Bioaerosol Studies Research Articles

Review of bioaerosols from different sources and their health impacts.

The emission of bioaerosols in the ambient atmosphere from different sources is a cause of concern for human health and the environment. Bioaerosols are a combination of biotic matter like microbes and pollens. The present review emphasizes the understanding of various sources of bioaerosols (industries, municipal solid waste, and medical facilities), their components, and their impact on human health. The study of bioaerosols is of great importance as large numbers of people are estimated to be exposed on the global scale. Bioaerosols exposure in different work environments results in health issues such as infectious diseases, allergies, toxic effects, and respiratory problems. Hence, extensive research is urged to establish an effective assessment of bioaerosols exposure in the workplace, risks involved, distribution, and validation. The present review is intended to explore the relationship between bioaerosols exposure to the atmosphere and its impacts on human health. Some of the preliminary findings, based on our analysis of bioaerosols arising from municipal solid waste at a landfill site and a waste transfer station in Hyderabad, India, are also discussed herein.

Modeling the infection risk and emergency evacuation from bioaerosol leakage around an urban vaccine factory

Mounting interest in modeling outdoor diffusion and transmission of bioaerosols due to the prevalence of COVID-19 in the urban environment has led to better knowledge of the issues concerning exposure risk and evacuation planning. In this study, the dispersion and deposition dynamics of bioaerosols around a vaccine factory were numerically investigated under various thermal conditions and leakage rates. To assess infection risk at the pedestrian level, the improved Wells-Riley equation was used. To predict the evacuation path, Dijkstra’s algorithm, a derived greedy algorithm based on the improved Wells-Riley equation, was applied. The results show that, driven by buoyancy force, the deposition of bioaerosols can reach 80 m on the windward sidewall of high-rise buildings. Compared with stable thermal stratification, the infection risk of unstable thermal stratification in the upstream portion of the study area can increase by 5.53% and 9.92% under a low and high leakage rate, respectively. A greater leakage rate leads to higher infection risk but a similar distribution of high-risk regions. The present work provides a promising approach for infection risk assessment and evacuation planning for the emergency response to urban bioaerosol leakage.

Bioaerosol and microbial exposures from residential evaporative coolers and their potential health outcomes: A review.

Evaporative cooling is an energy efficient form of air conditioning in dry climates that functions by pulling hot, dry outdoor air across a wet evaporative pad. While evaporative coolers can help save energy, they also have the potential to influence human health. Studies have shown residential evaporative coolers may pull outdoor air pollutants into the home or contribute to elevated levels of indoor bioaerosols that may be harmful to health. There is also evidence that evaporative coolers can enable a diverse microbial environment that may confer early-life immunological protection against the development of allergies and asthma or exacerbate these same hypersensitivities. This review summarizes the current knowledge of bioaerosol and microbiological studies associated with evaporative coolers, focusing on harmful and potentially helpful outcomes from their use. We evaluate the effects of evaporative coolers on indoor bacterial endotoxins, fungal β-(1 → 3)-D-glucans, dust mite antigens, residential microbial communities, and Legionella pneumophila. To our knowledge, this is the first review to summarize and evaluate studies on the influence that evaporative coolers have on the bioaerosol and microbiological profile of homes. This brings to light a gap in the literature on evaporative coolers, which is the lack of data on health effects associated with their use.

A review of the emergence of antibiotic resistance in bioaerosols and its monitoring methods.

Despite significant public health concerns regarding infectious diseases in air environments, potentially harmful microbiological indicators, such as antibiotic resistance genes (ARGs) in bioaerosols, have not received significant attention. Traditionally, bioaerosol studies have focused on the characterization of microbial communities; however, a more serious problem has recently arisen due to the presence of ARGs in bioaerosols, leading to an increased prevalence of horizontal gene transfer (HGT). This constitutes a process by which bacteria transfer genes to other environmental media and consequently cause infectious disease. Antibiotic resistance in water and soil environments has been extensively investigated in the past few years by applying advanced molecular and biotechnological methods. However, ARGs in bioaerosols have not received much attention. In addition, ARG and HGT profiling in air environments is greatly limited in field studies due to the absence of suitable methodological approaches. Therefore, this study comprehensively describes recent findings from published studies and some of the appropriate molecular and biotechnological methods for monitoring antibiotic resistance in bioaerosols. In addition, this review discusses the main knowledge gaps regarding current methodological issues and future research directions.

