Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of the current coronavirus disease 2019 (COVID-19) pandemic, is evolving. Thus, the risk of airborne transmission in confined spaces may be higher, and corresponding precautions should be re-appraised. Here, we obtained the quantum generation rate (q) value of three SARS-CoV-2 variants (Alpha, Delta, and Omicron) for the Wells-Riley equation with a reproductive number-based fitted approach and estimated the association between the infection probability and ventilation rates. The q value was 89–165 h⁻¹ for Alpha variant, 312–935 h⁻¹ for Delta variant, and 725–2,345 h⁻¹ for Omicron variant. The ventilation rates increased to ensure an infection probability of less than 1%, and were 8,000–14,000 m³ h⁻¹, 26,000–80,000 m³ h⁻¹, and 64,000–250,000 m³ h⁻¹ per infector for the Alpha, Delta, and Omicron variants, respectively. If the infector and susceptible person wore N95 masks, the required ventilation rates decreased to about 1/100 of the values required without masks, which can be achieved in most typical scenarios. An air purifier was ineffective for reducing transmission when used in scenarios without masks. Preventing prolonged exposure time in confined spaces remains critical in reducing the risk of airborne transmission for highly contagious SARS-CoV-2 variants.

In countries suffering from heavy ambient air pollution, ventilation is a problem, as ventilation intakes outdoor air pollutants, such as particulate matter with an aerodynamic diameter less than 2.5 μm (PM_2.5), while removing indoor air pollutants. Thus, it is important to identify appropriate ventilation-purification strategies to build healthy indoor environments with low energy consumption. This study reports the comparison of two sets of strategies, i.e., mechanical ventilation with filters and natural ventilation with indoor air cleaners, in respect to energy consumption and the PM_2.5 and carbon dioxide (CO₂) exposure of occupants in a typical apartment in Beijing, China. A dynamic mass balance model was employed to calculate the PM_2.5 and CO₂ exposure concentrations, while the energy consumption of heating and cooling was simulated with the Designer’s Simulation Toolkit. It was found that natural ventilation with air cleaners provided lower PM_2.5 exposure compared with that of mechanical ventilation with filters; however, mechanical ventilation achieved a lower CO₂ exposure concentration. The annual cooling, heating, and fan energy consumption of natural ventilation strategies are lower than those of mechanical ventilation strategies. With respect to natural ventilation, an infiltration rate of 0.3-0.4 h^-1 was the preferred setting, which led to low PM_2.5 and CO₂ exposure with lower energy consumption. The basic requirements for controlling indoor PM_2.5 could be met if the threshold is set at 25 μg/m³. The results provide guidelines on how to combine multiple ventilation purification strategies to improve indoor air quality with lower energy usage.

A growing number of cases have proved the possibility of airborne transmission of the coronavirus disease 2019 (COVID-19). Ensuring an adequate ventilation rate is essential to reduce the risk of infection in confined spaces. In this study, we estimated the association between the infection probability and ventilation rates with the Wells-Riley equation, where the quantum generation rate (q) by a COVID-19 infector was obtained using a reproductive number-based fitting approach. The estimated q value of COVID-19 is 14-48 h^-1. To ensure an infection probability of less than 1%, a ventilation rate larger than common values (100-350 m³/h per infector and 1200-4000 m³/h per infector for 0.25 h and 3 h of exposure, respectively) is required. If the infector and susceptible person wear masks, then the ventilation rate ensuring a less than 1% infection probability can be reduced to a quarter respectively, which is easier to achieve by the normal ventilation mode applied in typical scenarios, including offices, classrooms, buses, and aircraft cabins. Strict preventive measures (e.g., wearing masks and preventing asymptomatic infectors from entering public spaces using tests) that have been widely adopted should be effective in reducing the risk of infection in confined spaces.

Cooking can release high concentrations of different air pollutants indoors, including particulate matter, polycyclic aromatic hydrocarbons (PAHs), and other gaseous pollutants such as volatile organic compounds (VOCs), oxides of carbon (CO_x), and oxides of nitrogen (NO_x). Although some reviews have been conducted on emissions from cooking, they have not paid specific attention to Chinese cooking. Subsequent research, however, has focused on this aspect. We collected literature from 1995 to 2016 and summarized air pollutant emissions from Chinese cooking. We analyzed the characteristics of such pollutants based on different influential factors. It was found that the cooking method could have a predominant impact on emissions from Chinese cooking, and oil-based cooking produces air pollutants at much higher levels than water-based cooking. In addition, the use of gas stoves released more pollutants than electric stoves. Furthermore, the type and temperature of oil could have caused disparity in source strengths from the oil heating process. Ventilation patterns or the operation mode of range hoods could control indoor pollution levels. With more information focused on Chinese cooking emissions, we can propose more effective strategies for improving the indoor air environment in China.

