Aerosols aloft lift, thicken winter fog over North India: IIT-M study, Pg12

Key Highlights:

• IIT-Madras study using 15 years of CALIPSO satellite data reveals that aerosol loading above fog layers thickens winter fog over the Indo-Gangetic Plain.
• The study, published in Science Advances on January 9, found that increased AODFOG (aerosol loading) leads to a 17% thicker fog layer.
• Higher AODFOG correlates with larger water droplets near the top of the fog layer, as estimated using MODIS satellite data.
• A weather model replay of a January 2014 fog event suggests a self-strengthening cycle where pollutants increase fog droplet formation and thickness.

Detailed Insights:

• The research highlights a vicious cycle where aerosols fuel fog formation, which in turn traps pollution, impacting air quality, aviation, and daily life in North India.
• Increased pollutants act as condensation nuclei, leading to more fog droplets, releasing heat that stirs the fog upwards, while the fog layer efficiently emits infrared radiation, cooling the top and promoting further condensation.
• The study used a metric called AODFOG to quantify the amount of dust and smoke above the fog layer, comparing days with high and low AODFOG values to analyze fog thickness.
• A limitation acknowledged by the team is the poorly understood aerosol properties above the fog and sparse observations, preventing isolation of the "semi-direct" effect of soot absorbing sunlight and warming the air.

Scientific/Technical Concepts Involved:

• Aerosols: Tiny particles suspended in the air, including dust, smoke, and pollutants.
• CALIPSO: A NASA satellite dedicated to observing the vertical structure of the atmosphere using lidar technology.
• MODIS: A key instrument aboard NASA’s Terra and Aqua satellites, providing data on Earth’s land, ocean, and atmosphere.