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2020-04-18

A question came up this week: “is it just an impression, or is the sky clearer and “bluer” since the start of the lockdown?” To be clear, we’re not talking about the weather or clouds, but the colour of the sky itself.

To answer the question, our scientist, Christine Bingen, first wrote an article about where the blue colour of the sky comes from.

The sky might indeed seem bluer

In this period of COVID-19 crisis, human activity (industries, car traffic) has decreased, and with it some sources of pollution (more in some areas than others).

For this reason, the diffusion and absorption by fine particles and other pollutants has decreased noticeably, which certainly affects the colour of the sky, especially in cities with a higher level of pollution. This can give the impression of a purer, less yellowish sky during the day.

However, we should not lose sight of the fact that much of this phenomenon also depends on the other parameters influencing the colour of the sky (explained above), such as the cold and dry, magnificent weather that accompanied us into the first weeks of the epidemic.

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A blue sky with clouds illuminated from underneath. Source: PxHere
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Stratospheric balloon measurements performed by BIRA-IASB in the 80's, in Air sur l'Adour, France. The colour gradations from the horizon to the zenith are visible.
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Stratospheric balloon measurements performed by BIRA-IASB in the 80's, in Air sur l'Adour, France.