A three-stage collector was used to collect size-resolved cloud samples at the summit of Mt. Tai. Subsequently, analyses of pH values, water-soluble ions, and trace metals were performed and bacterial community were conducted using MiSeq amplicon sequencing. The pH values of the samples decreased as droplet sizes decreased. Sulfate (SO42−), nitrate (NO3−) and ammonium (NH4+) were the main secondary inorganic ions which their concentration distributed significantly different from size-resolved cloud water. The NH4+ concentration was higher in smaller droplets. The SO42− and NO3− concentrations were higher in larger droplets. The Ca2+ concentration increased as droplet size increased. Small droplet samples tended to have lower pH value, mainly because of the more acidic (SO42− and NO3−) and less acid-neutralizing (NH4+ and Ca2+) components. The bacterial community in size-resolved cloud samples were firstly recognized and dominated by the genera of Lactococcus (average abundance 34.9

Nitrogenous organic (CHON), crucial for secondary organic aerosol (SOA), forms through poorly studied mechanisms in clouds. Our study explores CHON transformation during cloud processes (CPs). These processes play a vital role in enhancing the variety of CHONs, leading to the formation of CHONs with oxygen atom counts ranging from 1 to 10 and double bond equivalent (DBE) values spanning from 2 to 10. We proposed that the CHONs formed during CPs are formed through aqueous phase reactions with CHO compound precursors via nucleophilic attacks by NH3. This scheme can be account for roughly three-quarters of the CHONs by number in cloud water, and near two-thirds of all CHONs are formed through reactions between NH3 and carbonyl-containing biogenic volatile organic compound (BVOC) ozonolysis intermediates. This study provides the first insights into the evolution of CHONs during CPs and reveals the significant roles of CPs in the formation of CHONs.

Metals are important components of PM2.5, with significant implications for the ecological environment and human health. This study comprehensively investigated the characteristics of 19 metals in PM2.5 samples collected in Jinan from 16 December 2020 to 15 December 2021. The total concentration of the studied metals accounted for 5.3

Nitrated phenolic compounds in the atmosphere are receiving increasing attention due to their light absorption and biological toxicity. In this study, particulate, gaseous, and cloud water samples were simultaneously collected during cloud events at the summit of Mount Tai in northern China in spring, summer, and winter and the contents of 11 nitrated phenolic compounds were determined. The seasonal average concentrations of the total nitrated phenolic compounds in particles were in the range of 7.3–27.1 ng m −3 , a little lower than those measured in the gas‐phase (18.3–70.6 ng m −3 ). Their concentrations in cloud water were at the levels of 168.4–438.5 μg L −1 . 4‐Nitrophenol and nitrosalicylic acids were the dominant compounds in particles, while 4‐nitrophenol and 2,4‐dinitrophenol were the most abundant in the gas phase and cloud water samples. During cloud events, most nitrated phenolic compounds were mainly distributed in the particle phase, except dinitrophenols which were mainly distributed in the gas phase in winter. The field‐derived effective Henry's law coefficients were several orders of magnitude higher than their theoretical values in pure water. Moreover, the measured concentrations of particulate nitrated phenolic compounds were substantially greater than the theoretical predictions, especially in spring. The above results indicate that nitrated phenolic compounds were partly formed via aqueous‐phase reactions inside the cloud droplets or on the wet particle surfaces, which changed their distribution patterns. The much higher ratios of 2,4‐dinitrophenol to the sum of 4‐nitrophenol and 5‐nitrosalicylic acid in cloud water than those in particles further confirm the enhanced formation via aqueous processes.

