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Source Identification, Monitoring, Health Effect and Control Technologies of Indoor Air Pollutants in Indoor Such as Subway Systems, Multi-Purpose Utilities, School Rooms

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A special issue of Toxics (ISSN 2305-6304). This special issue belongs to the section "Air Pollution and Health".

Deadline for manuscript submissions: closed (31 August 2022) | Viewed by 19402

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Special Issue Editors

Dr. Duckshin Park

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Guest Editor

Department of Transportation Environmental Research (BD No. 11), Cheoldobakmulkwanro 176, Uiwang-si 16105, Kyeonggi-do, Republic of Korea
Interests: indoor air quality; source identification; thermal comfortness; particulates; VOCs and radon control in subway systems
Special Issues, Collections and Topics in MDPI journals

Dr. Hak-Joon Kim

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Guest Editor

Department of Environmental Machinery, Korea Institute of Machinery and Materials (KIMM), 156 Gajeongbuk-ro, Yuseong-gu, Daejeon 34103, Republic of Korea
Interests: industrial exhaust gas cleaning; air cleaning for IAQ; electrostatics; electrostatic precipitation; wet scrubber; simultaneous removal of NOx/SOx/PMs; particle charging; particle collection; particle generation; particle filtration; particle and gas measurements; biofiltration; bioaerosols
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Se-Jin Yook

E-Mail Website
Guest Editor

Department of Mechanical Engineering, Hanyang University, Seoul 04763, Republic of Korea
Interests: aerosol technology; particle removal systems; particle samplers; indoor air quality; CFD
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Indoor air quality has become a real concern for all environmental researchers. Indoor air in urban environments contains more toxic pollutants with poor HVAC and natural ventilation systems. In indoor environments, various toxic pollutants, e.g., VOCs and PM_2.5, have adverse health effects. These health effects include lung, liver, and asthma diseases. Moreover, to overcome indoor air pollution, the increased ventilation rates do not play a vital role in air quality since outdoor air pollution is already high in urban environments. In the era of COVID-19, researchers are more focused on indoor air pollution and indoor air quality as we spend 90% of our lives in indoor environments. Keeping these scenarios in mind, this Special Issue will cover all new research and technologies that can play a vital role in combatting these issues. This will be helpful for further research and will improve human health and society. This can be helpful for future generations and stimulate new, better research in the field. The availability of this research will give those entering the field a better understanding of these topics, which may stimulate the development of future technologies.

With the above in mind, I would like to invite you to contribute to this Special Issue of Toxics.

Dr. Duckshin Park
Dr. Hak-Joon Kim
Prof. Dr. Se-jin Yook
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Toxics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

indoor air pollution
air quality
particulate matter
toxic air pollutants
human health
Volatile Organic Carbons (VOCs)
bioaerosols

Published Papers (12 papers)

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Research

17 pages, 5485 KiB

Open AccessArticle

Improvement of an In-Duct Two-Stage Electrostatic Precipitator via Diffusion Charging

by Ye-Sle Kim, Yeawan Lee, Yong-Jin Kim, Bangwoo Han and Hak-Joon Kim

Toxics 2022, 10(11), 686; https://doi.org/10.3390/toxics10110686 - 12 Nov 2022

Cited by 2 | Viewed by 1678

Abstract

An in-duct two-stage electrostatic precipitator (ESP) improved by ion diffusion effect was studied. We increased the collection efficiency of a two-stage electrostatic precipitator without additional energy input by adjusting the space arrangement of the charger and the collector, which increased the particle diffusion charging time. The collection efficiency and the particle charge were systematically investigated according to the occurrence of diffusion charging and electric field charging in the charger as generated by the negative ions. The collection efficiency of the separated two-stage ESP was 39% higher, on average, than the theoretical efficiency at the same power consumption. Through simulation, it was verified that the ions generated in the carbon fiber ionizer penetrated the charger. We proposed a modified charging mechanism assuming that the penetrated ions cause additional particle charge. The optimal separation distance between the charger and the collector, which showed the maximum collection efficiency, was derived through the modified charging model. Therefore, the in-duct two-stage ESP developed in this study is a promising energy-efficient and cost-saving design for indoor air management. Full article

(This article belongs to the Special Issue Source Identification, Monitoring, Health Effect and Control Technologies of Indoor Air Pollutants in Indoor Such as Subway Systems, Multi-Purpose Utilities, School Rooms)

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17 pages, 2677 KiB

Open AccessArticle

The Actual Efficacy of an Air Purifier at Different Outdoor PM_2.5 Concentrations in Residential Houses with Different Airtightness

by Dongho Shin, Younghun Kim, Keejung Hong, Gunhee Lee, Inyong Park and Bangwoo Han