A novel qPCR based-method for detection and quantification of three recurrent species of Penicillium isolated from bioaerosols in mold-damaged homes

Fungal contamination of indoor environments can cause respiratory diseases and induce damages to building materials. Among the fungal species found in mold-damaged homes, Penicillium brevicompactum, P. chrysogenum and P. crustosum can be considered as recurrent strains. In this study, we therefore propose a rapid and novel qPCR-based method in order to allow the monitoring of these three fungal species. The method developed allows the quantification of the target DNA of these three Penicillium species with a limit of quantification of 0.01 ng/μL without significant difference with spectrophotometry quantification assay for DNA concentrations between 5 and 100 ng/μL. This technique also enables the rapid detection of these three species in complex mixtures of DNA extracted from 15 bioaerosols collected in mold-damaged homes and previously cultured on agar plate. This new sensitive and specific qPCR technique can thus be easily integrated into bioaerosol studies.

Designing and Testing of a System for Aerosolization and Recovery of Viable Porcine Reproductive and Respiratory Syndrome Virus (PRRSV): Theoretical and Engineering Considerations.

Porcine reproductive and respiratory syndrome virus (PRRSV) infections cause significant economic losses to swine producers every year. Aerosols containing infectious PRRSV are an important route of transmission, and proper treatment of air could mitigate the airborne spread of the virus within and between barns. Previous bioaerosol studies focused on the microbiology of PRRSV aerosols; thus, the current study addressed the engineering aspects of virus aerosolization and collection. Specific objectives were to (1) build and test a virus aerosolization system, (2) achieve a uniform and repeatable aerosol generation and collection throughout all replicates, (3) identify and minimize sources of variation, and (4) verify that the collection system (impingers) performed similarly. The system for virus aerosolization was built and tested (Obj. 1). The uniform airflow distribution was confirmed using a physical tracer (<12% relative standard deviation) for all treatments and sound engineering control of flow rates (Obj. 2). Theoretical uncertainty analyses and mass balance calculations showed <3% loss of air mass flow rate between the inlet and outlet (Obj. 3). A comparison of TCID50 values among impinger fluids showed no statistical difference between any two of the three trials (p-value = 0.148, 0.357, 0.846) (Obj. 4). These results showed that the readiness of the system for research on virus aerosolization and treatment (e.g., by ultraviolet light), as well as its potential use for research on other types of airborne pathogens and their mitigation on a laboratory scale.

Detection and monitoring of insect traces in bioaerosols.

Studies on bioaerosols have primarily focused on their chemical and biological compositions and their impact on public health and the ecosystem. However, most bioaerosol studies have only focused on viruses, bacteria, fungi, and pollen. To assess the diversity and composition of airborne insect material in particulate matter (PM) for the first time, we attempted to detect DNA traces of insect origin in dust samples collected over a two-year period. These samples were systematically collected at one-month intervals and categorized into two groups, PM2.5 and PM10, based on the aerodynamic diameter of the aerosol particles. Cytochrome-c oxidase I (COI) was the barcoding region used to identify the origins of the extracted DNA. The airborne insect community in these samples was analyzed using the Illumina MiSeq platform. The most abundant insect sequences belonged to the order Hemiptera (true bugs), whereas order Diptera were also detected in both PM2.5 and PM10 samples. Additionally, we inferred the presence of particulates of insect origin, such as brochosomes and integument particles, using scanning electron microscopy (SEM). This provided additional confirmation of the molecular results. In this study, we demonstrated the benefits of detection and monitoring of insect information in bioaerosols for understanding the source and composition. Our results suggest that the PM2.5 and PM10 groups are rich in insect diversity. Lastly, the development of databases can improve the identification accuracy of the analytical results.

Aerosol Retention Barriers.

Aerosol Retention Barriers.

Transformative Approach To Investigate the Microphysical Factors Influencing Airborne Transmission of Pathogens.

