What is the best location for an Air Purifier?  We all have heard about environmental pollution and its effects on human health for many years. Strategies have been planned, adopted, and implemented to overcome and reduce air pollution. However, air pollution is not only a problem in the external environment, but also causes the same detrimental effects on human health in the indoor environment. The pollutants in an indoor environment include dust, bacteria, viruses, smoke residues, and fungal spores [1]. So, what is the solution? How the air inside the rooms can be purified to remove circulating harmful particulates?  

Here comes the air purifiers, cleaner, and filters that are used to cleanse the circulating air inside the room using various technologies [2]. These are being used for many years and continuous efforts are made to innovate more efficient systems to clean the indoor environment. These filter systems are either mounted in the ceiling to purify and provide clean air centrally or come in a portable form placed anywhere in the room.

With the Covid-19 pandemic, there have been changes in many aspects of our daily life needs, and the requirement for air cleaners has been increased more than ever. In many countries, the lockdown has been lifted, and students are returning to the classes. School administrations are obliged to maintain the indoor air quality of classrooms for the safety of students. Therefore, the demand for air purifiers is also being elevating, pressing the need to provide the best system of air cleaning to ensure the health of the students in classrooms. Also, WHO has given guidelines for school management to follow ensuring the safety of students. These guidelines also suggest the utilization of air purifiers to maintain the air quality of classrooms [3].

Ceiling mounted and portable units both can be utilized well. However, certain reasons make ceiling-mounted air purifiers better than portable units. Even though the portable systems are cheap and easier to use, the portable system does not purify air centrally, it only cleans the air circulating close to the portable unit. It is now well known that SARS-CoV2 particles remain in the air in the form of aerosols for a longer time and can travel a greater distance. Portable units placed on the floor are unable to clean the air at a greater distance and these particles may spread from the infected students to the non-infected healthier ones. Therefore, uniform quality of clean air cannot be maintained throughout the room and there will be no benefit of a purifier if the contaminated air keeps on recirculating in the room [4]. To prevent the spread of Covid-19, it is crucial to maintain a similar clean and pure quality of indoor air throughout the room [5].

As it is evident from the above image that in the centrally mounted air purifier the air from all directions of the room enters the purifier centrally while cleaned air is projected outward in all the directions to maintain a uniform pure air circulation throughout the classroom. Air purifiers have been reported to perform best when they are placed centrally [6] and the size of the room greatly influences the efficiency of the air purifier [7]. The portable units are good for smaller rooms or less crowded spaces [8]. For classrooms where at least 50 students are present, portable units are not the choice for air cleaning, and a more efficient centrally mounted purifier that can suck the smaller particles and aerosols should be installed to avoid the spread of infections.

A study conducted to evaluate the performance of air cleaners recorded the clean air delivery rate (CADR) exposure reduction effectiveness and age of air as the parameters to evaluate the performance of the air cleaner. They reported that the location of air purifiers significantly impacts their cleaning efficiency and found mounted purifiers more suitable than portable ones [9].

Therefore, using the centrally mounted air purifiers in the classrooms will be most effective in Covid times considering the safety of the children who are attending schools under one roof. Although lower prices and ease of use make portable cleaning units popular, their efficiency does not meet the requirement of cleaning the air in a room and may lead to the spread of viruses because of their sideways functionality. On the contrary, air purifiers mounted centrally in the ceiling create a vacuum sucking the air in the upward direction into the unit that helps to limit the spread of the infection.

1. Vijayan, V. K., Paramesh, H., Salvi, S. S., & Dalal, A. A. K. (2015). Enhancing indoor air quality–The air filter advantage. Lung India: Official Organ of Indian Chest Society, 32(5), 473.
2. Yoda, Y., Tamura, K., Adachi, S., Otani, N., Nakayama, S. F., & Shima, M. (2020). Effects of the Use of Air Purifier on Indoor Environment and Respiratory System among Healthy Adults. International Journal of Environmental Research and Public Health, 17(10), 3687.
3. https://www.who.int/emergencies/diseases/novel-coronavirus-2019/question-and-answers-hub/q-a-detail/coronavirus-disease-covid-19-schools.
4. https://www.webmd.com/lung/news/20201103/can-portable-air-cleaner-protect-you-from-covid 
5. https://enverid.com/blog/choosing-an-in-room-hepa-air-cleaner-fixed-or-portable/
6. https://www.publichealthontario.ca/-/media/documents/ncov/ipac/2021/01/faq-covid-19-portable-air-cleaners.pdf?la=en
7. https://www.edweek.org/leadership/air-purifiers-fans-and-filters-a-covid-19-explainer-for-schools/2020/10
8. https://aristair.com/blog/what-does-an-hvac-air-purifier-do/ 
9. Akbari, V., & Salmanzadeh, M. (2019). Numerical evaluation of the effect of air distribution system and location on performance of a portable air cleaner. Science and Technology for the Built Environment, 25(1), 34-45.