National helicopter carrier Pawan Hans on Monday told the Delhi government its aircraft cannot be used to sprinkle water to dissipate the smog in the city because of low visibility caused by the pollution, The Indian Express reported. On Friday, it had agreed to help the administration make it possible to aerially sprinkle water over Delhi.

Delhi Environment Minister Imran Hussain held a meeting with officials from Pawan Hans and the Civil Aviation Ministry on Monday, after which Pawan Hans Chairperson and Managing Director BP Sharma told The Indian Express that it was not possible for the helicopter carrier to carry out water sprinkling operations.

“Right now, with the prevailing smog, it is not possible for the helicopters to carry out operations,” he said. “We have communicated the same to the Delhi government.”

Delhi and several other parts of North India have been blanketed by a thick layer of smog for a week now. Pollution levels in the Capital declined marginally on Tuesday, going from “severe” to the “hazardous” category. At 3 pm, the Air Quality Index am read 348 at RK Puram and 333 in Punjabi Bagh.

Moreover, no-fly zones in the New Delhi district makes sprinkling possible only in a few areas, the Hindustan Times reported on Tuesday. A retired air traffic controller told the newspaper that sprinkling operations would be difficult in Delhi because areas such as Vasant Kunj and Dwarka are descending zones for civilian aircraft.

“Aircraft start descending at a height of 3,500 feet when they approach Delhi,” Gurcharan Bhatura said. “Areas like Vasant Kunj and Dwarka are descending zones. The Delhi airport is a busy airspace, so you cannot halt operations for water sprinkling. It will only be possible to operate choppers at a low height for long periods in North and East Delhi.”

The Aam Aadmi Party government in Delhi had offered to pay for the use of helicopters to sprinkle water over the city to settle pollutants. Union Environment Minister Harsh Vardhan had asked the Delhi government to examine whether the measure was cost-effective before implementing it.