Application Scheduling of Calcium Chloride As Fugitive-Dust Suppressant Using Micrometeorology Model.

Unpaved-roads are the major source for the PM₁₀ (particle diameter <10 μ) fugitive dust emission. Calcium chloride salt has hygroscopic property causing it to have high affinity to absorb water vapor from the ambient atmosphere. It also resists evaporation. The objective of this study was to formulate micrometeorology model able to predict application scheduling of CaCl₂ solution using daily weather data. The rate of water evapocondensation (ec, mm day^-1) from the salt treated soil surface layer was formulated by solving a steady two-dimensional equation of vapor diffusion in turbulent wind. The ec was a function of cross-wind road width, mean wind temperature, mean wind speed at 1 cm above ground surface, and the difference between relative humidity of the salt solution and wind. Negative and positive values of ec mean condensation (dilution) and evaporation (concentration), respectively. Used in the computation relative humidity data of CaCl₂ solutions at different temperatures (0 to 80^oC) and concentrations (0 to 60% CaCl₂) and their two-dimensional interpolated ones. The ec was computed using daily weather data (Davis, California) until the day at which relative humidity value of the CaCl₂ solution reached the value of saturated CaCl₂ solution. At this moment a new salt application similar to the initial one was applied and the computation continued to get application schedule for one year. The model successfully predicted the experimentally recommended practices in terms of concentration, rate, frequency, and emphasized application after rain or spraying the road before application. Sensitivity analysis indicated application scheduling was most affected by the water holding capacity of the surface soil layer and least affected by the road width. Weather related application schedules should be considered prior to implementing a dust control program.