Quantitative Analysis of WRF-Chem Simulated PM2.5 Over Delhi in Winter Season

Abhishek Upadhyay, Pramila Goyal, and Sagnik Dey


WRF-Chem, PM2.5, Meteorology


Exposure of ambient PM2.5 has resulted in about 0.8 million premature mortality in India. Thus PM2.5 is recognised as major pollutant with respect to health concern. In order to analyse the consequences of high PM2.5 concentrations, a detailed quantitative information of PM2.5 is required. Due to lack of diverse monitoring stations of PM2.5 in Delhi, the alternative methods like satellite data and air quality modelling are being used for such purposes. WRF-Chem is an online coupled chemical transport model, which has been used to simulate PM2.5 concentrations over India. The simulation has been made by using meteorological and emission data of different sources over India, winter season (DJF) has been selected for this simulation as the previous studies has shown the adverse impact of winter meteorology on air pollutant’s concentrations. Generally calm wind, less mixing and low dispersion prevail in winter season in India. The emissions of anthropogenic aerosol Black carbon (BC), Organic Carbon (OC) and Sulphur dioxide (SO2) have been taken from GOCART emission inventory of year 2006 and from RETRO and EDGAR. The initial and boundary meteorological conditions have been taken from GFS in this simulation. The simulations have shown the high concentrations of PM2.5 in Indo-Gangatic basin compared to other regions. The high concentration in this region is due of its geographical features and meteorological parameters. The model is capable to capture the high concentration in cities like Delhi, Kolkata etc. Delhi has been reported one of the most polluted city of world and the model captures it highest as a hotspot with average concentration of around 96.5 µg/m³, which is more than double of NAAQ standard. On the study period, the average observed concentration is found to be 123 µg/m³ at ITO monitoring station in Delhi, this shows that model is quantitatively under predicting. Diurnal analysis of concentrations shows a peak in concentration at early morning hours, which reduces when day advances and again in the later stage of day, it starts building up and remains almost constant in night. Vertical distribution of PM2.5 over Delhi shows the presence of PM2.5 concentrations up to 2km height and up to 500m when it is present in harmful amount (>60 µg/m³).

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