The process of frost formation has been studied as an important deposition pathway for removing atmospheric pollutants. However, the removal of organic species during frost formation remains unknown. Gas, PM2.5 and frost samples were collected in Wangdu, a severely polluted rural site in the North China Plain, during the winter of 2018. The concentrations, distributions, sources, and ecological and health risks of the 16 PAHs in the samples were determined. The 24 h-averaged concentrations of PAHs in the air (gas + PM2.5) reached 719 ng m−3, indicating that the local atmosphere was heavily contaminated by PAHs in winter. The average concentrations of PAHs in the frost insoluble reached 27.5 μg g−1, indicating the strong ambient PAHs deposition during the frost process. The distribution patterns of individual PAH species indicated that the PAHs in the gas influenced the frost samples, and the sources of PAHs in frost samples were highly similar to those in PM2.5 samples. The calculated lifetime lung cancer risk (LLCR) via inhalation of ambient PAHs was classified as high risks. The average total Benzo(a)pyrene toxic equivalent quotient (TEQ) of PAHs in the frost samples was estimated as 2.50 μg TEQ g−1, posing a high threat to the ecological environment and health. After the melting of frost, the PAHs are released into the soil. Although the concentrations are diluted, the PAH concentrations could adversely affect the growing vegetation or agricultural activities. The extremely high PAH concentrations and their ecological and health risks require special attention and strict regulation.

Aiming to understanding the impact of PM2.5 pollution on population health and local economies in Beijing during the “Five-year Clean Air Action Plan”, the health risk and economic losses of PM2.5 during the middle three years (2014–2016) were assessed. Results showed that the number of people affected by PM2.5 was gradually decreasing with the reduction of PM2.5 concentration from 2014 to 2016. The total impacted population reached 39573, 23207 and 20642 in 2014–2016, respectively. The premature death related to PM2.5 pollution respectively accounted for 7.85%, 4.32% and 3.56% to the total number of death in 2014–2016. And about 32% of premature death associated with PM2.5 was contributed by lung cancer. Respiratory hospital admission accounted for the largest number of people among the six health endpoints. The external costs associated with PM2.5 pollution might reach 2.9, 1.9 and 1.7 billions USD in 2014–2016, which accounted for 8.74‰, 5.37‰ and 4.51‰ of GDP in Beijing, respectively. Chaoyang and Haidian districts were the most affected area, while Yanqing, Huairou and Mentougou districts were the least affected areas.

Bioaerosol has been increasingly recognized as a hazardous factor, possibly leading to environmental issues and health risks. However, the driving factors were rarely investigated, which impeded comprehensive assessment of environmental quality. Herein ambient trace metals and bacterial community in PM 2.5 and their interactions during severe pollution were characterized in high time resolution. The results showed that the mass concentrations of total trace elements in PM 2.5 were 1.4–9.4 μg m −3 , with As and Cr exceeding the national standard, which might pose health risks to humans, especially children with frequently hand‐to‐mouth activity. The airborne bacterial community structure responded to the changing environmental and meteorological variables including PM 2.5 , related water‐soluble ions, SO 2 , O 3, temperature, relative humidity, and wind speed. Our results suggested that the trace metal was an overlooked factor in shaping the bacterial community compared to PM 2.5 , related water‐soluble inorganic ions, trace gases, and meteorological variables based on the aggregated boosted tree. Cd, Ga, and Nb were main trace metals factors affecting the bacterial community. The better knowledge of airborne bacterial diversity in high‐time resolution were essential to assess the environmental quality and help to explore the interactions of bioaerosols and atmospheric pollutants in PM 2.5 . The synergistic toxicity effects for the combination of trace metals and bioaerosol should be considered in future studies when evaluating their health effects.

The rapid formation of sulphate is the main driving force behind the explosive growth of PM2.5 in China. Our comprehensive study, combined with field observations, laboratory simulations and modelling, indicated that high concentration of hydroperoxide (H2O2) from heterogeneous reactions significantly promoted sulphate formation in winter north China. Unexpectedly, during the same campaign, a high proportion of sulphate has been observed in the frost. The chemical composition of the frost appeared to be independent of that of PM2.5. These findings can be important for the removal rate of SO2 in the atmosphere and for the occult deposition of sulphate. Also, we have investigated the contribution of oxidation channels to sulphate formation in the cloud at the summit of Mt. Tai (1545 m) in summer. Our results suggested that dissolved ozone is the dominant oxidant for the oxidation of S(IV), especially when the pH of the cloud water is less acidic (> 5.5). In recent years, with the increase of ozone concentration in China, the sulphate formation by ozone in the cloud will continue to be pronounced. References: Zhu, C., Li, J.R., Chen, H., Cheng, T.T., Wen, L., Herrmann, H., Xiao, H., Chen, J.M., 2020. Inorganic composition and occult deposition of frost collected under severe polluted area in winter in the North China Plain. Science of the Total Environment 722. Li, J.R., Zhu, C., Chen, H., Zhao, D.F., Xue, L.K., Wang, X.F., Li, H.Y., Liu, P.F., Liu, J.F., Zhang, C.L., Mu, Y.J., Zhang, W.J., Zhang, L.M., Herrmann, H., Li, K., Liu, M., Chen, J.M., 2020. The evolution of cloud and aerosol microphysics at the summit of Mt. Tai, China. Atmospheric Chemistry and Physics 20, 13735-13751.

