Bacterial Aerosols Research Articles

Research on the Spatial Distribution Characteristics and Inhalation Health Risk Assessment of Bacterial Aerosols in Spraying Environments

Research on the Spatial Distribution Characteristics and Inhalation Health Risk Assessment of Bacterial Aerosols in Spraying Environments

Unraveling the impact of operational parameters and environmental conditions on the quality of viable bacterial aerosols.

Viable pathogen-laden droplets of consistent quality are essential for reliably assessing the protection offered by facemasks against airborne infections. We identified a significant gap in guidance within standardized tests for evaluating the filtration efficiencies of facemask materials using viable bacteria-laden aerosol droplets. An aerosol platform, built according to the American Society for Testing and Materials standard F2101-19, was used to validate and standardize facemask filtration test procedures. We utilized this platform to investigate the impact of varying five operating parameters, namely suspension media composition, relative humidity, pathogen concentration, and atomizer airflow and feed flow rates, on the aerosol quality of viable bacteria-laden aerosols. We achieved consistent generation of 1,700 to 3,000 viable bacteria-laden droplets sized between 2.7 and 3.3 µm under the following optimized test conditions: 1.5% w/v peptone water concentration, ≥80% relative humidity at 24 ± 2 °C, 1 × 105 CFU/mL bacterial concentration, 1.5 L/min atomizer airflow rate, and 170 μL/min feed flow rate. We also explored the consequence of deviating from these optimized test parameters on viable bacteria-laden aerosol quality. These results highlight the importance of controlling these parameters when studying airborne transmission and control.

Dynamics of Microbial Ecology, Particulate Matter, and Bacterial Aerosols in Agriculture: Implications for Health and Sustainability

Dynamics of Microbial Ecology, Particulate Matter, and Bacterial Aerosols in Agriculture: Implications for Health and Sustainability

Long-lifespan, biodegradable, self-disinfecting, and gas-sensing electronic mask with a Janus-structured all-natural fiber network for personal healthcare

Conventional disposable surgical masks have become an integral part of our daily lives, however, present a limited filtration efficiency, brief operative lifespan, and inability to degrade naturally, bringing a heavy burden to the environment. Moreover, these masks cannot efficaciously eliminate bacteria, potentially causing secondary and cross infections among users, thereby failing to curb the spread of infectious diseases. Herein, a fire-new, long-lifespan, biodegradable, self-disinfecting, and gas-sensing electronic-mask is nano-engineered with a Janus-structured all-natural fiber network (SA-CPN) constructed from animal-collagen and plant-fibers. SA-CPN demonstrates exceptional filtration performance (99.9%) for PM2.5 and maintains outstanding filtration efficiency after 10 test-cycles or 32 h in high-humidity conditions. SA-CPN exhibits robust antibacterial origins for extended periods, with antibacterial rates of 98.30%, 99.36%, and 98.11% against P aeruginosa, S aureus, and E coli, respectively, and can effectively filter airborne bacterial aerosols. Moreover, SA-CPN achieves real-time detection of ammonia concentrations, effectively identifying ammonia levels in exhaled human breath and external environments, and monitoring the human respiratory rate, potentially identifying underlying health conditions. The directional water vapor transmission capability of SA-CPN improves comfort when wearing. Notably, SA-CPN can fully biodegrade within 5 h under enzyme action. The proposed multifunctional electronic mask, featuring biocompatibility, biodegradability, self-disinfection, and ammonia sensing capabilities, holds significant promise in personal medical protective equipment for health monitoring and disease prevention.

