Search

During the COVID-19 pandemic, schools in South Korea augmented ventilation rates by opening windows to avoid airborne transmission risks. However, this also elevated indoor PM 2.5 concentrations, creating a trade-off problem between the two risks. This study quantitatively analyzed the impact of ventilation rate on indoor PM 2.5 concentrations and COVID-19 transmission risk in a typical classroom. The results showed that indoor PM 2.5 concentrations asymptotically approached outdoor ones with the augmentation of ventilation. The impact of ventilation augmentation on indoor concentration decreased with the ventilation rate. The time evolution of air transmission risk was obtained from the balance equation of quanta generated by infected people to estimate the infection probability and effective reproduction number. The transmission risk was a complex function of the ventilation rate, quanta generation rate per infected person, and mask filtration efficiency. The combination of information from the analyses of the two risks provides feasible solutions to the problem of resolving the two conflicting risks simultaneously. For example, high ventilation rates are allowable in mild climates with low outdoor PM concentrations. They can ease mask filtration efficiencies and elevate allowable activity levels while wearing high-efficiency masks and limiting students' activity levels must be enforced under cold climates with high outdoor PM concentrations. This study provides important insights into the trade-off between ventilation rate and COVID-19 transmission risk in classrooms. In addition, the results can be used to develop strategies to mitigate both risks and ensure the safety of students and staff. • Airborne transmission risks fell with augmented ventilation during the pandemic. • Augmented ventilation increased the risk from indoor particulate matter. • The trade-off relation between the two risks was quantitatively investigated. • Wearing a proper mask, the two problems could be solved for most student activities, regardless of ventilation conditions. • Reducing student activity and using active ventilation could lower the required mask filtration efficiency. [ABSTRACT FROM AUTHOR]

Highlights: [•] Both amination and calcination, independently enhanced CO2 capacity and selectivity. [•] Dry phase modification such as amination favours coconut shell-based activated carbon while wet phase pre-treatment favours coal based activated carbon. [•] Nitride-like/aromatic N-imines, pyridinic and pyrollic nitrogen complexes were found to have high selective affinity towards CO2. [•] Integrating the two methods with Ca(NO3)2 impregnation produced the best treatment for both 0.3% and 10% CO2 selectivities. [Copyright &y& Elsevier]

The Korean government recommends intermittent operation of air purifiers (APs) as a measure to maintain indoor particulate matter (PM) concentrations below the mandatory standards and reduce exposure to indoor PM 2.5 (PM with a diameter smaller than 2.5 μm). However, there is no guideline to inform occupants of when and how long APs should be operated to comply with the standards. In this study, we developed a dynamic mass-balance model to predict indoor PM concentrations in an office considering penetration of outdoor particles, change in number of occupants, and operational status of the AP. The model fit and prediction accuracies were verified using the American Society for Testing and Materials (ASTM) D 5157 criteria and the k-fold validation technique. We observed that indoor PM 2.5 concentrations were determined by infiltration of outdoor PM 2.5 , and indoor generation/resuspension by occupants and removal. For PM 2.5-10 (2.5 μm < diameter <10 μm), the indoor concentrations were determined by interior door access and indoor generation/resuspension. The operation of an AP effectively decreased indoor PM 2.5 concentration but not PM 2.5-10. We found that our model accurately predicted indoor PM concentrations. Therefore, using the developed model, a guideline may recommend: 1) start the AP when the predicted indoor PM 2.5 concentrations under no AP operation approached the standard (e.g., 90% of the standard); and 2) stop the AP when the indoor PM 2.5 concentration predicted under the assumption of no AP operation fell below the standard (e.g., 80% of the standard). • A dynamic mass-balance model of indoor particle concentrations was developed. • Model accuracy was verified using the ASTM D 5157 criteria. • Particle penetration with air infiltration was the main source of indoor PM 2.5 • Occupants' door access was the main contributor of indoor coarse particle. • Impact of air purifier operation on indoor particle concentration was scrutinized. [ABSTRACT FROM AUTHOR]

