Evaluations of benzene impacts of a coke plant in a complex-topography urban area with the RAMS-CALMET-CALPUFF modelling system

Abstract

The RAMS-CALMET-CALPUFF modelling system, together with observations, has been used to analyse the benzene impacts of a coke plant located in a narrow river valley over a nearby urban area in the estuary of Bilbao. The initial aim of this study was to set up a methodology suitable for dispersion studies in very complex areas, where pollutant dynamics are highly affected by mesoscale processes. Emphasis was put on the validation and improvement of the simulated meteorology. High spatio-temporal resolution meteorological simulations were performed with the non-hydrostatic mesoscale meteorological model RAMS, initialized with NCEP reanalysis data, for two ten-day periods. Results were validated against data recorded both at surface stations and by a wind profiler radar (WPR). Comparisons against the WPR revealed inaccurate NCEP data for one of the periods. Alternative nudging with ECMWF ERA-Interim data improved the results. The RAMS output was downscaled from 1 km to 250 m resolution with the CALMET diagnostic model. The main flows that affect dispersion in the area were mostly well simulated, but important disagreements with observed drainage flows were found for some days. The assimilation of surface meteorological observations into CALMET, greatly improved the results. The meteorological fields were input into the CALPUFF non-steady-state puff dispersion model for dispersion simulations. The actual daily cycles of ground level benzene were well reproduced but concentration levels were underestimated. The availability of good meteorological observations in the area and good emission inventory has shown to be of prime importance. © 2013 WIT Press.