New Delhi: The air quality index at several monitoring stations in Delhi touched the extreme end of the severe category for several hours on Sunday. On a scale of zero to 500, Anand Vihar touched 497, followed by 491 each in Mundka and Rohini. All three are in the severe-plus range (451 and above).Out of 37 active continuous ambient air quality monitoring stations, the day’s standard reading — the one taken at 4pm — was severe (401-450) at 32 stations and very poor (301-400) at five. The lowest reading in the city was 356 in Ayanagar.
As the air started worsening from Saturday onwards, many stations saw the index remaining above 480 for long stretches on Sunday. Most of them are the usual pollution hotspots: Nehru Nagar in Lajpat Nagar (488), Sonia Vihar (487), Wazirpur (486), Ashok Vihar (485), Bawana (483), Jawaharlal Nehru Stadium (483) and North Campus of Delhi University (481). The index is calculated using eight individual pollutants — particulate matter 10, PM2.5, nitrogen dioxide, sulphur dioxide, carbon monoxide, ozone, ammonia and lead — at every monitoring location using its 24-hourly average concentration value (eight-hourly in the case of carbon monoxide and ozone). The worst sub-index is shown as the reading for that location. Many of these pollutants had much higher levels than the standard at several locations. In Anand Vihar, the hourly PM2.5 concentration reached 890 micrograms per cubic metre at 1 am. It was almost 15 times higher than the daily national ambient air quality standard of 60µg/m³ and 59 times higher than World Health Organisation’s daily safe guideline. In Nehru Nagar, it touched a peak of 952µg/m³ on Saturday night, data from Delhi Pollution Control Committee showed. Experts said local emissions and unfavourable meteorological conditions caused the index readings to shoot up.Dipankar Saha, former head of Central Pollution Control Board’s air laboratory, said, “Air quality is dependent on the local emissions and wind speed. Wind speed helps dispersion and dilution of these emissions. In the absence of adequate ventilation, pollutants may stagnate, resulting in poor air quality. Such stagnation is highly toxic and may cause ailments in the long run, particularly in children and the elderly.“