The project MarParCloud (Marine biological production, organic aerosol Particles and marine Clouds: a process chain) aims to improve our understanding of the genesis, modification and impact of marine organic matter (OM) from its biological production, to its export to marine aerosol particles and, finally, to its ability to act as ice-nucleating particles (INPs) and cloud condensation nuclei (CCN). A field campaign at the Cape Verde Atmospheric Observatory (CVAO) in the tropics in September–October 2017 formed the core of this project that was jointly performed with the project MARSU (MARine atmospheric Science Unravelled). A suite of chemical, physical, biological and meteorological techniques was applied, and comprehensive measurements of bulk water, the sea surface microlayer (SML), cloud water and ambient aerosol particles collected at a ground-based and a mountain station took place. Key variables comprised the chemical characterization of the atmospherically relevant OM components in the ocean and the atmosphere as well as measurements of INPs and CCN. Moreover, bacterial cell counts, mercury species and trace gases were analyzed. To interpret the results, the measurements were accompanied by various auxiliary parameters such as air mass back-trajectory analysis, vertical atmospheric profile analysis, cloud observations and pigment measurements in seawater. Additional modeling studies supported the experimental analysis. During the campaign, the CVAO exhibited marine air masses with low and partly moderate dust influences. The marine boundary layer was well mixed as indicated by an almost uniform particle number size distribution within the boundary layer. Lipid biomarkers were present in the aerosol particles in typical concentrations of marine background conditions. Accumulation- and coarse-mode particles served as CCN and were efficiently transferred to the cloud water. The ascent of ocean-derived compounds, such as sea salt and sugar-like compounds, to the cloud level, as derived from chemical analysis and atmospheric transfer modeling results, denotes an influence of marine emissions on cloud formation. Organic nitrogen compounds (free amino acids) were enriched by several orders of magnitude in submicron aerosol particles and in cloud water compared to seawater. However, INP measurements also indicated a significant contribution of other non-marine sources to the local INP concentration, as (biologically active) INPs were mainly present in supermicron aerosol particles that are not suggested to undergo strong enrichment during ocean–atmosphere transfer. In addition, the number of CCN at the supersaturation of 0.30 % was about 2.5 times higher during dust periods compared to marine periods. Lipids, sugar-like compounds, UV-absorbing (UV: ultraviolet) humic-like substances and low-molecular-weight neutral components were important organic compounds in the seawater, and highly surface-active lipids were enriched within the SML. The selective enrichment of specific organic compounds in the SML needs to be studied in further detail and implemented in an OM source function for emission modeling to better understand transfer patterns, the mechanisms of marine OM transformation in the atmosphere and the role of additional sources. In summary, when looking at particulate mass, we see oceanic compounds transferred to the atmospheric aerosol and to the cloud level, while from a perspective of particle number concentrations, sea spray aerosol (i.e., primary marine aerosol) contributions to both CCN and INPs are rather limited.

