On Thursday, Delhi experienced a decline in air quality, reaching the ‘poor’ category. Simultaneously, the minimum temperature dropped to its lowest this season at 16.4°C. This shift followed a change in wind direction, bringing the mercury below 20°C (specifically 19.4°C) after a span of five days.
As per the Central Pollution Control Board, the hourly Air Quality Index (AQI) stood at 204, categorizing it in the lower range of ‘poor’ at 9 am. The previous day, the average 24-hour AQI was 193, placing it in the upper range of ‘moderate’. For reference, an AQI of 0-50 is considered good, 51-100 is satisfactory, 101-200 is moderate, 201-300 is poor, 301-400 is very poor, and above 400 is severe.
At 8 am on Wednesday, an AQI of 196 (moderate) was recorded, a slight increase from 180 (moderate) the day before. The shift in wind direction to northwesterly, along with a decrease in local wind speed, is expected to maintain poor air quality until Friday.
Cold northwesterly winds have a negative impact on air quality. The drop in temperature slows down the dispersion of pollutants and brings smoke from the fields of Haryana and Punjab, where agricultural fires are common at this time of year.
The minimum temperature fell below 20°C for the first time last week, registering at 18.6°C. This was followed by a change in wind direction, causing the minimum temperature to rise to 20.9°C on Saturday. Subsequently, it increased to 23.1°C on Sunday and 24.4°C on Monday. On Tuesday, Delhi’s minimum temperature was 22.7°C, which is two degrees above the normal range.
Wednesday saw a minimum temperature two degrees below normal, with the maximum reaching 35°C, one degree above normal. The previous lowest temperature recorded this season was 18.3°C on October 3.
According to the Air Quality Early Warning System (AQEWS) forecast, the air quality is anticipated to remain in the lower range of ‘poor’ until Friday. The outlook for the following six days suggests that the air quality will fluctuate between ‘poor’ and ‘moderate’.
AQEWS, a forecasting system under the Union Earth Sciences Ministry, is relied upon by the Commission for Air Quality Management (CAQM) for preemptive measures against pollution.
Delhi experienced its first ‘poor’ air day of the winter season last Friday, with an AQI of 212. On the same day, CAQM implemented stage-I measures of the Graded Response Action Plan. These measures include the closure of construction and demolition sites over 500 sqm that are not registered with the government, reduction of road traffic, periodic mechanized sweeping, and water sprinkling on roads, among others.
On Saturday, the AQI worsened to 216 (poor) before improving to the ‘moderate’ range.
On Monday, CAQM reported that Delhi had seen 200 days of good to moderate air quality this year, marking only the second time since 2015. The previous instance occurred in 2020 during the Covid-19 pandemic and associated lockdowns.
Wednesday’s AQEWS report indicated that the prevailing surface wind is likely to originate from the northwest at speeds of 8-14 km per hour. On Thursday, the surface wind is expected to be from the west/northwest at speeds of 6-12 km per hour. On Friday, the wind is projected to come from the west/northwest with speeds of 8-16 km per hour.
