On-road particle size distributions weremeasured at the Tuscarora Mountain tunnel on the Pensylvania Turnpike in May 1999.The data were obtained using a scanning mobility particle sizer.The nucleation modes of the size distributions contain4ed most of the particles on a number concentration basis and exhibited peak diameters ranging from 11 to 17 nm.This observationis consisgnificant numbersof ultrafine aerosol particles can be expected in sloxe proximity to busy motorways.The experiment provided 4 case studies for which the tunnel in let data could be sued to correct data obtained at the outlet,allowing for estimates of particle production within thetunnel.Exhaust particle production rates per vehicle kilometer were estimated;the results are presented with the caveat that the measurements were affected by ambient dilution.The 4 case study nucleation mode sizes vaired inversely with the caveat that measurements were affected by ambient dilution.The 4 case study nucleation mode sizes varied inversely with ambient temperature.The light-duty vehicle contributions to the ultrafine particle distributions were apparently domainated by the heavy-duty vehicle contriubtions.
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