The problem of environmental pollution was troubling people in many cities in China, especially PM2.5 pollution. Aiming to a better understanding the influence of long-range transport sources and health effect of PM2.5 in Ji'nan, a field observation was carried out in from 23 December 2016 to 25 April 2017. The results showed that primary organic carbon (POC), secondary organic carbon (SOC) and element carbon (EC) during observation in Ji'nan were 5.45, 2.59 and 2.76 mu g m(3), respectively. In heavy pollution days, OC and EC likely had similar primary emission and transmission sources. While the contribution of SOC increased in PM2.5 in clear days. Based on the potential source contribution function (PSCF) analysis, the emission sources leading to aggravation of PM2.5 pollution in Ji'nan were mainly distributed in the surrounding area of Ji'nan, especially in the eastern and southeastern Shandong. The risk assessment results show that the premature death caused by PM2.5 pollution could reach 666 people, and about 1.47% of total annual deaths in Ji'nan in 2016. The medical consumption related to PM2.5 pollution was about 202 millions USD, accounting for 2.05 parts per thousand of the GDP in Ji'nan in 2016. Lung cancer mortality caused the highest economic cost of 47.97 millions USD, followed by respiratory mortality, chronic bronchitis, cardiovascular mortality, and acute bronchitis.

In this study, a multi-year period observation campaign of clouds at the summit of Mt. Tai was conducted. The chemical compositions of cloud water samples were measured and the S(IV) oxidation rates in cloud were analyzed. This study highlights the long-term characteristics and variation of chemical species in cloud at Mt. Tai. The high ambient O3 and the increase of aqueous phase pH made O3 pathway dominant the S(IV) oxidation in cloud at Mt. Tai.

Lockdown measures are essential to containing the spread of coronavirus disease 2019 (COVID-19), but they will slow down economic growth by reducing industrial and commercial activities. However, the benefits of activity control from containing the pandemic have not been examined and assessed. Here we use daily carbon dioxide (CO2) emission reduction in China estimated from statistical data for energy consumption and satellite data for nitrogen dioxide (NO2) measured by the Ozone Monitoring Instrument (OMI) as an indicator for reduced activities consecutive to a lockdown. We perform a correlation analysis to show that a 1% day-1 decrease in the rate of COVID-19 cases is associated with a reduction in daily CO2 emissions of 0.22% ± 0.02% using statistical data for energy consumption relative to emissions without COVID-19, or 0.20% ± 0.02% using satellite data for atmospheric column NO2. We estimate that swift action in China is effective in limiting the number of COVID-19 cases <100,000 with a reduction in CO2 emissions of up to 23% by the end of February 2020, whereas a 1-week delay would have required greater containment and a doubling of the emission reduction to meet the same goal. By analyzing the costs of health care and fatalities, we find that the benefits on public health due to reduced activities in China are 10-fold larger than the loss of gross domestic product. Our findings suggest an unprecedentedly high cost of maintaining activities and CO2 emissions during the COVID-19 pandemic and stress substantial benefits of containment in public health by taking early actions to reduce activities during the outbreak of COVID-19.

Frost as a kind of deposition plays an important role in the removal of atmospheric compounds. However, studies concerning frost in the atmospheric environment were rare although chemical composition in frost samples might be affected by the surrounding atmospheric environment. In this study, a total of 35 frost samples were collected by means of a homemade glass-plate frost condenser under severe polluted condition in the North China Plain (NCP) from Dec. 4, 2018 to Mar. 2, 2019. The pH values and water-soluble ions (WSI) were conducted. The extremely high concentrations of WSI were found, which reflected the severe pollution significantly affecting the level of chemical composition in frost. The major ions were Ca2+, SO42- and HCO3- with averaged concentrations of 1242, 1143, 1076 μeq L-1, respectively. These ions were at least one order of magnitude higher than the previous frost studies. HCO3- was one of the most abundant components in frost. Its high proportion contributed to the ionic balance and led to the alkaline characteristic of frost. SO42- had the almost doubled ratio in frost compared with the concurrent PM2.5 samples. Different from the huge diversity of chemical components in PM2.5, the frost had similar ratio of WSI under great variety of PM2.5 concentrations. It proved that PM2.5 had less effect on the ratio of WSI in frost. Nutrient ions of NH4+, NO3- and K+ accounted for 13.9%, 5.4% and 1.6% of the total averaged concentrations, respectively. On average, per square meter soil would receive 563 μg nitrogen and 123 μg potassium nutrient during a frost night. High occult deposition flux of ions indicated the strong scavenging effect from the frost event. In addition, the occult deposition flux of SO42- was comparable to the dry deposition flux, further emphasizing frost process as a non-negligible atmospheric removal pathway of SO42-.

