Even before the Diwali grey set in, Delhi’s air quality had already plummeted. And like every year, the most heated debate was on whether it is stubble burning that’s responsible for the poisonous air that engulfs Delhi-NCR from late Oct. Or, is the city simply choking on pollution from its own vehicles and industry? Even as the blame game on Diwali continues, the arguments over stubble burning should really settle down, once and for all. Because the evidence is crystal clear.