In 1980 Satyarthi founded the Bachpan Bachao Andolan (Save the Childhood Movement) and began raiding factories, brick kilns and carpet-making workshops where children and their indebted parents often pledge themselves to work for decades in return for a short-term loan.
Around half are thought to be in India, many working in brick kilns, quarries or the clothing trade.
In contrast, reducing emissions of the sooty particles known as black carbon, which are given off by inefficient combustion in cooking fires and brick kilns, and by dodgy diesel engines, offers rapid, huge and tangible public-health benefits (see article).
First, cement-makers are trying to make their kilns more efficient and so reduce the amount of energy needed per unit of output.
Cement-makers have been improving the efficiency of their kilns for over a century, leaving relatively little scope for further big gains.
Many of the tyres are blended into road surfaces or burned in cement kilns.
Short-lived forcings have the advantage of being comparatively cheap to cut: for black carbon tried and true measures include retiring old vehicles, filtering exhausts, getting people better stoves and cleaner fuel to burn in them, stopping widespread burning of agricultural waste, and modernising kilns and coking ovens.
The exhaust from the kilns mixes with diesel emissions and other fumes to form a vast brown smog, known as an atmospheric brown cloud, which is up to 3km thick and thousands of kilometres long.
These ovens, six among the 100,000 which turn out the 200 billion bricks made each year in India, are worked by dalits members of castes once regarded as untouchable.India's brick kilns are noxious sources of pollution, particularly soot, and working them means a life that is always nasty, frequently brutish and often short.
To make the cement, materials such as limestone and clay are heated in large kilns to over 1,000°C.
Vaccinators learned to attend especially to mobile populations, like seasonal workers at brick kilns, and found that many migrants are best reached not at home but in bus and railway stations.Good monitoring was crucial, too.
