Meteorological modeling with advanced urban canopy fomulations for air quality simulations with CMAQ at neighborhood scales

We present results from a study testing the new boundary layer parameterization method, the canopy drag approach (DA) which is designed to explicitly simulate the effects of buildings, street and tree canopies on the dynamic, thermodynamic structure and dispersion fields in urban areas. The objective is to provide realistic meteorological and air quality modeling of urban areas. This requires replacing the homogeneity in roughness and dominant land use requirements in current models with parameterizations that are based on actual surface distribution of urban morphological features. For this study, we additionally incorporate actual, within-grid land use variation with an advanced urbanized surface layer (soil-atmosphere) model (SM2-U). The implementation into the NCAR-Penn State Mesoscale Meteorological Model, Version 5 (MM5) is called DA-SM-2U/MM5. Requirements for this system include gridded urban canopy parameterizations (UCP) and a canopy layer structure into the model. For this study, a set of UCPs (combination of vertical profiles and surface values), gridded at 1 km was derived from a set of 3-D high resolution (order 1m) buildings and vegetation data. For our study, the data came from airborne lidar measurements, ancillary data from satellites, high altitude photography, as well as detailed residential, commercial and industrial maps.

Standard, coarse scale MM5 runs were performed at 36,12 and 4 km grid sizes; the latter used as IC/BC for the simulations at 1 km grid size. Both the drag approach (DA-SM2U) and for comparation purposes, the standard, roughness based approach (RA)were utilized. Improved meteorological fields were obtained when actual diurnally varying sea surface temperatures from satellite observations were used in place of the standard method. These multi-scale meteorology fields were used for air quality simulations using the USEPA's Community Multiscale Air Quality (CMAQ) Model. Considerable differences in the transport, in the characterization of the urban heat island and ultimately in the air quality simulations are apparent. The limited sets of observations support the use of the advanced approach.