Emerging outbreaks of airborne pathogenic infections worldwide, such as the current severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, have raised the need to understand parameters affecting the airborne survival of microbes in order to develop measures for effective infection control. We report a novel experimental strategy, TAMBAS (tandem approach for microphysical and biological assessment of airborne microorganism survival), to explore the synergistic interactions between the physicochemical and biological processes that impact airborne microbe survival in aerosol droplets. This innovative approach provides a unique and detailed understanding of the processes taking place from aerosol droplet generation through to equilibration and viability decay in the local environment, elucidating decay mechanisms not previously described. The impact of evaporation kinetics, solute hygroscopicity and concentration, particle morphology, and equilibrium particle size on airborne survival are reported, using Escherichia coli MRE162 as a benchmark system. For this system, we report that (i) particle crystallization does not directly impact microbe longevity, (ii) bacteria act as crystallization nuclei during droplet drying and equilibration, and (iii) the kinetics of size and compositional change appear to have a larger effect on microbe longevity than the equilibrium solute concentration.IMPORTANCE A transformative approach to identify the physicochemical processes that impact the biological decay rates of bacteria in aerosol droplets is described. It is shown that the evaporation process and changes in the phase and morphology of the aerosol particle during evaporation impact microorganism viability. The equilibrium droplet size was found to affect airborne bacterial viability. Furthermore, the presence of Escherichia coli MRE162 in a droplet does not affect aerosol growth/evaporation but influences the dynamic behavior of the aerosol by processing the culture medium prior to aerosolization, affecting the hygroscopicity of the culture medium; this highlights the importance of the inorganic and organic chemical composition within the aerosolized droplets that impact hygroscopicity. Bacteria also act as crystallization nuclei. The novel approach and data have implications for increased mechanistic understanding of aerosol survival and infectivity in bioaerosol studies spanning the medical, veterinary, farming, and agricultural fields, including the role of microorganisms in atmospheric processing and cloud formation.

An Overview of Bioinformatics Tools for DNA Meta-Barcoding Analysis of Microbial Communities of Bioaerosols: Digest for Microbiologists.

High-throughput DNA sequencing (HTS) has changed our understanding of the microbial composition present in a wide range of environments. Applying HTS methods to air samples from different environments allows the identification and quantification (relative abundance) of the microorganisms present and gives a better understanding of human exposure to indoor and outdoor bioaerosols. To make full use of the avalanche of information made available by these sequences, repeated measurements must be taken, community composition described, error estimates made, correlations of microbiota with covariates (variables) must be examined, and increasingly sophisticated statistical tests must be conducted, all by using bioinformatics tools. Knowing which analysis to conduct and which tools to apply remains confusing for bioaerosol scientists, as a litany of tools and data resources are now available for characterizing microbial communities. The goal of this review paper is to offer a guided tour through the bioinformatics tools that are useful in studying the microbial ecology of bioaerosols. This work explains microbial ecology features like alpha and beta diversity, multivariate analyses, differential abundances, taxonomic analyses, visualization tools and statistical tests using bioinformatics tools for bioaerosol scientists new to the field. It illustrates and promotes the use of selected bioinformatic tools in the study of bioaerosols and serves as a good source for learning the “dos and don’ts” involved in conducting a precise microbial ecology study.

Concentration and Size Distribution of Bacterial and Fungal Bioaerosols and the Related Exposure Dose

In this study, concentration and size distribution of bioaerosols (bacteria and fungi) were obtained in indoor at minimum ventilation and during the operation of air condition system (ACS). Indoo/Outdoor concentration ratio (I/O) of bacteria and fungi were also determined. In addition, the indoor exposure dose (IED) of bacteria and fungi were calculated. A six-stage Andersen cascade impactor was used for sampling the microorganisms during summer season at Minia University, El-Minia (Egypt). Mean bacterial and fungal concentrations were higher (727±160 and 252±60 CFU/m3, respectively ) at minimum ventilation than the concentrations during ACS (506±120 and 176±44 CFU/m3, respectively ). Indoor bacterial concentration level is three times higher than the fungal level. On the other hand, outdoor bacterial concentration (220±55 CFU/m3) is lower than the outdoor fungal level (300±77 CFU/m3). I/O concentration ratio of bacteria was greater than unity indicating that the main source of bacteria is the human occupancy while the corresponding I/O concentration ratio of fungi was less than unity indicating that the fungi are released from outdoor sources. Mean IED of bacteria (38.5 CFU/kg) was about three times higher than the IED of fungi (13.4 CFU/kg) .

Potential of Bioaerosol Emission in The Green House Laboratory and Research Laboratory at Environmental Engineering Department

In several countries in the world 24% of total atmospheric particles and 5% - 10% are suspended atmospheric particles are bioaerosols. In Indonesia, bioaerosol studies are mostly carried out in hospitals and school laboratories. The purpose of this research is to calculate potential bioaerosol emission in the research laboratory of the environmental engineering department. The method used is based on literature survey and observation of lab activities during waste composting. Based on our calculation, the bioaerosol flux emission from green house lab was 4.6 – 6.2 x103 cfu/s for Aspergillus Fumigatus, while for research lab it was 12.45 – 16.65 x 103 cfu/s. The emission flux of mesophilic actinomycetes was even bigger. The distribution of bioaerosol at GreenHouse lab declined at 3 m away, while for research lab it declined about 5 m away from the sources. Based on this study, schedule arrangement for the students in these lab is important to minimize bioaerosol exposure.

