Analysis of the photochemical production of ozone using Tropospheric Ultraviolet-Visible (TUV) Radiation Model in an Asian megacity

Abstract

A study of surface layer ozone (O3) and its primary precursors (NOx = NO + NO2) was carried out at Kolkata (22° 33′ N, 88° 30′ E), an urban site in eastern India from October 2010 to April 2011. A simple NOx cycle-based photochemical model for the net rate of production of tropospheric ozone was studied. Photolytic rate constants for NO2 (\( {j}_{{\mathrm{NO}}_2} \)) were estimated using the Tropospheric Ultraviolet and Visible (TUV) Radiation Model-Version 4.1. Relationships between predicted and measured ozone data were found to be sensitive with respect to time of the day. A correlation between the observed ozone and \( {j}_{{\mathrm{NO}}_2} \) during some case study days in the morning (R2 range, 0.34 to 0.96) and the late afternoon (R2 range, 0.79 to 0.99) implies that the NOx chemistry is predominant due to enhanced automobile emissions during the peak traffic hours. VOCs and some peroxy radicals play a vital role in the chemistry of ozone production (net). Computed air mass backward trajectories using HYSPLIT model established the source and transport pathways of the trace gases. The results obtained on different days indicate the importance of advection of gases from both continental as well as marine air mass on case-specific circumstances. Tropospheric columnar NO2 outputs were also compared to ground-based measurements, and these point towards a good regional contribution of NO2.