New research reveals a distinct north-south divide in India's urban pollution patterns, showing how transported dust can paradoxically make some highly polluted cities appear cleaner than their surroundings.

In the 18th and 19th century, Britain was abuzz with cranking steam engines, rattling power looms, and clattering machines. Amidst this daily ding, the world was witnessing a defining movement in human history—the Industrial Revolution—that soon spread to the rest of Western Europe. Powered by coal, the production of most things transitioned from hand to machine, spurring a rise in population and air pollution. For the next two centuries, London became infamous for its soot and smog, which turned fatal for about 12,000 people. Now, a new study has shown that this mal air has left its trace in the lofty Himalayan glaciers, thousands of kilometres away from Europe.

The city of Delhi has been consistently ranked as one of the world's most polluted cities. As the monsoon ends, haze sets in, with Deepawali around the corner, bringing the entire city to a standstill with low visibility. Besides vehicular emissions, smoke from diesel generators and construction dust, a significant contributor to this problem is the practice of crop residue burning by farmers in Punjab and Haryana. A recent study, published in the journal Nature Sustainability, suggests that groundwater conservation policies, adopted by Punjab and Haryana, have changed the patterns of rice production. These policies, the researchers argue, have led to the concentration of crop residue burning into a narrower period, later in the season.