Visibility fell sharply in Delhi this week as a toxic mixture of smoke and fog shrouded the national capital even before winter sets in.

Here is a look at the problem, and what triggered it.

HOW BAD WAS THE SMOG?

Delhi was swathed in ‘dense’ to ‘very dense’ smog early on Wednesday and Thursday. Visibility in the ‘very dense’ category falls into a range of zero to 50 m (164 ft), while ‘dense’ refers to visibility over 50 m to 200 m (164 ft to 656 ft).

The smog dispersed slightly on Thursday, when visibility stayed above 300 m (984 ft), after being too thick to see through in some areas the previous day, such as around the city’s international airport.

WHAT CAUSED THE SMOG?

Officials blamed weather conditions such as high humidity that allows the formation of fog droplets, low wind speed, and a slight drop in minimum temperature, to 16.1 degrees Celsius (61 degrees F) on Thursday from 17.9 C (64 F) on Tuesday.

WAS POLLUTION ALSO A FACTOR?

Authorities said pollution also contributed, pushing New Delhi to pole position as the world’s most polluted capital in Wednesday’s live rankings by Swiss group IQAir.

Daily air quality in the region crossed into the ‘severe’ category for the first time this season, or an index score higher than 400, which persisted on Thursday morning, with a reading of 430.

DID SMOG AFFLICT DELHI ALONE?

Dense smog has engulfed other parts of northern India, such as the states of Punjab and Uttar Pradesh, where visibility fell to zero in some areas on Thursday.

Neighbouring Pakistan’s Punjab province, which shares a border with India, also faces similar conditions.

WILL DELHI’S SITUATION IMPROVE SOON?

Delhi’s pollution is likely to remain ‘severe’ on Friday, but is expected to improve to the ‘very poor’ category afterwards, falling in an index range of 300 to 400.

Wind speed is also expected to increase from Friday.

Authorities expect both factors to disperse the smog in the city and improve visibility.

(REUTERS)