In a welcome meteorological shift, strong and persistent westerly winds swept across the Indo-Gangetic plains on Monday, delivering a rare and significant improvement in air quality for several major cities, even as dense fog continued to envelop the region. While Delhi remained under a toxic haze due to stagnant conditions, urban centres in Bihar and Uttar Pradesh, including Patna, Lucknow, Varanasi, and Prayagraj, recorded a notable drop in their Air Quality Index (AQI).
Sharp Drop in Pollution Levels Across Cities
Patna emerged as a standout example, with its AQI plunging to 88, placing it in the "satisfactory" category for the first time in December. This marked a dramatic improvement from Sunday's reading of around 116. The Central Pollution Control Board recorded this data at 4 PM, making it the lowest AQI the city has witnessed this month after enduring weeks of moderate to poor air.
The positive trend was mirrored in other parts of the plains. Lucknow recorded an AQI of 136 (moderate), Varanasi 76 (satisfactory), and Prayagraj 145 (moderate). This simultaneous improvement across a wide geographical stretch points to a broad regional weather change rather than isolated local efforts, according to environmental experts.
Role of Wind Speed and Direction in Clearing the Air
The primary driver behind the cleaner air was identified as consistent westerly winds blowing at speeds of 8-12 kilometres per hour. Devendra Kumar Shukla, Chairman of the Bihar State Pollution Control Board (BSPCB), explained that these winds played a dual role. They effectively dispersed accumulated pollutants and weakened the seasonal thermal inversion layer—a winter phenomenon in the plains that traps smog close to the ground by preventing vertical mixing of air.
"This time, it is becoming southwest more and mostly westerly is blowing. Previous year, it was mostly north-westerly wind, which brings more pollutants," Shukla stated. He emphasized that the wind speed was crucial in preventing pollutant accumulation, even with increased vehicle movement over the weekend.
Data from Patna's six monitoring stations largely reflected satisfactory conditions:
- Rajbanshi Nagar: 72
- Muradpur: 76
- DRM office-Khagaul: 77
- Planetarium: 82
Areas like Patna City and Samanpura recorded moderate levels of 113 and 109, respectively.
Patna's Advantage and a Cautionary Note
Chairman Shukla highlighted a structural advantage for Patna compared to the national capital. "Unlike Delhi, where heavy local industrial and household contributions keep AQI high regardless of external factors, Patna has negligible industrial pollution," he said. He credited measures like shifting industries to Piped Natural Gas (PNG) for substantially reducing local pollution sources. External dust from areas like the Ganga diara was also limited due to the favourable wind direction.
Furthermore, Shukla noted that despite the presence of the winter inversion layer, its impact was muted due to relatively low concentrations of the harmful PM2.5 particulate matter. "If it is very less, then the effect will also be very less," he added.
However, environmental experts have issued a caution, warning residents that this reprieve is likely temporary. Air quality is expected to deteriorate again if the wind speeds drop, allowing pollutants to accumulate once more. The episode underscores the critical role of meteorological factors in the perennial air pollution battle of the Indo-Gangetic region.
