According to Nasa, the changes in Wuhan – the central China city at the epicentre of the initial coronavirus outbreak – were particularly striking, while nitrogen dioxide levels across the whole of eastern and central China were 10 to 30 per cent lower than normal.

Nitrogen dioxide is produced by cars, power plants and other industrial facilities and is thought to exacerbate respiratory illnesses such as asthma.

The space agency said the decline in air pollution levels coincided with the restrictions imposed on transport and business activities.

That was consistent with official data from China’s National Development and Reform Commission, which recorded a 25 per cent fall in road freight volume and a 14 per cent decline in the consumption of oil products between January and February.

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Liu Qian, a senior climate campaigner for Greenpeace based in Beijing, said the restrictions on industry and travel were the primary reasons for the improvement in air quality.

According to official data, in February, the concentrations of PM2.5, nitrogen dioxide and sulphur dioxide – a toxic gas that comes mostly from industrial burning of coal and other fossil fuels – all fell, by 27 per cent, 28 per cent and 23 per cent, respectively.

“The causes of air pollution are complicated, but the suspension of industrial activity and a drop in public transport use will have helped to reduce levels,” Liu said.

Lauri Myllyvirta, lead analyst with the Centre for Research on Energy and Clean Air in Helsinki, said that levels of nitrogen dioxide pollution, measured both by Nasa satellites and official stations in China, started inching back up in the middle of March and had returned to normal levels by the end of the month.

That coincided with the centre’s findings – published on Carbon Brief, a British website on climate change – that coal consumption at power plants and oil refineries across China returned to their normal levels in the fourth week of March.

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Ma Jun, director of the Institute of Public & Environmental Affairs, a Beijing-based charity, said a stimulus plan to kick-start the economy would have a significant impact on air pollution.

“Once industrial production is fully resumed, so are the emission levels,” he said. “Unless another outbreak happens and triggers another lockdown, which would be terrible, the improvement achieved under the pandemic is unstable and won’t last long.”

After the 2008 financial crisis, Beijing launched a 4 trillion yuan (US$567.6 billion) stimulus package that included massive infrastructure investment, but also did huge damage to the environment. In the years that followed, air pollution rose to record highs and sparked a public backlash.

“Local governments have been under huge pressure since last year, and there are fears that environmental regulations will be sidelined [in the push to boost economic output],” Ma said.

But Beijing had the opportunity to get it right this time by investing more in green infrastructure projects rather than high-carbon projects, he said.

“A balance between economic development and environmental protection is key to achieving a green recovery, and that is what China needs.”