The present work investigated various binders to assist the fly ash particles'' coagulation within the intermediate sintering temperature zone. In order to find the appropriate binding agents for fly ash pelletization, some common materials were examined with focus on the compressive strength. The main experimental variables were heat treatment temperature and the binder/fly ash proportions. As a result of the close investigation, alkali and acidic materials such as sodium hydroxide, potassium hydroxide and phosphoric acid were found quite acceptable based on the strength and cost effectiveness. A few organic materials also acted as desirable binders, but they revealed a few critical limitations when used in aqueous solution and at hot fluid environment. Inorganic binders, such as cement and lime, showed excellent cost effectiveness, but seemed to be disadvantageous for the high temperature process. [Copyright &y& Elsevier]

Exposure to particulate matter (PM) in school environments has been associated with respiratory illnesses among children. Although using air cleaners was reported to reduce PM exposure and improve residents' health in homes, their effects in classrooms are not well understood. We examined how the use of air cleaners in classrooms and school/classroom characteristics affect the levels of indoor PM. Our environmental study included 102 classrooms from 34 elementary schools located on the mainland peninsula and an island in Korea. Indoor and outdoor PM were monitored simultaneously with portable aerosol spectrometers, and indoor gravimetric PM levels were measured with low volume, size-selective samplers during the class hours. Correlations among PM measurements were computed and final multiple regression models for indoor PM were constructed with a model building procedure. Correlation between indoor and outdoor PM 2.5 (PM < 2.5 μm in aerodynamic diameter) was higher (r = 0.78, p < 0.01) than that of PM 10 (PM < 10 μm) (r = 0.49, p < 0.01). School location, classroom occupant density, and ambient PM levels significantly (p-values<0.05) affected classroom PM concentrations. The adjusted PM levels in classrooms using air cleaners were significantly (p-values<0.01) lower by approximately 35% than in classrooms not using them. However, air cleaners appeared to remove PM 2.5 more effectively than PM 10 , perhaps because coarse particles settle more rapidly than fine particles on surfaces, or their resuspension and generation rate by occupants exceeds the removal rate by air cleaners. Our study suggests that routine cleaning to remove surface dust along with the use of air cleaners might be required to effectively reduce occupants' exposure in classrooms. • Indoor PM had proportionally more coarse PM (72%) than did outdoor PM (56%). • Correlation between classroom and outdoor PM 2.5 was higher than for PM 10. • Using air cleaners was significantly associated with a 35% reduction in PM levels. • PM 2.5 was more effectively removed by air cleaners than PM 10 in classrooms. • Combined use of surface cleaning and air cleaner is best to reduce PM exposure. [ABSTRACT FROM AUTHOR]

Highlights: [ • ] O3 oxidation enhanced both the textural and chemical properties of AC and the amination efficiency compared to H2O2. [ • ] UV-C reduced the amount of refractory SOFs, thereby increasing the proportion of those available for amination. [ • ] Carbonyl, carboxyl and hydroxyl aid the formation of pyridine and pyrrole groups, which showed high affinity toward CO2. [•] Narrower micropores achieved by O3 treatment enhanced the CO2 physisorption. [ABSTRACT FROM AUTHOR]

Abstract The effectiveness of a surface dielectric barrier discharge (DBD) reactor was evaluated over a range of relative humidiy (RH), discharge areas and applied powers. Primary goals included maximizing toluene decomposition efficiency and CO 2 selectivity while maintaining a high specific energy density and energy yield. Humidity was a limiting factor, although it did not significantly increase the energy efficiency of the system. A RH of 20% was found to be optimal for toluene abatement, and large discharge areas decreased the energy yield by increasing the rate of power consumption. At a frequency of 60 Hz and an applied voltage of 4.3 kV, 8.4, 6.4 and 4.3 g/kWh of toluene was removed at discharge areas of 215, 430 and 645 cm2, respectively. Energy efficiency was also reduced at high applied power by ozone formation in the reactor. Graphical abstract Image [ABSTRACT FROM AUTHOR]