Implementation and evaluation of plume volume molar ratio method (PVMRM) in AERMOD

During New Source Review modeling of proposed major sources of oxides of nitrogen (NOx), maximum impacts are often predicted to occur close to the source. Current modeling guidance consists of a tiered approach of screening techniques that may be overly conservative in estimating the fraction of nitrogen dioxide (NO2) in these plumes. Hanrahan (1999a) proposed a new technique called the Plume Volume Molar Ratio Method (PVMRM) that simulates the primary chemical mechanism for conversion of NO to NO2 within the plume in order to better estimate the ambient concentration of NO2. As with one of the existing techniques called the Ozone Limiting Method (OLM), the PVMRM approach limits the conversion of NO to NO2 based on the amount of ozone available. However, the PVMRM approach limits the conversion based on the amount of ozone within the volume of the plume. The NO2/NOx conversion ratio is therefore coupled with the dispersion of the plume. The PVMRM approach also incorporates a technique for merging plumes from nearby sources for purposes of calculating the NO2/NOx ratios. Hanrahan implemented the PVMRM approach as a postprocessor for the ISCST3 model, and evaluated the performance of the model using two aircraft studies, two long-term field studies, and a large eddy simulation (LES) model (Hanrahan, 1999b). This paper documents the adaptation and implementation of the PVMRM approach in the AERMOD dispersion model (Cimorelli, et al, 2004). The results of evaluating the performance of PVMRM in AERMOD against the same data bases used in the ISCST3 evaluation, and results from a sensitivity analysis of AERMOD with PVMRM are also presented.

Cimorelli, A. J., S. G. Perry, A. Venkatram, J. C. Weil, R. J. Paine, R. B. Wilson, R. F. Lee, W. D. Peters, R. W. Brode, and J. O. Paumier, 2004: AERMOD: Description of Model Formulation. EPA 454/R-03-004. U. S. Environmental Protection Agency, Research Triangle Park, NC.

Hanrahan, P.L., 1999a. “The plume volume molar ratio method for determining NO2/NOx ratios in modeling. Part I: Methodology,” J. Air & Waste Manage. Assoc., 49, 1324-1331.

Hanrahan, P.L., 1999b. “The plume volume molar ratio method for determining NO2/NOx ratios in modeling. Part II: Evaluation Studies,” J. Air & Waste Manage. Assoc., 49, 1332-1338.