New Delhi, Oct 15 : A noxious haze hung over the national capital on Thursday as its air turned foul and the quality index mounted to 'very poor' category, for the second time this week.
The East Delhi district recorded highest pollution.
Delhi's air quality index stood at 320 at noon, which falls in the 'very poor' category.
The particulate matter with the diameter of 2.5 microgram per cubic meter, which is too small to be filtered out of the body, is the main pollutant.
The System of Air Quality and Weather Forecasting and Research (SAFAR), which come under the aegis of the Ministry of Earth Sciences, categorizes air quality in the 0-50 range as good, 51-100 as satisfactory, 101-200 as moderate, 201-300 as poor, 301-400 as very poor and above 400 as severe.
As per the Central Pollution Control Board, out of the 36 pollution monitoring stations in Delhi, the air quality index at as many as 25 stations is in the 'very poor' category, eight stations recorded the index in the 'poor' category, one recorded it to be 'moderate' category while two remained non-functional.
Pollution monitoring station in East Delhi's Vivek Vihar area recorded the most polluted air at 373, followed by 361 at Shadipur and 357 at Patparganj and Mundka area.
Lodhi Road logged the least air quality index.
Delhi's neighbouring areas -- Gurugram, Ghaziabad, Faridabad, Noida and Greater Noida -- also recorded 'very poor' quality of air.
Greater Noida's air is currently the most polluted amongst all.
Nationwide, as many as 15 cities have very poor air quality.
Uttar Pradesh's Bhagpat tops the charts, followed by Rajasthan's Bhiwadi, Greater Noida, Meerut, Muzaffarnagar, Ghaziabad etc.
The air pollution reaches a crescendo every winter in Delhi and surrounding regions, when pollution from stubble burning combines with the suspended water droplets in the lower atmosphere to form a thick blanket of noxious smog.
According to SAFAR, an increase in stubble burning fire counts was observed around Haryana, Punjab, and neighbouring border regions with fire count estimated as 740, and transport wind direction is partly favourable and hence an increase in stubble contribution to PM2.5 is expected.
Pawan Gupta, a Universities Space Research Association scientist at NASA's Marshall Space Flight Centre, however, emphasized that farm fires are not only limited to Punjab, Haryana but a significant burning is also seen in various districts of Uttar Pradesh and Madhya Pradesh.
As per the India Meteorological Department (IMD), the spike in pollutants in the capital city is a result of low wind speeds, along with an increase in stubble burning in the neighbouring states of Punjab and Haryana.
"In summer, there is rainfall and thunderstorm activities due to which the wind speed touches 50-60 kilometre per hour, leading to dispersal of pollutants.
Whereas in October and November, the wind speed does not go beyond 15 kilometre per hour due to which the pollutants settle-in," said Kuldeep Srivastva, Head of IMD's Regional Weather Forecasting Centre.
After the return of monsoon, the weather patterns change, and the temperature starts to decline.
The effects of mist, fog are more, and they act as a trap for local pollution, stated an official of private weather forecasting agency - Skymet, adding that the pollution that arises does not go away and persists for a long time on the lower surface of the atmosphere.