Smog engulfs Delhi NCR as temperature dips In Delhi. Credit: Sunil Ghosh/Hindustan Times via Getty Images
A comprehensive analysis of air quality reveals that levels of nitrogen dioxide gas, a key air pollutant, dropped significantly across all states in India during the lockdown triggered by the COVID-19 pandemic1. But concentrations of ground-level ozone gas increased.
Nitrogen dioxide, generated by industrial processes and vehicle exhaust emissions, forms smog and exacerbates lung diseases such as asthma. Surface ozone at high concentrations is harmful to humans, animals and vegetation.
Scientists at the Indian Institute of Technology Kharagpur in West Bengal monitored changes in air quality before the lockdown, during the lockdown (April–May 2020) and after it was lifted (June-September 2020). They analyzed satellite data and ground-based measurements, and looked at the fluctuating levels of nitrogen dioxide and ground-level ozone.
The researchers, led by Jayanarayanan Kuttippurath, found a large decrease in nitrogen dioxide levels in Delhi, Bangalore and Ahmedabad during the lockdown.
Ozone concentrations increased during the lockdown from what they were pre-lockdown. The Indo-Gangetic Plain had the highest ozone. It also increased in northern and peninsular India. But once the lockdown ended, nitrogen dioxide concentrations gradually increased and ozone levels dipped in most regions.
The researchers say this reciprocal change in ozone and nitrogen dioxide levels during the lockdown is a warning that current regulations in particular sectors are not enough to control pollution. Careful planning is needed to implement any pollution control measure, they say.