The influence of aerosols, both natural and anthropogenic, remains a major area of uncertainty when predicting the properties and the behaviours of clouds and their influence on climate. In an attempt to better understand the microphysical properties of cloud droplets, the simultaneous variations in aerosol microphysics and their potential interactions during cloud life cycles in the North China Plain, an intensive observation took place from 17 June to 30 July 2018 at the summit of Mt. Tai. Cloud microphysical parameters were monitored simultaneously with number concentrations of cloud condensation nuclei (NCCN) at different supersaturations, PM2.5 mass concentrations, particle size distributions and meteorological parameters. Number concentrations of cloud droplets (NC), liquid water content (LWC) and effective radius of cloud droplets (reff) show large variations among 40 cloud events observed during the campaign. The low values of reff and LWC observed at Mt. Tai are comparable with urban fog. Clouds on clean days are more susceptible to the change in concentrations of particle number (NP), while clouds formed on polluted days might be more sensitive to meteorological parameters, such as updraft velocity and cloud base height. Through studying the size distributions of aerosol particles and cloud droplets, we find that particles larger than 150 nm play important roles in forming cloud droplets with the size of 5–10 µm. In general, LWC consistently varies with reff. As NC increases, reff changes from a trimodal distribution to a unimodal distribution and shifts to smaller size mode. By assuming a constant cloud thickness and ignoring any lifetime effects, increase in NC and decrease in reff would increase cloud albedo, which may induce a cooling effect on the local climate system. Our results contribute valuable information to enhance the understanding of cloud and aerosol properties, along with their potential interactions on the North China plain.

Predicting tropospheric cloud formation and subsequent nutrient deposition relies on understanding the sources and processes affecting aerosol constituents of the atmosphere that are preserved in cloud water. However, this challenge is difficult to address quantitatively based on the sole use of bulk chemical properties. Nitrogenous aerosols, mainly ammonium (NH4+) and nitrate (NO3-), play a particularly important role in tropospheric cloud formation. While dry and wet (mainly rainfall) deposition of NH4+ and NO3- are regularly assessed, cloud water deposition is often underappreciated. Here we collected cloud water samples at the summit of Mt. Tai (1545 m above sea level) in eastern China during a long-lasting biomass burning (BB) event and simultaneously measured for the first time the isotopic compositions (mean ±1σ) of cloud water nitrogen species (δ15N-NH4+ = −6.53 ‰ ± 4.96 ‰, δ15N-NO3- = −2.35 ‰ ± 2.00 ‰, δ18O-NO3- = 57.80 ‰ ± 4.23 ‰), allowing insights into their sources and potential transformation mechanism within the clouds. Large contributions of BB to the cloud water NH4+ (32.9 % ± 4.6 %) and NO3- (28.2 % ± 2.7 %) inventories were confirmed through a Bayesian isotopic mixing model, coupled with our newly developed computational quantum chemistry module. Despite an overall reduction in total anthropogenic NOx emission due to effective emission control actions and stricter emission standards for vehicles, the observed cloud δ15N-NO3- values suggest that NOx emissions from transportation may have exceeded emissions from coal combustion. δ18O-NO3- values imply that the reaction of OH with NO2 is the dominant pathway of NO3- formation (57 % ± 11 %), yet the contribution of heterogeneous hydrolysis of dinitrogen pentoxide was almost as important (43 % ± 11 %). Although the limited sample set used here results in a relatively large uncertainty with regards to the origin of cloud-associated nitrogen deposition, the high concentrations of inorganic nitrogen imply that clouds represent an important source of nitrogen, especially for nitrogen-limited ecosystems in remote areas. Further simultaneous and long-term sampling of aerosol, rainfall, and cloud water is vital for understanding the anthropogenic influence on nitrogen deposition in the study region.