Insights into bioaerosol contamination in the process of mineralized refuse mining: Microbial aerosolization behavior and potential pathogenicity

The landfill mining process is a main source of anthropogenic bioaerosol release, posing potential risks to the health of occupationally exposed personnel and nearby residents. In this study, microbial aerosolization behavior and potential pathogenicity during the landfill mining process were systematically investigated. The highest concentration of bacterial aerosols was measured in the refuse mining area, with a value of 5968 ± 1608 CFU/m3, while the highest concentration of fungal aerosols was 1196 ± 370 CFU/m3 in the refuse screening area. The bacterial and fungal aerosols were distributed primarily in the particle size ranges of 4.7–7.0 µm and > 7.0 µm, respectively. The pathogenic microbes Arthrobacter, Bacillus, Arthrobotrys and Aspergillus had high bioaerosol aerosolization capacities, with aerosolization indices of 100–329, 31–62, 2–14 and 1–11, respectively, when released from mineralized refuse. There are more than 100 types of pathogenic bacteria in bioaerosols. The microorganisms Lysobacter, Luteimonas and Mycolicibacterium, which carry virulence factor genes (VFGs) (pilG, Rv0440, pilT, etc.), can spread VFGs, aggravate bioaerosol pollution, and threaten the health of workers and nearby residents. This research will help further the understanding of bioaerosol contamination behaviors and potential pathogenicity risks from landfill mining activities.

Bacterial and fungal aerosols in poultry houses: PM2.5 metagenomics via single-molecule real-time sequencing

Microbial aerosol contamination is a common problem in poultry farms, posing potential health risks to poultry and their caretakers. Exploring the distribution and diversity of the microbial community in poultry farm aerosols is crucial for effective mitigation strategies. The composition of bacterial and fungal aerosols is poorly understood, particularly the prevalence of potential pathogenic microorganisms in fine particulate matter (PM2.5) in various types of poultry houses. In this study, 27 PM2.5 samples were collected from 5 chicken houses and 4 duck houses in Shandong Province, China. Species-level diversity of bacterial and fungal components in PM2.5 samples was determined using advanced single-molecule real-time sequencing (SMRT) technology, based on the 16S and internal transcribed spacer 1 (ITS) ribosomal genes. Microbial diversity and community composition varied significantly across the different poultry house. Notably, duck houses had higher concentrations (p < 0.01) of PM2.5 (92.8-143.1 μg/m3) than chicken houses (42.0-56.4 μg/m3). Furthermore, microbial variation in PM2.5 samples was associated with the type of poultry facility. The predominant pathogenic microorganisms included Aspergillus sydowii, Penicillium sp., Aspergillus insolitus, Cladosporium sp., Aspergillus sp., Aspergillus pseudoglaucus, Cladosporium sp. C4092-2-PD1, and Colletotrichum sp., all of which were classified as second category of pathogens. Aspergillus sydowii and Penicillium sp. were the dominant species in chicken houses, while Cladosporium sp., Aspergillus sp., and Aspergillus pseudoglaucus were the dominant species identified in duck houses. To our knowledge, this study is the first to investigate bacterial and fungal diversity in PM2.5 samples collected from various types of poultry houses. These findings advance our understanding of poultry environmental microbiology and have important implications for safeguarding the health of both poultry and their caretakers.

Temporal changes in the size resolved fractions of bacterial aerosols in urban and semi-urban residences

Despite the significant amount of time spent in the domestic environment, culture-independent size distribution data of bioaerosols are largely missing. This study investigated the temporal changes in size-resolved bacterial aerosols in urban and semi-urban residential settings. Overall, airborne bacterial taxa identified in both sites were dispersed across particles of various sizes. qPCR analysis showed that outdoors bacteria dominated particles > 8 μm, whilst indoor bacterial loadings were greater with 1–2 μm (winter) and 2–4 μm (summer) ranges. Indoor and outdoor aerosols harboured distinct bacterial communities due to the dominance of human-associated taxa (Staphylococcus, Micrococcus, Corynebacterium) in indoor air. The aerosol microbiome exhibited significant temporal variation, with Actinobacteria, Gammaproteobacteria and Bacilli predominant indoors, whereas Actinobacteria, Alphaproteobacteria and Gammaproteobacteria were the most abundant taxa outdoors. The variation between the two residences was mostly driven by particles < 2 μm, whereas differences between indoors and outdoors were mostly influenced by particles > 2 μm. Source-tracking analysis estimated that household surfaces accounted for the greatest source proportion of bacteria, surpassing that of outdoor air, which varied due to natural ventilation throughout the year. Our findings provide new insights into the factors governing the aerosol microbiome in residential environments which are crucial for exposure assessment.

