Efficiency of Air Purifiers  Infectious diseases caused by airborne bacteria and viruses are a major problem for both social and economic reasons. The significance of this phenomenon is particularly noticeable during the time of the coronavirus pandemic. One of the consequences is the increased interest in the air purifier (AP) market, which resulted in a significant increase in sales of these devices. In this study, we tested the efficiency of APs in removing bacterial air contamination in the educational context in the Upper Silesia region of Poland during the “cold season” of 2018/2019. During the 6 months of measuring microbiological air quality, an 18% decrease in the concentration of microbiological pollutants as a result of the action of the APs was recorded. Additionally, the results of the particle size distribution of the bacterial aerosols showed a reduction in the share of the respirable fraction (particles with an aerodynamic diameter below 3.3 μm) by an average of 20%. The dominance of gram-positive cocci in the indoor environment indicates that humans are the main source of most of the bacteria present in the building. We conclude that the use of APs may significantly decrease the level of concentration of microbiological air pollutants and reduce the negative health effects of indoor bioaerosols; however, further work that documents this phenomenon is needed. There is also limited evidence that these decreases result in improved cardiorespiratory health (Fisk, 2013; Morishita et al., 2015). APs usage has been associated with decreased blood pressure, reduced oxidative stress, reduced systemic inflammation, and enhanced lung function in a number of studies (Kelly and Fussell, 2019). The COVID-19 pandemic has forced a significant focus on indoor disinfection and air purification options. The most frequent applications are the local control of the source of pollution, disinfection of rooms and surfaces, and ventilation. The use of APs can be considered an additional complementary and preventive action in the spread of biological contamination. Adequate IAQ can be achieved mainly by reducing and constantly controlling the concentrations of harmful microorganisms in the air. The limited data on IAQ in Polish educational institutions and the lack of generalized standards for bioaerosol levels are the reason why the presented studies can increase awareness and focus more attention on IAQ issues. According to the Air Quality in Europe 2020 report published by the European Environment Agency (EEA), Poland has the European Union’s most polluted air. The report found that the concentration of both PM10 and PM2.5—two types of harmful airborne participate matter—was higher in Poland than in any other European Union (EU) country. The collected data can be used to assess the exposure of children and kindergarten staff in southern Silesia, which is one of the most polluted areas in the EU. The specific aims include (i) the evaluation of the impact of APs on the microbial IAQ, (ii) investigation of the concentration levels of culturable bacteria, (iii) determination of the size distributions with particular attention to the respirable fraction of bacterial aerosols, and (iv) examination of the bacterial community structure. Materials and Methods Sampling SitesThe study was carried out in a kindergarten located in Gliwice (50.324,666 N, 18.711,405 E). Gliwice is a typical example of a city located in the industrial region of Upper Silesia, Poland, with 178.186 thousand occupants. The surrounding area of the measurement point is characterized by compact building development. Buildings, roads, asphalt, etc., cover most of the surfaces in this part of the city. More detailed information about the main characteristics of the studied kindergarten in Gliwice is provided in Table 1. Air sampling was conducted during the “cold season,” from September 2018 to February 2019. The sampling was performed two times each week, with one sample taken outside the building and two indoors, one when the APs were turned off and the other after 60 min from turning the APs on (Table 2). Two sets of measurements were performed with the APs turned on. Samples were collected between 10:00 and 12:00 local time, in order to check the efficiency of the tested device. The kindergarten had natural ventilation and was insulated and windows were kept closed during the sampling. Epidemiologic studies indicate that indoor air pollution is correlated with morbidity caused by allergic diseases. We evaluated the effectiveness of reducing the levels of indoor fine particulate matter