Delhi was ranked the most polluted city in the world in 2014, — when the last listing was published — with an annual mean of PM2.5 recorded at 153 micrograms per cubic metre, based on data from 2013. In the updated database released on Thursday, Delhi has the 11 highest PM2.5 presence.

This may look like an improvement, but the numbers could be misleading. Similar to the last listing, the current one is also based on data from the year 2013 — but this time it has been taken from 10 monitoring stations, instead of the six used for the 2014 database.

“This is why the PM2.5 annual mean has gone down from 153 to 122 micrograms per cubic metre. Adding more data points through monitoring stations has diluted the previous result,” said Sunil Dahiya, an air pollution campaigner with Greenpeace.

Mr. Dahiya added that though steps had been taken to reduce pollution since 2013, they would reflect in data from later years. However, for some experts, the WHO database showed that things were going right.

SunitaNarain, Director-General of the Centre for Science and Environment, said: “It’s not just the WHO list, but the Delhi Pollution Control Committee’s data for 2015, which shows a declining trend”.

As per the DPCC, Ms. Narain said, the annual average of PM2.5 in 2015 was 102 micrograms per cubic metre.

AnumitaRoychowdhury, head of the CSE’s clean air programme, said: “We have managed to arrest the trend. The levels of PM are not increasing like they were, but there is a lot to be done to reduce levels substantially.”

The AamAadmi Party, meanwhile, wasted no time in taking credit for the perceived decreased in pollution. In a post on its Facebook page, the AAP wrote: “Thank you Delhi. We all know what changed from the time when it was the top polluted city & now.”

The post listed steps, including the odd-even scheme, car-pooling and a “long-lasting conversation on pollution”, taken by the Delhi government. “The change is beyond what is visible, the change is much bigger. Which other Govt in India even imitated any policy for environmental reforms? Together, the AAP Govt representatives and the representatives can achieve greater feats,” (sic) read the post.

While the government did not directly take credit, in a statement it said: “The decline in air pollution levels in Delhi is a collective effort and the government is committed to continue the war against air pollution with active cooperation of the residents of the national capital.”

The government statement said that as per the DPCC, increased awareness about pollution, action to control emissions from construction and control on industries had helped reduce pollution.