Toxics 2022, 10(10), 616; https://doi.org/10.3390/toxics10100616 - 17 Oct 2022

Cited by 1 | Viewed by 1442

Abstract

It is important to control airborne particles in residential houses for protecting human health. Indoor particulate matter of <2.5 μm (PM_2.5) can be effectively monitored and managed using an air purifier. In this study, the actual clean air delivery rates in residential houses (CADR_Actual) were acquired by comparing decay rates of fine particles with and without operations of the air purifier under actual conditions, following the standard CADR of an air purifier obtained in a closed test chamber. The measurements of CADR_Actual at different outdoor PM_2.5 concentrations over a month in two residential houses revealed different airtightness levels, compared to the standardized clean air delivery rate of the air purifier (CADR_AP). Air changes per hour at 50 Pa (ACH50) was 4.8 h⁻¹ for “house A” (built in 2007) and 2.1 h⁻¹ for “house B” (built in 2018). The CADR of the air purifier used in this study was 10.6 m³/min, while the averaged CADR_Actual at the “house A” was 7.2 m³/min (approximately 66% of the CADR of the air purifier) and 9.5 m³/min at “house B” (approximately 90% of the CADR of the air purifier). Under the outdoor PM_2.5 concentrations of <35 μg/m³, the averaged CADR_Actual of house A and house B were 7.8 ± 0.3 and 9.7 ± 0.4 m³/min, respectively. However, under the outdoor PM_2.5 concentrations of >35 μg/m³, the analogous averaged concentrations were 6.8 ± 0.6 and 9.6 ± 0.3 m³/min for houses A and B, respectively. The measured CADR_Actual agreed well with the theoretical estimates of CADR_Actual acquired by the mass balance equation using the infiltration rate of ACH50/20. We also estimated CADR_Actual/CADR_AP for house C built in 2017, where the ACH50 was 1.8 h⁻¹. Overall, this study demonstrated how CADR_Actual/CADR_AP of an air purifier at residential houses can be predicted according to outdoor PM_2.5 concentration and airtightness of the house. As shown, it can be closer to 1 at lower ACH50 houses and at lower outdoor PM_2.5 concentrations. Full article

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10 pages, 1504 KiB

Open AccessArticle

Effects of Brush-Type Ionizer Materials on Virus Inactivation

by Jaeseok Heo, Jooyeon Lee and Duckshin Park

Toxics 2022, 10(10), 611; https://doi.org/10.3390/toxics10100611 - 14 Oct 2022

Viewed by 1300

Abstract

Many studies have found that bioaerosols are harmful to humans. In particular, infectious viruses, such as the virus that causes COVID-19, are increasing. Therefore, the research on methods for reducing bioaerosols is becoming progressively more important. The purpose of this study was to improve the existing electrostatic precipitator, which generates high concentrations of ozone, by reducing bioaerosols effectively without significant ozone production. A brush-type ionizer was studied as a replacement for the existing electrostatic precipitator. The study, which was conducted at the laboratory scale, determined the amounts of ions generated with different ionizer materials (carbon, copper, and stainless steel) and voltages (−1, −2, and −3 kV), as well as it compared the virus inactivation efficiency under the various conditions. As a result, about two million ions were produced when a voltage of −3 kV was applied to all of the materials, and 99.9 ± 0.2% and 98.8 ± 0.6% virus inactivation efficiencies were confirmed in the cases of carbon and copper, respectively. In addition, an assessment of the effect of flow velocity confirmed that the inactivation efficiency decreased as the flow velocity increased. However, the results for the flow velocities of 0.2 and 0.4 m/s had similar trends. Therefore, this system can be used with flow velocities up to 0.4 m/s. Full article

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19 pages, 2387 KiB

Open AccessArticle

Efficient Energy Saving Scenarios for Indoor PM_2.5 Management in an Apartment of South Korea

by Younghun Kim, Dongho Shin, Kee-Jung Hong, Gunhee Lee, Sang Bok Kim, Inyong Park, Bangwoo Han and Jungho Hwang

