With the air quality in Delhi taking a turn for the worse, restrictions under the Graded Response Action Plan (GRAP) to check polluting activities have come into force. The dip in air quality was the result of low wind speed and a drop in temperature. Eight locations in the Capital clocked AQI higher than 300 on Monday. Why are we discussing something we have been doing ad nauseum for more than a decade. For a few simple reasons: there is now clear-cut data which links air pollution with death. That was not the case earlier. With this data, governments around the world have no objective reason not to act.