TA6 Atmospheric Transport and Fate
202 Oregon Ballroom
8:00 AM - 12:00 PM, Tuesday
() Atmospheric Dispersion versus Compartmental Mass Balance: A Model Comparison.
Maddalena, R1, Burch, D2, MacLeod, M1, Lee, R2, 1 Lawrence Berkeley National Laboratory, Berkeley, California, USA2 ICF Consulting, Research Triangle Park, North Carolina, USA
ABSTRACT- Two fundamentally different approaches have developed over the past several decades for modeling chemical fate in the environment. Receptor based models of atmospheric dispersion phenomena were originally developed for criteria pollutants. With the dispersion approach, deposition to surfaces is generally considered to be a one-way process where re-emission of deposited material from surfaces back to air is ignored. In contrast, the compartment based mass-balance models of multimedia fate and transport were developed for persistent and regional pollutants where two-directional intermedia transfer at the air/surface interface is included. Both approaches are used to support regulatory decisions and both are currently being used to model the full range of chemical property space. However, we currently lack a systematic comparison of these alternate modeling approaches. In this paper we compare the two approaches across a wide range of physical/chemical properties. An illustrative case study with a simple mass balance model is first used to identify regions of parameter space where re-emission from surfaces might influence environmental fate. We then use the ISCST3 and TRIM.FaTE models as surrogates for the dispersion and mass balance approaches, respectively, to evaluate how these approaches compare for specific combinations of values for the octanol/air (Koa) partition coefficient, the octanol/water (Kow) partition coefficient and environmental persistence. Where differences are found we identify the mass transfer processes and chemical properties that contribute to these differences. We conclude with a site-based comparison of the two modeling approaches for 12 chemicals (including seven polycyclic aromatic hydrocarbons (PAHs), three mercury species, and two dioxin-like compounds) at two different lead smelting facilities. We find that if chemical specific properties are used in the dispersion modeling, then the air concentrations and deposition rates predicted by the two approaches are generally similar.
Key words: ISCST3, TRIM.FaTE, mass balance modeling, dispersion modeling