Toxics 2022, 10(10), 609; https://doi.org/10.3390/toxics10100609 - 13 Oct 2022

Cited by 1 | Viewed by 1402

Abstract

Indoor PM_2.5 must be effectively controlled to minimize adverse impacts on public health. Cooking is one of the main sources of PM_2.5 in residential areas, and indoor air quality (IAQ) management methods such as natural and mechanical ventilation, range hood, and air purifier are typically used to reduce cooking-generated PM_2.5 concentrations. However, studies on the combined effects of various IAQ management methods on indoor PM_2.5 reduction and energy consumption are limited. In this study, a theoretical model was established to estimate the performance of various IAQ management methods for controlling indoor PM_2.5 concentrations and energy consumption. The model was verified by comparative experiments in which, various IAQ management methods were operated individually or combined. Seasonal energy consumption was calculated through the verified model, and energy consumption saving scenarios were derived for maintaining indoor PM_2.5 concentrations less than 10 μg/m³, a World Health Organization annual guideline, under fair and poor outdoor PM_2.5 concentrations of 15 and 50 μg/m³, respectively. Based on our results, we found that energy consumption could be reduced significantly by applying natural ventilation in spring, autumn, and summer and mechanical ventilation in winter. Our study identified efficient energy saving PM_2.5 management scenarios using various IAQ management methods by predicting indoor PM_2.5 concentration and energy consumption according to the annual life patterns of typical residents in South Korea. Full article

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11 pages, 3734 KiB

Open AccessFeature PaperArticle

Development of On-Demand Antiviral Electrostatic Precipitators with Electrothermal-Based Antiviral Surfaces against Airborne Virus Particles

by Dae Hoon Park, So-Hee An, Yeawan Lee, Yong-Jin Kim, Bangwoo Han and Hak-Joon Kim

Toxics 2022, 10(10), 601; https://doi.org/10.3390/toxics10100601 - 11 Oct 2022

Cited by 2 | Viewed by 1388

Abstract

Particulate matter, including airborne pathogens, is of particular concern because it can cause the spread of diseases through aerosol transmission. In this study, a new concept is proposed: on-demand antiviral electrostatic precipitators (ESPs) with electrothermal-based antiviral surfaces. We applied electrothermal-based antiviral surfaces to air-purifying applications and demonstrated that the proposed method is effective with regard to collecting airborne virus particles on collection plates in a two-stage ESP. With alternating current power, MS2 bacteriophage and H1N1 viruses were completely deactivated after exposure to 50 °C for 30 min. This remarkable antiviral performance via electrothermal effects indicates that on-demand platforms for self-antiviral surfaces can perform sterilization immediately without generating secondary pollutants, thus effectively preventing the spread of infectious microorganisms in public places. We believe that the results of this study can provide useful guidelines for the design and realization of practical and wearable devices for antiviral air-purifying applications. Full article

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16 pages, 5889 KiB

Open AccessArticle

Natural Ventilation and Air Purification for Effective Removal of Airborne Virus in Classrooms with Heater Operation

by Su-Hoon Park, Se-Jin Yook and Hyun Bon Koo

Toxics 2022, 10(10), 573; https://doi.org/10.3390/toxics10100573 - 30 Sep 2022

Cited by 2 | Viewed by 1397

Abstract

Mass COVID-19 infection cases in indoor spaces have been continuously reported since its global outbreak, generating increasing public interest in reducing the spread of the virus. This study considered a situation in which an infected individual continuously releases the virus into the air in a classroom, simulated by continuous injection of NaCl particles ≤ 5 μm, with heater operation during winter. The effects of applying natural ventilation and operating one or two air purifiers on the removal of virus-containing aerosols were experimentally compared and analyzed based on the spatiotemporal changes in NaCl concentration within the classroom. When a heater was operated with all windows shut, operating one and two air purifiers reduced the amount of the aerosol in indoor air by approximately 50 and 60%, respectively, compared to the case with no air purifier. Additionally, when the heater was operated with one or two air purifiers under natural ventilation, the amount of virus-containing aerosol in the air was reduced by 86–88% compared to the case with neither natural ventilation nor air purifier. Because natural ventilation significantly varies with weather conditions and particulate matter concentrations, combining natural ventilation with air purifiers in classrooms during winter needs to be adjusted appropriately. Full article

