Journal of Aerosol Science最新文献

The air in the metro or subway system, which is a major form of public transportation in many metropolises, contributes to the transmission of pathogenic microorganisms. In this study, 18 aerosol samples were collected from two typical Shanghai subway stations (A and B) in the summer, transition, and winter seasons. Bacterial communities and their associated antibiotic resistance genes (ARGs) were analyzed using shotgun metagenomic sequencing. Metagenomic analysis approaches and random forest classification were used to compare and screen the distribution of key target species and ARGs. Bacteria were the predominant microbial kingdom with a relative abundance of 88.28%. In total, 5303 bacterial species were identified in subway stations A and B. The top three abundant bacterial species were unclassified_Pseudomonas, Ewingella_americana, and Halalkalicoccus_subterraneus. Microbial diversity analysis revealed that the microbial communities significantly varied between the three seasons (P < 0.05). Additionally, factors, such as temperature, relative humidity, and fine particulate matter (PM_2.5) significantly influenced bacterial community structure (P < 0.05). The random forest algorithm was used to screen indicators in bacterial communities. Some of these bacterial communities, which were primarily derived from environmental sources, may pose health risks. In total, 312 ARGs subtypes related to 20 ARGs classes were identified in subway stations A and B. Random forest classification results revealed 20 indicative types of ARGs, including those involved in metabolizing aminoglycoside, beta-lactam, multidrug, and rifamycin-type antibiotics. This study provides novel insights into microbial communities and ARGs in typical subway micro-environments and their dissemination in subway environments.

This study develops a tri-variate moment projection method (TVMPM) for solving particle dynamics problems governed by the population balance equations involving any three internal coordinates of particles, such as volume, surface area, component mass, etc. By leveraging the concept of conditional moments, the multi-dimensional moments are expressed as the product of marginal moments and several conditional moments, facilitating the solution of high-dimensional moments. To obtain abscissas and conditional weights in different dimensions for reconstructing moments, a three-dimensional (3-D) adaptive Blumstein-Wheeler algorithm is proposed and implemented, which can also improve the stability in the third dimension, where ill-conditioning issues are more likely to arise. More importantly, by fixing the smallest particle abscissas, TVMPM can directly track the weight of the smallest particles, thereby closing the shrinkage and fragmentation terms. An analysis of the sources of errors arising from this approach is also presented. To mitigate potential interference from external factors, constant kernels for inception, growth, coagulation, shrinkage and fragmentation are employed to validate the effectiveness of TVMPM. The resulting moments from TVMPM are computed for both individual and combined processes, and subsequently compared with the moments derived from the direct simulation algorithm (DSA). The results demonstrate that TVMPM maintains a high level of accuracy across various numbers of quadrature nodes for particle dynamics with 3-D internal coordinates, while significantly reducing computational efforts compared to DSA. This study reveals that the developed algorithms and framework are promising for further extending MPM to higher dimensions. Moreover, owing to its accuracy and efficiency, TVMPM shows great potential for implementation in computational fluid dynamics (CFD) for particle dynamics in realistic systems.

Terrestrial vegetation emits vast quantities of monoterpenes to the atmosphere. These compounds, once oxidized, can contribute to the formation and growth of secondary organic aerosol (SOA) particles. However, studies report widely different SOA yields from atmospheric oxidation of different monoterpenes, despite their structural similarities. The NO₃-radical-initiated oxidation of $\alpha$-pinene for instance, leads to minimal SOA yields, whereas with $\Delta$-carene a high SOA yield is observed. A previous study indicated that their oxidation mechanisms diverge after formation of a nitrooxy–alkoxyl radical intermediate, whose C–C bond scission reactions can either lead to early termination of the oxidative chain, thus limiting the yield of condensable vapors, or further propagate it, leading to low-volatility products. In this study, we employ computational methods to investigate these reactions in the NO₃-radical oxidation of five other monoterpenes: limonene, sabinene, $\beta$-pinene, $\alpha$-thujene and camphene. Additionally, we explore the possibility of rearrangement via ring-opening of the nitrooxy-alkyl radical adducts produced immediately after NO₃ radical attack. Our calculations predict that alkyl radical rearrangement is dominant over O₂-addition for sabinene, minor but competitive for $\alpha$-thujene and $\beta$-pinene, and negligible for camphene. These rearrangements can induce further propagation of the oxidative chain, and thus higher SOA yields. Concerning alkoxyl radical C–C bond scissions, our results indicate that endocyclic nitrate species (derived from limonene and $\alpha$-thujene) react preferentially via the channel leading to oxidative chain termination, whereas exocyclic nitrate species (sabinene, $\beta$-pinene, and camphene) react preferentially via channels leading to further propagation.

