Simulation of trace gases over the Indian domain: evaluation of the SILAM model

The global-to-meso-scale dispersion model System for Integrated modeling for atmospheric composition (SILAM) has been implemented over the Indian region for operational air quality forecast. The regional SILAM model generates 96 hours forecasts over a domain at 3kmx3km horizontal resolution. The meteorological forcing is provided from the operational 3 km WRF model. The initial condition is derived from the forecast of the previous cycle of the regional SILAM model and the boundary condition is supplied from the global version of the model. Predicted mixing ratios of trace gases in the atmosphere are compared with the available ground-based observations over the North-Western Indian domain for two consecutive years (2021 and 2022). The paper presents a comprehensive evaluation of SILAM model performance against the observed surface data for trace gases (Surface O₃, NO_2, and CO). The spatial and temporal variability of trace gases over the domain is well simulated by the model.  The model was also able to catch well the seasonality of trace gases (Surface Ozone, NO₂, and CO) over the selected Indian domain. The forecast is found to be very skillful for trace gases and has been helping the air pollution control authorities in India to make informed decisions.