Mon Aug 18 14:26:51 UTC 2025: Okay, here’s a summary of the provided text, followed by a rewritten version as a news article suitable for The Hindu:

**Summary:**

A study by researchers at IIT Madras and SRM IST has found that air pollution in North India significantly impacts the air quality of Southeast Coastal India and the Bay of Bengal, particularly during December to March. Anticyclonic winds carry aerosols (primarily black carbon and aged organic carbon) from North India over a period of 2-4 days twice or thrice a month. These transported aerosols not only increase PM2.5 levels directly but also alter the atmospheric thermal structure. The presence of these aerosols leads to a cooling effect at the surface and warming at higher altitudes, stabilizing the lower atmosphere. This results in a reduced atmospheric boundary layer height (ABLH), which concentrates pollutants and increases PM2.5 levels, resulting in severe hazy episodes. The impact is especially significant in megacities like Chennai, where PM2.5 concentrations can increase by over 50% during these transport events. The researchers emphasize the need to consider transboundary aerosol transport in air quality management strategies and advocate for integrated modeling frameworks that account for aerosol-radiation interactions for accurate air quality forecasting.

**News Article:**

**North Indian Pollution Chokes Southeast Coast: Study Reveals Transboundary Aerosol Impact**

**Chennai, August 18, 2025:** A new study paints a grim picture of air quality in Southeast Coastal India, revealing that pollution generated in North India has a significant and direct impact on the region, particularly during winter months. Researchers from IIT Madras and SRM Institute of Science and Technology (SRM IST) have found that aerosols, primarily black carbon and aged organic carbon, are transported via anticyclonic wind circulation from North India to the southeast coast and the Bay of Bengal, exacerbating pollution levels.

The research, conducted between 2015 and 2024 and published in *Atmospheric Chemistry and Physics*, used satellite data, lidar sensors, radiosonde measurements, and back trajectory analysis to track the movement of these aerosols. The study reveals that this regional transport occurs for 2-4 days at a stretch, two to three times a month, between December and March.

“The transported aerosols are present between 1 km and 3 km altitude and are primarily absorbing types – black carbon and aged organic carbon,” explains Dr. Chandan Sarangi from the Department of Civil Engineering at IIT Madras, the corresponding author of the paper. These absorbing aerosols cause a surface cooling effect, reducing solar radiation absorption at the surface, while warming the atmosphere at higher altitudes. This altered thermal structure stabilises the lower atmosphere, leading to a reduction in the atmospheric boundary layer height (ABLH).

This reduced ABLH traps pollutants near the surface, leading to a significant increase in PM2.5 concentrations. The researchers found that this phenomenon is particularly pronounced in megacities. “In the case of Chennai, there is over a 50% increase in PM2.5 concentration during the days when aerosols are transported from North India,” notes Dr. Sanjay Mehta from the Department of Physics at SRM IST, a coauthor of the study.

The research also identified a positive feedback loop wherein transported aerosols lead to reduced ABLH, enhancing local pollution as the pollutants are less likely to be dispersed due to reduced ABLH causing further aerosol accumulation.

Researchers have discovered that regional transport of aerosols changes the atmospheric dynamics such that the atmosphere gets relatively warmer at higher altitudes and cools at the surface,” says Dr. Sarangi

The study underscores the limitations of addressing air pollution solely through local measures. “Our study demonstrates that air quality management in Chennai must consider transboundary aerosol transport,” emphasizes Dr. Sarangi. “It is essential to put in place strategies to reduce regional emissions, especially during seasons with strong north-south flow.”

The researchers advocate for the development and implementation of integrated modeling frameworks that include aerosol-radiation interactions for more accurate air quality forecasting and effective pollution control strategies. This highlights the need for a coordinated, regional approach to combat air pollution, recognizing that the problem transcends geographical boundaries.

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