Reduced economic activities during the pandemic-related lockdown had resulted in decrease of air pollution in most parts of India, but, contrary to the general trend, satellite observations show that parts of central-western India and north India showed an increase.
Based on state of the art satellite observations, scientists have identified that regions in the central-western part of India and north India are prone to higher air pollution exposure and hence, are exposed to greater risk of respiratory problems.
With multi-satellite remote sensing of air pollutants having evolved dramatically over the last decade, synergic measurements of satellite and in-situ observation provide a more comprehensive understanding of air pollution episodes. In 2020, a complete nationwide lockdown was imposed over India to impede the spread of coronavirus disease. This enormously disrupted the economy with a single positive side effect, a short-term improvement in the air quality near the surface.
The satellite-based observation of toxic trace gases – ozone, NO2, and carbon monoxide – near the surface and in the free troposphere mostly showed reduction of the pollutants over India.
“However, over some regions like western-central India, some parts of northern India, and remote Himalayas, an increase of ozone and other toxic gases was observed. This could have aggravated respiratory health risks around those regions during the pandemic,” the scientists said.
Scientists at the Aryabhatta Research Institute of Observational Sciences (ARIES), an autonomous institute under the Department of Science and Technology (DST), utilised the EUMETSAT and NASA satellite observations for the years 2018, 2019, and 2020, and investigated the influence of significant cut off of anthropogenic activities on the changes in the vertical and columnar distribution of ozone, CO, and NO2 during the lockdown period.
Published in ‘Environmental Science and Pollution Research’, the study led by senior research fellow at ARIES, Nainital, Prajjwal Rawat along with his research supervisor Dr Manish Naja, showed that ozone, carbon monoxide, and NO2 showed an increase of about 15 per cent over the central-western part of India, a release from the Ministry said.
According to the results, carbon monoxide showed a consistent increase (as high as 31 per cent) of concentration at higher heights during the lockdown. The long-range transport and downward transport from the stratosphere significantly increased ozone concentrations over north India during the lockdown, and remote regions like the Himalayas and coastal cities showed the bare minimum influence of lockdown in air quality, with a tendency to increase in criteria air pollutants.
The ARIES team said that ozone production and loss are constrained through the complex photochemistry involving its precursor gases like NOx and volatile organic chemicals (VOCs). A decrease in its precursor gases could also lead to enhancement of ozone, depending upon the chemical environment. Moreover, ozone concentrations are also altered via ambient meteorology and dynamics, including the downward transport of ozone-rich air from the stratosphere to the troposphere.
According to the ARIES team, this study helped to identify the regions prone to higher air pollution exposure, hence can identify areas at a greater health risk.
The team previously, with scientists from the ISRO, had showed INSAT-3D as a valuable Indian geostationary satellite to study ozone pollutants over India; however, for other criteria air pollutants (i.e., NO2, SO2, CO, VOCs, etc.), India is lacking in space-based observations and need air quality monitoring indigenous satellite in orbit, the release added.