Impact of ventilation system retrofitting on indoor air quality in a single-family building

Due to prolonged human occupancy within indoor environments, the quality of indoor air holds significant importance. This study evaluates the impact of retrofitting a ventilation system from natural to mechanical on indoor air quality (IAQ) in a bedroom during heating seasons in 2017/18 and 2020/21. Measurements were conducted before and after modernization to assess CO2 concentrations, temperature, humidity, particulate matter (PM) and bacterial and fungal aerosols levels indoors and outdoors. Results show a significant decrease in CO2 concentration (from 1000 ± 240 ppm to 806 ± 165 ppm) and relative humidity (from 53.0 ± 3.6 % to 28.2 ± 4.1 %) post-modernization. Notable reduction in CO2 concentrations averaging 20 % was recorded, thereby elevating air quality category from IDAIII to IDAII. Additionally, the study determined the infiltration coefficient for PM2.5, which increased from 0.48 under natural ventilation to 0.63 after retrofitting. PM2.5 concentrations increased indoors (from 23.49 ± 11.21 μg/m3 to 56.68 ± 13.47 μg/m3) due to higher infiltration rates with mechanical ventilation. Bioaerosol measurements indicate fluctuating concentrations, with bacterial aerosols peaking in the evening. The use of mechanical ventilation led to increased transport and dispersion of bacterial bioaerosols indoors. In contrast, this was not observed for fungal aerosols. Additionally, the study highlights limitations in ventilation filtration efficiency and recommends the installation of PM2.5 sensors to regulate airflow during periods of high outdoor PM2.5 concentrations. Overall, while mechanical ventilation improved some IAQ parameters, it posed challenges in controlling particulate matter infiltration, emphasizing the need for comprehensive ventilation strategies to ensure indoor air quality and occupants' well-being.

Microbial pollution assessment in semi-exposed relics: A case study of the K9901 pit of the mausoleum of emperor Qin Shihuang

Summer and autumn are peak tourist seasons, during which tourists congregate in semi-exposed site museums, heightening the possibility of damage both to the tourists and the exposed relics by airborne microorganisms. This study investigated the spatiotemporal distribution of microbial aerosols and the diversity of the microbial genera inside and outside the Emperor Qin Shihuang Mausoleum K9901 Pit. Furthermore, the risk of museum personnel exposure to microbial aerosols was also quantitatively assessed. The results showed that the bacterial aerosol concentrations were 3.5 and 2.5 times the WHO limits (500 CFU/m3) in summer and autumn, respectively. Similarly, the fungal aerosol concentrations in summer and autumn were, respectively, 0.9 and 4.3 times the ACGIH limits (500 CFU/m3). The percentages of bacterial and fungal aerosols in the museum with particle sizes smaller than 4.7 μm were as high as 80.2–89.5 % and 83.2 %–93.2 %, respectively. The count median diameter was at level V of the Anderson sampler (1.1–2.1 μm). The risk of these aerosols being inhaled by personnel and entering the lower respiratory tract was significant. The dominant microbial genera detected had conditional pathogenicity (e.g., Acinetobacter and Pseudomonas) and allergenicity (e.g., Aspergillus and Talaromyces). Regarding tourists, the potential exposure dose (PED) was higher for children than for adults and the elderly. Staff were exposed for longer periods and had 18 times the PED of tourists of the same age, which put them at greater risk. This study offers valuable insights for developing effective environmental optimization measures to protect site museums and public health.