Methicillin-resistant Staphylococcus aureus (MRSA) is a human and animal-associated opportunistic pathogen. The bioaerosols from livestock units have been identified to spread MRSA from indoor to outdoor ambient environments and represent a significant risk to public health. Different bioaerosol sampling methods (filtration, impingement, impaction, cyclone, condensation, electrostatic precipitation etc.) have been discussed based on their merits. In this report, we conducted a literature survey approach to understand the lineages of MRSA clones in various livestock air via molecular typing classification, as well as the function of bioaerosol transmission which could impose infection risk in other clean settings. Our analysis found that globally the spa types t011, t002, t034, t127, and t899 are widespread genotype lineages in different livestock's farm air. It is noteworthy that the MRSA clones ST398 and ST9 are most commonly found in livestock settings and carry various types of staphylococcal cassette chromosome mec (SCCmec) elements. In addition, the aerosolization process in livestock units helps to increase the load of MRSA colony in ambient air, which could transmit to the downwind direction of the livestock farms. Ultimately, in the molecular classification of prevalent MRSA clones in livestock settings, the air dynamics are essential in assessing the potential risk of bioaerosol transmission towards outdoor ambient environments. A basic hygiene-driven One-Health approach is critical in mitigating the risks associated with MRSA transmission from livestock settings and promoting public health. Furthermore, to avoid outbreaks, continuous surveillance and effective infection control measures are necessary to prevent the spread of MRSA and other antibiotic-resistant bacteria in both animal and human populations.

This study investigated the dispersion and evaporation characteristics of droplets and droplet nuclei emitted during human respiratory activities. A specially designed wind tunnel was filled with purified air, wherein selected subjects performed various respiratory activities with their heads positioned inside. An optical particle sizer was used to collect particles with sizes of 0.3–10 μm at 63 points in front of the mouth. The dilution factors were analyzed to investigate the impact of combining the exhaled airflow with ambient air on droplet evaporation. At a distance of 0.01 m from the mouth opening, the volume concentration of the particles was the highest during breathing, followed by coughing and speaking. The volumetric concentration of particles decreased with an increase in the distance from the inlet for all activities. The spatial volume concentration distribution of particles showed that coughing tended to disperse the particles in the forward direction, whereas speaking tended to disperse them laterally. Utilizing these findings in CFD analysis can provide in-depth insights into dispersion and evaporation dynamics. This can contribute significantly to the development of preventive measures through the implementation of proactive HVAC systems to effectively remove infectious particles and control the spread of infectious diseases. Future studies should explore a wider range of particle sizes and advanced sampling techniques for a clear understanding of respiratory particle dynamics and infection control strategies.

With the increasing prevalence of metro systems in urban transportation, there is a growing concern about the microbial pollution risks associated with these systems. To address this issue, this study employs metagenomic sequencing technology to investigate the distribution of Mycobacterium in aerosol samples collected from metro environments. Through the analysis of various environmental factors, insights into the factors influencing Mycobacterium contamination in metro systems are provided, aiming to offer evidence to support prevention and control measures against such pollution. In this study, a total of 90 species of Mycobacterium were detected in aerosol samples with a positivity rate of 30.77% including Mycobacterium tuberculosis that accounts for over 90% of the total abundance, as well as common opportunistic pathogens such as Mycobacterium gordonae, Mycobacterium avium, Mycobacterium intracellular, and Mycobacterium lentiflavum. Through correlation analysis, it was found that the distribution of Mycobacterium is related to season, temperature, CO₂, PM₁, PM_2.5, and PM₁₀ concentrations. In conclusion, it is recommended to adopt measures to control temperature and airborne concentrations of CO₂ and particulate matter (PM₁, PM_2.5, and PM₁₀) in order to minimize the risk of Mycobacterium contamination in metro systems. By implementing these recommendations, the prevention and control of Mycobacterium pollution can be effectively enhanced in the context of urban metros.

The formation of aerosol particles in the atmosphere is driven by the gas to particle conversion of extremely low volatile organic compounds (ELVOC), organic compounds with a particularly low saturation vapor pressure ($p_{\mathrm{Sat}}$). Identifying ELVOCs and their chemical structures is both experimentally and theoretically challenging: Measuring the very low $p_{\mathrm{Sat}}$ of ELVOCs is extremely difficult, and computing $p_{\mathrm{Sat}}$ for these often large molecules is computationally costly. Moreover, ELVOCs are underrepresented in available datasets of atmospheric organic species, which reduces the value of statistical models built on such data. We propose an active learning (AL) approach to efficiently identify ELVOCs in a data pool of atmospheric organic species with initially unknown $p_{\mathrm{Sat}}$. We assess the performance of our AL approach by comparing it to traditional machine learning regression methods, as well as ELVOC classification based on molecular properties. AL proves to be a highly efficient method for ELVOC identification with limitations on the type of ELVOC it can identify. We also show that traditional machine learning or molecular property-based methods can be adequate tools depending on the available data and desired degree of efficiency.

