Airborne Bacterial Communities in Three East Asian Cities of China, South Korea, and Japan

Characterization of Airborne Microbial Communities in Northern Thailand: Impacts of Smoke Haze Versus Non-Haze Conditions

Data on airborne microorganisms, particularly in Southeast Asia, are more limited compared to chemical data. This study is the first to examine the community and diversity of microorganisms on PM2.5 in an urban area of Northern Thailand during both smoke haze and non-smoke haze periods of 2020. This study evaluated the composition of airborne bacteria and fungi and analyzed their association with the chemical composition of PM2.5 and meteorological variables. Significantly higher concentrations of PM2.5 and more chemical compounds were observed during the smoke haze period compared to the non-smoke haze period. Increased PM2.5 concentrations significantly altered both bacterial and fungal communities. The diversity and richness of airborne bacteria increased, whereas those of fungi decreased. The level of PM2.5 concentration (the carrier), the chemical composition of PM2.5 (the resources for survival), and the local meteorological conditions (relative humidity (RH)) were associated with the differences in bacterial and fungal populations. In addition, air originating from the west of the receptor site, influenced by both terrestrial and marine air mass routes, contributed to higher bacterial diversity and richness during the smoke haze period. In contrast, fungal diversity and richness were greater when the air came from the southwest, following a marine route. However, the primary health concern is pathogens, which were present in both periods (such as Clostridium, Aspergillus, and Cladosporium) and were especially abundant during smoke haze periods. This study highlights those airborne microorganisms, along with the particles and their chemical composition, are important components that can impact health, including that of humans, animals, and the environment.

Differential associations of fine and coarse particulate air pollution with cause-specific pneumonia mortality: A nationwide, individual-level, case-crossover study

BACKGROUND

The connections between fine particulate matter (PM2.5) and coarse particulate matter (PM2.5-10) and daily mortality of viral pneumonia and bacterial pneumonia were unclear.

OBJECTIVES

To distinguish the connections between PM2.5 and PM2.5-10 and daily mortality due to viral pneumonia and bacterial pneumonia.

METHODS

Using a comprehensive national death registry encompassing all areas of mainland China, we conducted a case-crossover investigation from 2013 to 2019 at an individual level. Residential daily particle concentrations were evaluated using satellite-based models with a spatial resolution of 1 km. To analyze the data, we employed the conditional logistic regression model in conjunction with polynomial distributed lag models.

RESULTS

We included 221,507 pneumonia deaths in China. Every interquartile range (IQR) elevation in concentrations of PM2.5 (lag 0-2 d, 37.6 μg/m3) was associated with higher magnitude of mortality for viral pneumonia (3.03%) than bacterial pneumonia (2.14%), whereas the difference was not significant (p-value for difference = 0.38). An IQR increase in concentrations of PM2.5-10 (lag 0-2 d, 28.4 μg/m3) was also linked to higher magnitude of mortality from viral pneumonia (3.06%) compared to bacterial pneumonia (2.31%), whereas the difference was not significant (p-value for difference = 0.52). After controlling for gaseous pollutants, their effects were all stable; however, with mutual adjustment, the associations of PM2.5 remained, and those of PM2.5-10 were no longer statistically significant. Greater magnitude of associations was noted in individuals aged 75 years and above, as well as during the cold season.

CONCLUSION

This nationwide study presents compelling evidence that both PM2.5 and PM2.5-10 exposures could increase pneumonia mortality of viral and bacterial causes, highlighting the more robust effects of PM2.5 and somewhat higher sensitivity of viral pneumonia.

East Asian monsoon manipulates the richness and taxonomic composition of airborne bacteria over China coastal area

