Shifting Patterns of Air Quality in India: Insights from Recent Study
The winter of 2022-23 saw a significant drop in air pollution levels across northern India. PM2.5 levels, harmful fine particulate matter, were reduced by as much as 30% compared to the average over the previous three winters. Meanwhile, in peninsular India, cities like Mumbai faced a stark contrast, experiencing a 45% spike in the same pollution levels.
Fast forward to the winter of 2023-24, and the situation reversed dramatically. The North now grapples with rising PM2.5 levels, while peninsula regions observe a significant decrease. What caused this striking shift in a year? A recent study sheds light on this question, highlighting the influence of weather phenomena known as La Niña and El Niño.
The study, titled “Air quality in flux: The baffling ENSO transition in India,” was published in the journal Atmospheric Pollution Research. It indicates that the atmospheric conditions during the La Niña winter of 2022-23 and the following El Niño winter significantly altered how pollutants were transported and dispersed across the region.
According to researchers, while it’s widely understood that weather conditions can influence pollution levels, this study reveals just how differently the atmosphere can behave under these systems. They noted that even with consistent emissions, the location of high pollution levels can vary from year to year, depending on these atmospheric changes.
Gufran Beig, an atmospheric scientist and one of the authors of the study, emphasized that this year’s El Niño could be the strongest on record, but it does not mean that the air quality issues observed this winter are guaranteed to repeat in the future. He reminded that the past two years had unique weather patterns that were not usual.
In 2022-23, during the La Niña winter, strong winds helped to disperse pollution from sources such as agricultural stubble burning, directing these pollutants toward peninsular India. As a result, cities like Mumbai and Thiruvananthapuram saw drastically increased PM2.5 levels.
In contrast, the following winter under the El Niño influence saw weaker winds in northern India, allowing pollutants to linger, particularly in cities like Delhi and Jaipur. For instance, Jaipur recorded a nearly 50% increase in PM2.5 levels compared to averages from 2019-2022, while Delhi experienced over a 10% spike.
Weather also played a vital role; rain can help clear pollutants from the air, while high pressure and stagnant winds tend to trap them close to the ground. Different weather patterns meant that, during the La Niña winter, rainfall led to decreased pollution, whereas the following winter, high-pressure systems contributed to pollution spikes even after rain.
The researchers tracked the movements of air masses to understand where pollution was coming from. They found that during the winter of El Niño, cities like Jaipur continued to receive polluted air from northern regions, while Hyderabad benefited from cleaner southern and marine air.
Overall, the study highlights that air quality can vary significantly from year to year, with fluctuations in PM2.5 levels ranging from a 40% decrease to a 70% increase, despite no major changes in emission sources or pollution controls.
The findings have important implications for regions like Delhi and the National Capital Region, where relatively low emissions do not guarantee clean air if the larger atmospheric conditions become stagnant. Conversely, significant emissions might have lesser local impacts when strong winds are present to disperse them.
As our understanding of air quality evolves, it becomes clear that while local actions are important, the weather and broader atmospheric conditions play crucial roles in determining air quality, raising the stakes in the ongoing battle against pollution in India.
