Analysis of Ozone Photochemistry over Southern Tropical Megacity, Bengaluru, India

Abstract

Rapid infrastructure development, increased population, shift in land use practices and higher vehicular emissions have all influenced Ozone (O₃ ) production through its precursor gases in southern megacity, Bengaluru, India. We have investigated the photochemistry using hourly measurements of O₃ and associated precursor gases conducted in Bengaluru during January to December 2019. The rate of formation of O₃ is analyzed for Bengaluru for the first time using a photochemical model involving NOx cycle. On the diurnal scale, O₃ showed a midday peak (1200-1500 IST), while its precursors showed a bimodal trend with peaks at 0900 IST and 2100 IST. The photolytic rate constants for $j_{{\text{NO}}_2}$ and $j_{O_3}$ were derived from the tropospheric ultraviolet and visible (TUV) radiation model. Using the photolytic rate constants for $j_{{\text{NO}}_2}$ and $j_{O_3}$ under the triad NO-NO₂ -O₃ , photostationary state (PSS), Leighton ratio (Ф) and its deviations from unity were estimated over Bengaluru. Positive anomalies (Φ > 1) were obtained, and the computed Φ was utilized to determine the total mixing ratios of the peroxy radical (PO₂ ). The seasonal variation in $j_{{\text{O}}_3}$ revealed that in the presence of intense solar radiation and NOx, VOCs, CO and NMVOCs in the mixing layer, O₃ forms photochemically over the surface.