Environmental sensitivity and resilience of airborne bacteria and fungi with time-scale variation under stress of air pollution and snowfall

Microbes contained in bioaerosols are a significant component of organic aerosols owing to their unique biological characteristics, which pose health risks and have undeniable meteorological effects. However, the diurnal variation and health risks of microbes in PM_2.5 and their responses to atmospheric factors are not well understood. In this study, we conducted a high-time-resolution analysis of near-surface atmospheric microbial communities in PM_2.5 at an urban site in Beijing, focusing on microbial composition, seasonal and diurnal distribution patterns, and feedback mechanisms of microbes to environmental factors during typical PM_2.5 pollution episodes across different seasons. Additionally, the effects of snowfall on airborne microbes were investigated. This study revealed distinct seasonal and environmental dynamics in atmospheric fungal and bacterial communities. Fungi exhibit stronger seasonal sensitivity and are primarily influenced by meteorological factors, whereas bacteria display consistent temporal heterogeneity driven by fixed emission sources and environmental resilience. Niche differentiation occurred between fungi and bacteria in autumn, whereas summer bacterial communities were notably affected by ozone. Key bacterial genera are reliable biological markers of pollution. The composition of PM_2.5, rather than its concentration, significantly affects microbial communities, with bacteria being more susceptible to the formation of secondary inorganic aerosols. The presence of pathogenic microbes in the atmosphere cannot be overlooked. Pathogenic microorganisms show temporal heterogeneity, with fungal pathogens being more diverse but inhibited by SO₂ and OC, whereas pathogenic bacteria thrive in cleaner conditions. Snowfall does not efficiently remove airborne microbes but acts as a depositional sink for atmospheric micro-organisms. This study provides a profile of microbial communities in atmospheric aerosols during typical pollution periods and offers a new perspective for understanding the health effects associated with PM_2.5 exposure.