Laboratory study of bioaerosols: Traditional test systems, modern approaches, and environmental control

Biological aerosol particles have been studied in the laboratory for many decades to understand their roles in human health and disease and in environmental processes. These studies have used a var...

METODY BADAŃ MIKROBIOLOGICZNEGO ZANIECZYSZCZENIA POWIETRZA NA TERENACH OCZYSZCZALNI ŚCIEKÓW – PRZEGLĄD LITERATUROWY

W artykule przedstawiono podstawowe metody poboru i badań bioaerozolu emitowanego do atmosfery w otoczeniu oczyszczalni ścieków. Dokonano przeglądu literatury (ponad 100 pozycji), w której cytowane są liczne prace dotyczące mikrobiologicznego zanieczyszczenia powietrza na terenie i w sąsiedztwie oczyszczalni ścieków. Z tego względu, że każda z metod poboru próbek powietrza jest inna, bardzo trudno jest niekiedy porównać wyniki badań prowadzonych przez różnych autorów, badających powietrze różnymi metodami. Obecnie najbardziej powszechne są wolumetryczne sposoby poboru powietrza. W tym celu wykorzystuje się liczne urządzenia o różnych zasadach działania. W dostępnej literaturze stwierdza się także stosowanie bardzo różnych podłoży do hodowli tych samych d0robnoustrojów. W załączonych tabelach zestawiono najczęściej badane grupy mikroorganizmów, wykorzystywane pożywki, temperaturę i czas hodowli oraz autorów prac, którzy omawiają te metody hodowlane. Przyczyną takiej sytuacji jest najczęściej brak znormalizowanych przepisów obowiązujących w poszczególnych państwach, we wszystkich krajach lub np. na terenie Unii Europejskiej, według których można jednakowo ocenić stopień mikrobiologicznego zanieczyszczenia powietrza.

Uncovering prokaryotic biodiversity within aerosols of the pristine Amazon forest

Biological aerosols (bioaerosol) are atmospheric particles that act as a dispersion unit of living organisms across the globe thereby affecting the biogeographic distribution of organisms. Despite their importance, there is virtually no knowledge about bioaerosols emitted by pristine forests. Here we provide the very first survey of the prokaryotic community of a bioaerosol collected inside pristine Amazon forest at 2 m above ground. Total atmospheric particles were collected at the Amazon Tall Tower Observatory, subjected to metagenomic DNA extraction and the prokaryotic diversity was determined by 16S rRNA gene amplicon sequencing. A total of 271,577 reads of 250 bp of the 16S rRNA gene amplicon were obtained. Only 27% of the reads could be classified using the 16S SILVA database. Most belonged to Proteobacteria, Actinobacteria and Firmicutes which is in good agreement with other bioaerosol studies. Further inspection of the reads using Blast searches and the 18S SILVA database revealed that most of the dataset was composed of Fungi sequences. The identified microbes suggest that the atmosphere may act as an important gateway to interchange bacteria between plants, soil and water ecosystems.

Comparison of wastewater treatment plants based on the emissions of microbiological contaminants

This article presents the current and important results of bioaerosol studies which allow for the comparison of microbial contamination of air in 11 wastewater treatment plants (WWTPs), which differed in terms of capacity from 350 to 200,000 m3/day. The abundance of mesophilic bacteria, M+ and M− Staphylococcus, Pseudomonas fluorescens, Actinobacteria, coliform and psychrophilic bacteria, and microscopic fungi was determined. Additionally, the air temperature, relative humidity, wind velocity, and direction were also analyzed at each research station. The obtained very numerous results of bioaerosol and climate parameter studies were subjected to statistical analysis. The results regarding the minimum, maximum, and median abundance of the studied bacteria and microscopic fungi at 11 WWTPs and in background studies at control stations were presented in tables. Additionally, basic descriptive statistics for all studied microorganisms at specific seasons were presented. It was established that at the areas of WWTPs, the microscopic fungi were present that the highest concentrations (ranging from 0 to 1,148,530 CFU m−3), followed by psychrophilic bacteria (ranging from 40 to 225,000 CFU m−3) and mesophilic bacteria (ranging from 0 to 195,000 CFU m−3). The novel elaboration of bioaerosol study results based on cluster analysis and determination of a dendrogram allowed to compare the studied WWTPs. The similarity was decided based on the type of studied microorganisms and their dominance and abundance, while no similarities were observed in terms of capacity. In order to investigate the relation between the abundance of bacterial groups as well as microscopic fungi and microclimatic parameters (air temperature and humidity), a calculation of Spearman’s range correlation coefficients was conducted.

