Particles are forming in the atmosphere in an unexpected way

Particle formation in our atmosphere is an arena of constant interactions, much akin to a colossal chemistry set. Gaseous molecules and tiny particles are continually in motion, knocking and reacting with each other in complex, intricate ways.

Despite their minuscule size, often less than 1% of the thickness of a human hair, atmospheric particles exert enormous effects.

They are the foundation for cloud droplets, and their abundance influences the reflectance, quantity of clouds, rainfall, and the overall climate.

Atmospheric particle formation

In an exciting development, researchers at Washington University in St. Louis have unearthed a mechanism that significantly contributes to the production of particles in Earth’s atmosphere.

This study was led by Professor Jian Wang, director of the Center for Aerosol Science and Engineering at Washington University (WashU).

It was conducted in partnership with scientists from various institutions, including NASA, NOAA, NCA and several European universities.

The conventional wisdom stated that the majority of particle formation occurs in cloud outflow regions, where clouds ascend into the upper troposphere and eventually evaporate.

In this process, clouds resemble sponges being wrung out, with most particles being removed by the rain.

The resulting air in the outflow regions ends up clear and clean. This leaves some gaseous molecules with no option but to form new particles.

Unexpected particle formation discoveries

“Contrary to popular belief, using data collected from NASA’s global-scale aircraft measurements, we found that most of the new particles are not formed in the outflow regions,” revealed Professor Wang.

On digging deeper into this unexpected observation, Wang and his team stumbled upon a contrasting mechanism.

This mechanism triggers when the mixing of stratospheric and tropospheric air creates conditions conducive to particle formation.

Jiaoshi Zhang is the lead author of the study and a research scientist in Wang’s lab.

“Stratosphere air often dips into the troposphere due to a meandering jet stream. As the ozone-rich stratospheric air and moist tropospheric air mix, it leads to a high concentration of hydroxyl radical (OH), an essential oxidant that helps produce the type of molecules that nucleate and form new particles,” explained Zhang.

Global widespread phenomenon

“We found this phenomenon is widespread around the globe and likely occurs more frequently than the particle formation in the cloud outflows,” noted Zhang.

While humans contribute their share of particles in the form of air pollution, this study reveals a natural process occurring even in remote and pristine regions around the globe.

There is also evidence that stratospheric air will dip into the troposphere more frequently in future climate conditions.

“While we were puzzled by the observation initially, once we pieced everything together, it was not so surprising. It is well known that molecules forming new particles are generated through oxidation in the atmosphere,” said Zhang.

“When the stratosphere and troposphere air mix, the OH concentration is very high, and it’s primed for particle formation.”

Implications for climate modeling

This newfound understanding of particle formation has significant implications for climate modeling and environmental policies.

Accurate climate models rely on a thorough grasp of particle formation processes to predict future weather patterns, climate change impacts, and the behavior of pollutants.

The discovery of this widespread natural phenomenon means that models must be adjusted to account for particle formation even in clean, remote regions, and not just polluted or cloud outflow areas.

Moreover, environmental policies that aim to control air quality can benefit from this research.

By recognizing natural sources of particles, policymakers can better differentiate between anthropogenic pollutants and naturally occurring processes.

This distinction is crucial for crafting regulations that effectively address human impact without overlooking the inherent complexities of Earth’s atmosphere.

Ultimately, this breakthrough not only deepens our comprehension of atmospheric chemistry but also equips scientists and policymakers with the insights needed to navigate the challenges posed by a changing climate.

The study is published in the journal Science.

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