Delhi, known for its challenging air quality, particularly in the winter months, recorded an unexpected improvement in air conditions after Diwali. This year, the city witnessed the second cleanest air quality since 2015 for the post-Diwali period, surprising residents and experts alike. Though Delhi’s Air Quality Index (AQI) stayed within the “very poor” range rather than hitting “severe,” the improvement marked a significant achievement, considering the usual pollution spike during and after Diwali festivities.
The Impact of Favorable Winds on Delhi’s AQI
Delhi’s air quality saw a marked improvement, thanks to a powerful natural factor—strong winds. By late afternoon on Friday, the AQI had dropped to 339, further improving to 323 by the evening. According to experts, these strong winds, blowing at speeds of up to 16 kilometers per hour, played a vital role in dispersing the dense layer of smoke and pollutants that had settled over the city due to Diwali fireworks, stubble burning, and local emissions.
The winds, described as a form of “natural ventilation,” lifted pollution away from ground level, providing relief that minimized the usual Diwali-related smog. Mahesh Palawat, Vice President of meteorology at Skymet, noted, “Higher temperatures during the day also contributed to a favorable mixing height, allowing pollutants to disperse more freely.” In contrast, lower temperatures tend to trap pollutants closer to the ground, creating an inversion layer where pollutants linger in the air, leading to health concerns.
Delhi’s AQI Through the Diwali Period
Delhi’s air quality took a steep climb as Diwali celebrations set in, with the AQI moving from 328 on Thursday evening to 362 by Friday morning. This spike was largely due to Diwali fireworks and an increase in emissions from nearby stubble burning. Local sources of pollution, including vehicle emissions and industrial activity, added further pressure. However, strong winds and relatively warmer conditions helped in the rapid dissipation of pollutants, pulling Delhi’s AQI back down to “very poor” by the afternoon on Friday.
The city’s AQI this year reflects the complex interaction of seasonal factors and local sources of pollution. As the winds picked up and the temperature stayed relatively higher than expected, pollutants that would typically settle in the lower atmosphere found room to disperse. This phenomenon brought temporary relief to Delhi’s residents, though experts warn of challenges ahead as colder months settle in.
Diwali Pollution Sources and Stubble Burning Impact on Delhi’s Air
Delhi’s air pollution levels during Diwali can be attributed to a combination of firecracker usage, stubble burning from neighboring states, and emissions from local sources. While some residents in south Delhi made efforts to limit firecracker use, other parts of the city compensated with increased activity. Additionally, stubble burning from states like Punjab and Haryana contributed significantly, with its impact on PM2.5 levels reaching over 27% on Diwali day—up from less than 10% earlier in the week.
Anumita Roychowdhury, Executive Director of Research and Advocacy at the Centre for Science and Environment (CSE), emphasized that while natural ventilation provided short-term relief, Delhi’s overall pollution levels are concerning. “Despite minimal contribution from farm fires in October, the city experienced more ‘poor’ and ‘very poor’ air quality days, indicating substantial local pollution sources,” she explained. The trend suggests that local industrial emissions, vehicular pollution, and other urban factors continue to exacerbate Delhi’s air quality, even as the impact of crop burning is seasonal.
How Weather and Temperature Play a Role in Delhi’s Air Quality
The improved air quality can be partly credited to favorable weather conditions. Meteorologists report that on Diwali night, wind speeds ranged from 12 to 16 km/h, aiding in pollutant dispersal. However, as the night progressed, the wind speed fell slightly but picked up again by Friday morning. The timely arrival of wind, coupled with warmer-than-average temperatures, created an environment less conducive to pollutant trapping.
Palawat explained, “During winter, as temperatures drop, wind speeds slow down, and the mixing height drops to as low as 200-300 meters, trapping pollutants close to the ground.” This phenomenon, known as temperature inversion, often results in dense smog. However, this Diwali, the mixing height remained high, around 2,100 meters, facilitating pollutant dispersal and preventing the formation of a thick smog layer.
The Role of Policy and Public Awareness in Delhi’s Fight Against Pollution
While natural factors contributed to Delhi’s cleaner-than-usual post-Diwali air, consistent efforts are required to address long-term air quality issues in the city. In recent years, Delhi has implemented a range of policies, including restrictions on firecracker use, stricter emission regulations, and public awareness campaigns to curb pollution. However, enforcement challenges and public compliance remain obstacles. This year’s relative success could serve as an encouraging example for both policymakers and the public to continue adopting and adhering to pollution control measures.
At the same time, the local and regional pollution landscape underscores the need for coordinated efforts across state boundaries. Stubble burning, while a significant contributor, is one of many factors affecting Delhi’s air quality. Collaborative policies between states could help reduce crop residue burning, while enhanced public awareness can encourage individuals to contribute to a cleaner environment, particularly during festival seasons.
The Road Ahead for Delhi’s Air Quality
Although Delhi’s post-Diwali AQI this year marks a second-cleanest reading since 2015, experts caution that the city’s air quality remains vulnerable. As winter approaches, pollution levels are likely to spike once again due to the seasonal drop in temperatures and reduced wind speeds. Hourly spikes in PM2.5 levels in some areas of Delhi have already exceeded national permissible limits by as much as 30 times, underscoring the ongoing need for vigilance and proactive measures.
Addressing Delhi’s air pollution requires a combination of policy enforcement, public awareness, and cooperation across regions. While this year’s Diwali period highlights the positive impact of natural ventilation, long-term improvements hinge on tackling both local emissions and regional contributions. With continued efforts from policymakers and citizens alike, Delhi can strive for cleaner air year-round, not just during favorable weather conditions.
This year’s experience offers hope but also serves as a reminder of the critical challenges that lie ahead. If Delhi can harness the lessons from this post-Diwali period, it may pave the way toward sustainable improvements in air quality for the future.