The Commission for Air Quality Management on Tuesday imposed Stage 1 restrictions under the Graded Response Action Plan in Delhi and the adjoining National Capital Region after the air quality slipped into the “poor” category.GRAP is a set of incremental anti-pollution measures that are triggered to prevent further worsening of air quality once it reaches a certain threshold in the Delhi-NCR region.The first stage involves measures such as mechanical sweeping of roads and sprinkling water on them to keep dust from rising. It also bans some kinds of construction and demolition activities.The Commission for Air Quality Management said that in its meeting on Tuesday it reviewed the air quality scenario in the region and observed that Delhi’s Air Quality Index had shown an increasing trend and was recorded at 208, which is in the “poor” category.The statutory body noted that the AQI is likely to remain in the “poor” category in the coming days.As of 6.05 pm on Tuesday, Delhi recorded an average AQI of 206, showed the Sameer application, which provides hourly updates published by the Central Pollution Control Board.In Uttar Pradesh, while Noida recorded a “poor” AQI of 238 and Ghaziabad of 248, Greater Noida was in the “very poor” category at 304, the application showed.In Haryana, Gurugram recorded an AQI of 188 and Faridabad 196, both in the “moderate” category.An index value between 0 and 50 indicates “good” air quality, between 51 and 100 indicates “satisfactory” air quality and between 101 and 200 indicates “moderate” air quality. As the index value increases further, air quality deteriorates. A value of 201 and 300 means “poor” air quality, while between 301 and 400 indicates “very poor” air.Between 401 and 450 indicates “severe” air pollution, while anything above the 450 threshold is termed “severe plus”.Stage 1 of GRAP is activated when the AQI is in the “poor” category. The second, third and fourth stages are activated when the AQI crosses the “very poor”, “severe” and “severe plus” categories.IMD issues yellow alert for heatwave in DelhiThe India Meteorological Department on Tuesday issued a “yellow” alert for heatwave conditions in isolated parts of Delhi until May 25, with the maximum temperature expected to hover about 44 degrees Celsius.A yellow alert stands for “be updated”.The weather agency said that isolated areas are likely to experience heatwave-like conditions during the day.The IMD said that temperatures indicate that the level of heat is generally tolerable for the public but may pose a moderate health risk for vulnerable groups such as infants and elderly people with chronic illnesses.It advised people to avoid heat exposure, wear light-coloured, loose-fitting cotton clothing and cover their heads with a cloth, hat or umbrella. It also recommended drinking sufficient water frequently and keeping fire extinguishers at home and in vehicles.Written by Sara Varghese. Edited by Nachiket Deuskar.Also read:Delhi’s failure to act against the biggest source of its air pollution – vehiclesIndia’s car-first cities should prioritise walking to help tackle smogAir pollution can increase risk of motor neurone diseases, worsen outcomes