Worst in the country: Air quality hits severe

New Delhi: Delhi recorded the country's worst air quality on Wednesday as it turned 'severe' for the first time this season, with the AQI soaring to 418. Bihar's Hajipur, with an Air Quality Index (AQI) of 417, had the second-worst reading in the country, Central Pollution Control Board (CPCB) data showed.

Of Delhi's 36 monitoring stations, 30 reported air quality in the 'severe' category, the CPCB said. In comparison, the national capital's 24-hour average AQI -- recorded at 4 pm every day -- stood at 334 on Tuesday.

An AQI between zero and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', 401 and 450 'severe' and above 450 'severe plus'. According to the CPCB data, the city's AQI was in the 'severe' category for three days in January. On January 14, the AQI was recorded at 447, followed by 409 each on January 24 and 26.

The CPCB said 'severe' AQI affected healthy people and seriously impacted those with existing medical conditions. The air quality in the national capital had been in the 'very poor' category since it plunged to the level on October 30.

According to the Centre's Decision Support System for Air Quality Management, vehicular emission was the top contributor to Delhi's pollution, with an estimated share of approximately 13.3 per cent.

The other prominent pollutants were PM2.5 and PM10. PM2.5 and PM10 refer to fine particulate matter in the air, with the numbers indicating their size in micrometres. PM2.5 are fine particles with a diameter of 2.5 micrometres or less, about the width of a human hair.

These are so small that they can penetrate deep into the lungs and even enter the bloodstream, posing significant health risks. PM10 are coarser particles with a diameter of 10 micrometres or less, about the width of 10 human hairs.