Bioaerosol research: Yesterday, today and tomorrow

Bioaerosols have important impacts on many scientific fields, including atmospheric environment, ecology, climate change, food safety, anti-bioterrorism, infectious diseases, public health and environmental health. This review was carried out based on the scientific outcomes from the 600th Xiangshan Science Conference held in Beijing, for whcih 47 scientists including those overseas were invited to discuss the bioaerosol research progress. Over the past 10 years, great strides have been made in the bioaerosol field, such as the expansion of research directions, research broadness and also scientists. For example, atmospheric chemistry researchers have also started to carry out studies about bioaerosol impacts on the atmospheric environment, including those on the cloud droplets, the climate and bioaerosol dynamics during haze events. In addition, new methods and instruments for bioaerosol studies are increasingly being developed in bioaerosol monitoring and capture systems, various biosensors, microfluidics, high-throughput sequencing, and they have helped the scientific community obtain a better understanding of microbes in the air. In terms of health effects, human and indoor bioaerosol emissions have become one of the hot research areas. In addition, bioaerosols were also shown to directly affect the oxidation potential of atmospheric particles and thus on the human health, however, the relevant mechanisms remain to be very limited and could be far more complex than what we have known so far. On the other hand, respiratory infections/outbreaks, caused largely by the spread of bioaerosols, continue to be a major killer for humans, especially for younger children. Currently, although a significant progress has been made in high-throughput screening of respiratory pathogens, the airborne disease transmission mechanisms are still not well understood, including the influences on the pathogen viability and effective transmission distance. The risk of military conflicts in certain regions is increasing, which could potentially lead to possible use of biological weapons via bioaerosol for mass human destruction. In addition, the airborne transmission of antibiotic resistant genes has also received wide attention as an emerging biological pollutant. By integrating sampling, microfluidics, biosensors and electronics, the scientists have taken an important step towards real-time online bioaerosol screening and biological hazard early warning. As a special type of bioaerosol, biomarkers in exhaled breath are also increasingly being studied for early disease diagnosis and screening. At the same time, surgical and nosocomial infections caused by the spread of bioaerosols in the hospital settings are also receiving wide attention. The scientific researchers have also made significant advances in the controlling airborne biological agents, e.g., microwave irradiation, cold plasma and nanomaterial filtration. This review intends to broadly review current state-of-the-art advances in bioaerosol studies, to summarize and discuss the existing problems, correspondingly providing references for the future studies. Despite of great progress made in many aspects of bioaerosols, our understanding of its significance and relevant impacts on our surroundings and health is still quite limited. In the years to come, bioaerosol research is expected to turn a new chapter if multidisciplinary collaboration can be further strengthened.

Recent research progress and perspective of characteristics of ambient bioaerosols during hazy pollution in China

