Research on Indoor Air Cleaners for Particulate, Microbiological, and Gaseous Pollutants (2nd Edition)

A special issue of Atmosphere (ISSN 2073-4433). This special issue belongs to the section "Air Pollution Control".

Deadline for manuscript submissions: closed (30 November 2023) | Viewed by 4668

Special Issue Editor


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Guest Editor
Institut für Umwelt & Energie, Technik & Analytik e. V. (IUTA), 47229 Duisburg, Germany
Interests: aerosols; filtration; air cleaners; indoor air
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Special Issue Information

Dear Colleagues,

This Special Issue is a follow-up of the first Special Issue entitled “Research on Indoor Air Cleaners for Particulate, Microbiological and Gaseous Pollutants” (https://www.mdpi.com/journal/atmosphere/special_issues/Indoor_Air_Cleaners) published in Atmosphere in 2022.

With the growing awareness of air pollution, air cleaners have been used for decades to improve indoor air quality. This especially includes air cleaners for particulate pollutants, based either on established technologies such as fibrous (HEPA) filters and electrostatic precipitators or alternative filtration concepts. The relevant particle size range extends from ultrafine particles which are omnipresent in indoor environments up to coarse particles such as pollen or dust at workplaces. Throughout the COVID-19 pandemic, the global interest in indoor air cleaners has increased substantially as they can also contribute to minimizing infection risks by filtration or inactivation (e.g., by UV-C) of viruses or virus-carrying droplets. In addition to air cleaners for particulate pollutants, there are also solutions for gaseous pollutants, e.g., based on activated carbon or photocatalysis.

Although there has already been a lot of research on air cleaners, there are still many open questions: How can air cleaners be further optimized in terms of cleaning efficacy, power consumption, and noise emissions? How can long-term stability be determined and increased? How is the distribution of the cleaned air in a room affected by its geometry, furnishing, and occupancy? Can potential health benefits be tested with bioaerosols or demonstrated in toxicological or epidemiological studies? Scientific answers to these and further questions will at least deliver input for the current standardization project for indoor air cleaners of the International Electrotechnical Commission (IEC).

Contributions from all applicable fields are welcome, whether they deal with technical aspects of the devices and filters, new measurement techniques or methods for assessing the efficacy, observations or simulations in real environments, or studies on the health effects of indoor air cleaners.

Dr. Stefan Schumacher
Guest Editor

Manuscript Submission Information

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Keywords

  • indoor air cleaners
  • filtration
  • ultra-fine particles
  • bioaerosols
  • gaseous pollutants
  • COVID-19
  • test methods
  • simulations
  • field experiments
  • health effects

Published Papers (5 papers)

