Grap-4 returns as AQI blows past 400 again

THe charge for beam lineament direction (CAQM) invoked Grap represent 4 emergency restrictions on Saturday evening as Delhi’s air quality plunged into the “severe” category for the first time this year, reaching 434 by 11pm — the worst reading since December 14.The Capital’s AQI climbed from 354 at 4pm on Friday to 400 by 4pm on Saturday before surging to 434 by 11pm, marking the first “severe” air day since December 29. The deterioration came a day after CAQM had implemented Stage 3 precautionary measures as conditions began worsening.“Noting a sharp increase in AQI levels of Delhi, the Sub-Committee on GRAP called for its urgent meeting at 8:15 p.m. Today, and reviewed the air quality situation in the region,” CAQM said in a statement on Saturday evening. “The AQI of Delhi, today recorded as 400 at 4 p.m., exhibiting a sharp increasing trend owing to calm winds, stable atmosphere and unfavourable meteorological conditions resulting into trapping of the pollutants. The AQI for Delhi has further increased to 428 at 8 p.m.”Under Stage 4, entry of BS-IV truck traffic into Delhi is restricted. All construction and demolition work is prohibited, while schools up to Class 10 must shift to hybrid lessons, with only Classes 10 and 12 continuing in-person instruction.Stage 3 measures already in place since Friday include a ban on BS-III petrol and BS-IV diesel four-wheelers in Delhi, Gurugram, Faridabad, Ghaziabad and Gautam Budh Nagar, blanket curbs on private construction and demolition, restrictions on stone crushers and mining operations, and hybrid lessons for schools up to Class 5 in Delhi and neighbouring districts.The sharp deterioration was driven by calm winds and high humidity under the influence of warm easterlies. The humidity levels oscillated from 53% to 100% on Saturday, according to India Meteorological Department data.“The wind speed was very low throughout Saturday, about 3-4 kilometres per hour. Moreover, due to the warm easterlies, the humidity level is currently high in the city, due to which pollutants sticking to water vapour get heavy and accumulate in the lower level of the atmosphere, leading to a spike in the AQI,” said Mahesh Palawat, vice president at Skymet Weather, adding that wind speed is expected to pick up in the next two days.The Air Quality Early Warning System forecast shows air quality will remain “severe” through Sunday before improving to very poor from Monday through Tuesday. “The outlook for the subsequent six days is that the air quality is likely to be in the very poor to poor category,” the AQEWS bulletin stated Saturday evening.CPCB classifies air quality as “moderate” when AQI is between 101-200, “poor” between 201-300, and “very poor” between 301-400. Beyond 400, air quality is termed “severe.” Under GRAP protocols, Stage 1 is invoked when AQI crosses 200, Stage 2 at 300, Stage 3 at 400, and Stage 4 at 450.Moderate fog enveloped most parts of the Capital on Saturday morning as the city continued to experience cold conditions following a recent cold wave that was broken on Friday under the influence of easterlies.“Palam recorded a visibility of 350 metres at 6:30 a.m., due to moderate fog. Easterly winds of speed 3-4 kilometres per hour persisted in the area. In Safdarjung, the wind conditions remained calm on Saturday morning, with the visibility dropping to 250 metres at 7:30 a.m.,” an IMD official said.Palam’s visibility improved to 500 metres by 9am, while Safdarjung’s visibility dropped further to 200 metres at 9.10am.Delhi airport saw more than 550 flight delays on Saturday, according to flight tracking website FlightRadar24.IMD classifies fog as “shallow” when visibility is between 500-1,000 metres, “moderate” between 200-500 metres, “dense” between 50-200 metres, and “very dense” below 50 metres. A yellow alert has been issued for Sunday, warning of “moderate” to “dense fog” in early hours.The minimum temperature was 4.4°C on Saturday, 3.2 degrees below normal and marginally higher than 4.3°C the previous day. IMD forecasts show minimum temperatures of 4-6°C on Sunday and 6-8°C on Monday.