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Delhi's air quality, which had enjoyed an unprecedented clean period until mid-December, has taken a sharp downturn, plunging into the 'very poor' category with an average Air Quality Index (AQI) of 379. This drastic shift has prompted the reintroduction of anti-pollution measures, including a mandatory hybrid learning mode for junior classes and a ban on older petrol and diesel vehicles. The deterioration is primarily attributed to a confluence of factors, most significantly the unusually low wind speeds and the early onset of a cold wave. Understanding these contributing elements is crucial to mitigating the recurring problem of Delhi's severe air pollution.
The most immediate factor impacting Delhi's air quality is the remarkably low wind speed. Typically, strong winds disperse pollutants, preventing their accumulation in the atmosphere. However, the current situation is characterized by extremely calm winds, with speeds consistently below 6 kmph for extended periods. This stagnation traps pollutants close to the ground, leading to a sharp increase in their concentration. The phenomenon is further exacerbated by the low temperatures associated with the cold wave. Cold air is denser and holds pollutants more effectively, inhibiting their vertical dispersion. The inversion height, the atmospheric layer above which pollutants can typically rise and dissipate, is lowered during cold spells, effectively creating a pollution trap close to the ground. The India Meteorological Department (IMD) forecasts predict continued low wind speeds throughout the week, suggesting a continuation of poor air quality. The Central Pollution Control Board (CPCB) notes that wind speeds below 10 kmph are generally unfavourable for pollutant dispersal, highlighting the severity of the current conditions.
The unexpectedly early onset of cold wave conditions has further aggravated the situation. The IMD defines a cold wave as occurring when temperatures dip below 4.1 degrees Celsius or when there is a significant temperature departure from the normal minimum, provided the normal minimum is below 10 degrees Celsius. Delhi experienced its earliest cold wave in 23 years, with the first cold wave day occurring on December 11th, when the minimum temperature plummeted to 4.9 degrees Celsius. This early arrival of cold weather has significantly contributed to the trapping of pollutants, worsening the air quality. The prolonged cold wave, predicted to persist until at least Wednesday, further exacerbates the problem by maintaining the atmospheric conditions that favor pollution accumulation. The historical context further emphasizes the unusual nature of this early cold wave, underscoring its role in the current air quality crisis.
While meteorological factors play a dominant role, anthropogenic contributions cannot be ignored. Data from the Decision Support System for Air Quality Management in Delhi shows that the transport sector remains a significant contributor to pollution, accounting for 16.94 percent of the pollution as of December 12th. This highlights the ongoing challenge of managing emissions from vehicles, even during periods when other stringent measures are in effect. The industrial sector also plays a notable role, contributing 8.36 percent to particulate matter pollution. These figures underscore the need for sustained efforts to control emissions from various sources, coupled with effective measures to address the impact of meteorological conditions. The lack of significant rainfall also contributes, as rainfall acts as a natural cleansing mechanism, washing pollutants out of the atmosphere. The absence of any substantial rainfall in December and the lack of rainfall predicted for the coming week further compounds the problem.
The interplay between meteorological factors and anthropogenic emissions underscores the complexity of addressing Delhi's air pollution. The current situation highlights the urgent need for comprehensive and integrated strategies. These strategies must address both the short-term challenges of managing pollution during periods of low wind speed and cold waves, as well as long-term solutions focusing on emissions reduction from various sources. The reliance on short-term measures like hybrid learning and vehicle restrictions, while crucial in the immediate term, must be complemented by far-reaching measures to reduce the overall pollution load on Delhi’s atmosphere. Without a sustained multi-pronged approach that incorporates meteorological predictions into pollution management strategies and effectively addresses emissions from all sources, Delhi’s recurring air pollution crisis will continue to pose a serious public health risk.