Delhi air improves to “moderate” ahead of rainy weekend

The air quality index (AQI) of Delhi, as per the 24-hour average recorded at 4pm on Thursday, was 178, an improvement from the AQI of 225 (“poor”) on Wednesday and 302 on Tuesday, which was the first time in three months it was categorised “very poor”.

Moisture-laden easterly winds on Thursday helped settle local dust pollution and improve Delhi’s air quality to “moderate” level, according to the Central Pollution Control Board’s daily bulletin, after recording “very poor” and “poor” air quality over the past two days. The India Meteorological Department (IMD) said a western disturbance is likely to influence Delhi-NCR from Friday night, with chances of light rain in the Capital over the weekend.

The maximum temperature on Thursday was 38.8°C, which was a degree below normal. (Raj K Raj/HT Photo)

The air quality index (AQI) of Delhi, as per the 24-hour average recorded at 4pm on Thursday, was 178, an improvement from the AQI of 225 (“poor”) on Wednesday and 302 on Tuesday, which was the first time in three months it was categorised “very poor”. The last time the AQI crossed the 300 mark was on February 14, when the AQI was 336.

“We have seen gradual moisture intrusion from Wednesday, with easterly winds blowing towards Delhi. This is not only helping bring down dust, but also providing a slight cooling effect during the day. With a western disturbance approaching, we mainly expect drizzle and gusty winds on Saturday and Sunday. On Friday night, it may again become windy,” IMD scientist Kuldeep Srivastava said.

The strong easterlies also helped bring down mercury levels in the Capital. The maximum temperature on Thursday was 38.8°C, which was a degree below normal. It was 38.2°C on Wednesday and a season-high of 42°C on Tuesday.

Easterly winds blow towards Delhi from the Bay of Bengal and, therefore, bring moisture to the region. In comparison, westerly or northwesterly winds are dry and often bring dust towards Delhi.

Delhi’s minimum temperature on the day was 26°C, which was a degree above normal, but a drop from Wednesday’s minimum of 27.5°C, which is the highest this season, so far.

Delhi’s AQI was over the 200 mark (“poor”) for six consecutive days from May 3, marking Delhi’s worst spell of air quality in May since 2022, when there were nine consecutive days of “poor” air.

Dust is the primary source of pollution in summer, leading to a spike in PM10 (particulate matter with a diameter of 10 microns or less) concentration. In comparison, combustion sources are more dominant in winter and lead to a spike in PM 2.5 concentration.

CPCB’s daily bulletin showed PM 2.5 and O3 (Ozone) were the primary pollutants on Thursday, and not PM10, indicating the dust had settled.

IMD forecast the maximum temperature to touch 40°C on Friday, before dipping down to 37°C by Sunday, due to rain and overcast skies. The minimum is expected to remain around 26-27°C over the weekend, it said.