General formulation of characteristic travel distance for semivolatile chemicals in a multimedia environment

A relatively simple but informative methodology is introduced to determine the characteristic travel distance (CTD) for airborne semivolatile organic pollutants. The CTD is derived from a moving Lagrangian cell (representing the air) and a nonmoving compartment (representing soil or vegetation). The methodology is expanded to a fugacity based steady-state multimedia environmental framework including air, vegetation, and soil. Chemical transformations in air as well as partitioning to, and transformation in, vegetation and soil are considered. Concentrations are determined by interactions among the compartments and transformation rates. This method is most appropriate for continuous, large nonpoint emissions (such as emissions from an urban airshed). A case study for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) reveals that the CTD is on the same order of magnitude as the typical distance between urban centers. Vegetation is important for defining the regional transport processes for TCDD.