Explaining Delhi's Annual Airpocalypse

November 24, 2017 | Rishabh Srivastava | rishabh@loki.ai

Particulate Matter (PM2.5) levels in Delhi have been amongst the worst in the world this month. From November 1 to November 20, they were almost 11 times the EPA standard, and 17 times the Los Angeles average. While Beijing's Airpocalypse has received much attention in the West, Delhi's air is more than 5 times worse.

Stubble burning by farmers is a major cause of poor air quality

Surprisingly, the primary driver for India's pollution is not machinery - but a lack thereof. Farmers in the northern agricultural hub of Punjab are unable to afford machinery for clearing out stubble in the ground, and resort to stubble burning - the deliberate setting fire of the straw that remains after crops have been harvested - to boost yield. It is difficult to get accurate data for the number of stubble burning incidents, but fire mapping data by NASA serves as a good proxy.

Increase in fire activity seems to correlate with the increase in Delhi's pollution levels.

These fires occur almost exclusively in the agriculture-heavy state of Punjab, as shown in the map below.

Wind from the Punjab region generally flows in the South-East direction, which means that much of the particulate matter from stubble burning makes its way to Delhi. It is difficult to visualize the average wind-direction, but this screengrab show below (from windy.com) is a fairly accurate picture of how wind generally flows.

Unusual weather patterns exacerbate an already bad situation

Delhi's already bad air became absurdly poor from Nov 7 to Nov 12. This was caused by an increase in stubble burning in the previous week, along with an unfortuanate combination of weather conditions.

Wind in Delhi petered out during this period, while relative humidity soared. This led to particulate matter mixing with water vapour to cause smog, and also meant that the smog took a long time to clear out. Consequentually, Delhi's visibility fell to 50 meters at times, while its air became unbreathable.

Little hope of improvement

An increase in average wind speed on November 12 helped clear the air and gave temporary relief to Delhi-ites, but stubble continues to be burnt in Punjab. Farmers argue that it is the most cost-effective measure for making land fertile for the next harvest, and claim that they cannot afford machinery that farmers in developed use to avoid stubble burning.

The government of Punjab is ridden with debt, and is unable to finace this machinery for local farmers. While the government of Delhi has been trying to put pressure on the Punjab government to enforce the ban on stubble burning, little action has been taken so far.

Real-time Pollution Data

Near Real-time Fire Data