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Particulate matter with an aerodynamic diameter of 2.5 μm or less (PM 2.5 ) harbors a diverse microbial community. To assess the ecological dynamics and potential health risks associated with airborne microorganisms, it is crucial to understand the factors influencing microbial communities within PM 2.5 . This study investigated the influence of abiotic parameters, including air pollutants, PM 2.5 chemical composition (water-soluble ions and organics), and meteorological variables, on microbial communities in PM 2.5 samples collected in Seoul during the spring season. Results revealed a significant correlation between air pollutants and water-soluble ions of PM 2.5 with microbial α-diversity indices. Additionally, air pollutants exerted a dominant effect on the microbial community structure, with stronger correlations observed for fungi than bacteria, whereas meteorological variables including temperature, pressure, wind speed, and humidity exerted a limited influence on fungal α-diversity. Furthermore, the results revealed specific water-soluble ions, such as SO 4 2- , NO 3 - , and NH 4 + , as important factors influencing fungal α-diversity, whereas K + negatively correlated with both microbial α-diversity. Moreover, PM 2.5 microbial diversity was affected by organic compounds within PM 2.5 , with fatty acids exhibited a positive correlation with fungal diversity, while dicarboxylic acids exhibited a negative correlation with it. Furthermore, network analysis revealed direct links between air pollutants and dominant bacterial and fungal genera. The air pollutants exhibited a strong correlation with bacterial genera, such as Arthrospira and Clostridium, and fungal genera, including Aureobasidium and Cladosporium. These results will contribute to our understanding of the ecological dynamics of airborne microorganisms and provide insights into the potential risks associated with PM 2.5 exposure., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Kyung-Suk Cho reports financial support was provided by National research Foundation of Korea (NRF). If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Although the particle phase state is an important property, there is scant information on it, especially, for real-world aerosols. To explore the phase state of fine mode aerosols (PM 2.5 ) in two megacities, Seoul and Beijing, we collected PM 2.5 filter samples daily from Dec 2020 to Jan 2021. Using optical microscopy combined with the poke-and-flow technique, the phase states of the bulk of PM 2.5 as a function of relative humidity (RH) were determined and compared to the ambient RH ranges in the two cities. PM 2.5 was found to be liquid to semisolid in Seoul but mostly semisolid to solid in Beijing. The liquid state was dominant on polluted days, while a semisolid state was dominant on clean days in Seoul. These findings can be explained by the aerosol liquid water content related to the chemical compositions of the aerosols at ambient RH; the water content of PM 2.5 was much higher in Seoul than in Beijing. Furthermore, the overall phase states of PM 2.5 observed in Seoul and Beijing were interrelated with the particle size distribution. The results of this study aid in a better understanding of the fundamental physical properties of aerosols and in examining how these are linked to PM 2.5 in polluted urban atmospheres.

Atmospheric volatile organic compounds (VOCs) in Seoul, the capital of South Korea, have attracted increased attention owing to their emission, secondary formation, and human health risk. In this study, we collected 24 hourly samples once a month at an urban site in Seoul for a year (a total of 288 samples) using a sequential tube sampler. Analysis results revealed that toluene (9.08 ± 8.99 μg/m 3 ) exhibited the highest annual mean concentration, followed by ethyl acetate (5.55 ± 9.09 μg/m 3 ), m,p-xylenes (2.79 ± 4.57 μg/m 3 ), benzene (2.37 ± 1.55 μg/m 3 ), ethylbenzene (1.81 ± 2.27 μg/m 3 ), and o-xylene (0.91 ± 1.47 μg/m 3 ), indicating that these compounds accounted for 77.8-85.6% of the seasonal mean concentrations of the total (Σ 59 ) VOCs. The concentrations of the Σ 59 VOCs were statistically higher in spring and winter than in summer and fall because of meteorological conditions, and the concentrations of individual VOCs were higher during the daytime than nighttime owing