Publication Detail

Final Report: Traffic Generated PM-10 "Hot Spots"


Research Report

Suggested Citation:
Ashbaugh, Lowell L., Robert G. Flocchini, Daniel P. Chang, Vicente J. Garza, Omar F. Carvacho, T. A. James, R. T. Matsumura (1996) Final Report: Traffic Generated PM-10 "Hot Spots". Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-96-17

In the summer of 1994 the Crocker Nuclear Laboratory Air Quality Group found increased PM10 concentrations downwind of a California freeway, an urban roadway and a heavily traveled intersection. While the freeway and urban roadway only increased concentrations 5 to 7 µg/m3, the increase across the intersection was approximately ten times greater, i.e. about 80 µg/m3. The emission rates from the freeway and the urban roadway were estimated at 18 to 24 mgNKT and 19 to 34 VKT, respectively. The emission rate from the intersection was estimated to range from 259 to 1295 mgNKT. The intersection study was a preliminary experiment, however, and the majority of the intersection PM10 emissions could not be attributed to any particular source type.

In 1995, the Air Quality Group investigated paved road PM10 emissions generated at intersections in greater depth. We sampled at the same intersection with a more robust sampling array, and we increased the duration and frequency of sampling to four samples per day for three and one half days. The measured concentration change across the intersection in 1995 averaged 5 to 25 µg/m3 at the closest downwind sampler during typical summertime conditions. The corresponding PM2.5 concentrations increased by 0 to 13 µg/m3 at the closest downwind sampler.

The PM10 emission rate estimate ranged from 84 to 389 mgNKT, while the PM2.5 emission rate estimate ranged from 10 to 142 mgNKT. It should be noted that direct vehicular emissions were not subtracted from the measured downwind increase, so that the measured "re-entrained" dust emission factor is a slight overestimate.

These results indicate that the intersection is not likely to be a "PM10 hot spot" unless the background concentration is already close to the 150 µg/m3 24-hour standard. Furthermore, the elevated concentrations extended less than 100 meters downwind of the intersection in most cases. In other words, the concentrations at the far downwind sampling site (less than 100 meters downwind of the intersection) were close to the upwind concentrations during most sampling periods. The major contributor to high concentrations near the intersection was background PM10 from the urban area.