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Atmospheric dispersion study of deicing salt applied to roads : first progress report

 
 Volume/Number:  2000  
 Issuing Agency:  Illinois State Water Survey 0038
 Description:  This report describes the status of an initial effort to understand and describe the atmospheric transport of road salt in the form of sodium chloride (NaCl) applied to highways as a deicing material. The study area is a proposed 20.1 kilometer or km (12.5 mile) tollway that is planned to extend Interstate 355 (I-355) located west of Chicago, Illinois, to connect Interstate 55 (I-55) and Interstate 80 (I-80) southwest of Chicago near Lemont, Illinois. Prior to construction, which has not yet begun, the focus of the effort has been to establish background levels of the road salt aerosol, to construct permanent sites along the proposed route corridor from which to better monitor and measure road salt aerosol properties, and to identify important parameters for use in constructing a computer model to describe the salt emission and deposition. The present status of the proposed project is that construction plans have been delayed at least until approval of a supplement to the environmental impact statement. Results from chemical analysis of aerosol and snow samples are reported that show progress toward characterizing the road salt aerosol with respect to its size, mechanisms of emission, range of atmospheric transport, and mechanisms of deposition. Analysis of the preliminary data suggest: 1. A large portion of the salt aerosol that becomes aerosolized is emitted after the road surface has been cleared of snow and ice. 2. Approximately 90 percent of the airborne road salt is contained in aerosol particles of diameter larger than 2.5 micrometers or 10^-4 inches. 3. The salt deposition pattern near a treated roadway as determined by snow samples decreases consistently with distance from the road. Average deposition values for a single snow event are found here to yield an aerial deposition of 0.06 grams per square meter (0.6 pounds per acre) at 500 meters (1,640 feet) from the road. The corresponding value for the total deposition per length of roadway is 85 grams per meter or g/m (300 pounds per mile or lb/mi). Five permanent sampling sites are almost completed and will provide a flexible monitoring capability to better quantify the road salt emission, transport, and deposition. Road salt emissions in aerosol samples collected at the locations of two of the permanent sites are reported here. The sites are located 0.6 km (0.4 mi) and 1.0 km (0.6 mi) southeast of I-55 in the prevailing downwind direction, but could also be affected by salt emission from a secondary road in the vicinity. A comparison of the aerosol measurements at the two sampling sites during periods when salt was applied shows that the site nearer to the sources consistently had higher levels of NaCl. Most of the NaCl was found in particles with diameter larger than 10 micrometers (4x10^-4 inches). 
 Agency ID:  CR-2000-05 
 ISL ID:  000000000804   Original UID: 999999994094 
  Documents:  20060929190229_ISWSCR2000-05.pdf