to higher human activities during the daytime. The conditional bivariate probability function and concentration weighted trajectory analysis results suggested that domestic effects (e.g., vehicular exhaust and solvents) exhibited a dominant effect on the presence of VOCs in Seoul, as well as long-range atmospheric transport of VOCs. Further, the most important secondary organic aerosol formation potential (SOAFP) compounds included benzene, toluene, ethylbenzene, and m,p,o-xylenes, and the total SOAFP of nine VOCs accounted for 5-29% of the seasonal mean PM 2.5 concentrations. The cancer and non-cancer risks of the selected VOCs were below the tolerable (1 × 10 -4 ) and acceptable (Hazard quotient: HQ < 1) levels, respectively. Overall, this study highlighted the feasibility of the sequential sampling of VOCs and hybrid receptor modeling to further understand the source-receptor relationship of VOCs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Contribution of liquid water content (LWC) to the levels of the carcinogenic particulate nitro(so) compounds and the chemistry affecting LWC were investigated based on the observation of seven nitrosamines and two nitramines in rural (Seosan) and urban (Seoul) area in South Korea during October 2019 and a model simulation. The concentrations of both the total nitrosamines and nitramines were higher in Seosan (12.48 ± 16.12 ng/m 3 and 0.65 ± 0.71 ng/m 3 , respectively) than Seoul (7.41 ± 13.59 ng/m 3 and 0.24 ± 0.15 ng/m 3 , respectively). The estimated LWC using a thermodynamic model in Seosan (12.92 ± 9.77 μg/m 3 ) was higher than that in Seoul (6.20 ± 5.35 μg/m 3 ) mainly due to higher relative humidity (75 ± 9% (Seosan); 62 ± 10% (Seoul)) and higher concentrations of free ammonia (0.13 ± 0.09 μmol/m 3 (Seosan); 0.08 ± 0.01 μmol/m 3 (Seoul)) and total nitric acid (0.09 ± 0.07 μmol/m 3 (Seosan); 0.04 ± 0.02 μmol/m 3 (Seoul)) in Seosan while neither fog nor rain occurred during the sampling period. The relatively high concentrations of the particulate nitrosamines (>30 ng/m 3 ) only observed probably due to the higher LWC (>10 μg/m 3 ) in Seosan. It implies that aqueous phase reactions involving NO 2 and/or uptake from the gas phase enhanced by LWC could be promoted in Seosan. Strong correlation between the concentrations of nitrosodi-methylamine (NDMA), an example of nitrosamines, simulated by a kinetic box model including the aqueous phase reactions and the measured concentration of NDMA in Seosan (R = 0.77; 0.37 (Seoul)) indicates that the aqueous phase reactions dominantly enhanced the NDMA concentrations in Seosan. On the other hand, it is estimated that the formation of nitrosamines by aqueous phase reaction was not significant due to the relatively lower LWC in Seoul compared to that in Seosan. Furthermore, it is presumed that nitramines are mostly emitted from the primary emission sources. This study implies that the concentration of the particulate nitrosamines can be promoted by aqueous phase reaction enhanced by LWC., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Seven nitrosamines and three nitramines in particulate matter with an aerodynamic diameter of less than or equal to 2.5 μm (PM 2.5 ) collected in 2018 in Seoul, South Korea, were quantified. Annual mean concentrations of the sum of nitrosamines and nitramines were 9.81 ± 18.51 and 1.12 ± 0.70 ng/m 3 , respectively, and nitrosodi-methylamine (NDMA) and dimethyl-nitramine (DMN) comprised the largest portion of nitrosamines and nitramines, respectively. Statistical analyses such as non-parametric correlation analysis, positive matrix factorization, analysis of covariance, and orthogonal partial least squared discrimination analysis were carried out to identify contribution of the atmospheric reactions in producing NDMA and DMN. In addition, kinetic calculation using reaction information obtained from the previous chamber studies was performed to estimate concentrations of NDMA and DMN that might be produced from the atmospheric reactions. It was concluded that (1) the atmospheric reactions contributed to the concentrations of NDMA more than they did for those of DMN, (2) the contribution of atmospheric reactions to the concentrations of NDMA and DMN was significant due to high NO 2 concentrations in winter, and (3) primary emissions predominantly affected the ambient concentrations of NDMA and DMN in spring, summer, and autumn.

