Calculating Single Source Visibility Impacts Using a Reactive Puff Model

摘要

This paper describes the use of a puff model with chemistry to conduct visibility impact analysis of power plant emissions on downwind Class Ⅰ areas. The model, SCICHEM, is a state-of-the-science, non-steady-state Lagrangian puff model with complete chemistry treatment, including gas-phase chemistry, aerosol chemistry, and cloud chemistry modules that are based on those used in the U.S. EPA Community Multiscale Air Quality (CMAQ) model. The model represents a continuous plume by a series of Gaussian puffs governed by ordinary differential equations; puff transport is determined by atmospheric turbulence in addition to the mean winds and the terms representing puff interactions handle nonlinearities introduced by turbulent effects and concentration variations. SCICHEM can calculate the short-range and long-range impacts of individual sources and source complexes on downwind concentrations of primary and secondary pollutants, including ozone and fine particulate matter (PM_(2.5)). A post-processor provided with the model is used to perform Class Ⅰ analyses for Prevention of Significant Deterioration (PSD) permit applications, and Class Ⅱ analyses for PSD permits or Minor New Source Review, including changes in background visibility extinction due to the source. The model is publicly available and has been extensively tested with measurements from field studies of power plant plumes. The model is applied for hypothetical sources in 4 different regions in the U.S. with nearby Class Ⅰ areas and the visibility impacts are calculated and compared with impacts calculated using regional photochemical grid models.