Delhi air pollution: With air quality in Delhi-NCR deteriorating further, authorities have directed schools and colleges to suspend physical classes. Delhi air pollution: Delhi continues to grapple with hazardous air pollution as the Air Quality Index (AQI) reaches the "severe plus" category, touching the 500 mark in several areas. The overall AQI spiked to 494, marking one of the worst pollution spells that the city has recorded in the past few years.   According to the Central Pollution Control Board (CPCB), the air quality index in several areas of Delhi, including Anand Vihar, Ashok Vihar, Bawana, Jahangirpuri, and Major Dhyan Chand Stadium, reached 500 on Tuesday morning. 'Severe' air quality can have an adverse effect on both healthy individuals and people who already have medical conditions.   A thick layer of smog has engulfed Delhi, obscuring visibility and creating a hazy atmosphere as the Air Quality Index (AQI) surged to 494, marking the highest level of the season. The strictest restrictions under the Graded Response Action Plan (GRAP) IV are now in effect in the capital. The Supreme Court has directed authorities not to lift the curbs without its permission even if the AQI falls below 450.   AQI in parts of Delhi-NCR Alipur: 500 Anand vihar: 500 Ashok Vihar: 500 Bawana: 500 DUTL 496 Dwarka Sector-8: 496 Dilshad Garden: 500 JLN: 498 ITO: 386 Lodhi Road: 493 Mundka: 500 Mandir Marg: 500 Najafgarh: 491 Vivek Vihar: 500 Wazirpur: 500 Noida Sector 125: 405 Noida Sector 62: 497 Noida Sector 1: 413 Noida Sector 1: 422 Gurugram Sector 51: 403 Notably, an AQI between 0 and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', 401 and 450 'severe', and above 450 'severe plus'. Schools, colleges closed in Delhi-NCR The Supreme Court of India has ordered the closure of 10th and 12th grade classes across the Delhi-National Capital Region (NCR) due to the worsening air quality. The Court emphasised the need for all educational institutions to switch to online classes as a precautionary measure against hazardous air pollution levels. Earlier, the physical classes were discontinued for all students, except those in classes 10 and 12. According to the court's new order, now, all classes will be continued online for the sake of student's well-being.   The district administrations of Ghaziabad and Gautam Buddh Nagar (Noida) ordered the suspension of physical classes till Class 12 in all schools and said studies will continue online due to poor air quality in the region. Gurugram Deputy Commissioner Ajay Kumar also ordered the closure of schools up to 5th standard with effect from November 19 until further orders. Delhi University and Jawaharlal Nehru University (JNU) also decided to suspend physical classes and hold classes online till November 22. GRAP Stage-IV restrictions in Delhi-NCR According to the order, no trucks would be allowed into Delhi except for those carrying essential items or using clean fuel (LNG/CNG/BS-VI diesel/electric). Non-essential light commercial vehicles registered outside Delhi will also be prohibited, except for EVs, CNG and BS-VI diesel ones. All construction activities, including highways, roads, flyovers, power lines, pipelines and other public projects, have been suspended.