Airborne bacteria may have significant impacts on aerosol properties, public health and ecosystem depending on their taxonomic composition and transport. This study investigated the seasonal and spatial variations of bacterial composition and richness over the east coast of China and the roles of East Asian monsoon played through synchronous sampling and 16S rRNA sequencing analysis of airborne bacteria at Huaniao island of the East China Sea (ECS) and the urban and rural sites of Shanghai. Airborne bacteria showed higher richness over the land sites than Huaniao island with the highest values found in the urban and rural springs associated with the growing plants. For the island, the maximal richness occurred in winter as the result of prevailing terrestrial winds controlled by East Asian winter monsoon. Proteobacteria, Actinobacteria and Cyanobacteria were found to be top three phyla, together accounting for 75 % of total airborne bacteria. Radiation-resistant Deinococcus, Methylobacterium belonging to Rhizobiales (related to vegetation) and Mastigocladopsis_PCC_10914 originating from marine ecosystem were indicator genera for urban, rural and island sites, respectively. The Bray-Curits dissimilarity of taxonomic composition between the island and two land sites was the lowest in winter with the representative genera over island also typically from the soil. Our results reveal that seasonal change of monsoon wind directions evidently affects the richness and taxonomic composition of airborne bacteria in China coastal area. Particularly, prevailing terrestrial winds lead to the dominance of land-derived bacteria over the coastal ECS which may have a potential impact on marine ecosystem.

Urban Aerobiome and Effects on Human Health: A Systematic Review and Missing Evidence

Urban air pollutants are a major public health concern and include biological matters which composes about 25% of the atmospheric aerosol particles. Airborne microorganisms were traditionally characterized by culture-based methods recognizing just 1.5–15.3% of the total bacterial diversity that was evaluable by genome signature in the air environment (aerobiome). Despite the large number of exposed people, urban aerobiomes are still weakly described even if recently advanced literature has been published. This paper aims to systematically review the state of knowledge on the urban aerobiome and human health effects. A total of 24 papers that used next generation sequencing (NGS) techniques for characterization and comprised a seasonal analysis have been included. A core of Proteobacteria, Actinobacteria, Firmicutes, and Bacteroides and various factors that influenced the community structure were detected. Heterogenic methods and results were reported, for both sampling and aerobiome diversity analysis, highlighting the necessity of in-depth and homogenized assessment thus reducing the risk of bias. The aerobiome can include threats for human health, such as pathogens and resistome spreading; however, its diversity seems to be protective for human health and reduced by high levels of air pollution. Evidence of the urban aerobiome effects on human health need to be filled up quickly for urban public health purposes.

Indoor microbiome, air pollutants and asthma, rhinitis and eczema in preschool children - A repeated cross-sectional study

BACKGROUND

Indoor microbiome exposure is associated with asthma, rhinitis and eczema. However, no studies report the interactions between environmental characteristics, indoor microbiome and health effects in a repeated cross-sectional framework.

METHODS

1,279 and 1,121 preschool children in an industrial city (Taiyuan) of China were assessed for asthma, rhinitis and eczema symptoms in 2012 and 2019 by self-administered questionnaires, respectively. Bacteria and fungi in classroom vacuum dust were characterized by culture-independent amplicon sequencing. Multi-level logistic/linear regression was performed in two cross-sectional and two combined models to assess the associations.

RESULTS

The number of observed species in bacterial and fungal communities in classrooms increased significantly from 2012 to 2019, and the compositions of the microbial communities were drastically changed (p < 0.001). The temporal microbiome variation was significantly larger than the spatial variation within the city (p < 0.001). Annual average outdoor SO₂ concentration decreased by 60.7%, whereas NO₂ and PM₁₀ concentrations increased by 63.3% and 40.0% from 2012 to 2019, which were both associated with indoor microbiome variation (PERMANOVA p < 0.001). The prevalence of asthma (2.0% to 3.3%, p = 0.06) and rhinitis (28.0% to 25.3%, p = 0.13) were not significantly changed, but the prevalence of eczema was increased (3.6% to 7.0%; p < 0.001). Aspergillus subversicolor, Collinsella and Cutibacterium were positively associated with asthma, rhinitis and eczema, respectively (p < 0.01). Prevotella, Lactobacillus iners and Dolosigranulum were protectively (negatively) associated with rhinitis (p < 0.01), consistent with previous studies in the human respiratory tract. NO₂ and PM₁₀ concentrations were negatively associated with rhinitis in a bivariate model, but a multivariate mediation analysis revealed that Prevotella fully mediated the health effects.

CONCLUSIONS

This is the first study to report the interactions between environmental characteristics, indoor microbiome and health in a repeated cross-sectional framework. The mediating effects of indoor microorganisms suggest incorporating biological with chemical exposure for a comprehensive exposure assessment.

