The air quality in Delhi has begun deteriorating ahead of the winter season.

The Graded Response Action Plan to curb air pollution in Delhi-NCR will come into force on Tuesday, proactively rolling out stricter measures depending on the need to discourage private vehicles on roads, stop entry of trucks, use of diesel generators, and closing brick kilns and stone crushers.

The air quality in Delhi has begun deteriorating ahead of the winter season. On Sunday, it turned "very poor" with the overall Air Quality Index going beyond the 300 mark. On Monday, it improved by around 50 points but the situation has continued to oscillate between poor and very poor for the last 24 hours.

Biomass burning is likely to contribute 9 per cent to Delhi's PM2.5 concentration on October 15, the Centre-run System of Air Quality and Weather Forecasting and Research (SAFAR) said.

Prepared by the Central Pollution Control Board and first implemented in Delhi-NCR in 2017, the Graded Response Action Plan lists measures to curb air pollution according to the severity of the situation.

This year, GRAP will witness the return of Delhi government's odd-even car rationing scheme from November 4 and the extension of the ban on diesel gen-sets to NCR cities of Gurgaon, Ghaziabad, Noida, Greater Noida, Faridabad, Sonepat, Panipat and Bahadurgarh.

GRAP measures include increasing bus and metro services, hiking parking fees and stopping use of diesel gen-sets when the air quality turns "poor".

When it turns "severe", GRAP recommends closure of brick kilns, stone crushers and hot mix plants, sprinkling of water, frequent mechanised cleaning of roads and maximising power generation from natural gas.

The measures to be followed in "emergency" situation include stopping entry of trucks in Delhi, ban on construction and introduction of the odd-even car rationing scheme.

Experts have hailed GRAP for a gradual reduction in pollution levels over the years and fixing accountability as it clearly marks agency responsible for each action to be taken.

The Environment Pollution (Prevention and Control) Authority (EPCA) and the Central Pollution Control Board have been proactive and conducted several meetings to ensure strict implementation of anti-pollution measures by each state.

EPCA chairman Bhure Lal has visited pollution hot spots in Delhi-NCR and assessed preparedness for GRAP implementation. He has directed Delhi and the adjoining states to ensure pollution levels do not rise further even during adverse weather.

The top court-mandated panel has also sought local action plans for pollution hotspots - 14 in Delhi and five in NCR.

The Delhi Pollution Control Committee has started night patrolling and is penalising industries using non-PNG fuels and construction agencies for failing to prevent dust emission.

Strict vigil is being maintained to prevent open burning of garbage, plastic and rubber waste.