Scratching the Surface of Aerosols with Uncrewed Aerial Systems

Published: 23 May 2024

New method helps realize the potential of uncrewed aerial systems

This story was originally published on the Pacific Northwest National Laboratory website.

The ArcticShark uncrewed aerial system is shown on the tarmac.
Uncrewed aerial systems (UAS) can help atmospheric scientists efficiently collect a wide range of samples and data. ARM file photo.

Developing a picture of the atmosphere requires measurements from the ground and in the air. The advent of uncrewed aerial systems (UAS) has allowed researchers to develop new platforms for collecting data while in the air.

Aerosols are particularly important to measure. These tiny particles in the atmosphere affect clouds, alter the balance of energy hitting and leaving Earth, and change the weather and climate. Representing their behavior remains a major uncertainty in current earth system models.

Aerosol data collection has been a common part of atmospheric measurement for decades, but new techniques are allowing researchers to sample and better understand the realities of aerosols.

Work published in the March 2024 Bulletin of the American Meteorological Society (BAMS) combines UAS measurements with state-of-the-art surface analysis techniques such as time-of-flight secondary ion mass spectrometry to create a more accurate description of the three-dimensional (3D) structure of aerosol particles. The work also features capabilities of two U.S. Department of Energy (DOE) Office of Science user facilities.

A research team led by Fan Mei, an earth scientist at Pacific Northwest National Laboratory (PNNL) in Washington state, used aerosol data from DOE’s Atmospheric Radiation Measurement (ARM) user facility. The data were collected around ARM’s Southern Great Plains atmospheric observatory in Oklahoma, and the team used UAS and ground-based measurements to guide model simulations.

ARM, DOE’s Atmospheric System Research (ASR) program, and NASA supported this work. The aerosol analysis took place at the Environmental Molecular Sciences Laboratory (EMSL), which, like ARM, is a DOE Office of Science user facility.

“People talk about UAS measurements and how they can advance atmospheric research. However, there are still a lot of foundational gaps we need to fill. This work is a step in making the potential of UAS a reality.”

Fan Mei, lead author of a new paper using UAS data to help improve the description of the 3D structure of aerosol particles

Mei and her colleagues previously published a paper in Earth System Science Data describing the UAS data sets used in the new work. This is important foundational work as UAS data are becoming increasingly common in atmospheric sciences.

“People talk about UAS measurements and how they can advance atmospheric research,” said Mei, who also oversees science efforts for the ARM Aerial Facility. “However, there are still a lot of foundational gaps we need to fill. This work is a step in making the potential of UAS a reality.”

Studying the Surface of Aerosol Particles

Mei took inspiration from materials science for this work.

“I was talking to researchers across PNNL about the challenges of this project,” said Mei. “I discussed difficulties characterizing aerosols with experimentalists and how to use data to bridge the gap between the model simulation and the observation with modelers. I found that materials science already used the type of surface-sensitive technique we needed. We just had to adapt it to work with our samples, which is easier said than done.”

After extensive testing and optimization of the technique, the team collected aerosol samples from the Southern Great Plains observatory and characterized their surface structure at EMSL, which houses a collection of state-of-the-art surface analysis instruments.

ARM Aerial Facility science lead Fan Mei poses with the ArcticShark in the background at the Pendleton UAS Range in Oregon. ARM file.
ARM Aerial Facility Science Lead Fan Mei poses with ARM’s ArcticShark uncrewed aerial system in the background at the Pendleton UAS Range in Oregon. ARM file photo.

The results were surprising. Previous studies of entire particles reported similar aerosol composition, which was either half carbon-based, or organic, and half non-carbon-based, or inorganic. This led to model projections that consistently overestimated the presence of clouds, which form on aerosol particles.

The surface measurements told a different story. While the aerosols were half organic and half inorganic on average, their surfaces were effectively 100% organic. This means all the particles interact with the atmosphere as if they are purely organic aerosol.

“These surface measurements initially amazed me,” said Hailong Wang, an earth scientist at PNNL and a co-author of the study. “The earth system and cloud models I work with generally assume that the organic and inorganic aerosol components are mixed. We adjusted how our cloud model treats aerosol particles to reflect the realities of the aerosol surfaces. Combined with UAS data on particle size and number, our models show clouds that have fewer droplets and are less bright. These results are more accurate and better match the ARM remote sensing data.”

This work serves as a proof of concept for how the multidisciplinary techniques available at DOE user facilities can help atmospheric scientists and better link observation capabilities with modeling needs. The richer data can lead to more accurate models by filling in gaps through combined UAS measurements and advanced laboratory techniques. This can lead to a more holistic understanding of atmospheric processes.

“We need to collect more data that covers more space to provide observational constraints for aerosols in global models, such as the Department of Energy’s Energy Exascale Earth System Model,” said Wang.

Added Mei: “I think the future of UAS measurements is bright. As these measurements become more common, including on future ARM campaigns, it’s important to know what unique insights we can gain from them that are useful to improve global aerosol-cloud modeling and climate projection.”

The original article was written by Beth Mundy, PNNL.

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ARM is a DOE Office of Science user facility operated by nine DOE national laboratories.