According to the bulletin, the average AQI in Delhi was 399.

Fatehabad in Haryana had the worst average air quality in India over a period of 24 hours ending today evening, while the pollution levels in Lucknow in Uttar Pradesh and Patna in Bihar were worse than in Delhi, according to official figures.

Thirteen cities of the country had an average Air Quality Index (AQI) above 400, which falls in "severe" category, with seven of them in Uttar Pradesh, five in Haryana and one in Bihar, according to the Central Pollution Control Board (CPCB) bulletin of all places for the past 24 hours.

According to the bulletin, the average AQI in Delhi was 399. During the same period, Fatehabad recorded the worst average AQI at 493, while it was 428 in Patna and 422 in Lucknow.

Delhi and its neighbouring cities recorded the worst air quality of the season on Friday, forcing the authorities to declare a public health emergency. But pollution levels in the region dipped marginally on Saturday with slight increase in wind speed.

The average AQI of 18 cities fell between 300 and 400, which comes in the "very poor" category, and included 11 from Haryana, three from Uttar Pradesh, two from Punjab and one each from Bihar and Madhya Pradesh, the CPCB bulletin stated.

According to the CPCB, if the AQI falls in "severe" category, it affects healthy people and seriously impacts those with prevailing diseases, while "very poor" air quality can cause respiratory illness on prolonged exposure.

In Uttar Pradesh, Ghaziabad had the worst average AQI of 453, followed by Bulandshahr (446), Hapur (444), Greater Noida (438), Baghpat (435), Noida (432), Lucknow (422), Kanpur (379), Meerut (371) and Varanasi (328), the CPCB data showed.

Patna had an average AQI of 428, the only city in Bihar with "severe" air quality, followed by Muzaffarpur (382) which is in the "very poor" category". No other city from the state featured in either category, the CPCB said.

In Punjab, the average AQI in Bathinda was 308 and in Ludhiana it was 305, both in the "very poor" category. Singrauli, with an average AQI of 384, was Madhya Pradesh's only city to figure in the list of places with average AQI in the "severe" and "very poor" categories.

Particulate matter 2.5 and 10, which cause respiratory and heart ailments, among others, were the most prominent pollutants present in the air of these cities, the CPCB stated.

Lucknow resident Bharat Singh said he has been waking up to "cloudy conditions" for a couple of days now while the weather has been hot and humid all the while.

"Due to the deteriorating air quality in the city, it becomes very difficult to move on two-wheelers. We hope that it rains soon so that there could be some relief," Mr Singh said.

The CPCB figures on average AQI were available only for 100 cities, and as such people expressed the need for proper data collection in smaller towns and cities.

"Using the CPCB mobile app, I can find out AQI of several cities but not mine," Varun Bhandari, a resident of Amethi in Uttar Pradesh said.

"Amethi is almost equidistant from Lucknow and Kanpur, around 140 km, and both have alarming air quality. But we here have no reliable government data to know what kind of air we are breathing," he said.