Exposure characteristics and health risk differences of airborne viable microorganisms across different climate zones: Insights from eight typical cities in China.

Viable pathogenic microorganisms in atmospheric particles pose notable health risks, while their exposure characteristics and health risks across climate zones remain unclear. This study collected 399 particulate samples from automobile air conditioning filters in eight Chinese cities across five climate zones, analyzing microbial concentration, viability, and pathogenicity via microbial culture, fluorescence staining, and high-throughput sequencing. Health risks were evaluated with quantitative microbial risk assessment (QMRA) method. Results revealed distinct microbial patterns. Proportion of viable microorganisms was highest in tropical monsoon climate region (42.58 %). Conversely, plateau and mountain climate region exhibited lower microbial viability (25.12 %) and bacterial culturability ((1.58 ± 0.41) × 10 CFU/g). Bacterial genera like Acinetobacter were consistent across climate zones. However, dominant fungal genera manifested significant differences while pathogenic fungi such as Aspergillus and Cryptococcus were more abundant in temperate continental climate region. These may be attributed to different sources and microbial biogeographical characteristics, such as latitudinal distribution pattern. Annual infection risk and disease burden exceeds threshold of 10 and 10 in temperate, subtropical and tropical monsoon climate regions. Dermal contact demonstrated higher health risk. These insights into exposure characteristics of viable microorganisms can offer data support and theoretical basis for improving the air quality evaluation system and control of potential health risks.