Delhi, one of the world’s most polluted cities, enjoyed some respite up until September in part thanks to a virus lockdown.
Prolonged exposure to pollutants can cause diabetes, lung disease and cancer, and early evidence suggests air pollution may be linked to higher death rates among Covid-19 patients.
Unilever, the Anglo-Dutch consumer products company whose brands include Dove soap and Knorr soup, said it was responding to the "scale and urgency" of the climate change crisis.
Researchers are tracking dramatic drops in traditional air pollutants, such as nitrogen dioxide, smog and tiny particles as most people remain indoors amid coronavirus lockdowns across the world.
Images by the US space agency Nasa are clear, in February the concentration of nitrogen dioxide (NO2) fell dramatically in Wuhan, China, the epicentre of the Covid-19 pandemic, passing from an indicator that was red/orange to blue.
Burning fossil fuels, primarily coal, oil and gas, causes about 4.5 million deaths every year worldwide, more than three times the number of lives lost to road accidents, research says.
The business venture offers clean oxygen as the city's air contains tiny and toxic pollutants that penetrate lungs and bloodstreams and cause life-threatening diseases.
In recent years, smog has become a problem for some cities in Pakistan and neighboring India due to industrial and transport pollution and the practice by farmers to burn stubble crop.
According to independent online air quality index monitor AirVisual, New Delhi was the most polluted major city in the world, at twice the level of Lahore in Pakistan, which was a distant second.
Several cities in the sub-continent are smothered in toxic air, causing a major health emergency in the region.
The United Nations says Bosnia and Herzegovina is estimated to be the second worst country in the world for air pollution.
The study uses the word "risk" 561 times in a 740-page report but says changes in the way the world eats, buys things, gets its energy and handles its waste could help fix the problems.
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