Atmospheric Microplastic Transport & Deposition

Emission Source

Wind speed U 6.0 m/s

Particle diameter d 15 μm

Turbulence intensity 0.50

Emission rate 40 /s

Live Readouts

Airborne fibers

Deposited fibers

Settling velocity v_s

— mm/s

Mean deposit distance

— m

How it works

Each fiber is a rigid sphere-equivalent particle of diameter d and density ρ_p ≈ 920 kg/m³ (polyethylene/polypropylene fiber). In the slow, low-Reynolds-number regime typical of microplastic fibers in air, its terminal fall speed follows Stokes' law:

v_s = (ρ_p − ρ_air) · g · d² / (18 · μ_air)

ρ_air ≈ 1.2 kg/m³   μ_air ≈ 1.81×10⁻⁵ Pa·s   g = 9.81 m/s²

Position updates each frame combine three transport terms — mean horizontal wind advection, an isotropic turbulent random walk (magnitude set by the turbulence slider, representing atmospheric eddy diffusion), and steady Stokes settling:

x  += (U + turbulent_u) · dt
y  += (turbulent_v − v_s) · dt
z  +=  turbulent_w · dt

A fiber deposits the instant y reaches the ground (y = 0); the model then records its downwind travel distance. Because v_s grows with d², a 100 μm fragment falls roughly 45× faster than a 15 μm fiber and deposits close to the source, while sub-10 μm fibers can travel tens to hundreds of meters — this size-dependent settling is exactly why fine microplastic fibers are found in atmospheric deposition far from any obvious source, including remote mountains and polar ice.

Wind speed — mean horizontal transport; higher wind stretches the plume and pushes the deposition footprint further downwind.
Particle diameter — sets v_s via the d² term; small fibers stay airborne and disperse, large fragments settle almost immediately.
Turbulence intensity — random-walk strength that spreads the plume vertically and laterally, competing against steady settling.
Emission rate — new fibers released per second from the source stack.

Airborne microplastic fiber Ground deposition

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