Effect of Air Purification Systems on Particulate Matter and Airborne Bacteria in Public Buses

The indoor air quality in public transport systems is a major concern in South Korea. Within this context, we investigated the effect of air purification systems on the indoor air quality of intercity buses, one of the most popular transport options in South Korea. Air purifiers were custom designed and equipped with high-efficiency particulate air (HEPA) filters to remove particulate matter and ultraviolet light-emitting diodes (UV-LEDs) to remove airborne bacteria. To investigate the effectiveness of the air purification systems, we compared concentrations of particulate matter (PM2.5 and PM10), airborne bacteria, and carbon dioxide (CO2) in six buses (three with air purification systems and three without) along three bus routes (BUS1, BUS2, BUS3) in Gyeonggi Province, South Korea, between 6 April and 4 May 2021. Compared to the buses without air purification, those with air purification systems showed 34–60% and 25–61% lower average concentrations of PM2.5 and PM10, respectively. In addition, buses with air purification systems had 24–78% lower average airborne bacteria concentrations compared to those without air purification systems (when measured after 30 min of initial purification).

Seasonal changes dominate long-term variability of the urban air microbiome across space and time

Compared to soil or aquatic ecosystems, the atmosphere is still an underexplored environment for microbial diversity. In this study, we surveyed the composition, variability and sources of microbes (bacteria and fungi) in the near surface atmosphere of a highly populated area, spanning ~ 4,000 Km² around the city center of Madrid (Spain), in different seasonal periods along two years. We found a core of abundant bacterial genera robust across space and time, most of soil origin, while fungi were more sensitive to environmental conditions. Microbial communities showed clear seasonal patterns driven by variability of environmental factors, mainly temperature and accumulated rain, while local sources played a minor role. We also identified taxa in both groups characteristic of seasonal periods, but not of specific sampling sites or plant coverage. The present study suggests that the near surface atmosphere of urban environments contains an ecosystem stable across relatively large spatial and temporal scales, with a rather homogenous composition, modulated by climatic variations. As such, it contributes to our understanding of the long-term changes associated to the human exposome in the air of highly populated areas.

miR-30c-1 encourages human corneal endothelial cells to regenerate through ameliorating senescence

In the present study, we studied the role of microRNA-30c-1 (miR-30c-1) on transforming growth factor beta1 (TGF-β1)-induced senescence of hCECs. hCECs were transfected by miR-30c-1 and treated with TGF-β1 to assess the inhibitory effect of miR-30c-1 on TGF-β1-induced senescence. Cell viability and proliferation rate in miR-30c-1-transfected cells was elevated compared with control. Cell cycle analysis revealed that cell abundance in S phase was elevated in miR-30c-1-treated cells compared with control. TGF-β1 increased the senescence of hCECs; however, this was ameliorated by miR-30c-1. TGF-β1 increased the size of hCECs, the ratio of senescence-associated beta-galactosidase-stained cells, secretion of senescence-associated secretory phenotype factors, the oxidative stress, and arrested the cell cycle, all of which were ameliorated by miR-30c-1 treatment. miR-30c-1 also suppressed a TGF-β1-induced depolarization of mitochondrial membrane potential and a TGF-β1 stimulated increase in levels of cleaved poly (ADP-ribose) polymerase (PARP), cleaved caspase 3, and microtubule-associated proteins 1A/1B light chain 3B II. In conclusion, miR-30c-1 promoted the proliferation of hCECs through ameliorating the TGF- β1-induced senescence of hCECs and reducing cell death of hCECs. Thus, miR-30c-1 may be a therapeutic target for hCECs regeneration.

Assessment and statistical modelling of airborne microorganisms in Madrid

The limited evidence available suggests that the interaction between chemical pollutants and biological particles may intensify respiratory diseases caused by air pollution in urban areas. Unlike air pollutants, which are routinely measured, records of biotic component are scarce. While pollen concentrations are daily surveyed in most cities, data related to airborne bacteria or fungi are not usually available. This work presents the first effort to understand atmospheric pollution integrating both biotic and abiotic agents, trying to identify relationships among the Proteobacteria, Actinobacteria and Ascomycota phyla with palynological, meteorological and air quality variables using all biological historical records available in the Madrid Greater Region. The tools employed involve statistical hypothesis contrast tests such as Kruskal-Wallis and machine learning algorithms. A cluster analysis was performed to analyse which abiotic variables were able to separate the biotic variables into groups. Significant relationships were found for temperature and relative humidity. In addition, the relative abundance of the biological phyla studied was affected by PM₁₀ and O₃ ambient concentration. Preliminary Generalized Additive Models (GAMs) to predict the biotic relative abundances based on these atmospheric variables were developed. The results (r = 0.70) were acceptable taking into account the scarcity of the available data. These models can be used as an indication of the biotic composition when no measurements are available. They are also a good starting point to continue working in the development of more accurate models and to investigate causal relationships.

