Delhi Chief Minister Arvind Kejriwal on Monday claimed that the National Capital was no longer the most polluted city in the world and that the city has improved a lot on this parameter.

Kejriwal cited data from the World Air Quality Index published by Swiss air quality technology company IQAir, which said that Delhi was not amount the top ten most polluted cities in Asia on Sunday.

According to readings of the index on Sunday, Gurugram was the most polluted city on Sunday, followed by Dharuhera in Haryana and Muzaffarpur in Bihar, India Today reported. However, on Monday evening, the index still showed Delhi to be the most polluted city in the world,

The Delhi chief minister also cited a report by PTI that cited data from the Central Pollution Control Board that the National Capital’s air quality index was the lowest for the day before Diwali in seven years.

The city still recorded an air quality index of 259 on Sunday, which falls in the “poor” category.

“Some years back, Delhi was the most polluted city in the world.” Kejriwal remarked on Twitter. “Not any more! People of Delhi worked very hard. Today, we have improved a lot.”

The chief minister said that notwithstanding the improvement, there is a long way to go. “We will continue working hard so that we find a place in the best cities of the world,” he said.

Kejriwal said that while the improvement in air quality was encouraging, the city had not yet won the war against pollution. “We have to become world’s cleanest city,” he said. “That’s our goal.”

However, the National Capital recorded an air quality index in the “very poor” category at 323 on Monday evening, according to data from the Ministry of Earth Sciences’ SAFAR, or System of Air Quality and Weather Forecasting And Research.

According to the Central Pollution Control Board, the 24-hour average air quality index of Delhi was in the “very poor” category at 312 at 4 pm on Monday.

On September 7, the AAP government had banned the production, sale and use of firecrackers till January 1, 2023 to prevent the city’s air quality from worsening in winter.

On September 30, Delhi Chief Minister Arvind Kejriwal had also launched a Winter Action Plan to curb air pollution in the national capital. As part of the plan, the Delhi government will install 233 anti-smog guns and 150 mobile units of the device to curb pollution.

During winters, lower temperatures, wind speeds, and other factors such as industrial pollution cause the deterioration of air quality in much of northern India, including Delhi. Air quality typically deteriorates further during Diwali due to the bursting of firecrackers.