Diurnal Variations of Size-Resolved Bioaerosols During Autumn and Winter Over a Semi-Arid Megacity in Northwest China

Bioaerosols emission from source facilities in a wastewater treatment plant: Critical exposure time and sensitivity analysis

Overexposure of sewage workers to bioaerosol released from wastewater treatment plants (WWTPs) can cause serious infections, but practical method for controlling their health risk is lacking. In this study, reverse quantitative microbial risk assessment was used to estimate the daily critical exposure time (CET) of sewage workers exposing to Staphylococcus aureus bioaerosol emitted by three emission sources facilities in a WWTP based on either U.S. EPA or WHO benchmark, and sensitivity analysis was conducted to analyze the influence of various parameters on the outcomes of CET. The results showed that the CET of females was always 1.12-1.29 times that of males. In addition, the CET after wearing face masks was 28.28-52.37 times as long as before. The working time can be determined based on the CET results of male workers wearing face masks exposed to the inverted-umbrella aeration tank (14.73-550.98 min for U.S. EPA benchmark and 55.07-1972.24 min for WHO benchmark). In each scenario, the variable parameter exposure concentration (ec) always showed the most influence on the CET results. After wearing the face masks, the removal fraction by employing face masks also had a significant effect on the results, only second to ec. Therefore, the wearing of face mask is the most convenient and effective measure to prolong the CET. Furthermore, practical methods to reducing bioaerosol concentration in WWTPs exposure are also necessary to extend CET and safeguard worker health. This study enriches the application range of reverse quantitative microbial risk assessment framework and provides theoretical support for stakeholders to establish reasonable working time threshold guidelines, and practical method and novel perspective to protect the on-site health risks of sewage workers exposing to various facilities.

Development of an automatic measurement system using atmospheric pressure photoionization ultrahigh-resolution mass spectrometry and application for on-line analysis of particulate matter

On-line chemical characterization of atmospheric particulate matter (PM) with soft ionization technique and ultrahigh-resolution Mass Spectrometry (UHRMS) provides molecular information of organic constituents in real time. Here we describe the development and application of an automatic measurement system that incorporates PM2.5 sampling, thermal desorption, atmospheric pressure photoionization, and UHRMS analysis. Molecular formulas of detected organic compounds were deducted from the accurate (±10 ppm) molecular weights obtained at a mass resolution of 100,000, allowing the identification of small organic compounds in PM2.5. Detection efficiencies of 28 standard compounds were determined and we found a high sensitivity and selectivity towards organic amines with limits of detection below 10 pg. As a proof of principle, PM2.5 samples collected off-line in winter in the urban area of Beijing were analyzed using the Ionization Module and HRMS of the system. The automatic system was then applied to conduct on-line measurements during the summer time at a time resolution of 2 hr. The detected organic compounds comprised mainly CHON and CHN compounds below 350 m/z. Pronounced seasonal variations in elemental composition were observed with shorter carbon backbones and higher O/C ratios in summer than that in winter. This result is consistent with stronger photochemical reactions and thus a higher oxidation state of organics in summer. Diurnal variation in signal intensity of each formula provides crucial information to reveal its source and formation pathway. In summary, the automatic measurement system serves as an important tool for the on-line characterization and identification of organic species in PM2.5.

Bioaerosols in the atmosphere: A comprehensive review on detection methods, concentration and influencing factors

In the past few decades, especially since the outbreak of the coronavirus disease (COVID-19), the effects of atmospheric bioaerosols on human health, the environment, and climate have received great attention. To evaluate the impacts of bioaerosols quantitatively, it is crucial to determine the types of bioaerosols in the atmosphere and their spatial-temporal distribution. We provide a concise summary of the online and offline observation strategies employed by the global research community to sample and analyze atmospheric bioaerosols. In addition, the quantitative distribution of bioaerosols is described by considering the atmospheric bioaerosols concentrations at various time scales (daily and seasonal changes, for example), under various weather, and different underlying surfaces. Finally, a comprehensive summary of the reasons for the spatiotemporal distribution of bioaerosols is discussed, including differences in emission sources, the impact process of meteorological factors and environmental factors. This review of information on the latest research progress contributes to the emergence of further observation strategies that determine the quantitative dynamics of public health and ecological effects of bioaerosols.

