Analysis of High Ozone Pollution Episode Using WRF/Chem Model Over Megacity Delhi, India

Abstract

Concentration of pollutants namely Ozone (O 3) and its precursors Carbon monoxide (CO) and Nitrogen oxide (NO X) over urban agglomeration Delhi, remain high during favourable meteorological conditions. A regional chemical transport model (CTM) Weather Research and Forecasting (WRF/Chem) model coupled with chemistry has been used to simulate concentration of O 3 and its precursors over Delhi during June 2012 and June 2013 respectively. In 2013, unusually high levels of O 3 and NO 2 were observed during late evening hours. This study investigates the causes and the temporal dynamics of ozone pollution. The simulations show a trend of underestimating maximum and overestimation for minimum ozone concentrations. Hourly O 3 exhibits an overall correlation of 0.51 with the observed values. Daily O 3 maxima are overestimated by about 26% in 2012. In 2013, a correlation of 0.47 was found between hourly observed and simulated values of O 3 with an underestimation of 42% in peak values. Hourly nitrogen dioxide (NO 2) is underestimated within a range of 18% to 28% and 31% to 67% with an overall correlation of 0.60 and 0.31 during 2012 and 2013 respectively. Back trajectory simulations performed using Hybrid single particle Lagrangian Integrated Trajectory (HYSPLIT) model further support the claim that the long-range transport of dust, gaseous and anthropogenic pollutants from the surrounding region affect the concentration level of pollutants in the innermost domain.