Document 5LoD1R0y11pa0qvj48mNYJ7Vz

19 emissions can be approximated from the airborne tribution of asbestos from automobiles ranges asbestos emission rate of 3.82 pg/car mile, from 0.13 to 16% for large cities; the average r resulting in 11.9 pg/car mile. Considering maximum contribution is about 1.3%. these close results, we can infer that the Williams and Muhlbaier (4) estimated the asbestos emissions from automobiles contribute contribution of brake wear asbestos in New only a small portioa to the total natioaal York City by using a lead tracer model. In level. this model, the vehicle emission was assumed The total number of airborne asbestos to contribute to the ambient air at the same fibers emitted in this study was 3.0 x 107 ratio as lead emissions. In their study, a fibers/disc-brake mile; the fibers averaged lead emission rate from a car was found to be 0.59 pm in length. There were about 26,000 108 ng/mile, of which 60% remains airborne with fibers/ng of asbestos. Huhlbaier and Williams' a typical air concentration of 2 pg/m3-car. (3) reported compatible values, showing a Using the same ratios, we found an asbestos median fiber length of 0.5 pm and fiber density contribution of 0.12 ng/m3 for an emission of 90,000 fibers/ng of asbestos. rate of 3.8 pg/car mile. This value is close The results of these three typical inves to that obtained by Williams and Muhlbaier (4). tigations are summarized in Table 5. Other Since the asbestos concentration of ambient investigations also used an electron microscope air in New York City ranges from 8 to 41 for asbestos analysis. Anderson et al. (13) ng/m3 (1), the contribution from automobile used a brake dynamometer and concluded that brakes represents only 0.3 to 1.5%. particulates emitted from automobile brakes Considering the results of the dispersion contained only 0.005% asbestos. Rowson (14) and lead trace models, the maximum asbestos collected airborne particles, from a shrouded contribution from automobiles to the ambient brake assembly mounted on an inertia dyna air in cities is 0.25 ng/m3, and ranges from mometer and measured an asbestos concentration < 1 to 16%. less than 0.51 in wear debris. All these reports show the asbestos concentration to be SUMMARY AND CONCLUSIONS less than 0.51. RBC's and their frequency distribution CONTRIBUTION OF BRAKE ASBESTOS IN URBAN were found by statistically analyzing downtown AIR - The RBC's and the frequency distribution city driving in Raleigh, NC. The particulate used to measure particulate and asbestos emis as well as asbestos emissions from automobile r sions from automobile brakes in the current study were based on inner-city driving. brakes were characterized by simulating these RBC's on a computer-controlled dynamometer. Because most brake emissions are expected in Average total particulate emissions urban areas, it would be appropriate to esti (deposited plus airborne) were approximately mate automobile brake contributions to the 12 mg/disc-brake mile, of which 3.8 mg or 32% asbestos level in urban air by using meteoro remained airborne. The average aerodynamic logical models or surrogate models. These diameter of airborne particulates was 3.7 pm. models can determine the maximum possible con Based on the 1.6:1.1 wear ratio between disc tribution of brake emissions to the ambient and drum brakes, the estimated airborne par asbestos level, from which the corresponding ticulate emission rate was 12.8 mg/car mile. health effect can be inferred. Airborne particulates contained 0.018% Bradow (15) used dispersion models devel asbestos fibers, resulting in.an asbestos oped as a result of the U.S. Environmental emission rate of 1.1 pg/disc-brake mile or Protection Agency's Regional Air Pollution 3.8 pg/car mile for the same disc to drum brake Study to find automobile exhaust particulate contributions for the city of St. Louis, MO. In the calculations, the central city area had wear ratio. The average length of single fibers and fiber bundles was about 0.6 pm. From dispersion models for the city of a maximum annual average concentration of 13 St. Louis, M0, the maximum contribution of pg/m3 for the vehicle particulate emission rate asbestos emissions from automobiles to the of 0.195 g/mile. For the same models, the contribution of asbestos emissions from auto ambient air was 0.25 ng/m3 or 6500 fibers/m3. Assuming other big cities have similar disper mobiles in the current study is a maximum of 0.25 ng/m3 for the emission rate of 3.8 pg/car sion and emission factors, the contribution of automobile brakes varied from 0.13% to 16%, mile. Based on the measured value for the averaging 1.3%. number of fibers per unit mass (26,000 fibers/ng), the contribution is equivalent to Results from this investigation agree well with those of Williams and Muhlbaier (4). 6500 fibers/m3. The automobile asbestos emissions in St. Louis can be similiar to those for other large cities in the United States. From the data in Reference 1, the ambient asbestos concentrations in large cities (Dayton, OH, and Frankfort, KY, are excluded) Judging from the current and previous investi gations using electron microscope analysis, asbestos emissions from'automobile brakes con tribute little to the ambient asbestos level compared to other sources. vary from 1.6 to 200 ng/m3, averaging approxi mately 20 ng/m3. Therefore, the maximum con