Major Factors of Wind Erosion and Road Dust

Robert Surrago

Background

Fugitive/natural sources make up the majority of PM-10 and PM-2.5 emissions

Two main fugitive/natural sources are wind erosion and road dust (mainly from unpaved roads)

Wind Erosion - Factors

Wind speed Wind gusts are more important than

average wind speed - best indicator is fastest mile

Used in conjunction with reference height to calculate the friction velocity (u

= (u*/0.4) ln(z/zo))

Wind Erosion - Factors

Erosion potential (P) A function of the friction velocity (u*) &

the threshold friction velocity (ut* [observed

experimentally]) If u* < ut*, then there is no chance of

wind erosion (cannot overcome friction) Each event must be treated separately

Road Dust - Factors

Mean vehicle weight - the average weight of all the vehicles that traverse a given road The more weight, the more force acting

on the road more dust can be createdSurface material silt content - dust

emissions vary directly with the % of silt in the road surface material Varies with geographic location

Road Dust - Factors

Moisture content - more moisture = more particle cohesiveness less dust created Can be affected by precipitation

Mean vehicle speed/mean # of wheels Faster = more force applied to surface =

more dust created More wheels = more opportunities to

create more dust Both are minor factors

Wind and Road Relations

Both emission types have ways to account for frequency of disturbances Wind - total P is sum of all disturbances Road - mean vehicle conditions

Both types take into account material properties Wind - threshold friction velocity Road - silt and moisture contents

Summary

Factors are similar for fugitive dust emissions Different applications of factors yields

different equations/constantsWhat does the future hold?

Apply to present data? Generate emissions projections?

Questions/comments/suggestions