The Centre's air quality panel for Delhi-NCR Monday invoked restrictive measures under stage three of the air pollution control plan amid a sharp dip in air quality due to unfavourable meteorological conditions. Delhi's AQI stood at 367 at 2 pm. Poor air quality, caused by unfavourable weather conditions, often persists from November to January. Considering the highly unfavourable meteorological conditions including calm winds and very low mixing height leading the AQI of Delhi into the higher end of the very poor category, the panel's sub-committee on Graded Response Action Plan decides to impose stage 3 of the revised GRAP schedule (issued on Friday) in the entire NCR, with immediate effect, an official order said. According to the revised plan, schools and colleges in Delhi, Gurugram, Faridabad, Ghaziabad, and Gautam Budh Nagar are mandatorily required to shift classes up to Class V to hybrid mode under GRAP Stage III. Students and parents will have the option to choose online education wherever it is available. Stage 3 also entails a ban on non-essential diesel-operated medium goods vehicles with BS-IV or older standards within Delhi. Non-essential diesel light commercial vehicles of BS-IV or older standards, registered outside Delhi, are also not allowed to enter the city. Previously, such restrictions were applicable only to BS-III vehicles. Persons with disabilities are exempt from restrictions imposed on BS-III petrol and BS-IV diesel cars in Delhi and the districts of Gurugram, Faridabad, Ghaziabad, and Gautam Budh Nagar under stage III. The Delhi and NCR state governments have also been directed to stagger timings for public offices and municipal bodies under stage III. The Centre may decide on similar staggered timings for central government offices in Delhi-NCR. During winters, Delhi frequently enforces restrictions under the Graded Response Action Plan (GRAP), which categorises air quality into four stages -- Stage I (Poor) with AQI between 201 and 300, Stage II (Very Poor) between 301 and 400, Stage III (Severe) between 401 and 450, and Stage IV (Severe Plus) for AQI above 450