Numerical case study of spatial-temporal variations of surface nitrogen dioxide and ozone concentrations over Tehran using WRF-Chem model

Document Type : Research Article


1 M.Sc. graduate/ Institute of Geophysics, University of Tehran

2 Associate professor/Institute of Geophysics, University of Tehran

3 University of Tehran

4 Assistant Professor, Atmospheric Sciences Research Center, Iranian National Institute for Oceanography and Atmospheric Science, Tehran, Iran


This study aimed to evaluate the performance of the WRF-Chem model in estimating the amount of NO2 and O3 in the Tehran region during recent summers (2019 to 2021). First, by investigating the NO2 and O3 concentrations (including hourly and daily averages) from the Air Quality Control stations in Tehran city, the days of maximum ozone concentration in summer were selected to run the Weather Research and Forecasting Chemistry (WRF-Chem) model. The simulations were performed for 36-hours, and the first 12 hours were considered spin-up time. The simulations were conducted using two nests with 30 and 10 km resolution, respectively, so that the second domain covered the Tehran region. Also, in the model settings, 35 levels are considered in the vertical direction, and the pressure at the highest level is 50 hPa. In these simulations, the Global Forecast System (GFS) data with a spatial resolution of 0.5 degrees and 6-hours time step was used as the initial and boundary conditions. Physical parameterization schemes that performed well in previous studies in simulating atmospheric pollutants were used in the model configuration. The Rapid Radiation Transfer Model (RRTM) and the Goddard Shortwave scheme have been used to simulate the long- and short-wave radiation, respectively. The Monin-Obukhov scheme has been used to simulate surface layer fluxes and the Yonsei University (YSU) PBL scheme has been used to simulate boundary layer fluxes. The land surface fluxes were obtained from the NOAH model. In addition, the Grell and Devenyi ensemble scheme has been used to parameterize moist convection and the WRF-Single-Moment-Microphysics 5-class scheme has been used to parameterize microphysical processes. The RADM2 chemical mechanism was used in this configuration. The PREP–CHEM–SRC emissions preprocessor (version 1.5) has been used to produce anthropogenic, biogenic and biomass burning gridded emission over the user-specified simulation domain. The global emission data comes from RETRO and GOCART background emission data. Anthropogenic emissions of greenhouse gases and air pollutants including CO, NH3, NOx, SO2, NMVOC and CH4, were derived from the EDGAR_HTAP v5.0 Emissions Database 0.1 horizontal resolution. Primary anthropogenic aerosol emissions of BC, OC and DMS from GOCART model databases are used. Biogenic emissions were calculated using the MEGAN model. Also, 3BEM fire emissions which are prepared using PREP-CHEM-SRC are used. Evaluation of the results of WRF-Chem model simulations was performed by two methods of horizontal distribution and station evaluation. The evaluation results of the simulated horizontal distribution of NO2 and the one is taken from the OMI satellite data showed that considering the slight spatial displacement in the model results, the WRF-Chem model had good performance in simulating the maximum surface NO2 in all cases. Considering the spatial distribution of O3 in the days of maximum ozone pollution, the model has simulated areas of maximum ozone in the Tehran. However, in most cases, no comment can be made on the accuracy of the simulated maximum areas because of the satellite transits. The station evaluation showed an overestimate of ozone concentration and a high underestimate of NO2 concentration by the WRF-Chem model.


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