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Bioaerosols are a major source of pollution in indoor environments, where people spend approximately 90% of their time, and the microorganisms adhered to PM2.5 adversely affect human health. However, most research has focused on the concentration of these aerosols and the factors that influence it rather than the correlation between microbial activity and air quality. Thus, this study used a modified technique of fluorescein diacetate (FDA) hydrolysis to evaluate the activity of microorganisms in the PM2.5 during three seasons (summer, autumn and winter) in Beijing. 0.155-5.388 ng m -3 and 0.091-5.740 ng m -3 of sodium fluorescein, a marker of microbial activity, were measured indoors and outdoors, respectively; thus, no significant difference in concentration between the two environments was detected, but the indoor activity was affected by outdoor conditions to an extent. The most active season was autumn, followed by winter and summer. Furthermore, the highest activity in summer and autumn was observed during conditions of excellent air quality, and in summer, the activity during conditions of good air quality also obviously exceeded that during conditions of slight pollution. Additionally, the microbial activity in a room varied according to the room's ventilation (or lack thereof), suggesting a strong association between these parameters. In general, when the air quality was excellent, 20 minutes of ventilation achieved the optimal air exchange, but this duration should be reduced during polluted conditions. Our results provide new insights into evaluating the indoor air quality based on the microbial activity.

Grassland ecosystems are vital terrestrial ecosystems. As areas sensitive to climate change, they are critical for assessing the effects of global climate change. In China, grasslands account for over 40% of the land area. There is currently limited information on microbial diversity evolution in different grassland areas, particularly microorganisms with ice nucleation activity (INA) and their potential resources with potential influence to regulate regional precipitation and climate. We used Illumina MiSeq to sequence the 16S rRNA V3–V4 hypervariable region and performed a simple droplet freezing experiment to determine the variation in the grassland microbial community species composition and community structure. Rainwater and topsoil samples from the Hulunbuir Grassland in Inner Mongolia collected over three years were characterized. The dominant bacterial genus in the rainwater was Massilia , and the dominant fungus was Cladosporium . Additionally, the dominant bacteria in the soil were Sphingomonas , and the dominant fungus was Gibberella . There were differences in the microbial communities before and after the coronavirus disease epidemic. Pathogenic microorganisms exhibited inconsistent responses to environmental changes. The low relative abundance of known high-INA microorganisms and the higher freezing temperature indicated that unknown high-efficiency biological ice nucleating particles may be present. We found significant differences in species diversity and richness between the rainwater and soil populations in grassland areas by analyzing the sample community structures. Our research results revealed the species composition and structure of the microbiota in grassland ecosystems in China, indicating that environmental media and human activities may affect the microbiota in the grassland area and indicating underlying microorganisms with high INA.

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Summary The outbreak of the COVID‐19 epidemic is a reminder that aerosols have important health effects as a potential route for disease transmission. Biological components in aerosols (especially PM2.5) may pose potential threats to humans as pathogens and allergens. Research on PM2.5 and biological components currently focuses mainly on polluted conditions, with less emphasis on clean environments. Sampling has also been primarily based on a single point with a lack of data at different positions. In this study, a modified fluorescein diacetate hydrolysis method was used to measure microbial activity in PM2.5 at different altitudes over a year in Beijing, China. A high‐throughput sequencing method was used to study the microbial community. Results showed that microbial activity 1.5 m (0.0465 ng m−3) above the ground was higher than 31.5 m (0.0348 ng m−3). There was higher microbial activity at both heights during spring. Furthermore, a positive correlation was observed between microbial activity and relative abundance of dominant species. Microbial activity increased during autumn and winter increased alongside the pollution level, but in spring higher levels of microbial activity were observed in excellent or good weather conditions. The results from this study are valuable for further research regarding the biological components of atmospheric PM, the prevention of biological pollution, and establishing a comprehensive air quality evaluation system.