Organic aerosols can form semisolid state, glassy state and high viscous state in the atmosphere, which makes aerosols show nonequilibrium kinetic characteristics following the loss of water due to the extended timescales for diffusive mixing. In this study, aerosol optical tweezers (AOTs) and confocal Raman spectroscopy are utilized to investigate the mass transfer of water and the hygroscopicity of internally mixed glucose/ammonium sulfate aerosol droplets with different organic/inorganic molar ratios (OIRs). The characteristic time ratio between the droplet radius and the RH is calculated to describe the mass transfer of water in the droplets. The results shown that the characteristic time ratio of the mixed glucose/ammonium sulfate aerosol droplets is apparently lower than that of pure glucose droplets. And the characteristic time ratio of the mixed droplets decreases with the increase of ammonium sulfate. The hygroscopicity of mixed glucose/ammonium sulfate aerosol droplets is greatly affected by high viscosity organic matter, and the glassy state of glucose suppresses the crystallization of ammonium sulfate in the system. Compared with the pure ammonium sulfate droplets, the efflorescence relative humidity (ERH) of the mixed glucose/ammonium sulfate droplets is delayed and the deliquescence relative humidity (DRH) is advanced. The ERH of the mixed aerosol droplets with molar ratios of 1:4, 1:3 and 1:2 is 35 ± 2%, 32 ± 2.5% and 30 ± 1.5% RH, respectively. And the DRH of the mixed aerosol droplets is 78 ± 1.5%, 76 ± 2% and 74 ± 2.5% RH, respectively. These results improve the understanding of the physical and chemical properties of super viscous organic/inorganic mixed aerosols, and might have important implications for atmospheric chemistry.

This study focuses on speciation of air borne microbes in an office building and health impacts of these microbes in terms of Quantitative Microbial Risk Assessment (QMRA), Hazard Quotient (HQ) and Hazard Index (HI). This is important in the wake of Sustainability Development Goal 3 (Public Health and well-being) specially when there is a lack of standards in terms of microbial air quality in office buildings where people spend 8–10 h indoors. Air borne bacterial and fungal species in different floors of the office building with varying occupancy and work profile were identified. The load of bacterial count on an average for the entire building was found to be 1917 CFU/m3. Overall, Gram-positive bacteria were predominant (>53%). Based on V3–V4 sequencing Staphylococcus scuiri (causing UTIs) was the most abundant (93.7%) and other bacterial species found were Lactobacillus hamsteri, Prevotella copri, Bacteroides plebeius Faecalibacterium prausnitzii, Bacillus coagulans (gut commensals), Shigella boydii (causes bacillary dysentery), and Propionibacterium acnes (acne producing). Fungal load was 4000 CFU/m3. Based on ITS sequencing Aspergillus (45.6%) was the dominant fungus and other fungi found were Cunninghamella, Lichtheimia, Fusarium, and Circinella Grammothele, Chondrostereum, and Pseudolagarobasidium, Candida sp., Chondrostereum, Sarocladium. The QMRA of gram-negative air borne bacteria showed a high disease burden, well over the WHO benchmark values even though Hazard Quotient (HQ) and Hazard Index (HI) was found to be negligible. These findings can contribute to the development of guidelines for seemingly safe workplaces that may harbour disease-causing microbes and calls for an immediate attention from policy makers as it is a major cause of concern for public health.

During micro-cold spray deposition, also referred to as the aerosol deposition method or vacuum kinetic spraying, performed with conventional nozzles, the particle impact velocities decrease drastically with particle size for fine particles <500 nm in diameter due to slowing in the stagnation region. A new design for a nozzle that contains pressure relief channels is proposed that allows the pressure in the stagnation region downstream of the bow shock to be reduced. This reduced stagnation pressure results in less particle slowing compared to conventional nozzle geometries, particularly for smaller or less dense particles. The effects of the channel geometry on the particle impact velocity are systematically investigated by independently varying the channel parameters. Calculations show that the impact velocities for 100 and 200 nm yttria stabilized zirconia particles is increased by 111% and 31%, respectively, for a selected pressure relief channel nozzle when compared to a comparable conventional nozzle. Although impact velocities are increased, a tradeoff exists with this nozzle design in that the particle focusing in the nozzle is decreased and some of the particles may be removed from the aerosol by the channels. Experiments using a nitrogen as a carrier gas at ∼40 kPa upstream pressure show that, despite the loss of larger particles into the relief channels, the deposition efficiency is improved by 300% when depositing films from fine 8 YSZ powder with the pressure relief nozzle compared to a conventional nozzle.