Biomass burning (BB) in North China Plain has been urgent issue in recent years due to the severe environmental impaction. Bacteria and fungi are ubiquitous in particulate matter. Their taxonomic composition, concentration, ecophysiological functions have potentially important implications in atmospheric biochemical cycle and human health. However, current knowledge about airborne microbes during biomass burning period is scant. Here we investigated bacterial and fungal community composition, abundance and potential function in Yucheng, the center of the North China Plain during summer harvest season in 2014. Monthly field observation suggested serious pollution with high concentration of PM2.5 and water-soluble ions during biomass burning period. Elevated total bacterial and fungal concentration determined by real-time quantitative PCR was observed for samples during burning events. The predominant bacterial taxa were gram-negative, e.g. Acinetobacter, Cyanobacterium, Janthinobacterium, Massilia, Pseudomonas, accounted for 70.9% of total bacteria. The filamentous fungi Alternaria, Aspergillus, Cladosporium and Penicillium were predominant fungal genera. Metastats analysis showed significant disparity in terms of carbohydrate, amino acids metabolism, human and plant disease predicted by PICRUSt analysis between BB and non-BB events. Microbial community structure were mainly influenced by organic carbon and water-soluble ions (magnesium and potassium) suggested by redundancy analysis (RDA) and co-occurrence analysis. Our data yielded insights into microbial community dynamics following biomass burning disturbance. This study may provide potentially important reference for environmental, agricultural and health management.

Bacteria are ubiquitous in the near-surface atmosphere where they constitute an important component of aerosols with the potential to affect climate change, ecosystems, atmospheric process and human health. Limitation in tracking bacterial diversity accurately has thus far prevented the knowledge of airborne bacteria and their pathogenic properties. We performed a comprehensive assessment of bacterial abundance and diverse community in PM2.5 collected at Mt. Tai, via high-throughput sequencing and real-time PCR. The samples exhibited a high microbial biodiversity and complex chemical composition. The dominating populations were gram-negative bacteria including Burkholderia, Delftia, Bradyrhizobium, and Methylobacterium. The PM mass concentration, chemical composition, bacterial concentration and community structure varied under the influence of different air-mass trajectories. The highest mass concentration of PM2.5 (61 mu g m(-3)) and major chemical components were recorded during periods when marine southeasterly air masses were dominant. The local terrestrial air masses from Shandong peninsula and its adjacent areas harbored highest bacterial concentration loading (602 cells m(-3)) and more potential pathogens at the site. In contrast, samples influenced by the longdistance air flow from Siberia and Outer Mongolia were found to have a highest richness and diversity as an average, which was also marked by the increase of dust-associated bacteria (Brevibacillus and Staphylococcus). The primary research may serve as an important reference for the environmental microbiologist, health workers, and city planners.

The North China Plain is the agricultural heartland in China. High PM2.5 levels and elevated chemical pollutants have been observed during crop harvest seasons due to open biomass burning. Biomass burning in the wheat-harvest season may significantly deteriorate the regional air quality. The harmful ingredients in smoke particles also have severe implications for toxicity and health effects. Previous studies have illustrated the potential role of bioaerosols as ice-nuclei and cloud condensation nuclei and highlighted their influence on biochemical cycles and human health effects. In a monthly field observation campaign of biomass burning conducted at the summit of Mount Tai in July 2015, we reported the composition, potential role, size distribution of microorganisms in particulate matters PM1.0, PM2.5, and estimated their contribution to particles. The wide-range particle spectrometer suggested that the predominant particles were distributed in submicron particles (PM1.0), which resulted in a similar community structure for bacteria and fungi in PM1.0 and PM2.5. Among bacteria, the predominant Pseudomonas accounted for 18.06% and 21.29% in PM1.0 and PM2.5, respectively. Alternaria covered up to 69.01% and 72.76% of the fungal community in PM1.0 and PM2.5, respectively. A disparity between bacterial communities was identified by the abundance of rare species, such as Bacilli being higher in PM1.0 (2.4%) than in PM2.5 (1.8%), and Defluviicoccus being higher in PM2.5 (2.5%) than in PM1.0 (0.5%), which may be related to cell size and cell growth patterns. Quantitative PCR revealed that microbial cell numbers in PM2.5 were higher than in PM1.0, and that the bacterial cell number was about an order of magnitude greater than the fungal cell number. However, the mass concentration and contribution of fungi to particulate matter was much higher than that of bacteria, suggesting the underestimated role of fungi in atmospheric aerosols. Airborne microorganisms in alpine areas remained less characterized. The findings presented here illustrated the potentially important impacts on air quality and bioaerosol pollution by biomass burning, which provides an essential reference for understanding the transmission and health effects of bioaerosols.

