I-10

Grease Aerosol Deposition Pattern

SUMMARY How droplet size sets where escaped grease aerosol lands: Stokes settling velocity and ground-contact distance by particle size and wind speed (RB-011).

Reviewed by Mark Zuro, outdoor ventilation product specialist with 15+ years designing and engineering outdoor-rated range hoods. Published 2026-01-10 Updated 2026-09-26

Grease aerosol transport and deposition downwind of a partially effective hood, by droplet size (RB-011) Not-to-scale diagram of grease droplets escaping a partially effective hood in a 5 mph wind and depositing downwind in three practical zones from RB-011 §3.3: Zone 1, droplets larger than 50 micrometres, deposit within 1 metre (gravitational settling, ballistic; drip pan, grill exterior, adjacent countertop; about 40% of the escaped mass), settling velocity 0.068 to 0.27 m/s for 50 to 100 micrometres; Zone 2, 20 to 50 micrometres, 1 to 5 metres (gravitational settling; decking, furniture, siding within 5 m; about 30% of the mass), settling 0.011 to 0.068 m/s; Zone 3, 10 to 20 micrometres, 5 to 30 metres (settling plus turbulent diffusion; adjacent structures, vegetation, property boundary; about 15% of the mass), settling 0.0028 to 0.011 m/s. A neighbouring structure is drawn in Zone 3 with a grease film on its windward face. A secondary row gives the RB-011 Table 3.3a centreline-settling formula x_ground = H·U_w/v_s with H = 1.5 m, which ignores turbulent diffusion, impaction and ground effects and so overstates real travel: 50 to 100 micrometres 5–20 m at 2 mph, 12–49 m at 5 mph, 25–99 m at 10 mph; 20 to 50 micrometres 20–123 m, 49–307 m, 99–614 m; 10 to 20 micrometres 0.12–0.49 km, 0.31–1.2 km, 0.61–2.4 km. The secondary-row distances are model values from physics/grease.mjs with U_w = 0.447 m/s per mph; RB-011 Table 3.3a prints 50, 122, 308 and 615 m for those cells (50 micrometres at 5 mph; 20 micrometres at 2, 5 and 10 mph) using 2.24 and 0.89 m/s. For 5 micrometre droplets the formula gives 4.8 km at 5 mph; below about 10 micrometres gravitational settling is not the deposition mechanism (RB-011 §3.3). A deposition-intensity bar runs from heavy near the source to trace downwind. Grease Aerosol Transport and Deposition in Missed Plume Practical deposition distance by droplet size — RB-011 §3.3 (partially effective hood, 5 mph wind, RB-011 §3.4) · Not to scale NOT TO SCALE Grill Source Escaped plume Wind 5 mph ZONE 1 — <1 m >50 µm · ≈40% of mass Gravitational settling; ballistic ZONE 2 — 1–5 m 20–50 µm · ≈30% of mass Gravitational settling ZONE 3 — 5–30 m 10–20 µm · ≈15% of mass Settling + turbulent diffusion Grease film Neighbouring structure (5–30 m) hood 1 m 5 m 30 m v_s 0.068–0.27 m/s (50–100 µm) Drip pan, grill exterior, adjacent countertop v_s 0.011–0.068 m/s (20–50 µm) Decking, furniture, siding within 5 m v_s 0.0028–0.011 m/s (10–20 µm) Adjacent structures, vegetation, property boundary Secondary — centreline settling formula x_ground = H·U_w / v_s (H = 1.5 m; RB-011 Table 3.3a): no turbulent diffusion, impaction or ground effects, so it overstates real travel (RB-011 §3.3) 50–100 µm: 5–20 m @ 2 mph · 12–49 m @ 5 mph 25–99 m @ 10 mph 20–50 µm: 20–123 m @ 2 mph · 49–307 m @ 5 mph 99–614 m @ 10 mph 10–20 µm: 0.12–0.49 km @ 2 mph · 0.31–1.2 km @ 5 mph 0.61–2.4 km @ 10 mph formula distance at 2 / 5 / 10 mph: Model values from physics/grease.mjs (U_w = 0.447 m/s per mph); RB-011 Table 3.3a prints 50 / 122 / 308 / 615 m for 50 µm @ 5 mph and 20 µm @ 2 / 5 / 10 mph, using 2.24 and 0.89 m/s. 5 µm droplets: formula 4.8 km @ 5 mph — below ≈10 µm gravitational settling is not the deposition mechanism (turbulent diffusion, washout; RB-011 §3.3). Zone widths are not to scale. Deposition Intensity: Heavy Trace OVS-RB-011 | outdoorventilationstandard.com

I-10.1

Method & assumptions

When the buoyant cooking plume escapes the hood (partially or fully), grease aerosol is carried into the surrounding environment. This diagram shows how particle size determines how far the grease travels and where it deposits.