Ambient air pollution and respiratory bacterial infections, a troubling association: epidemiology, underlying mechanisms, and future challenges

The World Health Organization attributed more than four million premature deaths to ambient air pollution in 2016. Numerous epidemiologic studies demonstrate that acute respiratory tract infections and exacerbations of pre-existing chronic airway diseases can result from exposure to ambient (outdoor) air pollution. In this context, the atmosphere contains both chemical and microbial pollutants (bioaerosols), whose impact on human health remains unclear. Therefore, this review: summarises the findings from recent studies on the association between exposure to air pollutants-especially particulate matter and ozone-and onset or exacerbation of respiratory infections (e.g. pneumonia, cystic fibrosis lung infection, and tuberculosis); discusses the mechanisms underlying the relationship between air pollution and respiratory bacterial infections, which is necessary to define prevention and treatment strategies; demonstrates the relevance of air pollution modelling in investigating and preventing the impact of exposure to air pollutants on human health; and outlines future actions required to improve air quality and reduce morbidity and mortality related to air pollution.

Airborne Bacteria in Outdoor Air and Air of Mechanically Ventilated Buildings at City Scale in Hong Kong across Seasons

Studies of the indoor airborne microbiome have mostly been confined to a single location and time point. Here, we characterized, over the course of a year, the geographic variation, building-function dependence, and dispersal characteristics of indoor and outdoor airborne microbiomes (bacterial members only) of eight mechanically ventilated commercial buildings. Based on the Sloan neutral model, airborne microbiomes were randomly dispersed in the respective indoor and outdoor environments and between the two environments during each season. The dominant taxa in the indoor and outdoor environments showed minor variations at each location among seasons. The airborne microbiomes displayed weak seasonality for both indoor and outdoor environments, while a weak geographic variation was found only for the indoor environments. Source tracking results show that outdoor air and occupant skin were major contributors to the indoor airborne microbiomes, but the extent of the contribution from each source varied within and among buildings over the seasons, which suggests variations in local building use. Based on 32 cases of indoor airborne microbiome data, we determined that the indoor/outdoor (I/O) ratio of PM_2.5 was not a robust indicator of the sources found indoors. Alternatively, the indoor concentration of carbon dioxide was more closely correlated with the major sources of the indoor airborne microbiome in mechanically ventilated environments.

A Comparative Study of Associated Microbiota Between Pig Farm and Pig Slaughterhouse in Guangdong, China

The goal of this study was to compare the microbiota in different pig-present settings in China. Bioaerosol samples from pig farms and slaughterhouses and nasal samples from pig farmers and slaughterhouse workers were collected in Guangdong, southern China. The bacterial genomic DNA was isolated and subjected to 16S sequencing. The data were analyzed using QIIME2 with the DADA2 pipeline. A total of 14,923,551 clean reads and 2785 operational taxonomic units (OTUs) were obtained, which were mostly grouped into 4 phyla (Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria) and 220 families. The microbiota richness of nasal samples in pig-present workers was higher than that of bioaerosols collected in the vicinity of the pig enclosures. There were 31.7% (620/1954) shared OTUs between pig farm bioaerosols and pig farmers which was higher than that between pig slaughterhouses and slaughterhouse workers (23.4%, 364/1553) (p < 0.001). Acinetobacter and Pseudomonas were the most abundant in pig-present bioaerosols, and Staphylococcus, Pseudomonas, and Corynebacterium were dominant bacterial genus in pig farmers. The bacterial patterns are also specific to the location of sample collected. The results suggest that bioaerosol microbiota interact with human nasal microbes in the vicinity of the pig farm enclosures, providing the basis for further analysis of microbial transmission across hosts in pig-present settings.

