Soot’s climate-altering properties change within hours of entering atmosphere

Billions and billions of soot particles enter the earth’s atmosphere every second, totaling approximately 5.8 million metric tonnes per year, making a global warming impact previously estimated at almost a third of that of carbon dioxide.

Now, the researchers say that the properties modifying the climate of these particles can change in only hours after being in the air, rather than days as supposed previously.

A study led by researchers from the New Jersey Institute of Technology (NJIT) revealed the surprising speed to which the soot particles bring together chemicals and water vapor after being released in the atmosphere.

Researchers say that this rapid transformation of airborne soot – known as “atmospheric aging” – could mean that its impact on weather conditions, climate and air quality occurs more quickly, and in a way that is not entirely captured by current atmospheric models so far.

The results were highlighted on the coverage of Environmental sciences and technology.

“SOOT is a unique aerosol that absorbs extremely well the sunlight but barely disperses, which makes it a powerful climate agent from the moment it is issued,” said Alexei Khalizov, professor of chemistry at Njit and the main study of the study.

“What surprised us is how the soot changes the speed after entering the air, considerably modifying its ability to warm or cool the atmosphere. Our results suggest that the forecasting of SOOT’s climate impact is much more complex than that previously made.”

Until recently, Khalizov says, many remained unknown on the speed with which the soot nanoparticles change their shape and chemistry once in the air, and how these changes affect their ability to trap or reflect solar energy – known as radiative forcing.

According to Khalizov, soot particles quickly acquire chemical coatings by capillary condensation, a process where tiny crevices on irregular surfaces of soot particles attract chemical vapors. As humidity increases, the chemicals collected on soot particles help them absorb water, now by capillary condensation of water vapor. This water absorption transforms the shape and behavior of particles. These hydrated particles can also promote the formation of clouds, reflecting sunlight and cool the atmosphere.

“Until now, models have treated soot particles as simple spheres, but in reality, soot particles are aggregates – fires of many smaller particles. The lace shape allows soot to collect chemicals much faster than you thought,” said Khalizov. “This means that SOOT’s climatic properties are evolving more quickly, affecting both its warming and cooling effects, as well as its lifespan.”

In the aerosol chemistry laboratory and the atmosphere of Njit, the team used a tailor -made aerosol system to study how soot particles change after entry into the atmosphere, focusing on the particles about 240 nanometers wide – the typical atmospheric sooter. The group exposed these particles to draw gases such as sulfuric acid and oxidation products of volatile organic compounds (VOCs) in different humidity levels to imitate real atmospheric chemical and humid conditions.

The team followed the key changes linked to atmospheric aging in real time, measuring aspects such as particle size, mass and shape using advanced instruments. Samples were then taken and examined under electron scanning microscopes, revealing how particles have evolved in high resolution.

To complete their experiences, the researchers have collaborated with the Njit Laboratory For Materials interfaces led by Professor Gennady Gor to develop a new computer model to simulate how chemical vapors condense on the soot, forming liquid coverings that stimulate the capacity of particles to attract and form clouds- key factors of their climate.

Encouraged by the success of the model to describe laboratory results, they then extended their simulations to real atmospheric conditions in collaboration with Professor Nicole Riemer at the University of Illinois Urbana-Champaign.

The results have shown that soot particles are starting to form coatings and change the shape into tens of minutes, with almost 80% of the particles being treated after several hours. By way of comparison, in simulations where the soot was treated as spheres, only 20% were treated – and this took much more time.

This rapid transformation makes the particles more compact and increases their absorption of sunlight, intensifying their warming effect, according to Khalizov.

“Initially, these soft particles, after having mixed with other chemicals, change in shape into dense tufts and become more likely to absorb sunlight and convert it into heat, producing more warming,” he explained. “At the same time, they reflect more light and form clouds, leading to cooling. These two competing effects make it more difficult to predict the overall effect of the soot while its particles are suspended in the air.”

Khalizov said that the information on SOOT’s rapid atmospheric aging study could lead to more precise forecasts for its environmental effects, helping models to better represent how soot particles change and influence the quality of the climate and air over time.

The team now plans to explore how these changes affect soot’s lifespan in the atmosphere and its broader effects on weather conditions and public health.

“Our study has examined the aging of the soot in a distant environment. The next major questions are to determine the role of this new aging mechanism in a polluted urban environment and to test them in a large -scale climate model,” noted Khalizov. “To resolve them will be the key to the management of SOOT’s climate imprint more effectively.”