Seasonal day-night variation of ozone $(\mathbf{O}_{\mathbf{3}})$ in an eastern urban site, Bhubaneswar and its association with precursors ($\mathbf{NO}_{\mathbf{x}}$ and NMHC): More sensitivity of $\mathbf{O}_{\mathbf{3}}$ to NMHC than $\mathbf{NO}_{\mathbf{x}}$

Abstract

The study reports on the relationships between surface ozone $(\mathrm{O}_{3})$ and its principal precursors, nitrogen oxides $(\text{NO}_{\mathrm{x}})$ and non-methane hydrocarbons (NMHCs), due to their scientific importance, in addition to the implementation of policies aimed at reducing $\mathrm{O}_{3}$ pollution. Measurements and analyses of the mentioned trace gases revealed correlations between them in a city in Eastern India, Bhubaneswar, from October 2021 to May 2022. It demonstrates sensitivity to NMHCs when compared to $\text{NO}_{\mathrm{x}}$ as a whole. The $\text{NMHC} /\text{NO}_{\mathrm{x}}$ ratios confirm NMHC dominance in pre-winter and winter, while $\text{NO}_{\mathrm{x}}$ dominance is confirmed in summer (post-winter). A multivariate regression approach was also utilised to develop a model to predict $\mathrm{O}_{3}$ concentrations based on precursor concentrations, which offers significant information on the precursors ($\text{NO}_{\mathrm{x}}$ and NMHCs) that contribute to $\mathrm{O}_{3}$ synthesis. The slope and intercept derived from the prediction model indicatethat, while these precursors can explain a significant portion of the concentration, there are other unidentified contributions from other precursors and some mysterious chemical activities going on (especially at night) that has remained unrevealed. Thus, the study emphasizes the necessity of identifying additional precursors via other methodologies such as remote sensing and limiting NMHC emissions, which could play a crucial role in both understanding and lowering ground-level ozone in the current scenario.