Mechanistic insights into humidity-triggered bioaerosol emissions in greenhouses: Source dynamics and physics-based modeling.

Airborne microbial contaminants accumulate in semi-enclosed greenhouses, yet the source dynamics driving nocturnal bioaerosol peaks remain poorly constrained. This study integrates field monitoring, microstructural characterization, and physics-based modeling to quantify a humidity-triggered emission pathway using the Pseudomonas amygdali pv. Lachrymans-cucurbit system. Airborne concentrations exhibited pronounced nocturnal maxima, averaging 3233 CFU m-3, during near-saturation conditions (RH > 90%) and quiescent airflow. Microstructural analysis at lesion margins revealed discrete rupture vents ranging from 1.3 to 180 μm2, consistent with episodic emission events. By coupling exopolysaccharide-driven osmotic pressurization with tissue tensile resistance, simulations identified a critical hydrodynamic threshold for source activation. Internal pressure reached 0.35 MPa, exceeding the conservative rupture criterion of 0.19 MPa. Furthermore, a near-source trajectory model indicated that rupture-driven ejection initiates short-range transport with horizontal displacements up to 0.12 m within milliseconds, explaining pollutant dispersal even in quiescent air. Collectively, these results establish a threshold-governed "humidity-pressure-rupture" mechanism as a key source term for bioaerosols, providing quantitative trigger conditions for greenhouse air quality management and environmental risk control.