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Indoor air pollution directly threatens human health, with prolonged exposure to pollutants leading to respiratory problems, immune system issues, and even cancer. Thus, implementing advanced air purification technologies is crucial to effectively mitigate indoor pollutants. The current common air purifiers have low removal efficiency for pollutants, a high cost of replacing adsorption materials, and a single function. Therefore, a novel air purification system that provides high-efficiency and rapid air purification and enhances the reusability of adsorption materials is in demand. This study evaluated the purification effect of the New Air Purification System under the internal circulation mode using computational fluid dynamics. The results showed that (1) the air exchange rates of the New Air Purification System were adjusted to 42.6, 85.2, and 127.8 h−1, respectively, when the release rates of 222Rn were 2.268, 4.536, 6.804, and 9.072 Bqm−2h−1. The indoor 222Rn concentration was reduced to < 21% of the background 222Rn concentration. (2) The initial concentration of indoor formaldehyde was 0.1 mg/m3 and increased to 0.0204, 0.0181, and 0.0174 mg/m3, respectively. These values were less than the World Health Organization’s recommended limits. This study provides a solid foundation for designing and optimising the New Air Purification System, provides technical guidance for the next step in its design, and would substantially help in improving indoor air quality and living conditions.

Since COVID-19 pandemic, indoor air quality control has become a priority, and the development of air purification devices effective for disinfecting airborne viruses and bacteria is of outmost relevance. In this work, a photocatalytic device for the removal of airborne microorganisms is presented. It is an annular reactor filled with TiO 2 -coated glass rings and irradiated internally and externally by UV-A lamps. B. subtilis spores and vegetative cells have been employed as model biological pollutants. Three types of assays with aerosolized bacterial suspensions were performed to evaluate distinct purification processes: filtration, photocatalytic inactivation in the air phase, and photocatalytic inactivation over the TiO 2 -coated rings. The radiation distribution inside the reactor was analysed by performing Monte Carlo simulations of photon absorption in the photocatalytic bed. Complete removal of a high load of microorganisms in the air stream could be achieved in 1 h. Nevertheless, inactivation of retained bacteria in the reactor bed required longer irradiation periods: after 8 h under internal and external irradiation, the initial concentration of retained spores and vegetative cells was reduced by 68% and 99%, respectively. Efficiency parameters were also calculated to evaluate the influence of the irradiation conditions on the photocatalytic inactivation of bacteria attached at the coated rings.

Indoor air purification received more attention recently. In this study, the effects of six common indoor ornamental plants ( Epripremnum aureum , Chlorphytum comosum , Aloe vera , Sedum sediforme , Cereus cv. Fairy Castle , and Sedum adolphii ) and three kinds of microalgae ( Chlorella sp. HQ, Scenedesmus sp. LX1, and C. vulgaris ) on the removal of four types of air pollutants (particulate matters less than 2.5 (PM 2.5 ) and 10 μm (PM 10 ) in size, formaldehyde (HCHO) and total volatile organic compounds (VOC S )) in test chamber compared with common physical purification methods (high efficiency particulate air filter and nano activated carbon absorption) were investigated. Their effects on oxygen, carbon dioxide, and relative humidity were also evaluated. The results showed that microalgae, especially C. vulgaris , was more suitable for removing PM 2.5 and PM 10 , and the removal rates were 55.42 ± 25.77% and 45.76 ± 5.32%, respectively. The removal rates of HCHO and VOCs by all three kings of microalgae could reach 100%. Part of ornamental plants took a longer time to achieve 100% removal of HCHO and VOCs. Physical methods were weaker than ornamental plants and microalgae in terms of increased relative humidity and O 2 content. In general, microalgae, especially C. vulgaris could purify indoor air pollutants more efficiently. The above studies provided data and theoretical support for the purification of indoor air pollutants by microalgae.

The development of clean and sustainable teleology is vital to treat the critical environmental pollutants. In the last decade, the use of photocatalytic reactors has been widely reported for organic pollutants degradation. From photocatalysis’s application in environmental remediation, the primary technical issue to scientists is always the efficiency. The enhanced photocatalytic efficiency is mainly depended on the materials improvement. However, the design of photoreactors lags behind the development of photocatalysts, which strongly limit the widespread use of photocatalysis technology in environmental remediation. The nanoparticles separation, mass transfer limitation, and photonic efficiency have always been problematic and restrict the high photocatalytic efficiency of photoreactors. To overcome these bottleneck problems, the most popular or newfangled designs of photoreactors employed in air and water treatment has been reviewed. The purpose of this review is to systematize designs and synthesis of innovative TiO2-based photoreactors and provides detailed survey and discussion on the enhanced mechanism of photocatalytic performance in different TiO2-based photoreactors. The most studied photoreactors are the following: packed bed reactor, film reactor and membrane reactor, which have some limitations and advantages. A comprehensive comparison between the different photocatalytic performance of TiO2-based photoreactors is presented. This work aims to summarize the progress of TiO2-based photoreactors and provides useful information for the further research and development of photocatalysis for water and air purification.

Urban forests, as an integral part of nature-based solutions (NBS), are significant contributors to improving urban air quality, delivering ecological service functions and environmental benefits to human health and well-being. Suitable urban forest management, including proper species selection, needs to be defined to efficiently reduce air pollutants in cities, with a focus on the removal ability of the main air pollutants (PM2.5, PM10, O3, and NO2), the ecological adaptability to O3 and NO2, and allergenic effects. This study ranked 73 urban greening tree species in northern Chinese cities based on their ability to maximize air quality and minimize disservices. This study proposed a novel Species-Specific Air Purification Index (S-API), which is suitable for air quality improvement for tree/shrub species. Urban managers are recommended to select species with an S-API > 1.47—that is, species that have a high removal capacity of PM2.5, PM10, O3, and NO2, are O3- and NO2-tolerant, and are non-allergenic (e.g., Castanea mollissima Blume, Ginkgo biloba L., Hibiscus syriacus L., Ilex chinensis Sims, Juniperus procumbens (Endl.) Iwata et Kusaka, Liriodendron chinense (Hemsl.) Sarg., Morus alba L., Styphnolobium japonicum (L.) Schott, Syringa oblata Lindl., and Ulmus pumila L.). The S-API of urban greening species thus represents a potentially useful metric for air pollutant risk assessment and for selecting appropriate species for urban greening in cities facing serious air pollution challenges.

