The air pollution levels have shown a significant decline worldwide since the outbreak of the novel coronavirus. On March 22, the average pollution level of nitrogen dioxide (NO2) – a dangerous pollutant responsible for thousands of deaths every year – was at its lowest in India’s metro cities. This was the day when people observed a nationwide ‘Janata Curfew’ after an appeal by Prime Minister Narendra Modi to stay at home.

This fact has been explained by two air pollution experts, Lauri Myllyvirta and Sunil Dahiya, after analysing the pollution levels in the last four years. The cities included in the study were Delhi, Mumbai, Chennai, Kolkata, Bengaluru, Ghaziabad, Howrah, Hyderabad, Jaipur, Lucknow, Noida and Patna.

NO2 is mainly emitted by vehicles and thermal power plants and it is responsible for 3.5 lakh new cases of child asthma and 16,000 premature deaths every year in India. The country recorded the lowest NO2 levels on an all-India scale last Sunday, when data from all operating continuous ambient air quality monitoring systems (CAAQMS) across cities was averaged.

The rise of nitrogen dioxide also causes the surge of PM 2.5 level in the air through secondary particulate formation. PM 2.5 is another highly hazardous pollutant behind several health problems like asthma, bronchitis, blood pressure and nervous disorder.

“What’s noticeable is that the fall in pollution levels is not led by the largest metropolises, where the pollution grabs most attention from policymakers and media. This indicates that the fall in pollution levels is driven by broader economic factors more than air quality policies, which currently are highly localized,” says the study done by the two experts.

According to World Air Quality Report, 2019 – which was compiled by IQ Air Visual – among the 30 worst polluted cities of the world, 21 are from India. Ghaziabad is the most polluted city of the world and Delhi is worst polluted capital of any country.

The analysis reveals that average NO2 level of all cities recorded by CAAQMS was approximately 20 microgram per cubic metre which was the record lowest since 2017. The average NO2 level of all cities last week was around 32 microgram per cubic metre.

“Other dangerous pollutants, PM 2.5 and PM 10, also dropped steeply (on March 22) but didn’t break records. These pollutants have much longer atmospheric lifetimes and cars are a much smaller contributor to their levels,” write Mallyvirta and Dahiya in an article published in the Centre for Research on Energy and Clean Air (CREA) – a research organisation focussing on the trends, causes, and health impacts of air pollution.

“While most cities recorded low levels of PM 2.5 as well, cities in northern India still have higher levels of PM 2.5 concentrations (Delhi 74, Ghaziabad 101, Noida, 57 and Patna 77 microgram/m3) indicating that the transport sector is not the only major source leading to deteriorating air quality, in absence of major portion of transportation in cities as well as biomass burning season not being around,” Dahiya told News 18.

To prevent the spread of the highly contagious coronavirus, India is now observing a complete shutdown for the next three weeks, except the delivery of essential services. This may show further dip in pollution in the coming days. But to deal with the problem of poor air quality, the country needs a better plan as pollution will rise again when the pandemic is over and economic activity and daily life returns to normal.

“The COVID-19 crisis is resulting in widespread human suffering around the world. Air pollution levels are plummeting in many countries as an unintended result of measures against the virus; this should not be seen as a 'silver lining', but it does show how normalised the massive death toll from air pollution has become. Once the COVID-19 crisis is over, there are far more effective ways for governments to address air pollution than shutting down large parts of the economy, such as enforcing emissions standards for large polluters,” Dahiya told News 18.