Due to their important roles in salt-producing acid-base reactions, new particle formation (NPF), and as precursors in secondary organic aerosol (SOA) producing reactions, the atmospheric concentrations of particulate volatile amines (dimethylamine (DMA), ethylamine, diethylamine (DEA), propylamine, and butylamine) at Seoul were analyzed and evaluated. To quantify the presence of volatile amines in particulate matter with aerodynamic diameters less than or equal to a nominal 2.5 μm (PM 2.5 ), an efficient and rapid analytical method based on in-matrix ethyl chloroformate (ECF) derivatization followed by headspace solid-phase microextraction (HS-SPME) was developed and validated using gas chromatography coupled with tandem mass spectrometry (GC-MS/MS) in the multiple reaction monitoring (MRM) mode. The annual mean concentration of the total 5 target amines was 5.56±2.76 ng/m 3 and the seasonal difference was small. The concentrations of particulate amines measured in this study were lower than those observed in Zongludak, Turkey, Nanjing, China, and Jeju, Korea but slightly higher than that reported in Kobe, Japan. The concentrations of the nitrosamines (nitrosodimethylamine (NDMA) and nitrosodiethylamine (NDEA)), and of the nitramines (dimethylnitramine (DMN) and diethylnitramine (DEN)) measured along with those of the target amines were used in a simple linear regression analysis. It indicates the contribution of DMA to the formation of NDMA in all seasons (except the fall) and DEA to the formation of NDEA in the summer, while DMA and DEA did not significantly contribute to the formation of nitramines., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Background: Epidemiologic studies have suggested that elevated concentrations of particulate matter (PM) are strongly associated with an increased risk of developing cardiovascular diseases, including arrhythmia. However, the cellular and molecular mechanisms by which PM exposure causes arrhythmia and the component that is mainly responsible for this adverse effect remains to be established. In this study, the arrhythmogenicity of mobilized organic matter from two different types of PM collected during summer (SPM) and winter (WPM) seasons in the Seoul metropolitan area was evaluated. In addition, differential effects between polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (oxy-PAHs) on the induction of electrophysiological instability were examined., Results: We extracted the bioavailable organic contents of ambient PM, measuring 10 μm or less in diameter, collected from the Seoul metropolitan area using a high-volume air sampler. Significant alterations in all factors tested for association with electrophysiological instability, such as intracellular Ca 2+ levels, reactive oxygen species (ROS) generation, and mRNA levels of the Ca 2+ -regulating proteins, sarcoplasmic reticulum Ca 2+ ATPase (SERCA2a), Ca 2+ /calmodulin-dependent protein kinase II (CaMK II), and ryanodine receptor 2 (RyR2) were observed in cardiomyocytes treated with PM. Moreover, the alterations were higher in WPM-treated cardiomyocytes than in SPM-treated cardiomyocytes. Three-fold more oxy-PAH concentrations were observed in WPM than SPM. As expected, electrophysiological instability was induced higher in oxy-PAHs (9,10-anthraquinone, AQ or 7,12-benz(a) anthraquinone, BAQ)-treated cardiomyocytes than in PAHs (anthracene, ANT or benz(a) anthracene, BaA)-treated cardiomyocytes; oxy-PAHs infusion of cells mediated by aryl hydrocarbon receptor (AhR) was faster than PAHs infusion. In addition, ROS formation and expression of calcium-related genes were markedly more altered in cells treated with oxy-PAHs compared to those treated with PAHs., Conclusions: The concentrations of oxy-PAHs in PM were found to be higher in winter than in summer, which might lead to greater electrophysiological instability through the ROS generation and disruption of calcium regulation.

Polycyclic Aromatic Hydrocarbons (PAHs) and n-alkanes in particulate matter with an aerodynamic diameter of 2.5 micrometers or less (PM2.5) were quantified at Seoul, Korea in 2018. The seasonal differences in the total concentration of PAHs and n-Alkanes were clear, where winter showed a higher concentration than that of summer. Compared to the PAHs measurements in 2002 at Seoul, the sum of PAHs concentrations in 2018 were reduced from 26.6 to 5.6 ng m -3 . Major sources of the observed PAHs and n-alkanes were deduced from various indicators such as diagnostic ratios for PAHs and Cmax, CPI, and WNA (%) indices for n-alkanes. It was found that in winter coal and biomass combustions, and vehicular exhaust were major sources, while, in summer vehicular exhaust was major source. In addition, in winter, major emission sources were located outside of Seoul. The health effect from the recent level of PAHs was estimated and compared to the previous studies observed in Seoul, and it was found that, recently, the toxicity of PAHs in PM 2.5 was significantly decreased, except for in the winter., Competing Interests: The authors declare no conflicts of interest.