Characteristics of bioaerosol emissions from a municipal wastewater treatment plant: Health risk assessment and microbial composition

Bioaerosols released from municipal wastewater treatment plants (MWWTPs) contain pathogenic microorganisms, if dispersed into the atmosphere, which pose potential health risks to humans. In this study, the concentrations and size distribution of bioaerosol, factors on the bioaerosol emission, exposure risk, and microbial composition in different treatment units of a MWWTP were investigated. The results showed that bioaerosol was released to different degrees in each treatment unit, with the concentrations of bioaerosol varied widely, ranging from 978 to 3710 CFU/m3. FG and PST were primary bioaerosol emission sources in MWWTP. COD concentration, wind speed (WS) and relative humidity (RH) significantly influenced bioaerosol concentrations. The proportion of inhalable particles (< 4.7 μm) ranged from 51.35 % to 83.33 %, and bioaerosol emitted from WWTP caused a non-carcinogenic risk to children by the exposure risk assessment (HI > 1), which need to be paid more attention. Bacterial, fungal and actinomycete aerosols were detected in each treatment unit of MWWTP. Among these bioaerosols, bacterial aerosol was dominant. Importantly, several pathogenic bacteria including Sphingobium, Brevundimonas, Romboutsia, Arcobacter, Acinetobacter, and Mycobacterium were identified within the airborne bacteria population, most of which originated from wastewater or sludge, particularly in the ambient air of AeT. Pathogenic bacteria from MWWTP should be studied further to determine their long-term behavior and possible health risks.

Evasion of the Immune System by Mycobacterium tuberculosis: A Special Review on Macrophages

Mycobacterium tuberculosis, the bacterium that caused tuberculosis, is estimated to affect 10 million people worldwide in 2019. This bacterium is an intracellular pathogen that is spread through the inhalation of bacterial aerosol particles. The innate immune system in the lungs is prepared to phagocytize these bacteria, particularly macrophages, dendritic cells, monocytes, and neutrophils. M. tuberculosis can evade attacks by the host immune system and has developed strategies to infect successfully, especially macrophages. This intracellular bacterium can inhibit phagolysosome fusion, which is associated with lipoarabinomannan (LAM) in the bacterial cell wall. M. tuberculosis also can persist in phagolysosomes by inhibiting acidification and also inhibiting the action of NOX2 from producing ROS. This ability also allows these bacteria to avoid autophagy within macrophages. Knowledge of the power of these bacteria to manipulate and evade the immune system, especially macrophages, is beneficial in developing medicines and vaccines in the future.

Unveiling the airborne microbial menace: Novel insights into pathogenic bacteria and fungi in bioaerosols from nursery schools to universities

Bacterial and fungal aerosol pollution is widespread in indoor school environments, and poses potential health risks to students and staff. Understanding the distribution and diversity of microbial communities within aerosols is crucial to mitigate their adverse effects. Existing knowledge regarding the composition of bacterial and fungal aerosols, particularly the presence of potential pathogenic microorganisms in fine particulate matter (PM2.5) from nursery schools to universities, is limited. To bridge this knowledge gap, in the present study, we collected PM2.5 samples from five types of schools (i.e., nursery schools, primary schools, junior schools, and high schools and universities) in China. We used advanced single-molecule real-time sequencing to analyze the species-level diversity of bacterial and fungal components in PM2.5 samples based on 16S and ITS ribosomal genes, respectively. We found significant differences in microbial diversity and community composition among the samples obtained from different educational institutions and pollution levels. In particularly, junior schools exhibited higher PM2.5 concentrations (62.2–86.6 μg/m3) than other schools (14.4–48.4 μg/m3). Moreover, microbial variations in PM2.5 samples were associated with institution type. Notably, the prevailing pathogenic microorganisms included Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus haemolyticus, Streptococcus pneumoniae, and Schizophyllum commune, all of which were identified as Class II Pathogenic Microorganisms in school settings. Four potentially novel strains of S. commune were identified in PM2.5 samples collected from the university; the four strains showed 92.4 %–94.1 % ITS sequence similarity to known Schizophyllum isolates. To the best of our knowledge, this is the first study to explore bacterial and fungal diversity within PM2.5 samples from nursery schools to universities. Overall, these findings contribute to the existing knowledge of school environmental microbiology to ensure the health and safety of students and staff and impacting public health.

