Chennai: Foggy and misty mornings since Sunday may have offered a pleasant start to the week for morning walkers, but they also trapped pollutants close to the ground, spiking air quality in some parts of the city to unhealthy levels. For the last three days, a few monitoring stations recorded air quality index (AQI) values above 100 and 200 at 6am, categorized as ‘moderate’ and ‘poor’. By Tuesday evening, pollution levels worsened, with Kodungaiyur’s AQI breaching 350 and slipping into the ‘very poor’ category. Data from Tuesday (Feb 10) highlighted the spike. At 6am, Kodungaiyur recorded an AQI of 276 (poor), while Arumbakkam (129), Manali (176), Perungudi (111) and Royapuram (145) were in the ‘moderate’ range. By 7pm, Kodungaiyur deteriorated to 359 (very poor), while Manali and Royapuram climbed to 205 and 244, shifting from ‘moderate’ to ‘poor’, despite wind speeds improving to 12-15km/h. While Perungudi and Kodungaiyur, which have the dump yards, had PM2.5 as the prominent pollutant, the rest of the stations recorded PM10.
There was a decline in the early morning air quality from previous days. At 6am on Feb 9, AQI largely stayed in the ‘moderate’ category, with Kodungaiyur recording the highest at 122. There was insufficient data pertaining to Manali and Velachery. It was better than Feb 8, when dense fog blanketed much of the city. Velachery recorded 284 (poor), while Manali (173), Arumbakkam (132) and Kodungaiyur (112) were in the ‘moderate’ range, showing a gradual but steady worsening since Sunday.Meteorologists said fog and mist formed due to the interaction of northerly and north-north-easterly winds with moist easterlies from the Bay of Bengal. This led to condensation, causing pollutants to attach to water vapour and remain suspended near the surface, instead of dispersing, under calm wind conditions.While emissions were largely from local sources such as vehicles, power plants, dump yards, burning of waste and construction, pollution expert Sunil Dahiya warned that worsening air quality despite favourable coastal winds was a concern. “For coastal cities like Chennai and Mumbai, sea breezes usually disperse pollutants. If air quality continues to worsen despite good winds, it means emissions exceeded the city’s carrying capacity. Chennai must act now,” he said.IMD forecast mist or haze to persist in isolated pockets over Chennai, Tiruvallur, Kancheepuram and Chengalpet. Mahesh Palawat, chief meteorologist at Skymet Weather, said early morning mist may last another two to three days. “Winters are nearing their end across the country. Temperatures may gradually rise, a trend already visible over parts of north India,” he said.
