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Air Quality in Lockdown

Analysis of air quality across India during the lockdown using Sentinel 5

Is clean air a luxury that only people living in rural India have? As the world battles this unprecedented crisis which is not a third World War but rather a virus, we explore the environmental impact humans have left on the planet.

Still from a busy metropolitan during the lockdown. Image Credits: Reuters

The impact of COVID-19 has caused wide-scale disruptions to our economy and our social fabric. It has forced the government across the world to put the countries in lockdown, restricting the movement of people, like a dystopian world we imagined just a year back but a reality today.

While we sit at our home, praying the lockdown opens up so we can meet and hug our friends, there is some good news that air pollution is down. 3 million people die each year from ailments caused by air pollution, and that more than 80% of people living in urban areas are exposed to air quality levels that exceed safe limits. The situation is worse in low-income countries, where 98% of cities fail to meet WHO air quality standards. With 10 of 15 Indian cities appearing in the worst polluted city, we decided to explore whether restricting human activities helps?

Air pollution is usually measured by PM2.5 and PM10. In this post, we explore the two main sources of pollution, NO2 (Nitrogen dioxide) and SO2 (Sulfur dioxide).

NO2 (Nitrogen dioxide)

The primary source of NO2 is burning off fuel mainly from emissions from cars, trucks and buses, power plants, and off-road equipment.

Breathing air with a high concentration of NO2 can irritate airways in the human respiratory system. Short period exposure includes aggravated respiratory diseases, especially asthma (2 crore patients in India).

NO2 along with other NOx reacts with other chemicals in the air to form both particulate matter (PM) and ozone (O3).

The environmental effects include making the air hazy, effectively reducing visibility along reacting with water and other gases in the environment resulting in acidic rain.

SO2 (Sulfur dioxide)

The largest source of SO2 in the atmosphere is the burning of fossil fuels by power plants and other industrial facilities. Smaller sources of SO2 emissions include industrial processes such as extracting metal as well as burning of fuel in heavy equipment, ships, and locomotives from ore along with natural sources such as volcanoes.

Short-term exposure to SO2 can harm the human respiratory system and make breathing difficult.

SO2 emissions that lead to high concentrations of SO2 in the air generally also lead to the formation of other sulfur oxides (SOx). SOx can react with other compounds in the atmosphere to form small particles. These particles contribute to particulate matter (PM) pollution.

At high concentrations, gaseous SOx can harm trees and plants by damaging foliage and decreasing growth.

Overall India

NO2 emissions in India in the month of February and March

In the month of February and March, the NO2 emissions are quite visible quite evidently in the urban centers as well as the industrial belt across the country; but post lockdown, the pollution in urban centers has reduced significantly. But if we focus on the Jharkhand-Chhattisgarh belt, it does not see any reduction in emission, which can be attributed to active industrial activities.

NO2 emissions in India in the month of April and May

In the picture below, we explore the SO2 emissions across the country. While in the bottom-left image, there are clear red spots visible throughout the country which acts as the baseline as pre-lockdown during the month of February; in the middle picture taken in March, you can see almost negligible emissions of this gas while in the month of May, when the industries were opened in non-urban centers, there is yet again rise in emissions. These emissions are quite scattered throughout the country which is clear evidence that activities in major urban regions have still not been restored.

SO2 across India in Feb, March, and May Mumbai Region
NO2 emissions in Mumbai. Left: February 1 –10; Right: March 1–10

In the Financial Capital, NO2 emissions have exponentially fallen as well as economic activity came to standstill. In the top image, clear red layers are visible, but in the bottom left, partial blue color can be seen which explains the city never sleeps has come to standstill. In the bottom right image, in May, there has been a minor rise in levels as we move towards partially starting the economic activities. The absence of gases over Mumbai city clearly shows that there is an absence of cars in the city, and you would not experience the “Mumbai traffic.”

NO2 emissions in Mumbai. Left: April 1–10; Right: May 1–10

In the SO2 emissions across the city, in the pre-COVID, during the lockdown, and partial opening era, it is quite easy to spot these patterns. With a dramatic drop in February and March SO2 emissions, it hints that SO2 is a major issue in Mumbai. In the right image, in the month of May, as some industries open up, we see some rise in SO2 emission, which is in line with essential industries opening up.

SO2 Emission across months-Mumbai

SO2 across Mumbai in February, March, and May NCR Region

NO2 emissions in Delhi. Left: February 1 –10; Right: March 1–10

In the Capital of Delhi, Delhiites finally managed to experience clean air in the month of April overshadowed by lockdown when there was no economic activity in the NCR region. In the top image, Delhi air has all the pollution marked with red spots. But in the below image, on the right, as we entered a nationwide lockdown, there the air is super clean, while the right image taken in the month of May explains that there is the partial opening of some industries in the region.

NO2 emissions in Delhi. Left: April 1–10; Right: May 1–10

The below image depicts the SO2 emissions in the NCR region over the period of 4 months, mainly February which acts as a pre-lockdown period, March during the lockdown, and May which provides insights on what happens when we open up the partial plants. In this region, the construction activity which has stalled in the month of March and May explains that these heavy machineries are responsible for quite a lot of emissions, and the governments in the NCR regions have to work together and come up with a sustainable plan to protect the respiratory system of people in the region.

SO2 across Delhi in February, March, and May

Jharkhand-Chhattisgarh Industrial belt

NO2 emissions over 4 months (February — May)

SO2 has mining plants as its major constituent. In the pre-lockdown period(left) and during lockdown(center), there is a sudden drop in emissions, which explains the closure of these plants. But nonetheless, there are still some emissions., which can be attributed to the functioning of power plants. The picture on right can be attributed to the reopening of some of these industrial outlets.

SO2 emissions in February, March, and May

Closing Thoughts

While mother earth is completely delighted to see such reductions in air pollution and we all are saying the earth is healing, it is a strange thing that humans are staying indoors. While earth is our home (yeah we looking forward to space colonization) and it needs to be in good shape, what’s the point of a home if you are just restricted to one building?

Moving ahead, all of us are excited to meet our old friends, get back to the offices and talk to co-workers in person, children are excited to meet their friends in school; we can take some steps in reducing air pollution and make our cities more habitable and probably move the factories out of city limit, as well as the same time, let us all pledge to use public transport when possible.

Stay Healthy, Stay Safe!

Data Source:

  1. All data is taken from the Sentinel-5 data satellite using Google Earth Engine.
  2. All data is visualized on a 7-point scale: [‘black’, ‘blue’, ‘purple’, ‘cyan’, ‘green’, ‘yellow’, ‘red’], where black depicts 0 value, while red is the highest value.

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Written by Chinmay Shah, former Software Developer, SatSure. This article was first published on our Medium.



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