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

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