EMSL, ARM team up for characterization of aerosols above agricultural fields

The molecular composition of organic aerosols over agricultural regions is largely unstudied and uncharacterized, despite their immense impacts on climate, crops, and air quality. 

That is why researchers at the Environmental Molecular Sciences Laboratory (EMSL) teamed up with staff from the Atmospheric Radiation Measurement (ARM) user facility to detail the composition of organic aerosols over the Southern Great Plains, an agricultural region in Oklahoma. 

While agricultural regions differ across land uses and locations, the team’s research helps address an important knowledge gap, said Gregory Vandergrift, an EMSL postdoctoral researcher. Agricultural land, he said, comprises 55 percent of the Earth’s ice-free land. 

“There have been a lot of molecular characterization studies of aerosols, but not a lot for aerosols collected above agricultural areas,” Vandergrift said. “Given the extensive proportion of the U.S. that is agricultural land, we feel we are filling in a pretty big knowledge gap of the molecular composition of aerosols.” 

The team’s research revealed aerosol origins and makeup, as well as patterns of dispersion and reactivity during the day compared to at night. Their work was recently featured on the cover of ACS Earth and Space Chemistry.  

Revealing new details 

Atmospheric aerosols affect climate processes, both through how they interact with solar radiation and by acting as cloud cover, which helps regulate the temperature, weather patterns, and molecular composition of the atmosphere. Disruptions in their typical formation, or adding chemical compounds that are unusual to what is typical, can have various effects—especially when examining their impacts on climate change, air quality, and human health, Vandergrift said. 

Through their partnership with ARM, the team was able to collect a high density of samples using ARM’s atmospheric observation facilities, Vandergrift said. With their data collection, they received supplemental data on wind direction and relative humidity, in addition to complex particle size distribution. 

The EMSL team was then able to use their expertise in cutting-edge sample characterization techniques to study and analyze the samples. They used nanoDESI mass spectrometry, which can detail unique sample information such as data on organosulfates, a type of secondary organic aerosol (a type of fine particle) that contains sulfur and other elements. The instrumentation and technique, Vandergrift said, proved to be an ideal fit for the characterization needed. 

One interesting angle from the study, Vandergrift said, is in regard to wind direction. He said their results showed that when aerosols came from urban areas or those heavily influenced by anthropogenic sources, the compounds they saw were very different.  

“Things we, as humans, were doing hundreds of miles away were being transported to broad surrounding areas,” he said. “We were looking at an area in Oklahoma, but we were seeing influences from winds coming from Texas. With aerosol composition, climate, and weather, it is not just a local problem to understand. It reiterated the importance that you need to have a broad look at these environmental impacts and problems. Oftentimes, what you’re studying locally is significantly impacted by far distances away.” 

The team also revealed that the molecular composition of the aerosols is different and that aerosols react differently during the day compared to at night. Specifically, the aerosols featured varying compositions of carbon, hydrogen, oxygen, nitrogen, and sulfur, with higher organosulfate proportions during the day at 41% compared to night at 31%. The team also found that due to high relative humidity, the nighttime aerosol phase state was found to be more liquid-like than daytime aerosols. 

The day-to-night comparisons they observed are not novel in the grand scheme of aerosol compositions, Vandergrift said. However, the team was excited about their results because not many people have studied aerosols over those regions, he said. 

Ideal partnership for robust characterization 

While their work continues and there are more regions to explore, Vandergrift said the EMSL team’s partnership with ARM was a crucial factor in the success of their research thus far. The collaborative relationship between the two teams provided a complete suite of expertise that allowed them to do and analyze more. 

“Without ARM, we wouldn’t be able to have the density of samples or the supporting pieces of data that they collected,” he said. “These observation facilities are operating continually and therefore allow for long-term observations and can help contextualize more episodic observations.” 

EMSL chemist Swarup China said what also helped set this study apart from others was that they went beyond molecular characterization. He said Vandergrift took the data to the next level to try to understand some of the physics behind the aerosols, which entail important properties from a modeling perspective. 

“We look at the volatility of the particles, and then that goes into a model,” he said. “We use high-resolution mass spectrometry and combine it with information for modeling. We are starting to do that now, and it is very useful. It is an important component for the atmospheric system research and ARM community.” 

Additionally, China said they had a range of talented scientists collaborating on the research. Some of those individuals included Darielle Dexheimer, an atmospheric scientist at Sandia National Laboratories, and Abu Shawon, who helped in the analysis of ARM data and did an internship with the EMSL team before moving to Los Alamos National Laboratory.  

PNNL Earth scientist Fan Mei, who oversees science activities for the ARM Aerial Facility, and Maria Zawadowicz, environmental scientist at Brookhaven National Laboratory and ARM aerosol instrument mentor, were also crucial team members for analyzing the ARM data.  

China said the team looks forward to the continuous momentum of their research and their capacity for exploring other regions and aspects to unveil even more information as it pertains to aerosols over agricultural areas. 

“This is just the start,” he said. “We need to understand the effects in different seasons. And as part of a next level of complexity, we are looking at composition of the aerosols at different altitudes. We have a lot of different work that we are completing in the coming months and years. Ultimately, this project is very exciting."