Non-thermal plasma for decontamination of bacteria trapped in particulate matter filters: plasma source characteristics and antibacterial potential

The aims of this study encompass the characterization of process parameters and the antimicrobial potential during operation of a novel non-thermal plasma (NTP) source in a duct system containing a particulate matter (PM) filter thus mimicking the interior of an air purifier. Simulating conditions of a long-term operation scenario, in which bacterial aerosols in indoor environments accumulate on PM filters, the filter surfaces were artificially inoculated with Escherichia coli (E. coli) and exposed to an air stream enriched with reactive species. Electrical power consumption, key plasma parameters, volume flow and air flow velocity, reactive gas species concentrations as well as inactivation rates of E. coli were assessed. The NTP operated at a gas temperature close to ambient air temperature and featured a mean electron energy of 9.4 eV and an electron density of 1∙1019 m−3. Ozone was found to be the dominating reactive gas species with concentrations of approx. 10 ppm in close vicinity to the PM filters. An inactivation rate of 99.96 % could be observed after exposure of the PM filters to the gas stream for 15 min. This inactivation efficiency appears very competitive in combating realistic bacterial aerosol concentrations in indoor environments.

Impact of different hand-drying methods on surrounding environment: aerosolization of virus and bacteria, and transfer to surfaces

In recent years, hand drying has been highlighted as a key step in appropriate hand hygiene, as moisture on hands can increase the transfer of micro-organisms from hands to surfaces and vice versa. To understand bacterial and viral aerosolization following hand drying, and study the transfer of micro-organisms from hands to surfaces after drying using different methods. Groups of five volunteers had their hands pre-washed with soap, rinsed and dried, then inoculated with a concentrated mixture of Pseudomonas fluorescens and MS2 bacteriophage. Volunteers entered an empty washroom, one at a time, and rinsed their hands with water or washed their hands with soap prior to drying with a jet dryer or paper towels. Each volunteer applied one hand successively to various surfaces, while their other hand was sampled using the glove juice method. Both residual bacteria and viruses were quantified from the washroom air, surface swabs and hand samples. P.fluorescens and MS2 bacteriophages were rarely aerosolized while drying hands for any of the drying methods studied. Results also showed limited, and similar, transfer of both micro-organisms studied on to surfaces for all drying methods. The use of jet dryers or paper towels produces low levels of aerosolization when drying hands in a washroom. Similarly, all drying methods result in low transfer to surfaces. While the coronavirus disease 2019 pandemic raised concerns regarding public washrooms, this study shows that all methods tested are hygienic solutions for dry washed hands.

Health risk assessment and characterization of PM2.5 bound bioaerosols at the municipal solid waste landfill site of Nagpur, India

Landfill being the reservoir of organic waste, serves as the most important source in the generation and emission of bioaerosols in the environment, and these bioaerosols have a significant impact on the environment and public health. In India, there are limited studies on the characterization of culturable bacteria and fungi in the bioaerosols originating from landfills. Therefore, the present study aimed to quantify and identify the bioaerosols and study their characteristics at a landfill site in Nagpur, India. The study describes the seasonal variation of PM2.5, PM2.5-associated bacteria and fungi in the landfill air, their molecular identification, antibiotic resistance, pathogenicity, dispersion and health risk assessment during winter and pre-monsoon seasons at the landfill site and surrounding residential sites in upwind and downwind directions. The study showed PM2.5 concentration was highest in the winter season (265.56 μg/m3) followed by the pre-monsoon season (173.1 μg/m3) at the landfill site. The culturable bioaerosol level was also significantly higher in winter (11056 CFU/m3) in comparison to pre-monsoon season (2244 CFU/m3) at the landfill site. Upon isolating and characterizing the microorganisms in the bioaerosols, some of the bacterial isolates, like Bacillus, Staphylococcus gallinarum, and Streptomyces speibonae were found to be resistant to chloramphenicol, netillin, nitrofurantoin, streptomycin etc. About 30% of the bacterial isolates were found to show β-hemolytic virulence activity. This indicated the presence of multi-drug resistant and potentially pathogenic bacteria in the bioaerosols over the landfill. The health risk assessment in adults indicated that the workers at the landfill site were at risk of bacterial aerosol in the winter season (hazard quotient i.e., HQ>1). The impact of bioaerosols on children needs to be investigated in the further studies and regular monitoring of bioaerosols is suggested to avoid any morbidity. To the best of our knowledge, this is the first study on the characterization of microorganisms from the bioaerosols over an open landfill site in India.

