Delhi woke up to an alarming AQI of 484 on Monday morning, remaining in the ‘severe’ air pollution category for the fourth consecutive day. Medical experts say that the toxic air poses a significant risk, not only to people with lung or heart conditions, but also to healthy individuals exposed for prolonged periods. The Supreme Court, on Monday, directed strict enforcement of measures under Stage IV of the Graded Response Action Plan, or GRAP, in the Delhi-NCR region. Here’s a look at the key pollutants contributing to the toxic air in the national capital and surrounding areas.