According to data shared by the Centre in the Lok Sabha today, the number of severe air quality days were 28 in 2016, as compared to eight in 2015, between May and December.

It also said that there was "minimal increase" in the number of patients with respiratory ailments between 2013 and 2015.

Pollution intensity is considered severe when the air quality index (AQI), as monitored by the Central Pollution Control Board (CPCB), is between 401-500.

It affects healthy people and seriously impacts those with existing respiratory diseases, the CPCB says.

Although month-wise data was not immediately available, the steep rise can be attributed to the smog episode of November, which was described the Centre for Science and Environment (CSE) as the worst in 17 years.

Other details in Union Environment Minister Anil Daves reply to the Lok Sabha further establishes the fact that air quality was indeed bad in 2016.

In terms of the national AQI, it had 24 satisfactory days, 85 moderate days, 120 poor days and 97 very poor days.

The figures for 2015, from May to December, were 23 satisfactory days, 77 moderate days, 73 poor days and 54 very poor days.

Responding to whether there has been any increase in the number of patients with respiratory diseases, the government said it has been "minimal" between 2013 and 2015.

"The data does not reflect manifold increase. Further, air pollution is one of the aggravating factors for respiratory diseases. There are several other factors that may lead to respiratory ailments like smoking, age, genetic causes etc," the Union minister said.

A recent study had claimed that surpassing China, India now accounts for the maximum number of premature deaths from ozone pollution and was second in terms of early deaths due to ultrafine particulate matters of PM 2.5.

Dave had expressed his reservations on the State of Global Air 2017 report, saying "such reports" are often based on extrapolation "without" due scientific validation.