As the world’s largest open-pit coal producer, China faces severe dust pollution in mining operations. Cabins of mining equipment (electric shovels, haul trucks, drills) exhibit unique micro-environmental contamination due to dual-source pollution (external infiltration and internal secondary dust generation), posing severe health risks to miners. This study focused on electric shovel cabins at the Heidaigou open-pit coal mine to address cabin dust pollution. Through analysis of dust physicochemical properties, a pollution characteristic database was established. Field measurements and statistical methods revealed temporal–spatial variation patterns of dust concentrations, quantifying occupational exposure risks and providing theoretical foundations for dust control. A novel gradient-pressurized air purification system was developed for harsh mining conditions. Key findings include the following. (1) Both coal-shovel and rock-shovel operators were exposed to Level I (mild hazard level), with rock-shovel operators approaching Level II (moderate hazard level). (2) The system reduced respirable dust concentrations from 0.313 mg/m3 to 0.208 mg/m3 (≥33.34% improvement) in coal-shovel cabins and from 0.625 mg/m3 to 0.421 mg/m3 (≥32.64% improvement) in rock-shovel cabins. These findings offer vital guidance for optimizing cabin design, improving dust control, and developing scientific management strategies, thereby effectively protecting miners’ health and ensuring operational safety.

SARS-CoV-2 is mainly transmitted via airborne aerosols. We determined the efficacy of two different indoor air-purification systems and compared them to conventional measures of room ventilation. Radioactive particles with a mass median aerodynamic diameter of 0.6 ± 0.4 µm were nebulized from the head position of a simulated patient inside a 38 m 3 measuring room. Air samples were drawn using an artificial lung from outside the room from the head and belly position of the simulated patient. The radioactivity from these air samples was determined in % of the minute-by-minute release of aerosol by the simulated patient. The samples were taken with the windows closed, with the windows open and with two different air purification systems in different locations. Opening the windows while the fan was working did not reduce the cumulative mass of sampled particles during ongoing nebulization. Only the more powerful air purifier was able to decrease cumulative sampled radioactivity almost to zero when positioned close to the emitting particle source. We observed air-turbulences caused by the air intake of the air purifier resulting in regional particle concentration peaks. Measurements and calculations demonstrate that indoor air purification systems can be effective measures to eliminate airborne particles. The air cleaning capacity of the system must be matched to the room size and the air intake of the units should be positioned close to the particle source.

Numerous management strategies are implemented for the improvement in urban air quality worldwide, including control at tailpipe emissions. Control at the source is one of the best practices for pollution control, but this approach needs very stringent enforcement, public support, and monitoring for implementation. Besides, scientific processes-based technology to remove the pollutants from the ambient environment is also one of the approaches to improve air quality; however, high efficiency of such devices is one of the major challenges for the researchers. The present article is an attempt to review the state-of-the-art literature on such science-based technologies used to remove the pollutants from the ambient environment. The article highlighted the issues of high spatiotemporal variations in air pollution level in urban areas and methodologies available for the removal of pollutants. The efficiency of developed prototypes/devices using these processes is also compared worldwide. The technologies are available for particulate matter, and/or for gaseous pollutants. The air purification devices are designed and developed using scientific principles of bio-filtration, ionization, phytoremediation, photo-catalytic, and physical filtration. Based on the literature, it is found that ionization and physical filtration can remove particulate matter in the range of 61–95% and ~ 70%, respectively, while phytoremediation can remove in the range of 24–40%. The phytoremediation can remove NOx in the range of 10–15%. The efficiency of devices varies as pollution load and particle size distribution pattern varies. It is suggested that such control devices would be very useful in the reduction in air pollution at the hot spot area having high spatiotemporal variations.Graphic abstract

Air pollution has become a significant environmental issue in the twenty-first century, causing a negative impact on the quality of life and human health. Various international organizations have been working to address air pollution issues and provide potential solutions. One of the primary tools used to measure air quality is the Air Quality Index (AQI), which ranges from 0 to 500, indicating levels of different air pollutants in the ambient air. Particulate matter (PM) is one of the most hazardous air pollutants. Outdoor air purification towers are a promising technology to address air quality issues, and this project aims to design and fabricate an air purification tower for Karachi, biggest city of Pakistan and an industrial hub with significant air pollution issues. The lack of air purification devices throughout the country is a significant motivation behind this project, and the main objectives include observing the current situation of ambient air quality in Karachi, testing the performance of the air purification tower, and evaluating the feasibility of the project to be replicated on a larger scale. The project’s methodology includes a review of existing literature and engineering knowledge, followed by design calculations based on heat losses, velocities, and volume flow rates. A parametric study and economic analysis were used to select feasible dimensions, and a CAD model was developed. The report outlines the project’s chronology, including an introduction, literature review, assessment of air quality in Karachi, heat loss coefficient, velocity and flow rate calculations, and a parametric study to reach optimal dimensions for the model used in fabrication. The project’s significance lies in addressing air pollution issues and providing a solution for Karachi’s air quality problems. The success of this project could inspire further replication of air purification towers on a larger scale in Pakistan and other countries facing similar air pollution issues.