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  • Writer's pictureArpit Shah

Air Pollution in India during Coronavirus Lockdown

Updated: Jun 13, 2023

With ESA's Copernicus Sentinel-5 Precursor (S-5P) satellite, it is now possible to access near-real-time updates pertaining to atmospheric conditions and trace gases above virtually any region of our planet, on a daily basis. Learning about Copernicus platform from University of Luxembourg's MOOC, I am in awe about this ambitious and abundantly useful Earth Observation Programme.


While the Covid-19 related nationwide lockdown is unfortunate, it presented a suitable opportunity to use their data to visualize and compare the changes in pollution levels in India on a Y-o-Y basis to see the difference between periods of with and without significant economic activity. I was fascinated too read news reports on residents of Jalandhar being able to view the Himalayan range from their terraces as well as on clear blue skies greeting residents of New Delhi.


Below is the output for for Tropospheric Nitrogen Dioxide (NO2) Vertical Column Density (VCD) levels (2020 April vs 2019 April) and my observations. NO2 is a major & harmful air pollutant- Burning of fuel, be it from power plants or from vehicles, being its common emission source.


I have used S-5P L2 Offline Product for this comparison and the scale is from a minimum of 0 NO2 molecules per centimeter square to a maximum of 4.52*10^15 NO2 molecules per centimeter square.

Tropospheric NO2 in India (excl. North Eastern states) - 2020 (lockdown) vs 2019 comparison - Output extracted from Sentinel-5P satellite observations
Figure 1: Tropospheric NO2 in India (excl. North Eastern states) - 2020 (lockdown) vs 2019 comparison - Output extracted from Sentinel-5P satellite observations

- As you would discern, there has been a considerable drop in NO2 levels, the biggest benefactor being North India followed by West India.


- NO2 levels in South India has reduced considerably as well.


- However, East India (excluding the North-East as it was part of another satellite imagery product) still has numerous NO2 hotspots, albeit of a lower intensity. This can be attributed due to the mining / manufacturing operations. Being part of the essentials supply chain, these industries continue to remain operational despite the nationwide lockdown. However, one can still infer that the economic activity has also reduced here, resulting in lower pollution levels. The hotspots are a cause of concern nonetheless, given the looming climate crisis. What measures can you think of to mitigate this risk on an individual or at an organizational capacity?


- Notice the red spot(s) on Gujarat coastline. Those are located around the petroleum refinery area in Jamnagar. Also, notice the tiny red spot on Sri Lanka. Exactly where Colombo (its economic hub) is located. The satellite data is so illuminating! What else could you infer?


- However, please note that the image is not depicting Surface NO2 levels commonly measured in ppm (parts per million). These are above-surface NO2 levels i.e. located in our troposphere and factors such as wind speed and temperature can affect the concentration and spread of the gas.


- Apart from Nitrogen Dioxide, the TROPOMI instrument on-board Sentinel-5P monitors Sulphur Dioxide, Ozone, Aerosols, Carbon Monoxide, Methane among other trace gases. Which one would you like to measure and why?

As you might concur, mapping is a very useful medium to depict and to analyze vast quantities of geodata. Imagine being given a spreadsheet with NO2 levels for each co-ordinate. It would be difficult to infer much from it.
 

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Regards,

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