Pollution levels (Trop. NO2) during Lockdown

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

Due to the unfortunate Covid-19 related nation-wide lockdown, this presented a suitable time to use the data to visualize and compare the changes in pollution levels on a year on year basis. After all, I too was fascinated reading about the news reports about residents of Jalandhar being able to view the Himalayan range as well as about clear blue skies above New Delhi.

Below is the output for for Tropospheric Nitrogen Dioxide (NO2) Vertical Column Density (VCD) levels and my observations/inferences. NO2 is one of the major harmful air pollutants - Burning of fuel - be it from power plants or from vehicles - being the common emission source.

I have used S5P L2 Offline Product for this comparison and the scale is from a minimum of 0 NO2 molecules per cm square to a maximum of 4.52*10^15 NO2 molecules per cm square.

- As you would discern, there has been a considerable drop in NO2 levels, the biggest benefactor being North India / NCR region followed by West India. (The top image is from 2020 and the bottom image is from 2019).

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

- However, East India (excluding North East) still has numerous hotspots albeit of a lower intensity. This can be due to the presence of fossil fuel / mining / alloys / manufacturing operations that are located in this region. Being part of the essentials supply chain, these industries continue to remain operational. However, one can infer that the production levels have reduced resulting in slightly lower pollution levels. The hotspots are a cause of concern nevertheless, and evidence enough to take action to reduce it in the future. What measures can you think of, to mitigate this risk on an individual or 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 is located. The satellite data is so precise! 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 the surface NO2 levels i.e. located in our troposphere and factors such as wind speeds can affect the concentration and spread of the gas under observation.

- 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 plot and observe and why? Feel free to share your observations or queries in the comments section.

As you may concur, mapping is a very useful method in depicting and analyzing vast quantities of data (geo-data in this case). Imagine being given a spreadsheet with NO2 levels for each co-ordinate. It would be very time consuming to plot and make sense of the data.

The beauty about the latest advancements in mapping is that it can be clubbed with publicly available and/or internally compiled data-sets as well as with new technologies to create custom solutions for commercial enterprises.

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Regards,

Arpit