Discovering How Transport and Source Affect Properties of Aerosol Particles

The Science 

Tiny aerosol particles in the atmosphere can form the basis for cloud droplets or ice nuclei, depending on their chemical composition and physical properties. To better understand the formation of droplets and ice nuclei, it is important to understand whether the aerosols are in a solid phase or whether they are semisolids or liquids. And, what causes these aerosols to change phase as the wind carries them thousands of miles from their origin also has to be understood. In this research, a team of scientists studied the individual particles that had been transported in the troposphere—the part of the atmosphere closest to Earth—across the North Atlantic Ocean. They discovered that the phases of the particles varied far more widely than expected and were influenced by their source and their transport. 

The Impact 

The troposphere is the part of the Earth’s atmosphere that encompasses most clouds and is the source of most weather events. Aerosol particles found in this part of the atmosphere play a vital role in regional and global climate processes, and that role is heavily influenced by the phase of those aerosols. Understanding how they change phases during transport therefore becomes an important factor in predicting both weather and longer-term climate changes. The data and modeling results from this study of aerosol particles can also serve to support atmospheric system models. 

Summary 

Capturing aerosol particles over the ocean can be tricky. To probe particle phase types, states, and changes following long-range transport, a multi-institutional team of scientists used modeling and a variety of advanced analytical tools, including a new analytical approach that uses a tilted stage with an advanced imaging technology called the environmental scanning electron microscope (ESEM). Using the ESEM available from EMSL, the Environmental Molecular Sciences Laboratory, a U.S. Department of Energy (DOE) Office of Science User Facility, the team looked deeply into the chemical composition and phase of individual particles. They were able to study the phases of the particles after long-range transport based on the shape each particle made as it hit the sampler. Additional analyses were conducted at the Advanced Light Source at Berkeley National Laboratory, another DOE Office of Science User Facility. The scientists combined data from these analyses with a computer particle dispersion model to chart the origin and path of the sampled air and found that most particles came from North America and were transported over the North Atlantic Ocean. A major fraction of particles was liquid when sampled, but the results proved the particles had previously been solid and semisolid. One of the largest determinants of the change was their source, such as wildfires. Overall, these findings provide insights that will help scientists better predict the effects of aerosol particles on climate. 

Contacts 

Zezhen Cheng, Environmental Molecular Sciences Laboratory, zezhen.cheng@pnnl.gov 

Swarup China, Environmental Molecular Sciences Laboratory, swarup.china@pnnl.gov 

Claudio Mazzoleni, Michigan Technological University, cmazzoleni@mtu.edu 

Funding 

This work was funded by the DOE Office of Science’s Atmospheric System Research Program. Some analyses were conducted at EMSL, the Environmental Molecular Sciences Laboratory at Pacific Northwest National Laboratory, and the Advanced Light Source at Lawrence Berkeley National Laboratory, both DOE Office of Science User Facilities. Sample collection at the Observatory at Mount Pico was supported by funding from the National Science Foundation, DOE, NASA’s Earth and Space Science Graduate Fellowships, and the German Science Foundation. 

Publication 

Z. Cheng, et al., “Particle phase-state variability in the North Atlantic free troposphere during summertime is determined by atmospheric transport patterns and sources.” Atmospheric Chemistry and Physics 22, 9033 (2022). [DOI: 10.5194/acp-22-9033-2022] 

Related Publications 

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