The major chemical constituents of PM2.5 and airborne bacterial community phyla in Beijing, Seoul, and Nagasaki

Ambient particle (PM_2.5) samples were collected in three East Asian cities (Beijing, China; Seoul, South Korea; Nagasaki, Japan) from December 2014 to November 2015 to quantitatively investigate airborne bacteria at the phylum level. Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes, and Cyanobacteria represented the top five airborne bacterial phyla in all three cities. The most dominant airborne phylum, Proteobacteria, was more prevalent during the winter (at rates of 67.2%, 79.9%, and 87.0% for Beijing, Seoul, and Nagasaki, respectively). Correlations among airborne bacteria and environmental factors including PM_2.5, its major chemical constituents, and meteorological factors were calculated. Temperature correlated negatively with Proteobacteria but positively with Firmicutes and Bacteroidetes. The abundance of Cyanobacteria correlated positively with particulate NO₃^- and SO₄^2- levels in Beijing (R = 0.46 and R = 0.35 for NO₃^- and SO₄^2-, respectively) but negatively in Seoul (R = -0.14 and R = -0.19 for NO₃^- and SO₄^2-, respectively) and Nagasaki (R = -0.05 and R = -0.03 for NO₃^- and SO₄^2-, respectively). Backward trajectory analysis was applied for 72 h and three clusters were classified in each city. Five dominant bacteria and other bacterial groups showed significant differences (p < 0.05) in local clustering, as compared to the long-range transport clusters from Beijing. The proportions of the five bacterial phyla in Seoul were significantly different in each cluster. A local cluster in Nagasaki had higher ratios of all major airborne bacterial phyla, except Proteobacteria.

Longitudinal survey of microbiome associated with particulate matter in a megacity

BACKGROUND

While the physical and chemical properties of airborne particulate matter (PM) have been extensively studied, their associated microbiome remains largely unexplored. Here, we performed a longitudinal metagenomic survey of 106 samples of airborne PM_2.5 and PM₁₀ in Beijing over a period of 6 months in 2012 and 2013, including those from several historically severe smog events.

RESULTS

We observed that the microbiome composition and functional potential were conserved between PM_2.5 and PM₁₀, although considerable temporal variations existed. Among the airborne microorganisms, Propionibacterium acnes, Escherichia coli, Acinetobacter lwoffii, Lactobacillus amylovorus, and Lactobacillus reuteri dominated, along with several viral species. We further identified an extensive repertoire of genes involved in antibiotic resistance and detoxification, including transporters, transpeptidases, and thioredoxins. Sample stratification based on Air Quality Index (AQI) demonstrated that many microbial species, including those associated with human, dog, and mouse feces, exhibit AQI-dependent incidence dynamics. The phylogenetic and functional diversity of air microbiome is comparable to those of soil and water environments, as its composition likely derives from a wide variety of sources.

CONCLUSIONS

Airborne particulate matter accommodates rich and dynamic microbial communities, including a range of microbial elements that are associated with potential health consequences.

Structural Characteristics and Functional Implications of PM2.5 Bacterial Communities During Fall in Beijing and Shanghai, China

Air pollution characterized by fine particulate matter (PM_2.5) frequently has occurred in China, and has posed threats to human health. The physiochemical characteristics of airborne PM_2.5 have been extensively studied, but its bacterial structures and functions have not yet been well studied. Herein, we focused on the structural characteristics and functional implications of airborne bacteria under different pollution levels in Beijing and Shanghai. The α- and β-diversities showed no obvious difference in two cities (p > 0.05). The dominant phyla Proteobacteria, Firmicutes, and Actinobacteria with total abundance of over 92% were found in all PM_2.5 samples. The results of weighted unifrac non-metric multidimensional scaling (NMDS) suggested that air pollution was no obviously correlated with bacterial community but dispersed disorderly. Furthermore, canonical correlation analysis (CCA) and permutation test indicated that NH4+, SO42-, and wind speed were the key factors that associated with airborne bacterial community structure. Chemical components of particulate matter played more important role in structuring bacterial community than meteorological conditions based on the result of partial CCA. In addition, the annotation of metabolic pathway suggested that the predominant genus Pseudomonas was obviously correlated with disease infections. Several dominant species might contribute to organic degradation, nitrogen cycles, and ice-nuclei activities in environments. Overall, this work enhanced our understanding of functions of airborne bacteria and highlighted their potential role in atmospheric chemical progresses.

