Sensitivity of PBL schemes of WRF-ARW Model in Simulating Boundary Layer Flow Parameters and coupling with AERMOD in the Dispersion of NOX over a Tropical Station

Abstract:

Meso-scale atmospheric circulations play important role in air pollution transport and local air quality issues. Rapid industrialization and urbanization are leading to increased air pollution. In most of the metro cities, it is necessary to find the dispersion and ground level concentration (GLCs) of the pollutants emitted from the industries. In the present study AERMOD model has been used for simulation of pollutant dispersion over Nagpur, India. This model requires surface and upper air meteorological observations and various PBL parameters with good temporal resolution in the stand alone mode and mostly not available over India. To fill this gap, in the present study uses WRF-ARW model in getting these boundary layer parameters then will be offline coupled with AERMOD dispersion model. In the study we modified a pre-processor coupler for offline these models. High resolution simulations are conducted with triple nested domains having horizontal resolution of 27, 9 and 3 km; 27 vertical levels by using the 1x1 degree NCEP Final Analysis meteorological fields for initial and boundary conditions. In the study, eight fair weather days in winter and pre-monsoon season (January and April 2009). Sensitivity experiments of WRF-ARW model are conducted with two non-local [Yonsei University (YSU), Asymmetric Convective Model version 2 (ACM2)] and three local turbulence kinetic energy (TKE) closure [Mellor- Yamada Nakanishi and Niino Level 2.5 PBL (MYNN2), Mellor-Yamada-Janjic (MYJ), and quasi-normal scale elimination (QNSE)] turbulence diffusion parameterizations to study the evolution of PBL parameters and thermodynamic structure during the study period for providing the better meteorological parameters to AERMOD model. Sensitivity studies of PBL parameterization schemes after validation and statistical analysis reveal that the non-local PBL scheme YSU and local scheme MYJ could capture the characteristic variations of surface meteorological variables, vertical atmospheric structure as seen in observations. These simulations are coupled with AERMOD model is employed to evaluate the dispersion of NO_X. After validating with monitored air quality data it is found that the integrated model with YSU followed by MYJ schemes performed better.

Keywords: WRF, AERMOD, Dispersion, Planetary Boundary Layer