PI-SWIRL: A New Technique for Measuring

Wind Blown Dust Emission Potential

Vic Etyemezian, Sean Ahonen, John Gillies, Hampden Kuhns, Hans Moosmüller, Djordje Nikolic

DRI, Las Vegas, NV 89119

and

Marc PitchfordNOAA, Las Vegas, NV 89119

Sources of Windblown Dust

• Windblown dust – Vacant lands: Human disturbance makes it worse– Storage Piles– Construction sites

• Windblown Dust Requires wind– Emission Factor = where N is # disturbances/yr

– e.g. AP-42

∑=

N

iiPk

1

( ) ( )**2** 2558 tt uuuuP −+−=

Mechanisms of Windblown Dust Suspension

• “Creep”v0.5 - 2 mm particles roll due to pressure differential

• “Saltation”v0.1 - 0.5 mm particles suspended, travel parallel to

ground 1-5 m, re-impactvCause release of additional particles

• “Emission”v0.001 - 0.1 mm particles suspended and transported

between 10 – 10,000 m

USDA-ARS Wind Erosion Research Unit http://www.weru.ksu.edu/vids

Measurement of Wind Erosion

• Measure What/Why:– Threshold friction velocity– Emissions at given friction velocity– Emissions dependence on

• Surface parameters (texture, moisture, vegetative cover), location, time of year

– Substantial heterogeneities make exhaustive test matrix difficult

– Information necessary for accurate modeling

In-Situ Surface Stability Tests• Several Alternatives

– Large Wind Tunnel (LWT): Probably best method, but requires ~10-30 man hours per sample location

– Small Wind Tunnel (SWT): Less accurate than LWT, but requires less time

– PI-SWIRL: Comparable to Small Wind Tunnel; requires ~10 minutes per sample; potentially man-portable

LWT at Ft. Bliss, TX

•J. Gillies and B. Nickling testing emission flux potential

•LWT is closest measurement to a “standard”

•SWT - e.g. D. James (UNLV), D. Gillette (NOAA)

•Concerns with boundary layer development, maximum wind speeds, and accounting for saltation

Portable In-Situ Wind Erosion Laboratory:The PI-SWIRL concept

Philosophy: Don’t try to simulate atmospheric flow, instead simulate shear stress experienced by soil surface (i.e. u*)

Plate moving with respect to ground

Ground

Velocity gradient results in shear at ground, suspending loose particles

Plate moving with respect to ground

Ground

Velocity gradient results in shear at ground, suspending loose particles

PI-SWIRL Schematic

Side View Bottom View

Computer Controller/ Data System PM Monitor

Sample Tube

Open-bottomed Cylindrical Chamber

Variable Speed Motor

Annular Ring

60 cm

40 cm

Side View Bottom View

Computer Controller/ Data System PM Monitor

Sample Tube

Open-bottomed Cylindrical Chamber

Variable Speed Motor

Annular Ring

Side View Bottom View

Computer Controller/ Data System PM Monitor

Sample Tube

Open-bottomed Cylindrical Chamber

Variable Speed Motor

Annular Ring

60 cm

40 cm

Blower for clean air injection

PI-SWIRL v.2

Wind Vectors in PI-SWIRL

Sand grain motion in PI-SWIRL Cavity - To be Confirmed

The PI-SWIRL-ogram

-2

-1

0

1

2

3

4

5

6

7

8

3 4 5 6 7 8 9

l n ( R P M )

Ero

sio

n In

dex

Hardened gravel -coveredsur faceSofet r sur face wi th loose sandand si l tSofter

Softer surface with loose sand and silt

Hardened, gravel-covered surface

PI-SWIRL-ogram Parts

-4

-2

0

2

4

6

8

10

3 4 5 6 7 8 9

ln (RPM)

Em

issi

on

Ind

ex

11:13:55

11:14:38

11:15:22

11:16:05

11:16:48

11:17:31

11:18:14

11:18:58

11:19:41

11:20:24

Tim

e

Emission Index vs. RPM (Left Axis)Ln (RPM) vs. Time (right axis)

Loose, suspendable PM10

Moderately Unstable “Puffs” region

Heavy saltation-like emission mode

PI-SWIRL: Advantages/Disadvantages

• Advantages: – Fast, semi-portable, measures index based on shear stress– Symmetry bypasses boundary layer issue– Geometry allows simulation of “saltation-like” emissions

• Disadvantage: At present – relative standard– calibrate against LWT?– characterize shear stresses distribution with

• Internal sensors?• Modeling?

Interpreting In-Canopy Data

1. u* measured here

2. ut* measured

here

3. Does soil surface experience u*?

1. u* measured here

2. ut* measured

here

3. Does soil surface experience u*?

SWIRLER: Future priorities1. Characterize shear stresses/flow as f (RPM)2. Establish equivalent emission factors3. Investigate importance of dimensions

a. Does height have effect on measurement?b. Should rotor blade be wider/narrower?c. How small can you go without losing physics?

4. Establish equivalent u*t for in-canopy work

5. Replace DustTrak with rugged light-based measure

Thank you

• DRI• Encapco Inc – NTS Soil Stabilization