The novel SARS-CoV-2 coronavirus that emerged in the city of Wuhan, China, last year has since become the COVID-19 pandemic across all continents. To restrict the spread of the virus pandemic, the Government of India imposed a lockdown from 25 March 2020. In India, Kannur district was identified as the first “hotspot” of virus transmission and a “triple-lockdown” was implemented for a span of twenty days from 20 April 2020. This article highlights the variations of surface O₃, NO, NO₂, CO, SO_2, NH₃, VOC’s, PM₁₀, PM_2.5 and meteorological parameters at the time of pre-lockdown, lockdown and triple-lockdown days at Kannur town in south India using ground-based analyzers. From pre-lockdown days to triple-lockdown days, surface O₃ concentration was found to increase by 22% in this VOC limited environment. NO and NO₂ concentrations were decreased by 61% and 71% respectively. The concentration of PM₁₀ and PM_2.5 were observed to decline significantly by 61% and 53% respectively. Reduction in PM₁₀ during lockdown and triple-lockdown days enhanced the intensity of solar radiation reaching the lower troposphere, and increased air temperature and reduced the relative humidity. Owing to this, surface O₃ production over Kannur was found to have increased during triple-lockdown days. The concentration of CO (67%), VOCs (61%), SO₂ (62%) and NH₃ (16%) were found to decrease significantly from pre-lockdown days to triple-lockdown days. The air quality index revealed that the air quality at the observational site was clean during the lockdown.

Ozone at ground level (O₃) is an air pollutant that is formed from primary precursor gases like nitrogen oxides (NOx) and volatile organic compounds (VOCs). It plays a significant role as a precursor to highly reactive hydroxyl (OH) radicals, which ultimately influence the lifespan of various gases in the atmosphere. The elevated surface O₃ levels resulting from anthropogenic activities have detrimental effects on both human health and agricultural productivity. This paper provides a comprehensive analysis of the variations in surface O₃ levels across various regions in the Indian subcontinent, focusing on both spatial and temporal changes. The study is based on an in-depth review of literature spanning the last thirty years in India. Based on the findings of the latest study, the spatial distribution of surface O₃ indicates a rise of approximately 50–70 ppbv during the summer and pre-monsoon periods in the northern region and Indo-Gangetic Plain. Moreover, elevated levels of surface O₃ (40–70 ppbv) are observed during the pre-monsoon/summer season in the western, southern, and peninsular Indian regions. The investigation also underscores the ground-based observations of diurnal and seasonal alterations in surface O₃ levels at two separate sites (rural and urban) in Kannur district, located in southern India, over a duration of nine years starting from January 2016. The O₃ concentration exhibits an increasing trend of 7.91% (rural site) and 5.41% (urban site), ascribed to the rise in vehicular and industrial operations. This review also presents a succinct summary of O₃ fluctuations during solar eclipses and nocturnal firework displays in the subcontinent.

Atmospheric ozone (O₃) in the surface level plays a central role in determining air quality and atmospheric oxidizing capacity. In this paper, we review our comprehensive results of simultaneous measurements of surface ozone (O₃) and its precursor gas (NOx) and weather parameters that were carried out continuously for a span of six years (January 2013–December 2018) at a typical rural coastal site, Kannur (11.9° N, 75.4° E) in South India. Surface O₃ concentration reached its maximum during daytime hours and minimum during the night time. The influence of solar radiation and water content on variations of O₃ are discussed. A Multi-Layer Perceptron (MLP) artificial neural network technique has been used to understand the effect of atmospheric temperature on the increase in O₃ over the past six years. This has been found that temperature has been a major contributor to the increase in O₃ levels over the years. The National Centre for Atmospheric Research- Master Mechanism (NCAR-MM) Photochemical box model study was conducted to validate the variations of O₃ in different seasons and years, and the results were shown to be in good agreement with observed trends.

This study looked at the variation in air quality during the periods of fireworks as assessed from the change in ambient concentrations of air pollutants like particulate matter (PM₁₀), O₃, and NO₂ for pre-, post-, and Vishu days for four consecutive years in 2015, 2016, 2017, and 2018 in Kannur, India. Enhanced levels of O₃, NO₂, NO, and PM₁₀ were observed during the intense usage of fireworks. The concentration of metals in PM₁₀ increased and the percent increase was found to be different for metal traces. A pronounced increase in the aerosol optical depth (AOD) in the lower wavelength region of solar radiation reveals the abundance of fine mode particles. The concentrations of O₃ and NO₂ were observed to increase by more than 100% on Vishu day than the control days for the observational period. Simulation using the National Center for Atmospheric Research (NCAR) Master Mechanism photochemical box model indicates a more than 100% enhancement in NO₂ photolysis rates during the fireworks episode, which leads to a 100% increase in the surface ozone production. Observations as well as model simulations indicate that the enhanced photochemical ozone production from NO₂ photolysis is possibly the main driver of ozone production during the Vishu at this site. The air quality index (AQI) revealed the deterioration of air quality at the observational site during the period of Vishu.