Delhi wakes up to a shallow fog a day after rain, AQI remains ‘satisfactory’

Delhi recorded an air quality index (AQI) of 95 at 6am on Saturday, compared with 60 in the Central Pollution Control Board's (CPCB) 4pm bulletin on Friday.

A day after record-breaking rain washed pollutants out of Delhi's air and brought Delhi its cleanest October day in four years, shallow fog enveloped the national capital on Saturday morning, even as air quality remained in the satisfactory category.

The air quality remained in the satisfactory category, although the increase indicated a deterioration from the previous day's unusually clean conditions. (HT Photo)

Delhi recorded an air quality index (AQI) of 95 at 6am on Saturday, compared with 60 in the Central Pollution Control Board's (CPCB) 4pm bulletin on Friday. The air quality remained in the satisfactory category, although the increase indicated a deterioration from the previous day's unusually clean conditions.

At 6am , CPCB data showed PM2.5 as the predominant pollutant at 17 of Delhi's 58 reporting stations and PM10 at four stations. At the same time on Friday, PM2.5 was the main pollutant at 42 of 53 reporting stations, while PM10 was recorded as the main pollutant at 10 stations.

Drop in visibility

Visibility dropped sharply at Delhi's weather stations, which stood at 500 metres at Safdarjung around 6.30am on Saturday , against 4,000 metres at the same time on Friday. At Palam, it was recorded at 800 metres, also down from 4,000 metres a day earlier, according to India Meteorological Department (IMD) data.

The visibility at Safdarjung remained steady at 500 metres from 2.30am, while at Palam it remained unchanged at 800 metres from 5am. Both stations reported shallow fog.

According to IMD classification, visibility between 999 metres and 500 metres is categorised as shallow fog. Visibility between 499 metres and 200 metres is classified as moderate fog, while 199 metres to 50 metres is dense fog. Visibility below 50 metres is categorised as very dense fog.

The fog comes a day after an unusual interaction between Cyclone Arnab and a western disturbance triggered heavy rain and thunderstorms across the Capital, washing pollutants out of the atmosphere.

Delhi recorded an AQI of 60 in Friday's 4pm bulletin, its cleanest October day in four years. The average AQI for the first 30 days of October stood at 167, putting the city on course to record its cleanest October since CPCB began publishing daily AQI bulletins in 2015.

Dip in temperature

The rain also brought an unprecedented dip in daytime temperatures. Safdarjung, Delhi's base weather station, recorded a maximum temperature of 20.7°C on Friday, 10.3 degrees below normal and the lowest October maximum in records dating back to 1951.

The station recorded 61.4mm of rainfall in the 24 hours ending 8.30am on Friday, the sixth-highest 24-hour rainfall for October since 1951.

Forecast

The IMD has forecast mainly clear skies for the day with the maximum and minimum temperature likely to settle between 25 to 27 degrees Celsius and 15 to 17 degrees Celsius respectively.