The Commission for Air Quality Management on Saturday tightened the particulate matter emission norms for 17 categories of industries in Delhi and the National Capital Region, directing them to comply with a revised standard of 50 mg/Nm³ by October.

The commission is a statutory body formed in 2020 to address pollution in the NCR and adjoining areas.

Under the new direction, large and medium industries must meet the 50 milligram per cubic metre or mg/Nm3 limit by August 1, while the remaining identified industries have until October 1 to comply.

The revised norm replaces the March 2022 standards, which set a maximum permissible particulate matter emission limit of 80 mg/Nm³ and an advisory target of 50 mg/Nm³.

Air quality deteriorates sharply in the winter months in Delhi, which is often ranked the world’s most polluted capital. Stubble burning in Punjab and Haryana, vehicular pollution, along with the lighting of firecrackers during Diwali, falling temperatures, decreased wind speeds and emissions from industries and coal-fired plants contribute to the problem.

The new norms will apply to highly polluting industries identified by the Central Pollution Control Board, including red category medium and large air-polluting units, food and food processing industries operating boilers or thermic fluid heaters, textile units with similar equipment and metal industries operating furnaces.

“Industrial stack emissions are a significant source of aggravating PM levels in Delhi-NCR and also contribute to secondary particulate formation, thereby impacting air quality of the region,” read a notice by the commission.

It added that the revised standard was based on recommendations of the Central Pollution Control Board, backed by a technical study conducted by the Indian Institute of Technology, Kanpur, which assessed emission control technologies, feasibility and costs for the targeted sectors.

The 50 mg/Nm³ benchmark was found to be “technically achievable and environmentally necessary”, the panel said.

It also noted that the revised norm will not apply to industrial units that are already subject to stricter PM emission standards of less than 50 mg/Nm³, such as thermal power plants or waste-to-energy plants.

State governments of Delhi, Haryana, Uttar Pradesh and Rajasthan, along with their respective pollution control boards and the Delhi Pollution Control Committee, have been directed to publicise the order, undertake stakeholder sensitisation and ensure strict implementation.