Research advances in microfluidic collection and detection of virus, bacterial, and fungal bioaerosols.

Bioaerosols are airborne suspensions of fine solid or liquid particles containing biological substances such as viruses, bacteria, cellular debris, fungal spores, mycelium, and byproducts of microbial metabolism. The global Coronavirus disease 2019 (COVID-19) pandemic and the previous emergence of severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and influenza have increased the need for reliable and effective monitoring tools for bioaerosols. Bioaerosol collection and detection have aroused considerable attention. Current bioaerosol sampling and detection techniques suffer from long response time, low sensitivity, and high costs, and these drawbacks have forced the development of novel monitoring strategies. Microfluidic technique is considered a breakthrough for high performance analysis of bioaerosols. In recent years, several emerging methods based on microfluidics have been developed and reported for collection and detection of bioaerosols. The unique advantages of microfluidic technique have enabled the integration of bioaerosol collection and detection, which has a higher efficiency over conventional methods. This review focused on the research progress of bioaerosol collection and detection methods based on microfluidic techniques, with special attention on virus aerosols and bacterial aerosols. Different from the existing reviews, this work took a unique perspective of the targets to be collected and detected in bioaerosols, which would provide a direct index of bioaerosol categories readers may be interested in. We also discussed integrated microfluidic monitoring system for bioaerosols. Additionally, the application of bioaerosol detection in biomedicine was presented. Finally, the current challenges in the field of bioaerosol monitoring are presented and an outlook given of future developments.

Experimental assessment of low temperature plasma devices for bacterial aerosol inactivation in the air duct of HVAC systems.

In light of growing concerns about indoor air quality and the transmission of pathogens, this study aims to evaluate the effectiveness of low temperature plasma (LTP) devices in inactivating bacterial aerosols in the air duct of HVAC systems, exploring methods to enhance air purification efficiency. This research employed experimental methods to explore the deactivation effects of LTP on common bacteria such as E. coli and Bacillus subtilis, focusing on the role of air parameters such as the airflow rate, relative humidity, and temperature in influencing the device's performance. Notably, the study determined that an operational voltage of 3000 V for the LTP device, combined with conditions of low airflow, low humidity, and high temperature, significantly enhances the inactivation of bacterial aerosols, achieving an 82% inactivation rate at a negative ion concentration of 2.4 × 1011 ions per m3 and a wind speed of 3 m s-1. Despite the generation of ozone and ultraviolet light as by-products, their concentrations were found to be within safe limits for human exposure. In addition, this study identified an effective inactivation range, alongside an optimal arrangement for the airflow direction within ducts, to maximize the sterilization efficiency of the LTP device. Given these promising results, the study advocates for the integration of LTP technology into the air duct of HVAC systems of public buildings to improve air quality and reduce the risk of airborne disease transmission.

