Non-monotonic response of net dust deposition kinetics to low wind speeds

Dry deposition is a major sink for mineral dust, yet its behavior under weak winds remains poorly constrained and is often parameterized monotonically with wind speed. Here we quantify size-resolved dust net accumulation kinetics in a closed-circuit recirculating wind tunnel using a two-stage protocol (brief high-wind loading followed by low-wind deposition at 0, 2, 4, and 6 m s −1 ). Cumulative retained-mass time series were measured with an array of collection trays, with the initial suspended dust loading recorded by an online concentration monitor. Particle sizes were characterized by laser diffraction and grouped into six diameter-threshold classes (PM 2.5 –PM 63 ). A first-order kinetic model described the temporal accumulation dynamics and yielded a fitted asymptotic retained mass ( a ), effective net-accumulation rate coefficient ( k ), characteristic time scale (τ=1/k), and initial net accumulation flux ( J 0 = a k ). The observed  J 0 was highest at 2 m s −1 for PM 2.5 –PM 30 , and 4 m s −1 for PM 40 and PM 63 , while  J 0 declined markedly at 6 m s −1 for the lower diameter thresholds. Quadratic fits across the four wind-speed levels suggest a potential maximum near 2–3 m s −1 for PM 2.5 –PM 40 . These measurements quantify the size-dependent response of effective surface retention to low wind speeds and provide benchmark behavior for coupled deposition, retention, and re-entrainment parameterizations.