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Research

23 pages, 4171 KiB  
Article
Evaluation of Surrogate Aerosol Experiments to Predict Spreading and Removal of Virus-Laden Aerosols
by Janis Beimdiek and Hans-Joachim Schmid
Atmosphere 2024, 15(3), 305; https://doi.org/10.3390/atmos15030305 - 29 Feb 2024
Viewed by 663
Abstract
Estimating the infection risks of indoor environments comprises the assessment of the behavior of virus-laden aerosols, i.e., their spreading, mixing, removal by air purifiers, etc. A promising experimental approach is based on using non-hazardous surrogate aerosols of a similar size, e.g., salt particles, [...] Read more.
Estimating the infection risks of indoor environments comprises the assessment of the behavior of virus-laden aerosols, i.e., their spreading, mixing, removal by air purifiers, etc. A promising experimental approach is based on using non-hazardous surrogate aerosols of a similar size, e.g., salt particles, to mimic virus aerosol behavior. This manuscript addresses the issue of how a successful transfer of such experiments can be accomplished. Corresponding experiments in two very different environments, a large community hall and a seminar room, with the optional use of air purifiers in various constellations, are conducted. While high particle concentrations are advantageous in terms of avoiding the influence of background aerosol concentrations, it is shown that the appropriate consideration of aggregation and settling are vital to theoretically describe the experimentally determined course of particle concentrations. A corresponding model equation for a well-mixed situation is derived, and the required parameters are thoroughly determined in separate experiments independently. It is demonstrated that the clean air delivery rates (CADRs) of air purifiers determined with this approach may differ substantially from common approaches which do not explicitly take aggregation into account. Full article
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12 pages, 1801 KiB  
Article
The Drawback of Optimizing Air Cleaner Filters for the Adsorption of Formaldehyde
by Stefan Schumacher, Anna Caspari, Ute Schneiderwind, Katharina Staack, Uta Sager and Christof Asbach
Atmosphere 2024, 15(1), 109; https://doi.org/10.3390/atmos15010109 - 16 Jan 2024
Cited by 1 | Viewed by 697
Abstract
Air cleaners with activated carbon (AC) filters for the adsorption of gaseous pollutants are often used to improve indoor air quality. As formaldehyde is a common and health-relevant indoor air pollutant, many testing standards for air cleaners, such as GB/T 18801:2015, require the [...] Read more.
Air cleaners with activated carbon (AC) filters for the adsorption of gaseous pollutants are often used to improve indoor air quality. As formaldehyde is a common and health-relevant indoor air pollutant, many testing standards for air cleaners, such as GB/T 18801:2015, require the cleaning efficacy to be tested with this substance. This often persuades manufacturers to optimize the employed filters specifically for formaldehyde. However, in regions where indoor formaldehyde levels are far below the guideline values, other gaseous pollutants might be more relevant. Thus, the question arises of whether the optimization for formaldehyde can have a negative impact on the adsorption of other gases. To address this question, the clean air delivery rate (CADR) of an air cleaner was determined for different test gases with either a standard AC filter or an AC filter modified for improved formaldehyde adsorption. Although the modified AC filter performed substantially better for formaldehyde, a strong reduction in the CADR was observed for toluene and nitrogen dioxide. This is a drawback for situations in which these gases are more problematic than formaldehyde. The findings suggest using either specialized filters for different applications or blends of different adsorbants to find the best compromise for the most relevant pollutants. Full article
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10 pages, 1796 KiB  
Communication
Air Purification Study Based on the Adhesion Effect between Low-Curvature Liquid Surfaces and Air Convection Friction
by Haotian Weng, Yaozhong Zhang, Xiaolu Huang, Hewei Yuan and Yafei Zhang
Atmosphere 2023, 14(12), 1831; https://doi.org/10.3390/atmos14121831 - 16 Dec 2023
Viewed by 915
Abstract
Rapid urbanization and industrialization have heightened concerns about air quality worldwide. Conventional air purification methods, reliant on chemicals or energy-intensive processes, fall short in open spaces and in combating emerging pollutants. Addressing these limitations, this study presents a novel water-film air purification prototype [...] Read more.
Rapid urbanization and industrialization have heightened concerns about air quality worldwide. Conventional air purification methods, reliant on chemicals or energy-intensive processes, fall short in open spaces and in combating emerging pollutants. Addressing these limitations, this study presents a novel water-film air purification prototype leveraging the adhesion between low-curvature liquid surfaces and air convection friction. Uniquely designed, this prototype effectively targets toxic gases (e.g., formaldehyde, SO2, NO2) and particulate matter (such as PM2.5) while allowing continuous airflow. This research explores the adhesion and sedimentation capabilities of a low-curvature water solution surface under convection friction, reducing the surface energy to remove airborne pollutants efficiently. The prototype was able to reduce the initial concentration in a 30 m³ chamber within 180 min by 91% for formaldehyde, 78% for nitrogen dioxide (NO2), 99% for sulfur dioxide (SO2), and 96% for PM2.5. Experimentally validated indicators—decay constants, CADR, and purification efficiency—enable a comprehensive evaluation of the purification device, demonstrating its efficacy in mitigating air pollution. This innovative design, which is cost-effective due to its use of easily accessible components and water as the primary medium, indicates strong potential for large-scale deployment. This study points to an environmentally friendly and economical approach to air purification, shedding light on a promising direction for enhancing indoor air quality. Further optimization and exploration of diverse pollutants and environmental conditions will propel the practical applications of this pioneering technology. Full article
