Clear blue skies, AQI at 41 bring some good news
NEW DELHI: Delhi woke up to clear blue skies yet again on Saturday, Day 4 of the 21-day lockout announced by the government to halt the spread of Covid-19.
Clear blue skies have become the norm rather than the exception in the National Capital Region (NCR) around Delhi for the past week. Data, too, shows a sharp decline in pollution.
Morning and evening peaks in the level of PM 2.5 (particulate matter 2.5, or fine,
respirable pollution particles) have flattened out in the four days since the lockdown came into force, according to a new analysis by the Centre for Science and Environment (CSE). The air quality index for the Capital, according to the Central Pollution Control Board’s 4pm bulletin was 45, which falls in the “good” zone -- rare in a city where a reading in the “poor ” category is otherwise considered good. The reduction in nitrogen dioxide (NO2) concentrations is even more pronounced because the major source of NO2 emissions are vehicles , which have gone off the roads, and industries, which have been ordered to close to reduce the risk of infection.
The hourly pollution trend in Delhi and in the neighbouring cities of Gurugram, Faridabad, Noida and Ghaziabad analysed by CSE used to be influenced by traffic peaks in the mornings and evenings, a factor hasn’t been relevant in the past four days.
For example, in Delhi the daily peak PM 2.5 concentrations has declined on a lockdown day by about 57% compared to a regular day and the peak on the “Janta Curfew” day (Sunday, March 22) dropped by about 24% compared to a regular day. The peak concentrations of NO2 dropped by 66% on a lockdown day compared to a regular day and by 32% on the people’s curfew day. The so-called Janta Curfew was called for by Prime Minister Narendra Modi as a sort of a trial in social distancing and selfisolation. The lockdown was announced two days later.
“This analysis brings out the pronounced effect of traffic on hourly pollution trend and on daily exposures to toxic vehicular pollution. With traffic minimised, hourly trends plummet. This is sharply evident in NO2 trends,” CSE said in its analysis.
The fact that the impact was comparatively lower on Janta Curfew may have had to do with its shorter duration of 14 hours, the study said. “Subsequent lockdown is more rigorous and pertains to 24 hours with curfew rules in place,” it said. There’s also the cumulative effect to be taken into account.
The main source of NO2 emissions is fuel combustion by vehicles and industries. NO2 is more reactive than PM 2.5, and being exposed to high NO2 emissions even for a short duration can aggravate respiratory disease particularly asthma, according to the US Environment Protection Agency.
Globally, four million new child asthma cases are attributable to NO2 pollution a year; 64% of these occur in urban centres, according to a study published in Lancet Planetary Health.