Simulating the influence of convective decay parameterization for a case study in Houston, TX

Abstract

In this study, we performed meteorological and chemical sensitivity studies employing two different Weather Research and Forecasting model with Chemistry (WRF-Chem) simulations: one with the standard Planetary Boundary Layer (PBL) Yonsei scheme (YSU), and one with a modified YSU PBL scheme proposed in a previous work. The WRF-Chem results were compared to observational temporally highly resolved boundary layer data obtained during the Vertical Mixing Experiment (VME) which was part of the 2006 TexAQS-II radical and aerosol measurement project (TRAMP) campaign. The analysis of meteorological variables indicates that in particular during the morning transition of the PBL (at 10 CDT), which is a critical time period for pollutant dispersion, the statistical scores presented improvements for all variables, when the modified YSU PBL scheme was used. Overall, the sensitivity of pollutant concentrations in the WRF-Chem model towards the representation of diffusion processes of the evening transition in the vertical mixing calculation showed reasonably good agreement with observations during the VME period. The comparison of vertical profiles of O3 showed appreciable differences (up to ∼ 8 ppbv) between the standard and modified YSU scheme during the morning hours; in the afternoon, the modified YSU presented only a slight improvement in the simulation of O3 precursors concentrations such as CO and NOx. These improvements were possible without a significant increase in complexity or computer time. However, the model still oversimplifies the vertical mixing within the PBL, and uncertainties in the turbulence structure of the PBL in the WRF-Chem still remain.