Haze Exposure Changes the Skin Fungal Community and Promotes the Growth of Talaromyces Strains

Haze pollution has been a public health issue. The skin microbiota, as a component of the first line of defense, is disturbed by environmental pollutants, which may have an impact on human health. A total of 74 skin samples from healthy students were collected during haze and nonhaze days in spring and winter. Significant differences of skin fungal community composition between haze and nonhaze days were observed in female and male samples in spring and male samples in winter based on unweighted UniFrac distance analysis. Phylogenetic diversity whole-tree indices and observed features were significantly increased during haze days in male samples in winter compared to nonhaze days, but no significant difference was observed in other groups. Dothideomycetes, Capnodiales, Mycosphaerellaceae, etc. were significantly enriched during nonhaze days, whereas Trichocomaceae, Talaromyces, and Pezizaceae were significantly enriched during haze days. Thus, five Talaromyces strains were isolated, and an in vitro culture experiment revealed that the growth of representative Talaromyces strains was increased at high concentrations of particulate matter, confirming the sequencing results. Furthermore, during haze days, the fungal community assembly was better fitted to a niche-based assembly model than during nonhaze days. Talaromyces enriched during haze days deviated from the neutral assembly process. Our findings provided a comprehensive characterization of the skin fungal community during haze and nonhaze days and elucidated novel insights into how haze exposure influences the skin fungal community. IMPORTANCE Skin fungi play an important role in human health. Particulate matter (PM), the main haze pollutant, has been a public environmental threat. However, few studies have assessed the effects of air pollutants on skin fungi. Here, haze exposure influenced the diversity and composition of the skin fungal community. In an in vitro experiment, a high concentration of PM promoted the growth of Talaromyces strains. The fungal community assembly is better fitted to a niche-based assembly model during haze days. We anticipate that this study may provide new insights on the role of haze exposure disturbing the skin fungal community. It lays the groundwork for further clarifying the association between the changes of the skin fungal community and adverse health outcomes. Our study is the first to report the changes in the skin fungal community during haze and nonhaze days, which expands the understanding of the relationship between haze and skin fungi.

Number size distribution of bacterial aerosols in terrestrial and marine airflows at a coastal site of Japan

Size-differentiated concentration of bacterial aerosols is essential for investigating their dissemination via the atmosphere. In this study, the number size distribution of bacterial aerosols was measured at a coastal site in southwestern Japan (32.324°N, 129.993°E) using a size-segregated eight-stage (>11, 7.0-11, 4.7-7.0, 3.3-4.7, 2.1-3.3, 1.1-2.1, 0.65-1.1, and 0.43-0.65μm) sampler. The results showed that the distribution differed according to the source areas: terrestrial air, oceanic air, or a combination of the two. The distribution in the long-distance transported terrestrial air from the Asian continent was monomodal, with a peak of 3.3-4.7 μm. The distribution in local land breeze air was bimodal, with the peaks at 0.43-1.1 and 3.3-4.7 μm. A similar bimodal distribution was encountered when the local island air and long-distance transported terrestrial air mixed. In contrast, the size distribution did not show clear peaks in the air from either nearby or remote marine areas. According to the air mass backward trajectories, the further the distance the air moved in the 72 h before arriving at the site, the lower the concentration of total bacterial aerosols. The estimation of dry deposition fluxes of bacterial cells showed that the deposition was dominated by cells larger than 1.1 μm with a relative contribution from 70.5 % to 93.7 %, except for the local land breeze cases, where the contributions in the size ranges larger and smaller than 1.1 μm were similar. These results show the distinctive number size distributions and removal processes of bacterial aerosols in different types of air. In addition, they indicate that size-dependent characteristics of airborne bacteria should be considered when studying their activities and roles in the atmospheric environment.

