measurements of temperature, relative humidity, CO2 concentration, and window opening for three seven-month measurement periods from September 1 to March 31. The measurements are complemented by in-depth user feedback and an audit of the building structure and installed HVAC systems. A clear correlation was observed between the values of relative humidity and carbon dioxide concentration and the type of ventilation strategy. A significant influence of residents’ behavior on the achieved indoor air parameters was observed.