Study to Aid Efforts to Model Climate Change and Reduce Pollution

Researchers at Carnegie Mellon University collaborated with an international team of researchers and identified a previously unknown mechanism that enables the quick formation of atmospheric particles under specific conditions.

The study was published in the Nature journal and could assist measures to model climate change and decrease particle pollution in cities.

The only real uncertainties in our understanding of climate in the atmosphere have to do with fine particles and clouds, how these have changed over time and how they will respond to climate change.

Neil Donahue, Professor of Chemistry, Thomas Lord University

Donahue is also a professor in the departments of Chemical Engineering, and Engineering and Public Policy.

The number of particles present in the atmosphere at any specified time can have significant impacts locally and globally, such as causing unhealthy smog in cities and affecting the climate of the Earth. But particles should reach a specific size of about100 nm in diameter to contribute to those impacts, explained Donahue.

If particles do not attain that size, they rapidly combine with other, larger particles. This implies that one would expect a few new particles to be produced in polluted urban surroundings where the atmosphere is already filled with larger particles that could devour small and new particles.

However, new particle formation is more prevalent in those surroundings, as plainly observed when haze reforms quickly following the rainfall in cities across the globe.

Donahue believes the solution to that conundrum might lie in this new study.

We found a new way for tiny nucleated particles in the atmosphere to grow up quickly to become large enough to affect climate and health.

Neil Donahue, Professor of Chemistry, Thomas Lord University

For a long time, Donahue’s laboratory group has been associated with the CLOUD experiment, an international collaboration of researchers that makes use of an exclusive chamber at CERN in Switzerland to investigate the way cosmic rays influence the formation of clouds and particles in the air. The chamber enables scientists to accurately combine vaporous compounds and notice how particles develop and grow from them.

In this research, devised by Carnegie Mellon chemistry doctoral candidate Mingyi Wang, the CLOUD team condensed vapors of ammonia and nitric acid throughout an extensive temperature range and determined that the resulting new particles can grow 10 to 100 times quicker than observed earlier, enabling them to reach sizes that are sufficiently large to prevent being gobbled up by other particles.

The compound that was developed from those two vapors was ammonium nitrate (a common fertilizer), which was earlier known to be a contributor to air pollution within larger particles; however, its role in helping the tiny particles to grow was not familiar so far.

This may help explain how nucleated particles grow up in polluted urban conditions in mega-cities, which has been a big puzzle, as well as how they form in the upper parts of the atmosphere, where they can have a strong climate effect.

Neil Donahue, Professor of Chemistry, Thomas Lord University

Currently, the researchers are working to analyze how this mechanism works in Earth’s upper atmosphere.

For Wang, who was the study co-leader, this research has origin in his keen intent to understand air pollution. Following an undergraduate research project where he was able to sample and examine PM2.5, Wang intended to remain in this research field to better investigate how such tiny particles can cause such a huge effect on the planet and how that impact could be mitigated.

According to Wang, “I realized that those atmospheric particulate matters have never been a simple air quality problem that only Asia needs to deal with. Rather, they are a global challenge due to their health and climate effects.”

Journal Reference:

Wang, M., et al (2020) Rapid growth of new atmospheric particles by nitric acid and ammonia condensation. Nature. doi.org/10.1038/s41586-020-2270-4.