NEW DELHI: Just two days ahead of Diwali , the air quality of the national capital plunged to a 'very poor' category. At 8:30 am, the air quality index was docking at 326.In Dhirpur, the AQI was 351 which falls in the 'very poor' quality while in Delhi University vicinity, the AQI was 357 and in Chandni Chowk it was 325.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', and 401 and 500 'severe'.The System of Air Quality and Weather Forecasting And Research (SAFAR) has advised 'Sensitive Groups' to reduce prolonged or heavy exertion. The locals are advised to take more breaks and do less intense activities.The asthmatics have been advised to keep medicine ready if symptoms of coughing or shortness of breath occur. "Heart patients, see the doctor, if get palpitations, shortness of breath, or unusual fatigue," the organisation stated in its advisory.Not only that, it is believed that the smoke generated from the stubble burning in Punjab and Haryana are responsible for the spike in air pollution in Delhi and its adjoining regions.Last month, NASA satellite images also recorded several incidents of farm fires across Haryana and Punjab, indicating that the stubble burning season had started in the two states.From October 15, stringent measures to combat air pollution have come into force in the national capital and its nearby regions as part of the Graded Response Action Plan.This plan which was first implemented in Delhi and NCR in 2017 includes increasing bus and metro services, hiking parking fees and stopping the use of diesel generator when the air quality turns poor.Other major cities such as Kolkata, Mumbai, and Chennai, as compared to Delhi, have much better air quality.The highest PM2.5 exposure level was in Delhi, followed by the other north Indian states of Uttar Pradesh, Bihar and Haryana.