UV aerosol index from 380 and 340 nm over Northern Africa as acquired by Sentinel-5P on August 6, 2018 (processed by Sinergise). See it in EO Browser.

Measuring Air Pollution from Space

Sabina Dolenc
May 13 · 5 min read

Air pollution is a global problem and it does not recognize borders. According to the World Health Organization (WHO), air pollution results in more than 4.2 million premature deaths every year. The European Environment Agency reports that around 90% of city inhabitants in Europe are exposed to dangerous air pollutants. Improving air quality demands sustained and coordinated action. It is therefore addressed in the United Nations’ Sustainable Development Goals (SDGs) to make cities and human settlements inclusive, safe, resilient and sustainable. On the way to achieving these goals, satellite data is playing an important role as one of the resources helping governments and decision-makers to form appropriate mitigation strategies.

Source: UN Department of Economic and Social Affairs

Gaseous Air Pollutants of Primary Concern

Air pollution is a release of various gases into the atmosphere, such as solids and dispersed liquid aerosols which cannot be absorbed in the environment. There are six common air pollutants also known as criteria air pollutants defined by the U.S. Environmental Protection Agency (EPA) which can harm our health and the environment:

Sources of Air Pollution

A substantial part of harmful pollutants is the direct or indirect result of human activity such as burning of fossil fuels in electricity generation, transport, industry and households, industrial processes and solvent use (e.g. in chemical and mineral industries), agriculture and waste treatment.

However, contributors to a global air pollution are also a large number of natural emission sources such as volcanic eruptions (release of SO₂), wildfires (release of CO) or windblown dust (higher PM concentrations), sea-salt spray and emissions of volatile organic compounds from plants.

Alongside their already mentioned natural origins, SO₂, NO₂ and CO are also formed in the urban settings and emitted directly into the air from burning of fossil fuels.

In the lower atmosphere O₃ is formed after complex chemical reactions occurring between NO₂ and various volatile organic compounds. Higher up our atmosphere (around 10 to 50 km) ozone occurs naturally and plays an important role in filtering out the sun’s harmful UV radiation. Ozone near the ground, however, can cause serious respiratory illnesses.

PM or particle pollution comes in many sizes and shapes and can be made up of hundreds of different chemicals. They are emitted by various industrial processes, coal- or oil-burning power plants, residential heating systems, and automobiles.

Major sources of lead in the air are ore and metals processing and piston-engine aircraft operating on leaded aviation fuel. Further sources are waste incinerators, utilities, and lead-acid battery manufacturers, as well as lead smelters as the producers of the highest air concentrations of lead.

Monitoring Air Pollution with Satellites

The reasons for air quality monitoring are obvious, and the need to develop appropriate improvement strategies even more so. During the process of development these strategies, decision-makers rely on different resources. The main ones are satellite data and different computer models which show how pollution accumulates and how it is carried in the air.

There have been several satellite missions devoted to monitoring our atmosphere in the past. The most recognizable ones were the European Space Agency (ESA)’s Envisat and NASA’s Aura missions. Since the instruments on both come to the end of their lifetimes, and the launch of the Sentinel-5 mission is planned for the time frame 2020, the Copernicus Sentinel-5 Precursor (Sentinel-5P) mission was launched in October 2017. It is dedicated to monitoring our atmosphere to fill the gap between the mentioned missions.

Sentinel-5P (Image credit: ESA)

Sentinel-5P Data

The TROPOspheric Monitoring Instrument (TROPOMI) on board of the Sentinel-5P satellite is a hyperspectral imager with a swath width of 2600 km covering bands in ultraviolet and visible (270–495 nm), near infrared (675–775 nm) and shortwave infrared (2305–2385 nm), at a spatial resolution as high as 7 km x 3.5 km.

This information can then be used to derive atmospheric measurements, relating to air quality, climate forcing, ozone and UV radiation with high spatio-temporal resolution. Its data is used, among other applications, for the monitoring of the concentration of CO, NO₂ and O₃ in the air as well as UV aerosol index monitoring and measuring different geophysical parameters of clouds.

Mapping the global atmosphere every day, the Sentinel-5P satellite provides high-resolution data on a multitude of trace gases and information on aerosols that affect air quality and climate. (Image credit: ESA)

Start Exploring

To browse the data and observe the concentration of air pollution we recommend using the EO Browser, which beside other data sources, serves level 2 geophysical products of the Sentinel-5P. The data is available since April 2018 with one day revisit time, and it covers almost the whole globe.

NO₂ levels over China and South Korea as seen with Sentinel-5P on May 9, 2019. Follow the link to EO Browser and browse through the history of data.

Sentinel-5P level 2 geophysical products which can be easily inspected through the EO Browser are:

  • AER_AI — UV aerosol index
  • CH₄ — Methane
  • CLOUD — various geophysical parameters of clouds
  • CO — Carbon Monoxide
  • HCHO — Formaldehyde
  • NO₂ — Nitrogen Dioxide
  • O₃ — Ground-level Ozone
  • SO₂ — Sulfur Dioxide
High levels of CH₄ over Nigeria (Sentinel-5P, acquired on February 17, 2019 — link to EO Browser). — Methane is a potent greenhouse gas that enters the atmosphere mainly from the fossil fuel industry, landfill sites, livestock farming, rice agriculture and wetlands.
Left: A time-lapse of O levels over the Atlantic ocean and its surrounding continents (Sentinel-5P, data acquired between March 15 and April 30, 2019). Right: The area being covered with the time-lapse. The time-lapse can be easily created within EO Browser. In order to use this feature yourself, you will need to register for a free account.

Air Pollution Use Case on Sentinel Hub Education Page

For a better understanding and to learn more about monitoring and measuring air pollution from space we also invite you to visit our Sentinel Hub Education page, where you will be able to explore useful links and tools addressing different Earth observation subjects.

The air pollution use case, as well as some other resources, was prepared with support from the ESA and using Copernicus data. (Image credit: Sentinel Hub)

The currently demonstrated use cases (wildfires, volcanoes, air pollution) are presented within Jupyter Notebook. In the same manner we intend to also include other cases such as flooding, deforestation, agriculture monitoring, ice melting, landslides, urban growth, etc.

On the way toward our goal, your help would be most appreciated. You can either help us raise awareness about remote sensing or prepare a new use case which could be shared through our educational channels. This way we could together help others to explore and protect our only planet.

Contact us, if you have any questions or suggestions. We would happily chat about options.


Some useful links about air pollution:

Ambient (outdoor) air quality and health by World Health Organization
Introduction to air pollution by Encyclopedia Britannica
Air pollution by European Environment Agency

Sentinel Hub Blog

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Sabina Dolenc

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Sentinel Hub Blog

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