Delhi's air quality 'very poor', several areas battle severe pollution

Delhi's air quality was recorded in the 'severe' category for three consecutive days till Wednesday morning and improved slightly by evening, Central Pollution Control Board data said.

The wind speed improved from 2.5 kilometre per hour to 4 kilometre per hour, the Centre-run System of Air Quality and Weather Forecasting (SAFAR) said.

The CPCB recorded an overall air quality index (AQI) of 384 which falls in the 'very poor' category.

An AQI between 201 and 300 is considered 'poor', 301 and 400 'very poor' and 401 and 500 'severe'.

The AQI on Monday was recorded at 412, 415 on Tuesday and  413 on Wednesday morning.

The SAFAR said the overall Delhi air quality will improve slowly and steadily to 'very poor' level by tonight.

"The isolated drizzling last night was counterproductive as it could not wash away particulate pollutants but increased the air holding capacity by introducing more moisture. Other than the surface wind speed, rest all meteorological factors are likely to be unfavourable even on Thursday," it said.

"However, the wind speed is one of the major players in the winter air quality of Delhi due to its landlocked geography," the SAFAR added.

The air quality of neighbouring Ghaziabad, Faridabad and Noida was also recorded in the 'very poor' category, CPCB data showed.

Ten areas in Delhi recorded 'severe' air quality and in 26 areas it was at 'very poor', they added.

The overall PM2.5 level -- fine particulate matter in the air with a diameter of less than 2.5 micrometre -- was recorded at 250 and the PM10 level at 405, it said.

The SAFAR said weather conditions leading to insufficient rain led to deterioration of the air quality.

"There is a fall in temperature and good amount of moisture is present in the air. Moist air is passing over Delhi's cool surface leading to fog formation and calm winds are not allowing pollutants to disperse," the SAFAR said.

The relative humidity was recorded at 98 per cent on Wednesday, the Meteorological (MeT) officials said.

"Levels of gaseous pollutants NOx and CO are forecast to be enhanced up to a moderate range after a long time due to a fall in the boundary layer height and reduced vertical mixing," it said.

According to the Indian Institute of Tropical Meteorology, the maximum ventilation index is likely to be 3,500 sqm/second from December 10-12.

The ventilation index lower than 6,000 sqm/second with an average wind speed of less than 10 kmph is unfavourable for dispersion of pollutants.

The wind speed, ventilation index and higher moisture are highly unfavourable for dispersion of pollutants, the IITM added.