NASA Study Finds A Decrease In Ship Tracks In 2020 – What Are The Possible Causes?

When ships and vessels tread oceans, they leave a trail of sulfur-rich fuel. These trails pollute the marine ecosystem and form “clouds” of ship tracks visible through satellite imagery. Thus, it is possible to identify, analyze, and sample them to reduce pollution.

Recently, NASA conducted a study and shared satellite observations and images from 2020, showing lesser-than-usual sulfur-containing tracks from the North Pacific to the Mediterranean.

Author of the study, Tianle Yuan, an atmospheric scientist at NASA’s Goddard Space Flight Centre in Maryland, and his colleagues credit the fuel regulation standard by the International Maritime Organization (IMO) for this commendable achievement.

Here is everything you should know about the study and its potential benefits to environmental pollution.

What Are Ship Tracks?

Ship tracks are clouds of pollution that form over the trail left behind by ships and vessels crossing the oceans. These tracks form due to the emission of sulfur-rich droplets from the ship exhaust.

The fuel floats on water due to differences in its specific gravity and thus remains trackable.

How Do Satellites Capture Ship Tracks?

Satellites detect and capture the clouds of pollution that form over ship tracks. These clouds form due to the merging of water vapors around the small particle pollutants emitted from the ship exhaust.

These water droplets are highly-dense and can scatter more light than the moisture content generally found in the atmosphere. When the light hits this high-density zone, it appears brighter than the rest of the atmosphere.

Satellites use the light gradient and changes in brightness to detect ship trails.

Scientists Mapped Ship Tracks Across 17 Years To Create Global Climatology Of Ship Tracks

In 2020, scientists used images from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) to form a map with ship tracks from 2003-2020. They paired the record with artificial intelligence and came up with the first-ever global climatology of ship tracks.

The comprehensive results and their graphical representation were crucial in understanding the root, severity, cause, and solution of the problem.

The history of measurements (climatology) indicated that there had been a significant decrease in the number of detected ship tracks in the year 2020.

Causes Of Decrease In Ship Tracks Density In 2020

Lead scientist Yuan and his team correlated the drop in the density of ship tracks with two significant factors – the COVID-19 pandemic and the fuel regulation standard imposed by the IMO.

1. COVID-19 Pandemic

The global outbreak of the Novel Coronavirus disrupted international trade and travel in 2020. The number of ships crossing the oceans was significantly lower than usual. Thus, the number of tracks decreased.

But according to the researchers, the pandemic alone could not have such an enormous impact. The data indicated that the ship traffic decreased by only 1.4% for a few months of lockdown. Hence, while the pandemic affected the density of ship tracks, it only played a secondary role.

2. Global Fuel Regulation

The International Maritime Organization (IMO) changed its standards of ship exhaust composition in 2020. According to the new regulations, the sulfur content of the fuel should be no more than 0.5%. Until then, the range was as high as 3.5%.

Capping down the sulfur content automatically diminished the small pollutant particles that formed a visible cloud over the ship trails.

Similar IMO regulations, for instance, the IMO Emission Control Area, have been in effect in Canada and the US’s west coast since 2015. But they achieved no significant result because it was easy for ships to take a longer route and avoid the zones in which it was operational.

The comprehensive study of ship tracks and their satellite imagery by NASA scientists concluded that reducing sulfur content in ship fuel played a primary role in lowering the air pollution caused by shipping.

Furthermore, according to Yuan, “Ship tracks are great natural laboratories for studying the interaction between aerosols and low clouds.”

Worried about your air quality?

Monitor the Particulate Matter levels around the world with our free, real-time PurpleAir Map. or join PurpleAir's mission to make air quality data accessible to everyone by investing in an air quality monitor for your home. 

Together, we can be informed and make changes in our daily habits and the community to improve air quality.