Bacillus-Dominant Airborne Bacterial Communities Identified During Asian Dust Events

Asian dust (AD) events have received significant attention due to their adverse effects on ecosystems and human health. However, detailed information about airborne pathogens associated with AD events is limited. This study monitored airborne bacterial communities and identified AD-specific bacteria and the potential hazards associated with these bacteria during AD events. Over a 33-month period, 40 air samples were collected under normal atmospheric conditions (non-AD events; n = 34) and during AD events (n = 6). The airborne bacterial communities in the air samples collected during non-AD events (non-AD sample) and AD events (AD sample) were evaluated using both culture-dependent and culture-independent methods. The bacterial diversity increased significantly, along with the 16S rRNA gene copy number, in AD samples (p < 0.05) and was positively correlated with PM₁₀ concentration. High throughput sequencing of the 16S rRNA gene revealed that the relative abundance of the phylum Firmicutes increased substantially in AD samples (44.3 ± 5.0%) compared with non-AD samples (27.8 ± 4.3%). Within the phylum Firmicutes, AD samples included a greater abundance of Bacillus species (almost 23.8%) than non-AD samples (almost 13.3%). Both culture-dependent and culture-independent methods detected common predominant species closely related to Bacillus cereus during AD events. Subsequent multilocus sequence typing (MLST) and enterotoxin gene assays confirmed the presence of virulence factors in B. cereus isolates from AD samples. Furthermore, the abundance of bceT, encoding enterotoxin in B. cereus, was significantly higher in AD samples (p < 0.05). The systematic characterization of airborne bacterial communities in AD samples in this study suggests that B. cereus pose risks to public health.

Comparison of Bacterial Diversity in Air and Water of a Major Urban Center

The interaction of wind with aquatic and terrestrial surfaces is known to control the creation of microbial aerosols allowing for their entrainment into air masses that can be transported regionally and globally. Near surface interactions between urban waterways and urban air are understudied but some level of interaction among these bacterial communities would be expected and may be relevant to understanding both urban air and water quality. To address this gap related to patterns of local air-water microbial exchange, we utilized next-generation sequencing of 16S rRNA genes from paired air and water samples collected from 3 urban waterfront sites and evaluated their relative bacterial diversity. Aerosol samples at all sites were significantly more diverse than water samples. Only 17–22% of each site’s bacterial aerosol OTUs were present at every site. These shared aerosol OTUs included taxa associated with terrestrial systems (e.g., Bacillus), aquatic systems (e.g., Planktomarina) and sewage (e.g., Enterococcus). In fact, sewage-associated genera were detected in both aerosol and water samples, (e.g., Bifidobacterium, Blautia, and Faecalibacterium), demonstrating the widespread influence of similar pollution sources across these urban environments. However, the majority (50–61%) of the aerosol OTUs at each site were unique to that site, suggesting that local sources are an important influence on bioaerosols. According to indicator species analysis, each site’s aerosols harbored the highest percentage of bacterial OTUs statistically determined to uniquely represent that site’s aquatic bacterial community, further demonstrating a local connection between water quality and air quality in the urban environment.

Global Ramifications of Dust and Sandstorm Microbiota

Dust and sandstorm events inject substantial quantities of foreign microorganisms into global ecosystems, with the ability to impact distant environments. The majority of these microorganisms originate from deserts and drylands where the soil is laden with highly stress-resistant microbes capable of thriving under extreme environmental conditions, and a substantial portion of them survive long journeys through the atmosphere. This large-scale transmission of highly resilient alien microbial contaminants raises concerns with regards to the invasion of sensitive and/or pristine sink environments, and to human health-concerns exacerbated by increases in the rate of desertification. Further increases in the transport of dust-associated microbiota could extend the spread of foreign microbes to new ecosystems, increase their load in present sink environments, disrupt ecosystem balance, and potentially introduce new pathogens. Our present understanding of these microorganisms, their phylogenic affiliations and functional significance, is insufficient to determine their impact. The purpose of this review is to provide an overview of available data regarding dust and sandstorm microbiota and their potential ramifications on human and ecosystem health. We conclude by discussing current gaps in dust and sandstorm microbiota research, and the need for collaborative studies involving high-resolution meta-omic approaches in conjunction with extensive ecological time-series studies to advance the field towards an improved and sufficient understanding of these invisible atmospheric travelers and their global ramifications.