Comparison of CALMET/CALPUFF Model Results to Existing ISC2 and CTDMPLUS Model Results in a Valley Location

摘要

The Industrial Source Complex 2 (ISC2) and the Complex Terrain Dispersion Model Plus Algorithms for Unstable Situations (CTDMPLUS) models were used in the East Helena, Montana State Implementation Plan (SIP) for the sulfur dioxide (SO_2) National Ambient Air Quality Standard (NAAQS) compliance demonstration, which included the ASARCO lead smelting facility as summarized by Catizone. In the decade since this analysis, there have been additional advances in dispersion models, e.g. the promulgation of CALMET/CALPUFF for near field impacts in complex flow regimes. The topographical and meteorological complexity of the area, along with availability of an existing high-quality meteorological dataset from the SIP analysis, provide an opportunity to evaluate the performance of the CALMET/CALPLUFF modeling system with respect to the previous modeling study.The objective of this independent analysis was to integrate the existing meteorological dataset into CALMET, then run CALPUFF with inputs from the prior modeling study and assess the performance of the various models. The final CALMET wind field properly modeled terrain effects and was able to simulate strong down-slope flows that are known to exist in the area. Similar to Catizone, CALPUFF performance was measured relative to NAAQS design concentrations and monitor values. The CALPUFF model provided similar design concentrations in complex terrain if measured turbulence or turbulence-based dispersion was employed, but Pasquill-Gifford dispersion curves yield overly-conservative results similar to the Rough Terrain Dispersion Model (RTDM). In the flat terrain near the facility, CALPUFF provided much higher impacts than the previous analysis, although at two monitor locations there is some prediction improvement relative to monitored concentrations.