Aerosol levels drop 50% in MumbaiUpdated: Apr 27, 2020 23:30 IST
The concentration of aerosols — tiny solid and liquid particles suspended in air — dropped by half in Mumbai during lockdown, says a study by Ministry of Earth Sciences (MoES).
The study used satellite images of aerosol concentration which showed a 50% decline over Mumbai region and about 65% over Indo-Gangetic plains, said Madhavan Rajeevan, secretary, MoES.
Aerosols include particulate matter (PM) which is a mix of organic and chemical particles that can be harmful if inhaled. Southeast Asian countries generally witness high aerosol concentration between January and April.
“Our satellite study for aerosol optical depth (AOD) from the last week of March to third week of April showed a marked decline in concentration, especially across northern parts of the country, owing to reduction in anthropogenic sources such as industrial and transport related emissions,” said Rajeevan adding that AOD is the measure of light reflected by airborne particles revealing the quantitative aerosol concentration of the whole atmospheric column. “For Mumbai and surrounding areas, the reduction was significant due to drop in transport pollution, which accounts for 30%-35% of all pollution sources.”
Last week, an analysis by System of Air Quality Weather Forecasting and Research (SAFAR), under MoES, showed air pollution hotspots across major cities turned from ‘red’ to ‘green’ zones with clean air quality. Mumbai saw a 60% decline in nitrogen dioxide levels, 49% in PM10 and 45% in PM2.5 concentration during lockdown.
“Our analysis goes a step ahead and assesses the overall atmospheric scenario vis-à-vis falling human-induced emissions,” said Rajeevan.
A similar AOD study done by US-based National Aeronautics and Space Administration (NASA) compared satellite images for the period of March 31 to April 5 from 2016 with that of 2020, which showed air pollution over the Indo-Gangetic plain has dropped to a 20-year low.
Another factor that has been relatively less researched is the declining trend in surface ozone (O3) during lockdown, said Rajeevan. O3 is photochemical oxidant formed when pollutants like volatile organic compounds and oxides of nitrogen chemically react in the presence of sunlight. High ozone concentration, which can be dangerous, is generally witnessed during this time of the year across major metropolitan cities, he said adding that it can lead to a lot of health problems such as asthma and cardiovascular diseases.
“However, O3 levels recorded by SAFAR across Delhi, Mumbai, Ahmedabad and Pune, and a few of the India Meteorological Department (IMD) stations have seen a sharp decline during lockdown due to a drop in human activities,” the MoES secretary said. “SAFAR and IMD have been directed to analyse this data and publish a detailed report.”
Rajeevan also addressed concerns of predicted rise in air pollution after lockdown owing to an expected surge in private vehicles and industrial emissions. “There is a need for cultural and behavioural change post lockdown where we try to increase the frequency of working from home, cycling or walking. While it may not be possible for all, especially those working in factories, construction sites etc, such alterations are essential,” he said.
In addition, the ministry also studied the drop in overall human-induced noise from transport, aviation and construction sectors, which helped scientists detect and identify smaller earthquakes. “During the lockdown, we were able to easily detect earthquakes less than 2.8 or 2.5 on the Richter scale, and in some cases as low as 2.2 magnitude,” said Rajeevan. “Overall, the lockdown is giving us a natural laboratory to understand what background pollution levels are expected to be in cities. When it is over and activities pickup, pollution will rise again, and we need to calibrate and compare levels to come up with effective solutions.”