India’s Air Appears Different From Space – Here Is Why

The air over India and some of the surrounding countries South Asia have something very distinct.

It is the existence of the gas formaldehyde which is a colourless gas emitted naturally by vegetation as well as from a number of polluting activities.

Europe’s new Sentinel-5P satellite has observed the elevated concentrations. The satellite was launched last October for tracking track air quality globally.

The aim is to provide these types of information for cleaning up the atmosphere.

The signal from formaldehyde (HCHO) is typically very small compared to other gases like nitrogen and oxygen. There would be just a few molecules of HCHO in every billion air molecules just. According to Isabelle De Smedt from the Royal Belgian Institute for Space Aeronomy (BIRA-IASB, the gas can be a signal of more general pollution problems.

“The formaldehyde column is composed of different sorts of volatile organic compounds, and the source can be from vegetation – so, from natural origin – but also from fires and pollution,” she said.

“It depends on the region but 50-80% of the signal is from some biogenic origin. But above that you have pollution and fire. And the fire can be from coal burning or wildfires, but in India, yes, you have a lot of agricultural fires.”

Significant amount of wood is used for cooking and heating in India.

Ground-level ozone is produced from the reaction when nitrogen dioxide (NO₂, from fossil fuel burning), volatile organic compounds and sunlight are brought together.

This causes severe irritation for respiration and can cause severe health issues.

Study has found the comparatively low levels of formaldehyde was recorded in the north-west part of India where there is extensive desert land such as in Rajasthan where there is much less vegetation and lesser number of people

The Tropomi instrument of the Sentinel-5P satellite is able to detect the existence in the atmosphere of a number of other trace gases apart from formaldehyde such as nitrogen dioxide, ozone, sulphur dioxide (SO₂), methane, carbon monoxide (CO) and aerosols (small droplets and particles).

These elements all impact the air breathed by people and several of these gases also has a role in climate change.

The Tropomi instrument itself is a significant technological development compared ot its predecessor the spectrometer system which is known as Omi.

“We already had really good data, but we needed many more days of observations, sometimes years of observations, to get this kind of quality,” said Dr De Smedt.

“The new (India) map contains four months of data. Tropomi can do in one month what Omi did in six.

“We now see much faster the details, the small emissions, the cities – the kind of signals we didn’t see so well before. We needed 10 years of data to see the emissions around Tehran, for example. In this map you can see them from only four months of Tropomi data.”

(Adapted from

Categories: Sustainability, Uncategorized

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