Delhi’s air quality remained in the poor category on Thursday morning on the hourly air quality index (AQI) of the Central Pollution Control Board (CPCB), while the city is likely to see shallow fog and a minimum temperature of about 9 degree Celsius, according to the India Meteorological Department (IMD) forecast.
According to the CPCB’s website, the hourly AQI at 7 am stood at 259 on Thursday, the middle end of the “poor” category. The average 24-hour AQI on Wednesday was 237.
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’, and 401 and 500 ‘severe’. Prolonged exposure to air in the poor category leads to breathing discomfort to most people.
As far as Delhi’s weather is concerned, the maximum temperature is likely to be at 24 degree Celsius while minimum temperature is predicted to be around 9 degree Celsius. The minimum temperature on Thursday was 10.1 degree Celsius, one notch above normal. The maximum temperature was 24 degree Celsius, usual during this time of the year.
On Thursday, the Union ministry of earth science’s air quality monitoring centre, System of Air Quality and Weather Forecasting and Research (Safar) said, “As predicted by Safar, the air quality improved significantly. However, the improvement was higher than expected and AQI slipped to ‘Moderate’ today implying that control measures seem to be effective and are yielding results.”
Safar follows a different air quality index metric.
“For the next four days (8th to 11th), winds are likely to be moderate increasing ventilation of pollutants. Minimum temperatures are likely to drop gradually leading to more stable boundary layer during night time that helps accumulation of pollutants. With mostly clear sky conditions during day time, the peak mixing layer height is likely to be around 1.5 km causing moderate vertical mixing of air mass. The net effect is that air quality for the next four days likely to improve gradually but within ‘Moderate’ or ‘lower end of Poor’ category.”
Mixing height is an invisible boundary layer of the atmosphere within which movement of air and particles can take place. The lower the mixing height, the lesser the room for pollutants to move or disperse.