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16 pages, 11563 KiB

Open AccessArticle

Study on the Ventilation Method to Maintain the PM₁₀ Concentration in a Subway Cabin below 35 μg/m³

by Eun-Seo Choi, Se-Jin Yook, Minjeong Kim and Duckshin Park

Toxics 2022, 10(10), 560; https://doi.org/10.3390/toxics10100560 - 25 Sep 2022

Viewed by 1387

Abstract

The city of Seoul will limit the maximum particulate matter (PM₁₀) concentration to ≤35 μg/m³ (from 2024). Herein, a numerical parametric study was conducted on the PM removal efficiency of the heating, ventilation, and air conditioning (HVAC) filters installed in the ceiling of subway cabins. The PM₁₀ concentration distribution was explored according to the flow rate and flow rate ratio of the air introduced into the cabin. Under the current ventilation conditions of the subway train HVAC system, the PM₁₀ concentration was highest in the cabin central area where exhaust outlets are located and decreased toward both ends of the cabin. The indoor airflow was improved and the PM₁₀ concentration was reduced by increasing the flow rate of the supplied air at both ends of the cabin while decreasing it in the central area. It was found that the strengthened PM₁₀ concentration criterion of Seoul can be met by increasing the ventilation flow rate to 700 CMH (currently, 500 CMH) and the filter efficiency to 85% (currently, 70%) while maintaining the current flow rate ratio. These results are expected to be used as important reference data for reducing the PM concentration in subway cabins and thereby improving indoor air quality. Full article

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15 pages, 8927 KiB

Open AccessArticle

Deep Learning-Based Indoor Air Quality Forecasting Framework for Indoor Subway Station Platforms

by Ahtesham Bakht, Shambhavi Sharma, Duckshin Park and Hyunsoo Lee

Toxics 2022, 10(10), 557; https://doi.org/10.3390/toxics10100557 - 23 Sep 2022

Cited by 9 | Viewed by 2007

Abstract

Particulate matter (PM) of sizes less than 10 µm (

P M_{10}

) and 2.5 µm (

P M_{2.5}

) found in the environment is a major health concern. As PM is more prevalent in an enclosed environment, such as a [...] Read more.

Particulate matter (PM) of sizes less than 10 µm (

P M_{10}

) and 2.5 µm (

P M_{2.5}

) found in the environment is a major health concern. As PM is more prevalent in an enclosed environment, such as a subway station, this can have a negative impact on the health of commuters and staff. Therefore, it is essential to continuously monitor PM on underground subway platforms and control it using a subway ventilation control system. In order to operate the ventilation system in a predictive way, a credible prediction model for indoor air quality (IAQ) is proposed. While the existing deterministic methods require extensive calculations and domain knowledge, deep learning-based approaches showed good performance in recent studies. In this study, we develop an effective hybrid deep learning framework to forecast future

P M_{10}

and

P M_{2.5}

on a subway platform using past air quality data. This hybrid framework is an integration of several deep learning frameworks, namely, convolution neural network (CNN), long short-term memory (LSTM), and deep neural network (DNN), and is called hybrid CNN-LSTM-DNN; it has the characteristics to capture temporal patterns and informative characteristics from the indoor and outdoor air quality parameters compared with the standalone deep learning models. The effectiveness of the proposed

P M_{10}

and

P M_{2.5}

forecasting framework is demonstrated using comparisons with the different existing deep learning models. Full article

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14 pages, 8866 KiB

Open AccessArticle

Enhancement and Homogenization of Indoor Air Quality in a Classroom Using a Vertical Airflow Ventilation Scheme

by Su-Hoon Park, Kyung-Rae Lee, Se-Jin Yook and Hyun Bon Koo

Toxics 2022, 10(9), 545; https://doi.org/10.3390/toxics10090545 - 19 Sep 2022

Cited by 4 | Viewed by 1672

Abstract

Since air quality has a great influence on students’ health and learning ability, enhancing air quality in classrooms is important. Currently, widely distributed ventilation systems operate by moving airflow horizontally from ventilation inlets and outlets on the ceiling. This method can reduce the average pollution in a space by diluting it through air exchange; however, it is limited regarding homogeneous cleanliness due to air stagnation at some locations. Therefore, in this study, a new ventilation system was devised to improve indoor air quality and spatial homogeneity by installing ventilation inlets on the ceiling and numerous outlets on the floor, creating a vertical airflow in the interior space; this system was then applied to a middle school classroom. Using the age of air as an index, air quality improvement between the existing and newly designed ventilation systems was compared. In the classroom with the existing ventilation system, the age of air was low in the area near the ventilation inlets, while air congestion areas were widely distributed and air age was high near the outlets. Conversely, in the vertical airflow classroom, the average age of air was approximately 15% lower than that with the existing ventilation system, and the deviation of air age for each position in the classroom space was also reduced, showing a uniform air age distribution. Therefore, the vertical airflow ventilation system proposed in this study can be an effective ventilation scheme for enhancing and homogenizing indoor air quality. Full article

