* Corresponding author. E-mail address: hkuhns@dri.edu (H. Kuhns). 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 Atmospheric Environment 35 (2001) 2815}2825 Testing Re-entrained Aerosol Kinetic Emissions from Roads (TRAKER): a new approach to infer silt loading on roadways H. Kuhns*, V. Etyemezian, D. Landwehr, C. MacDougall, M. Pitchford, M. Green Division of Atmospheric Sciences, Desert Research Institute, 755 E. Flamingo Rd., Las Vegas, NV 89119, USA Dames & Moore, Las Vegas, NV 89119, USA National Oceanic and Atmospheric Administration, Las Vegas, NV 89119, USA Received 8 June 2000; received in revised form 20 December 2000; accepted 22 December 2000 Abstract PM  and PM  emissions from roadways are currently estimated using the silt loading on the road surface as a surrogate for the emissions potential of road dust. While the United States Environmental Protection Agency prescribes this method in AP-42, there is considerable cost associated with silt loading measurements, it is feasible to sample only a small portion of a roadway network. A new approach for measuring the concentration of suspendable PM  aboveroadsurfaceshasbeendevelopedtoobtainamorespatiallyrepresentativeestimateofaroad'spotentialto emitdust.TheTestingRe-entrainedAerosolsKineticEmissionsfromRoads(TRAKER)systemusesreal-timeaerosol sensors mounted on a vehicle to measure the concentration of dust suspended from the road while the vehicle is in motion.WhencoupledwithaGlobalPositioningSystem(GPS)instrument,TRAKERcanbeusedtoe$cientlysurvey the changes in the suspendable particle reservoir due to varying road conditions over a large spatial domain. In a recent study on paved roads in Las Vegas, the TRAKER system was compared with collocated silt loading measurements. The TRAKER system was also used to survey the relative amounts of suspendable road dust on approximately300milesofpavedroads.Thesystemprovidesauniqueperspectiveonroaddustsourcesandtheirspatial distribution. Results of this study indicated that the di!erence of the PM  concentrations measured behind the tire and on the hoodisexponentiallyrelatedtovehiclespeed.Thiswasaninteresting "ndingbecausecurrentAP-42roaddustemissions estimation methods do not include vehicle speed as a factor in the emissions calculations. The experiment also demonstratedthatthedistributionofsuspendablematerialonroadwaysishighlyvariableandthatalargenumberof samples are needed to represent road dust emissions potential on an urban scale for a variety of road and activity conditions.  2001 Published by Elsevier Science Ltd. Keywords: Road dust; Area sources; Fugitive emissions; Resuspension; Particle entrainment 1. Introduction Paved and unpaved road dust emissions calculated using United States Environmental Protection Agency (US EPA) prescribed methodology in AP-42 typically accountformorethan20%ofthetotalPM  emissions inmanywesterncities(USEPA,1993).IntheCalifornia South Coast Air Basin, paved road dust accounts for 65% of the PM  emissions (C.A.R.B., 1998) and in Boise, ID, 43% of the wintertime PM  emissions are fromroaddust(SAIC,1997).Therelativecontributionof road dust emissions to total PM  emissions in Las Vegas is estimated to be 27% when track out from constructionsitesisconsidered(DRI,1996).Despiteroad dust's signi"cant contribution to the inventory, the 1352-2310/01/$-see front matter  2001 Published by Elsevier Science Ltd. PII:S1352-2310(01)00079-6