WRF-Chem modeling study of heat wave driven ozone over southeast region, India

Abstract

Present study examines how ozone concentration changed under heatwave (HW) condition with emphasis on meteorological parameters in respect to non-heatwave (NHW) days. In this perspective, Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) has been used to simulate the surface O₃ (SfO₃) and maximum temperature (T_max) during NHW (11^th-19^th May 2015) and HW days (21^st-29^th May 2015) over southeast (SE), India. The WRF-Chem simulated meteorological and chemical variables have been evaluated against the ERA5 and CAMS reanalysis dataset. A significant correlation of 55-95% is found for all the meteorological and chemical variables. The influencing parameters shows positive correlation of ozone with temperature, which reaches 75-78 ppbv under HW condition. Day to day trend analysis reveal an increasing pattern of maximum temperature and SfO₃ concentration under HW condition. During HW, mixing of ozone-rich air aloft with near-surface air leading a rise in SfO₃, as indicated by both ERA5 (with a maximum Planetary Boundary Layer Height (PBLH) of 1000 m) and WRF-Chem simulations (1600 m). Furthermore, the diurnal cycle of SfO₃, temperature, PBLH reaches a peak at afternoon, while the other variables like nitrogen oxides (NO_x), Relative Humidity (RH) shows a high concentration at night-time. Overall, WRF-Chem model effectively captures the diurnal fluctuations of SfO₃, NO_x and the meteorological variables during the HW event over the SE, India. Result shows that HW may cause a strong contribution to the rate of increase in SfO₃ (22.17%). Thus, it is required to consider contribution of HW driven ozone when developing long-term strategies to mitigate regional ozone pollution.

Keywords: Air quality; CAMS; Heat wave; Surface Ozone; Temperature; WRF-Chem.