Reductions in Sulfur Dioxide & Nitrogen Dioxide Air Pollution over South Asia Associated with Efforts to Control the Spread of COVID-19

On March 24, 2020, Prime Minister Modi ordered a nationwide stay-at-home order for India’s 1.3 billion citizens in an attempt to slow the spread of COVID-19. As a consequence, less fossil fuels are being consumed and, subsequently, less air pollution is being emitted in India and also in neighboring countries, including Pakistan, Nepal, Bangladesh, and Sri Lanka.

The images show OMI data of Sulfur Dioxide (SO₂) and Nitrogen Dioxide (NO₂) over South Asia as an average of March 25 – April 25. The top images show the means of the period in previous years, while the bottom images show the means for 2020.

Sulfur Dioxide before and after restrictions

The highest SO₂ levels are over eastern India and primarily associated with electricity generation; the coal burned has sulfur impurities. Independent estimates indicate that electricity generation for India was down about 10% and 25% in March and April 2020, respectively, as compared to March and April 2019. One exception is in southern India which could be related to increased thermal power generation that came on line before the stay-at-home order. However, there was not a similar increase in NO₂, so possibly coal with higher sulfur content was used in 2020 relative to 2019 without a significant increase in coal consumed.

Nitrogen Dioxide before and after restrictions

NO₂ is primarily emitted from fossil fuel use. The images show that widespread decreases (~30-60%) in NO₂ levels have occurred over most of South Asia. The highest NO₂ levels are in eastern India and are primarily associated with electricity generation.

The OMI NO₂ and SO₂ data will enable scientific and applied research. The following are a few examples:

• Air Quality: While air pollution is decreasing around the world due to lockdown orders, the US government has relaxed pollution emission restrictions on some industrial sectors (e.g., power plants). Therefore, the changes in air pollution associated with the pandemic will serve as a natural experiment in how the atmosphere responds to changes in pollutant emissions from various sources.
• Climate: Several recent studies by the proposers have shown that NO₂ emissions inferred from satellite data serve as an effective proxy for co-emitted CO₂ emissions from cities and power plants. Therefore, researchers may be able to assess the impact of the pandemic on climate gas emissions.
• Economics: Given that most world economies are driven by fossil fuels, economists may use NO₂ data, a non-traditional source of data for this community, to assess the impact of the pandemic on economic activity around the world, including in countries without reliable economic data.
• Intelligence Agencies: The global intelligence community will likely find interesting uses of the NO₂ data for assessing the impact of the pandemic on world countries, including with world governments that purposely misrepresent or withhold the true extent of the pandemic’s impact.
• Health Professionals: The NO₂ data may be used to gauge the effectiveness (e.g., reduction in emissions from traffic and industry) of lockdown efforts to contain or slow the pandemic in a given area.

Caution: Further analysis is required to rigorously quantify the amount of the change in levels associated with changes in pollutant emissions versus natural variations in weather.

Data Sources:
Satellite-derived emission estimates are based on SO₂ and NO₂ measurements from the Aura Ozone Monitoring Instrument (OMI). OMI is a Dutch–Finnish contribution to the NASA Aura mission.

Technical description of figures:
SO₂: India recently became the world’s largest emitter of sulfur dioxide (SO₂). The highest SO₂ levels are over eastern India and are primarily associated with electricity generation. SO₂ is emitted during electricity generation if the coal burned has sulfur impurities. Other major sources in India include the ceramics industry and metal smelting. The decrease in SO₂ levels in 2020 mostly reflect decreased power generation, including because of the shuttering of businesses during India’s stay-at-home order. Independent estimates indicate that electricity generation for India was down about 10% and 25% in March and April 2020, respectively, as compared to March and April 2019.

NO₂: NO₂ is primarily emitted from burning fossil fuels (diesel, gasoline, coal). The images show that widespread decreases (~30-60%) in NO₂ levels have occurred over most of South Asia. For instance NO₂ levels decreased by about 45% in Lahore, Pakistan, 45% in Dhaka, and 55% in Delhi, India. The highest NO₂ levels that remain in South Asia are located in eastern India and are primarily associated with electricity generation by thermal power plants.

References: Can Li, Lok Lamsal, Yasuko Yoshida, Joanna Joiner, Bryan Duncan + GSFC Aura OMI Team. The images are free and publicly-available and may be downloaded at https://airquality.gsfc.nasa.gov/.

7.2020