Delhi holds breath as burning farms herald pollution season

ISHARGARH, India - Harpal Singh struck a match and watched his fields burn, the acrid smoke drifting toward New Delhi, where a lethal smog cocktail is once again intensifying over the world's most polluted megacity.

Every November, air pollution in northern India reaches levels unimaginable in most parts of the world, forcing schools shut and filling hospital wards with wheezing patients.

As winter descends, cooler air traps car fumes, factory emissions and construction dust close to the ground, fomenting a toxic brew of harmful pollutants that regularly exceed 30 times the World Health Organization safe limit.