Since the haze event occurred in many areas of central and eastern China in 2013, haze pollution has become one of the most important environmental issues and has attracted more and more attention from government, industry circle, scholars and the general public in China. Haze pollution is characterized by atmospheric particular matter (PM) being one of the top pollutants. A large number of studies have been conducted to investigate the chemical components of atmospheric PM during haze pollution, while little is known about the biological components and characteristics of PM in the atmosphere, especially during haze pollution. Biological particles in the atmosphere, generally defined as bioaerosols, are airborne particles or large molecules carrying living organisms or released from living organisms (e.g., bacteria, fungi, viruses, pollen, bacterial endotoxins and mycotoxins, etc.). Bioaerosols not only pose potential risks on air quality and human health, but also have direct effects on the alteration of global climate and atmospheric physical and chemical processes. Up to now, however, the concentration and size distribution, diversity, and abundance of different types of bioaerosols as well as their temporal and spatial variability are not well characterized on hazy days. Moreover, due to the changeable community structure, flexible biological activity and comprehensive influential factors, the knowledge involving how haze pollution affects bioaerosols, to what extent it affects, and the influence mechanism is still unclear so far. Therefore, this review first has presented an overview of the state of bioaerosol research during haze pollution, including concentration level, size distribution and community structure of microorganisms in bioaerosols. Subsequently, the current understanding and open questions have been emphatically discussed concerning the characteristics of bioaerosols at different air pollution levels and effects of air pollution on airborne microbes. Finally, we suggest that the following research activities should be pursued in future studies of bioaerosols during haze pollution: (1) It is extremely urgent to develop and establish uniform standardized sampling and identification criterion to better judge and measure the numerous monitoring data from different researchers. It is also essential to develop advanced, sensitive, real-time and online detection techniques to quantify the biological properties of bioaerosols. (2) The nationwide field monitoring of bioaerosols covering more climate types and pollution levels at various time scales should be carried out to obtain more comprehensive data for fully understanding the temporal and spatial variability of bioaerosols and its influential factors. Some other meteorological influential factors (e.g., boundary-layer height, atmospheric extreme temperature, extreme wind speed, and atmospheric pressure, etc.), and pollution factors such as the concentration of heavy metal and polycyclic aromatic hydrocarbon (PAHs) in PM should be taken into account to deeply understand the effect of haze pollution on bioaerosols. (3) Current studies have shown that many gaseous and particulate pollutants are related to the concentration of bioaerosols. However, little is known about the influence mechanisms of pollutants. Therefore, in addition to field monitoring, it is also necessary to design and conduct the laboratory experiment of smog chamber to determine the influence mechanism of each single environmental factor or pollution factor on bioaerosols. (4) In addition to different degrees of haze pollution, there are different kinds of haze pollution including the formation of haze by photochemical reaction in summer and liquid phase reaction at high RH in winter. Therefore, it is also essential to examine the distribution and variation of bioaerosols during different haze formation processes in order to improve our understanding of haze pollution effects on bioaerosols. (5) It is necessary to develop a biological source-tracking technology based on the bioaerosol species and community composition to reveal the possible sources of bioaerosols during haze episodes.

Seasonal variation characteristic of inhalable microbial communities in PM2.5 in Beijing city, China

Bacteria and fungi are primary constituents of airborne microbes in fine particulate matter (PM2.5) and significantly impact human health. However, hitherto, seasonal variation and effect of air pollution on microbial community composition and structure are poorly understood. This study analyzed the bacterial and fungal composition of PM2.5 under different air pollution levels during different seasons in Beijing. We altogether collected 75PM2.5 samples during four seasons from April 2014 to January 2015, under different air pollution levels and employed high-throughput sequencing methods to analyze microbial composition. The results showed that air pollution decreased species richness and community diversity of bacteria in PM2.5. The variation in bacterial and fungal community composition and structure was significantly related to the season but there was no correlation between their abundance and pollution levels. Pathogenic bacteria and fungi were more abundant in winter than other seasons. To best of our knowledge, this is the first study that demonstrates seasonal variation characteristics of bacteria and fungi in PM2.5 in heavy haze contaminated areas and highlights the effects of air pollution on the atmospheric microbial community. This study would be useful to other bioaerosol studies focusing on the role of the atmospheric particulate matter on human health.

Urban Enhancement of PM10 Bioaerosol Tracers Relative to Background Locations in the Midwestern United States.

Bioaerosols are well-known immune-active particles that exacerbate respiratory diseases. Human exposures to bioaerosols and their resultant health impacts depend on their ambient concentrations, seasonal and spatial variation, and co-pollutants, which are not yet widely characterized. In this study, chemical and biological tracers of bioaerosols were quantified in respirable particulate matter (PM10) collected at three urban and three background sites in the Midwestern United States across four seasons in 2012. Endotoxins from gram negative bacteria (and a few gram positive bacteria), water-soluble proteins, and tracers for fungal spores (fungal glucans, arabitol and mannitol) were ubiquitous and showed significant seasonal variation and dependence on temperature. Fungal spores were elevated in spring and peaked in summer, following the seasonal growing cycle, while endotoxins peaked in autumn during the row crop harvesting season. Paired comparisons of bioaerosols in urban and background sites revealed significant urban enhancements in PM10, fungal glucans, endotoxins and water-soluble proteins relative to background locations, such that urban populations have a greater outdoor exposure to bioaerosols. These bioaerosols contribute, in part, to the urban excesses in PM10. Higher bioaerosol mass fractions in urban areas relative to background sites indicate that urban areas serve as a source of bioaerosols. Similar urban enhancements in water-soluble calcium and its correlation with bioaerosol tracers point towards wind-blown soil as an important source of bioaerosols in urban areas.