Size distribution, community composition, and influencing factors of bioaerosols on haze and non-haze days in a megacity in Northwest China

Bioaerosols have become a major environmental concern in recent years. In this study, the diurnal variations and size distributions of bioaerosols, as well as airborne bacterial community compositions and their influencing factors on haze and non-haze days in Xi'an, China, were compared. The results indicated that the mean bacteria and fungi concentrations on non-haze days were 1.7 and 1.4 times of those on haze days, respectively, whereas the mean total airborne microbe (TAM) concentration was higher on haze days. Bacteria concentrations were the lowest in the afternoon, and the TAM concentration exhibited a bimodal distribution with two peaks coinciding with traffic rush hours. On haze days airborne fungi was mainly attached to PM_2.5, whereas bacteria and TAM were mainly distributed in coarse PM. The relative abundance of Chao1, Shannon and Simpson indices of bacterial communities were higher in the non-haze day samples, for the reason that high PM_2.5 levels with a large specific surface area may absorb more toxic and harmful substances on haze days, which should affect microbial growth. At the generic level, the relative abundance of Rhodococcus, Paracoccus, Acinetobacter, and Kocuria on haze days was higher than that on non-haze days, indicating a higher risk of contracting pathogenic pneumonia. The results of the redundancy analysis revealed that PM_2.5 and water-soluble inorganic ions (WSIIs, NO₃^-, SO₄²⁺, and NH₄⁺) strongly affected the bacterial communities on non-haze days, especially Acinetobacter. The atmospheric oxidation capacity (O_x) had a significant effect on bacterial communities during haze episodes, which were positively correlated with Paracoccus, Deinococcus, Sphingomonas, and Rubellimicrobium and were negatively correlated with Rhodococcus. These results provide valuable data to elucidate the formation and evolution of bioaerosol between haze and non-haze events and its potential threats to human health.

Isolation, Characterization, and Antimicrobial Activity of Bacterial and Fungal Representatives Associated With Particulate Matter During Haze and Non-haze Days

Particulate matter (PM) has been a threat to the environment and public health in the metropolises of developing industrial countries such as Beijing. The microorganisms associated with PM have an impact on human health if they are exposed to the respiratory tract persistently. There are few reports on the microbial resources collected from PM and their antimicrobial activities. In this study, we greatly expanded the diversity of available commensal organisms by collecting 1,258 bacterial and 456 fungal isolates from 63 PM samples. A total of 77 bacterial genera and 35 fungal genera were included in our pure cultures, with Bacillus as the most prevalent cultured bacterial genus, Aspergillus, and Penicillium as the most prevalent fungal ones. During heavy-haze days, the numbers of colony-forming units (CFUs) and isolates of bacteria and fungi were decreased. Bacillus, Paenibacillus, and Chaetomium were found to be enriched during haze days, while Kocuria, Microbacterium, and Penicillium were found to be enriched during non-haze days. Antimicrobial activity against common pathogens have been found in 40 bacterial representatives and 1 fungal representative. The collection of airborne strains will provide a basis to greatly increase our understanding of the relationship between bacteria and fungi associated with PM and human health.

Quantifying Air Pollutant Variations during COVID-19 Lockdown in a Capital City in Northwest China

In the context of the outbreak of coronavirus disease 2019 (COVID-19), strict lockdown policies were implemented to control nonessential human activities in Xi’an, northwest China, which greatly limited the spread of the pandemic and affected air quality. Compared with pre-lockdown, the air quality index and concentrations of PM2.5, PM10, SO2, and CO during the lockdown reduced, but the reductions were not very significant. NO2 levels exhibited the largest decrease (52%) during lockdown, owing to the remarkable decreased motor vehicle emissions. The highest K+ and lowest Ca2+ concentrations in PM2.5 samples could be attributed to the increase in household biomass fuel consumption in suburbs and rural areas around Xi’an and the decrease in human physical activities in Xi’an (e.g., human travel, vehicle emissions, construction activities), respectively, during the lockdown period. Secondary chemical reactions in the atmosphere increased in the lockdown period, as evidenced by the increased O3 level (increased by 160%) and OC/EC ratios in PM2.5 (increased by 26%), compared with pre-lockdown levels. The results, based on a natural experiment in this study, can be used as a reference for studying the formation and source of air pollution in Xi’an and provide evidence for establishing future long-term air pollution control policies.