NEW DELHI: Delhiites could see poison in the air on Sunday. A thick layer of toxic smog enveloped the capital, turning the city into a gas chamber with air quality plunging to ‘severe-plus’ category for the first time this year.The city’s 24-hour average air quality index stood at 461, the second-worst recorded in Dec and the worst in nearly 13 months. Since the scale began in April 2015, only once has a higher AQI been recorded in Dec – 469 on Dec 21, 2017. For any month, the last time Delhiites a suffered worst AQI was on Nov 18 last year (494).
AQI Severe-Plus, Delhi’s Worst In More Than 1 Yr
High moisture, low temperatures and calm winds effectively trapped pollution close to the surface even as a grey smog screened out the sun for most of the day. Winds are predicted to pick up slightly post-noon on Monday, which could disperse some pollutants.On Sunday, atmospheric ‘inversion’ made the situation worse. This occurs when cooler air near the ground gets trapped un-der warmer air above, stop ping pollutants from dispers ing. Though meteorological conditions remained unfa-vourable for the dispersion of pollutants, local emissions continued to remain high.“This is a true depiction. of Delhi’s local emissions be cause wind speeds are almost zero, meaning there is hardly any inflow or outflow of air. Vertical ventilation is con-fined to a column of just 600 metres, which means whatev er remains in the box-Delhi is largely its own emis sions. Under these condi-tions, the contribution of dust is negligible. When dust is released from construction activity, it usually spreads to other areas due to wind, but with winds nearly calm, it cannot pollute places beyond the immediate site of re-lease,” said Gufran Beig. founder of the System of Air Quality and Weather Fore-casting and Research (SA-FAR) and Chair Professor at the National Institute of Ad-vanced Studies (NIAS).Of the total 39 active air quality monitoring stations, 38 saw ‘severe’ AQI while only Shadipur was placed in the ‘ve-ry poor category at 375. Of these, three stations Wazir pur, Rohini and Ashok Vihar maxed out at 500, while several others reported AQI above 490.This is the second spell of severe air days in Delhi this season. The city had recorded three consecutive severe days from Nov 11 to 13. In this win-ter season, the city has re-corded five such days, when AQI surpassed 400.After air quality started rapidly deteriorating on Saturday, the Graded Response Action Plan’s stage III was im-posed in the morning. Stage IV was invoked on Saturday eve ning as AQI showed no sign of improvement. Currently, all stages of GRAP are in force.Delhi’s highest-ever AQI of 497 was recorded on Nov 6, 2016. The second-worst air quality day followed on Nov 18 last year with AQI reaching 494.