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16 pages, 7486 KiB  
Article
Numerical Evaluation of the Efficiency of an Indoor Air Cleaner under Different Heating Conditions
by Andrejs Sabanskis, Dagis Daniels Vidulejs, Jevgēnijs Teličko, Jānis Virbulis and Andris Jakovičs
Atmosphere 2023, 14(12), 1706; https://doi.org/10.3390/atmos14121706 - 21 Nov 2023
Cited by 3 | Viewed by 664
Abstract
For an efficient indoor air purification, it is important to know the detailed airflow distribution in the room. A series of numerical simulations are carried out for five heating regimes using an air–air heat pump, capillary mat on the ceiling, capillary mat on [...] Read more.
For an efficient indoor air purification, it is important to know the detailed airflow distribution in the room. A series of numerical simulations are carried out for five heating regimes using an air–air heat pump, capillary mat on the ceiling, capillary mat on the walls, heated floor, and radiator. The most homogeneous temperature field is obtained for the case with the heated floor. The highest velocity is obtained for the air–air heat pump, while the lowest is obtained for the capillary mat on the ceiling. A portable air cleaner based on the prototype device is introduced into the model and its influence on the velocity and temperature distributions is calculated. Our simulations additionally consider is the transport of an infectious aerosol and its purification inside the air cleaner. The time dependency of the concentration is exponential, and the purification rate depends on the air cleaner’s orientation and heating regime. The efficiency is higher for a purifier with flow in the upwards direction compared to in a horizontal one. In the experimental part, an NaCl solution is dispersed into the air, and the efficiency of purification in the case of the air–air heat pump is evaluated by measuring the time-dependent particle concentrations. These experimental results corroborate the numerical model. Full article
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23 pages, 3169 KiB  
Article
Comparison of Portable and Large Mobile Air Cleaners for Use in Classrooms and the Effect of Increasing Filter Loading on Particle Number Concentration Reduction Efficiency
by Finn Felix Duill, Florian Schulz, Aman Jain, Berend van Wachem and Frank Beyrau
Atmosphere 2023, 14(9), 1437; https://doi.org/10.3390/atmos14091437 - 14 Sep 2023
Cited by 1 | Viewed by 1129
Abstract
This study focuses on the effect of portable and large filter-based air cleaners (HEPA filters), which became popular indoors during the COVID-19 pandemic, and their suitability for classrooms (here 186 m3). The decay rates of the particle number concentration (PNC) were [...] Read more.
This study focuses on the effect of portable and large filter-based air cleaners (HEPA filters), which became popular indoors during the COVID-19 pandemic, and their suitability for classrooms (here 186 m3). The decay rates of the particle number concentration (PNC) were measured simultaneously at up to four positions in the room. It was found that the different air outlet configurations of the units have an effect on the actual PNC removal in the room when operated at the same volume flow rates. This effect of the airflow efficiency of the air cleaners (AP) in a classroom is quantified with an introduced Air Cleaning Efficiency Factor in this study to identify beneficial airflows. In this context, the effect of filter loading in long-term operation on the cleaning effect is also investigated. The emitted sound pressure levels of the APs are given special attention as this is a critical factor for use in schools, as well as power consumption. A total of six different devices were tested—two portable APs and four large APs. In order to achieve the necessary volume flow rates, three or four of the portable units were used simultaneously in one room, while only one of the large units was used per room. When used at the same air circulation rates in the room, the portable APs exhibit higher sound pressure levels compared to the large APs. At air circulation rates of 4–5 h−1, the portable APs exceeded a value of 45 dB(A). Two of the four large units reach sound pressure levels below 40 dB(A) at air circulation rates of 4–5 h−1, whereby both large units, which are positioned on the rear wall, realize a homogeneous dilution of the room air. This is achieved by an air outlet directed horizontally at a height above 2 m or diagonally towards the ceiling, which points into the room and partly to the sides. On the other hand, an air outlet directed exclusively to the sides or horizontally into the room at floor level to all sides achieves lower particle decay rates. To investigate the influence of the filter loading, three large APs were operated in a school for a period of one year (190 days with 8 h each). For the three APs, long-term operation leads to different changes in PNC reduction efficiency, ranging from −3% to −34%. It is found that not only the size of the prefilter and main filter has a significant influence, but also whether there is a prefilter bypass that negatively affects the loading level of the main filter. At the same time, it was shown that one type of AP, measuring the pressure drop across the filters and readjusting the fan, kept the circulation rate almost constant (up to −3%) over a year. Full article
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