Reference readings

Representative values below are computed directly from the same settling and transport functions (physics/grease.mjs) driving the instrument’s deposition view — Stokes settling with the Cunningham slip correction, and the ground-contact distance x_ground = H · U_w / v_s for aerosol released at H = 1.5 m, the representative escape height RB-011 uses [RB-011 §2.3, §3.3]. The table is regenerated by scripts/generate-reference-tables.mjs, never typed by hand.

Droplet diameter	Settling velocity v_s	Ground contact at 2 mph	Ground contact at 5 mph	Ground contact at 8 mph	Ground contact at 10 mph
5 µm	6.99e-4 m/s	1.9 km	4.8 km	7.7 km	9.6 km
10 µm	2.75e-3 m/s	487.5 m	1.2 km	1.9 km	2.4 km
20 µm	0.011 m/s	122.9 m	307.2 m	491.5 m	614.3 m
50 µm	0.068 m/s	19.8 m	49.4 m	79.0 m	98.8 m
100 µm	0.271 m/s	4.9 m	12.4 m	19.8 m	24.7 m

Settling velocity rises with the square of droplet diameter, so transport distance falls with it: a 100 µm droplet settles at about 0.271 m/s and reaches the ground about 12.4 m downwind in a 5 mph wind, while a 10 µm droplet (0.0028 m/s) would travel about 1.2 km before gravitational settling alone brought it down [RB-011 Table 3.3a]. That is the whole deposition story in one line — the coarse droplets that carry most of the escaped grease mass land within metres of the grill, and the fine fraction is not deposited locally by settling at all [RB-011 §3.3, §4.2]. For droplets below about 5 µm the settling distances run to kilometres, which RB-011 reads as a sign that gravitational settling is not the relevant removal mechanism for them; they leave by turbulent diffusion, rain-out and coagulation instead [RB-011 §3.3].

The Three Deposition Zones

Zone 1: Coarse droplets above 50 micrometers — within about 1 meter. The largest droplets settle fastest (Stokes settling velocity roughly 0.07–0.27 m/s) and land on the surfaces immediately adjacent to the cooking station — the drip pan, grill exterior, and adjacent countertop [RB-011 §3.4].

Zone 2: 20–50 micrometers — 1 to 5 meters downwind. Gravitational settling still dominates, but the wind carries these droplets further before they land: decking, outdoor furniture, and siding within about 5 meters [RB-011 §3.4].

Zone 3: 10–20 micrometers — 5 to 30 meters downwind. Settling plus turbulent diffusion deposits this band on adjacent structures, vegetation, and out to a neighboring property boundary [RB-011 §3.4].

The zone distances are RB-011’s near-field mass-balance estimate for a partially effective hood in a 5 mph wind, which accounts for the aerosol escaping at and below hood height and dispersing as it falls; the single-droplet ground-contact distances in the table above bound them from above [RB-011 §3.4]. Mass is concentrated at the coarse end: the coarse mode as a whole (2.5–100 micrometers) carries 50–80% of total grease mass [RB-011 §2.2]. Below about 5 micrometers, the fine fraction — the accumulation mode (0.1–2.5 micrometers, 20–40% of mass) and the ultrafine mode (under 0.1 micrometers, less than 5%) — disperses too broadly to matter for local deposition; it is the PM2.5 fraction most relevant to respiratory exposure, removed by atmospheric processes rather than local settling [RB-011 §2.2, §3.3].

Fire Risk Implications

Accumulated grease deposits from Zone 1 and Zone 2 on combustible surfaces (wood siding, vinyl, fabric awnings) represent a fire hazard. The accumulation rate depends on cooking frequency, source type (wood-fired produces the most aerosol), and capture efficiency of the installed hood [RB-011 §3.6].

Source Paper

RB-011: Grease Aerosol Transport and Deposition — Stokes settling (§2.3), transport distances (§3.3), deposition pattern (§3.4)

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Papers

RB-011: Grease Aerosol Transport and Deposition in Open Environments

HOW TO CITE

Outdoor Ventilation Standard (2026). “Grease Aerosol Deposition Pattern.” Interactive Tool, Outdoor Ventilation Standard. https://outdoorventilationstandard.com/tools/grease-aerosol-deposition/