Occupants’ interactions with windows influence both building energy consumption and exposure to airborne pollutants indoors. Occupants’ window opening behavior varies from region to region due to physical environmental factors and social reasons. China is now confronting severe atmospheric pollution, which may affect occupants’ window opening behaviors. A field study was conducted in 8 naturally ventilated residential apartments in Beijing and Nanjing, China. This involved periodically monitoring window states of eight residential apartments within each season from October 2013 to December 2014 by magnetic induction devices (TJHY, CKJM-1). Relationships between the probability of window opening (p) and explanatory variables, including outdoor air temperature (t_o), outdoor relative humidity (RH), outdoor wind speed (V_s), and ambient PM_2.5 (particles with aerodynamic diameter less than 2.5 microns) concentrations (C_p), were analyzed. Stochastic models of occupants’ interactions with windows in monitored residences were established via univariate and multivariate linear logistic regression for both cities. According to the results, t_o is the most important explanatory variable affecting occupants’ interactions with windows in monitored residences. The best multivariate linear logistic model result from the "backward selection" procedure based on "Akaike Information Criterion" (AIC) includes t_o, RH, V_s and C_p as explanatory variables, which implied that outdoor air quality, represented by C_p, has become a concern affecting Chinese residents’ interactions with windows.

As one of the commonly found tracer gas to evaluate the air quality, high concentration of carbon dioxide (CO₂) can cause exhaustion and drowsiness in enclosed spaces, especially those environments with very limited spaces, such as aircraft cabins. The phenomenon that CO₂ concentration keeps high due to the eddy airflow in some certain zones is named the CO₂ lockup phenomenon in this study. This CO₂ lockup phenomenon has not been clearly identified in previous research in relation to air quality in aircraft cabins. This paper presents the numerical study on the CO₂ lockup phenomenon in aircraft cabins. Firstly, the airflow, temperature and sulfur hexafluoride (SF₆) concentration fields in a simulated aircraft cabin mock-up with seven rows were numerically calculated by computational fluid dynamics (CFD) approach and then the results were compared with the experimental data to verify the reliability of the numerical methods. Secondly, the air velocity and CO₂ concentration distribution were further calculated in two aircraft cabin mock-ups (i.e. Boeing 737-200 and Airbus A330-300) to investigate the CO₂ lockup phenomenon. Finally, different ventilation strategies were numerically tested by changing air supply velocity and direction to optimize the ventilation scheme for the purpose of reducing the impact of the CO₂ lockup phenomenon and improving air quality in aircraft cabins.

Outdoor particles are a major contributor to indoor particles which influence the indoor air quality. The outdoor particle concentration also affects the outdoor air quality but the real outdoor particle concentration around buildings may differ from monitored concentrations at monitoring sites. One main factor is the effect of vegetation, especially trees. Numerical simulations were used to investigate the effects of trees on particle concentration distributions around target buildings. The drift flux model was combined with the Reynolds-Averaged Navier-Stokes (RANS) model to model the particle distribution and the airflow. Thirteen cases were analyzed to compare the effects of tree type, tree-building distance and tree canopy-canopy distance on the outdoor particle concentration distribution. The results show that cypress trees reduce the outdoor particle concentration more than pine trees, that shorter tree-building distances (TBD) reduce the particle concentration more than longer tree-building distances, and that a zero tree canopy-canopy distance (CCD) reduces the particle concentration more than CCD=2 m. These results provide guidelines for determining the most effective configuration for trees to reduce outdoor particle concentrations near buildings.

University cafeteria is a kind of building with unique characteristics: there are lots of people dining besides the large cooking area. It is of great importance to study the impact of the cooking generated contaminants on the indoor air quality in the cafeteria since cooking is regarded as the main source of indoor contaminants. This study presents the particulate matter (PM) concentrations measured in three different university cafeterias followed by a series of cases studied with CFD and multizone model simulation. Based on the results, the possible strategies to tackle the indoor air quality (IAQ) problem due to cooking are discussed. It is concluded that using up exhaust, setting up partition between cooking area with other zones and adding scuttles are helpful to reduce the cooking generated particle pollution in the cafeterias.