After the World Health Organization declared COVID-19 as pandemic on 11th March 2020, the Indian government adopted a complete phased lockdown strategy starting from 23rd March until 31st May 2020. During this period, road/rail/air traffic, industrial operations and offices were completely restricted except for the essential services. Here, an attempt was made to assess the effect of the lockdown period on five pollutants: PM10, PM2.5, SO2, NOx, and ozone at three sites, Jahangirpuri in North Delhi and Sonipat and Panipat townships located along the national highway leading to north India. These pollutants, except ozone, decreased at all sites during lockdown phase 1 compared to before lockdown. PM2.5 load reduced by 28.1, 33.5, and 40.8 % at Jahangirpuri, Sonipat and Panipat, respectively. PM10 remained either close to or higher than National Ambient Air Quality Standards (NAAQS) due to prevailing high-speed winds. NO2, a precursor for formation of O3 decreased consistently at all sites, except an increase in phase 3 at Panipat whereas O3 consistently increased. This was a paradoxical situation as O3 is formed by photochemical reactions among NOx and volatile organic compounds, which require further detailed studies. These observations indicate that air pollutants decreased specific to the site(s) and pollutant(s). Such restriction can be applied in the future to control air pollution in this region.

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