Why does India's air look different from space?

There is something very distinct about the air over India and the surrounding countries in South Asia.
It is the presence of formaldehyde - a colourless gas that is naturally released by vegetation but also from a number of polluting activities.
The elevated concentrations have been observed by Europe's new Sentinel-5P satellite, which was launched last October to track air quality worldwide.
It is information that will inform policies to clean up the atmosphere. New Sentinel satellite tracks dirty air.Compared to the major constituents like nitrogen and oxygen, the formaldehyde signal is actually very small; in every billion air molecules just a few will be CH₂O. But it can be a signifier of more general pollution problems, says Isabelle De Smedt from the Royal Belgian Institute for Space Aeronomy (BIRA-IASB).

"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."  [ 1 image, 1 link, 3 quotations, 230 words]