Investigation of Indoor Airborne Bacteria in the Severe Cold Region in China: Genera, Levels, and the Influencing Factors of Concentration

In regions experiencing severe cold, inadequate ventilation during winter months often leads to increased concentrations of indoor pollutants. While there have been several studies on indoor particulate matter and inorganic pollutants in such regions, bioaerosol pollution has not been as extensively investigated. This study examines the indoor bioaerosol situation in a university located in one of the severe cold regions in China, focusing on bacteria as a representative pollutant. It investigated random samples of an office and a dormitory (including washrooms) and spanned heating and nonheating periods. The findings indicated that bacterial abundance in the dormitory and office was approximately equivalent. The predominant airborne bacterial communities identified were Proteobacteria, Bacteroidota, Actinobacteriota, Firmicutes, and Myxococcota. Opening windows effectively reduced bacterial concentrations during both heating and nonheating periods. When windows remained closed, bacterial concentrations exceeded the standard by 9.1% during the nonheating period and by 14.3% during the heating period. Furthermore, temperature and relative humidity influenced bacterial particle size, activity, and consequently, aerosol concentrations. In the office, the highest percentage of bioaerosols was observed in particle sizes &lt;1.1 and 1.1–2.1 μm, with smaller percentages observed in other particle sizes. Conversely, the percentage of particle sizes 2.1–3.3 μm in the dormitory was higher. The highest bacterial aerosol concentrations were detected in the morning in both the dormitory and office, during heating and nonheating periods. Bacterial concentrations in the office were lower on weekends than on weekdays, whereas in the dormitory, concentrations were higher on weekends than on weekdays. The above results indicate that indoor bacterial aerosol pollution is serious in winter in severe cold regions, which needs more attention.

Assessment of personal deposited dose and particle size distribution of bacterial aerosol in kindergarten located in southern Poland

The study's primary focus lies in examining the relationship between respiratory and deposition doses of bacterial aerosols in urban kindergarten, providing valuable insights into the specific doses absorbed by individuals in different sections of their respiratory systems based on the aerodynamic diameter of bacterial particles. Samples were collected twice a week, using by an Andersen cascade impactor during autumn and winter seasons 2018/2019 resulting in a total of 1152 Petri dishes analyzed. The highest average concentration of bacterial aerosol was observed during autumn (1698 ± 663 CFU/m3) in comparison to winter months (723 ± 134 CFU/m3). Respirable doses for children and staff were 2945 and 2441 CFU/day during winter and 5988 and 4964 CFU/day during autumn, respectively. Deposition doses incorporated from empirical models for regional deposition in the respiratory tract showed that children in kindergarten absorb 33% less of bacteria into alveolar region if breath by nose instead of mouth. Additionally, risk assessment results indicate that the hazard indices for children attending kindergartens for 3 years and for staff working 25 years are below 1, suggesting minor risks associated with the inhalation of bioaerosols during autumn and winter. HI was <1, so the non-carcinogenic effects are on an acceptable level, but the indoor/outdoor ratio were 3.5 and 2.4 for autumn and winter, respectively, indicating children's and adult's exposure to bacterial aerosol should be reduced.

Ambient Air Quality in Upper Silesia Region Pre-During, and Post-COVID-19 Periods

Abstract Governments worldwide have established lockdowns to limit the spread of COVID-19 during the pandemic. The restrictions on travel and reduction of economic activity have led to a temporary improvement in air quality in several countries, especially in urban areas. This study investigates the changes in concentration levels of air pollutants (PM10, PM2.5, SO2, NO2, and bacterial aerosol) in the Upper Silesia Region of Southern Poland, during three periods: pre (March 2018 and 2019), during (March 2020, and 2021) and post-COVID-19 lockdown period (March 2022 and 2023). Our findings indicate that COVID-19 restrictions had a moderate impact on PM10 levels in comparison to pre- and post-COVID-19 periods. PM2.5 during lockdown was significantly lower than in the pre-COVID period and not significantly higher after COVID. PM10 and PM2.5 average concentrations decreased during COVID-19 restrictions by 27.8% and 12.7%, respectively. Compared with the results from the pre-COVID-19 phase, the reductions in NO2 and SO2 during the lockdown were 9.5% and 34.0%. Among other pollutants, bacterial aerosol (BA) concentrations also decreased during the lockdown by 23.0%, compared to the results from the pre-COVID-19 period.