Once a luxury product, air purifiers have increasingly become a necessity as sales surge amid a rise in Delhi's pollution levels that are now just a notch below the 'Severe Plus' category.

According to Central Pollution Control Board data, Delhi's overall Air Quality Index (AQI) stood at 426 at 9.30 am on Friday. An AQI of above 400 is considered 'Severe' and can affect healthy people and seriously impact those with existing illnesses. On Thursday, the 24-hour average AQI stood at 450 at 4 pm, just a notch below the 'Severe Plus' category.

Demand for air purifiers have risen in the national capital, particularly after Diwali, which witnessed widespread bursting of firecrackers despite a ban.

"The air quality in India is deteriorating due to many activities industrial expansion in cities, population density, improper waste management, crop burning, increased automobile use and a few natural causes. There is evidence that air pollution, both outdoor and indoor, is on the rise and is behind higher morbidity and mortality rates," said Kartik Singhal, founder of O2 Cure and managing director at Zeco Aircon Ltd.

The spike in air purifier sales reflect the deteriorating air quality levels, he said, adding that buyers from major cities such as Delhi, Gurgaon, Noida had become more aware and responsible about indoor purification.

"This has led to an increase in the air purifier sector where we have also observed a massive jump in sales during the past few weeks," Singhal added.

A representative from Mehra Electronics in Khan Market concurred.

"This is the need of the hour. It is peak pollution time and the sales have seen an increase," he said.

Market experts said air purifier sales were higher in south Delhi since people living there had higher purchasing power and better awareness.

The appliance has become a necessity now and even doctors are advising patients to use it, said Manish Seth, secretary of Daryaganj Traders' Association and the owner of an electronics store.

"Companies have also realised this and reduced the prices. Purifiers that were earlier available for Rs 15,000 to Rs 20,000 are now being sold for Rs 7,000 to Rs 8,000. In some south Delhi stores, the sales are higher because people have better awareness and higher purchasing power. The product is also moving on its own in the online space," he said.

Mohit Singh, a sales executive at Atmo Pure in Jangpura, said the cost of air purifiers at their store ranged between Rs 7,000 and Rs 60,000, depending on the technology, the filters used and the coverage area.

"We have seen a sharp rise in demand for air purifiers around this time for the last few years. It is literally the cost of your breath, a health investment as important as your regular health insurance," he added.

Singh said a larger number of users bought the purifiers for their children and the elderly and invested in equipment with a low maintenance cost.

Nitin Sharma, a senior executive at Global Gadgets Store in Khan Market, said, "As the air quality deteriorated after Diwali, sales have gone up. The sales will go up in the upcoming days."

The store sold 30 air purifier units on Thursday.

However, buying an air purifier is not enough as it requires maintenance with regular cleaning of the filters to ensure proper functioning.

"People forget to clean the filters and that affects its life span. You should clean the filters every week to ensure longevity for the filter and the machine," said Parth Ahuja, a purification expert at Dyson.

Many doctors are also recommending patients, especially the vulnerable such as the elderly, children and people with respiratory ailments, to use air filters at home and avoid stepping out during early mornings and evenings.

Dr Rahul Sharma, additional director (pulmonology) at Fortis Hospital in Noida, said, "HEPA (high efficiency particulate) filters work well and we recommend them to patients, especially those who are homebound.

"The purifier works in a limited cubic metre of space. While buying a purifier one should check the capacity of how much air it can purify in accordance with the capacity of your home. Another important thing is that there are HEPA filters and HEPA-like filters, which are not as effective as HEPA filters and are also very expensive."