Bacteria are widely distributed in atmospheric aerosols and are indispensable components of clouds, playing an important role in the atmospheric hydrological cycle. However, limited information is available about the bacterial community structure and function, especially for the increasing air pollution in the North China Plain. Here, we present a comprehensive characterization of bacterial community composition, function, variation, and environmental influence for cloud water collected at Mt Tai from 24 July to 23 August 2014. Using Miseq 16S rRNA gene sequencing, the highly diverse bacterial community in cloud water and the predominant phyla of Proteobacteria, Bacteroidetes, Cyanobacteria, and Firmicutes were investigated. Bacteria that survive at low temperature, radiation, and poor nutrient conditions were found in cloud water, suggesting adaption to an extreme environment. The bacterial gene functions predicted from the 16S rRNA gene using the Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) suggested that the pathways related to metabolism and disease infections were significantly correlated with the predominant genera. The abundant genera Acinetobacter, Stenotrophomonas, Pseudomonas, and Empedobacter originated from a wide range of habitats including cloud condensation nuclei and ice nuclei active species, opportunistic pathogens, and functional species, demonstrating the importance of ecology and health in cloud water. Cluster analysis including hierarchical cluster (Hcluster) and principal coordinate analysis (PCoA) indicated a significant disparity between polluted and non-polluted samples. Linear discriminant analysis effect size (LEfSe) demonstrated that potential pathogens were enriched in the polluted cloud samples, whereas the diverse ecological function groups were significant in the non-polluted samples. Discrepant community structure determined by redundancy analysis (RDA) indicated that the major ions in cloud water and PM2.5 in the atmosphere have a negative impact on bacteria, playing a vital role in shaping microbial community structure. The major ions might provide nutrition to bacteria and directly influence the bacterial community, whereas PM2.5 in air has an indirect impact on bacterial community structure. During wet deposition, soluble particulate matter was dissolved in water droplets resulting in elevated concentration in cloud water. PM2.5 was possibly associated with different origins and pathways of air mass as determined using source tracking by the backward trajectory, mainly related to long-range transport. This work enhanced our understanding of the characteristics of bacterial ecology in the atmospheric aqueous phase, highlighting the potential influence of environmental variables on the bacterial community in cloud processes. It may provide fundamental information of the bacterial community response in cloud water under increasing pollution. However, due to the limited sample size (13 samples) collected at the summit of Mt Tai, these issues need in-depth discussion. Further studies based on an annual series of field observation experiments and laboratory simulations will continue to track these issues.

Fungi are ubiquitous throughout the near-surface atmosphere, where they represent an important component of primary biological aerosol particles. This study combined internal transcribed spacer region sequencing and quantitative real-time polymerase chain reaction (qPCR) to investigate the ambient fungi in fine (PM2. 5, 50 % cutoff aerodynamic diameter Da50 = 2.5 µm, geometric standard deviation of collection efficiency σg = 1.2) and submicron (PM1, Da50 = 1 µm, σg = 1.2) particles at the summit of Mt. Tai located in the North China Plain, China. Fungal abundance values were 9.4 × 104 and 1.3 × 105 copies m−3 in PM2. 5 and PM1, respectively. Most of the fungal sequences were from Ascomycota and Basidiomycota, which are known to actively discharge spores into the atmosphere. The fungal community showed a significant seasonal shift across different size fractions according to Metastats analysis and the Kruskal–Wallis rank sum test. The abundance of Glomerella and Zasmidium increased in larger particles in autumn, whereas Penicillium, Bullera, and Phaeosphaeria increased in smaller particles in winter. Environmental factors, namely Ca2+, humidity, and temperature, were found to be crucial for the seasonal variation in the fungal community. This study might serve as an important reference for fungal contribution to primary biological aerosol particles.