Annual patterns of airborne bacteria governed by local generation and regional dispersal

Airborne bacteria represent a critical yet highly variable component of atmospheric ecosystems, driven by a complex interplay of local generation (LG) and regional dispersal (RD). Through extensive monitoring over 3 years (315 aerosol samples), we quantified airborne bacterial populations using quantitative PCR combined with high-throughput sequencing, revealing substantial fluctuations (2.8-5.8 log₁₀ copy·m^-3) characterized by dramatic spring peaks and summer minima. Strikingly, episodic dust events and PM₁₀ spikes from distant arid regions thousands of kilometers away increased local bacterial abundance by 5.5- and 6.2-fold (P < 0.05), respectively. Correlation network analysis identified strong positive associations among bacterial abundance, desert PM₁₀, and local PM₁₀, alongside negative relationships with temperature, humidity, and precipitation. Time-series analyses further revealed robust, synchronized annual cycles for bacterial abundance, desert PM₁₀, and local PM₁₀ (P < 0.05), with parametric modeling capturing a 4-week lag between desert dust emissions and subsequent local microbial peaks. Structural equation modeling provided quantitative confirmation that both LG and RD significantly influenced airborne bacterial dynamics (P < 0.05), with RD predominating during peak spring dust storm activity. Collectively, our findings highlight the substantial role of transcontinental dust transport as a primary source of airborne bacteria, complementing and sometimes overshadowing LGs in determining atmospheric bacterial communities.IMPORTANCEThis study enhances understanding of how airborne bacterial populations vary throughout the year in Busan, South Korea, by analyzing both local generation and long-distance transport. Over 3 years of continuous monitoring, we observed consistent spring peaks in bacterial abundance, closely linked to dust storms originating in the arid regions of China and Mongolia. These dust events transport large quantities of particles carrying bacteria over thousands of kilometers, temporarily raising local airborne bacterial levels above typical background levels. The findings show that while bacteria are continuously emitted from local sources, regional dust transport can be the dominant driver, particularly during the spring dust storm season. This combination of local and regional influences results in complex seasonal cycles of bacterial abundance. Understanding how these processes interact is critical for predicting changes in air quality, evaluating potential health risks, and recognizing the ecological connections that link distant desert environments with downwind areas.