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20 pages, 8284 KiB

Open AccessArticle

Reducing PM₁₀ and PM_2.5 Concentrations in a Subway Station by Changing the Diffuser Arrangement

by Seong-Gyu Kim, Gibong Sung, Se-Jin Yook, Minjeong Kim and Duckshin Park

Toxics 2022, 10(9), 537; https://doi.org/10.3390/toxics10090537 - 15 Sep 2022

Viewed by 1513

Abstract

According to the stringent regulations on particulate matter (PM) concentrations in Seoul, Korea, the PM₁₀ and PM_2.5 concentrations in subway stations must be maintained below 50 and 30 μg/m³, respectively, by 2024. Therefore, the PM concentrations in a subway station were analyzed considering air-conditioning diffuser arrangement and filtration efficiency, with the total ventilation flow rate of the station maintained constant. Dynamic analysis was performed under a worst-case scenario, wherein outdoor air was introduced through ground entrances and high-concentration dust (PM₁₀, PM_2.5) was introduced from stationary train cabins into the platforms through open platform screen doors (PSDs). Although the average PM concentrations were predicted to satisfy the reinforced criteria of Seoul under the existing operating conditions, the recommended limits were exceeded in certain local areas. To address this, the PM concentrations were predicted by changing the diffuser arrangement in the waiting room and maintaining the total ventilation flow rate constant. When the diffusers were placed near the waiting room walls, the PM₁₀ and PM_2.5 concentrations were reduced by approximately 10.5 and 5%, respectively, compared to the previous diffuser arrangement. Thus, the required PM concentration criteria were satisfied in nearly all areas of the target station, except for certain areas close to PSDs. The study findings can form the basis for improving the air quality of other subway stations. Full article

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15 pages, 3646 KiB

Open AccessArticle

Comparison of Indoor Air Quality in Summer and Winter According to Four-Way Cassette Fan Coil Unit Operation in a Four-Bed Ward

by Jungsuk Lee, Ik-Hyun An, Su-Hoon Park, Kyung-Rae Lee, Young-Won Kim and Se-Jin Yook

Toxics 2022, 10(9), 504; https://doi.org/10.3390/toxics10090504 - 28 Aug 2022

Cited by 3 | Viewed by 1489

Abstract

This study targeted a four-bed ward with a ventilation system and a four-way cassette fan coil unit (4-way FCU) installed on the ceiling. The indoor air quality under summer and winter conditions was comparatively analyzed. The age of air was calculated by conducting tests and simulations under diverse conditions, assuming that the ventilation system and 4-way FCU were continuously operating. The use of an air cleaner and ward curtain was investigated for its impact on the air quality in the breathing zone of a patient lying on the bed, and effects of the airflow and discharge angle of the 4-way FCU were considered. Because the 4-way FCU was installed in the central part of the ceiling, where indoor air is sucked in and subsequently discharged in four directions, the age of air at each bed was found to vary depending on the airflow and discharge angle of the 4-way FCU. When the airflow and discharge angle of the 4-way FCU was fixed, the age of air at each bed appeared to be lower during winter heating than in summer cooling mode. The age of air was significantly lowered at each bed, depending on the use of the curtain and the air cleaner along with the ventilation system and 4-way FCU, and appropriate seasonal operating conditions were identified to maintain a lower age of air at each bed. Full article

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13 pages, 3961 KiB

Open AccessFeature PaperArticle

Investigation of the Optimal Operating Position of an Air Cleaner in Terms of Indoor Air Quality in a Four-Bed Hospital Ward

by Jungsuk Lee, Su-Hoon Park, Ik-Hyun An, Young-Won Kim and Se-Jin Yook

Toxics 2022, 10(7), 360; https://doi.org/10.3390/toxics10070360 - 30 Jun 2022

Cited by 4 | Viewed by 1571

Abstract

The use of air cleaners indoors has increased with the increase in indoor activities driven by the COVID-19 outbreak. In this study, the indoor air quality was determined at the location of each patient’s respirator in a four-bed hospital ward equipped with a ventilation system and curtains, by varying the position of one air cleaner. By operating the air cleaner alone without the ventilation system, it was confirmed that it is better to place the air cleaner close to the center of the ward, regardless of whether curtains are used. It was further identified that the farther away the air cleaner is from the center, the worse the age of air could be, compared to the case of operating it in the center. Moreover, the situation where the ventilation system and air cleaner were operated simultaneously in the hospital ward was considered. It was discovered that operating the air cleaner close to the ventilation inlets in the absence of curtains helps to improve the indoor air quality. Furthermore, it was found that the age of the air is generally low near the location where the air cleaner is operated in the presence of curtains. Selecting an optimal position for the air cleaner can improve the air quality at the location of each bed in a four-bed hospital ward. Full article

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