Organonitrates in Atmospheric Particles Vary with Altitude

The Science  

While atmospheric particles directly affect climate (e.g., cloud formation), sampling atmospheric particles aloft is practically challenging. Therefore, a full understanding of how particle composition is linked to environmental function remains limited. To address this issue, a multi-institutional team of researchers used a tethered balloon system to collect atmospheric particles in a vertical profile up to 750 meters above ground level. Collected atmospheric particles were subsequently analyzed to determine the constituent organic molecules to examine the difference in composition between ground and aloft samples. The team found that aloft particles contained more organonitrate molecules than those collected at ground level, and that increase was affected by cloud coverage, relative humidity, and wind variance. This research reveals new information that can be applied to atmospheric models. 

The Impact 

While measuring and determining the composition of atmospheric particles collected at ground level is comparatively straightforward, this study shows that such a strategy may misrepresent the true vertically resolved composition of the atmosphere. In particular, the varied, vertically resolved composition may significantly change the atmospheric function and lifetime of particles, resulting in corresponding impacts on climate.  

Summary 

Using measurements supported by the Atmospheric Radiation Measurement (ARM) user facility, a Department of Energy (DOE) Office of Science user facility, a tethered balloon system was used at the Southern Great Plains atmospheric observatory in Oklahoma to collect atmospheric particles from ground and aloft levels. Collected samples were later analyzed for their organic molecular composition using high-resolution mass spectrometry at the Environmental Molecular Sciences Laboratory (EMSL), also a DOE Office of Science user facility. The team observed that organic molecules identified aloft were situationally dominated by organonitrates. These aloft organonitrates featured elevated oxygenation compared to organonitrates observed at the ground level. The occurrence of unique aloft organic molecular composition was positively associated with increased cloud coverage, increased relative humidity aloft, and decreased vertical wind variance. Overall, this study highlights the importance of considering vertically resolved organic molecular composition (particularly for organonitrates) and hypothesizes that aqueous-phase transformations and vertical wind variance may be key variables affecting the molecular composition of organic aerosols above the Earth’s surface. 

Contacts 

Gregory Vandergrift, EMSL, gregory.vandergrift@pnnl.gov  

Swarup China, EMSL, swarup.china@pnnl.gov  

Darielle Dexheimer, Sandia National Laboratories, ddexhei@sandia.gov  

Funding 

The study was supported by the Atmospheric System Research program, with measurements supported by ARM, a DOE Office of Science user facility—both are sponsored by the Biological and Environmental Research program. A portion of the research was performed through Large-Scale Research awards from EMSL, also a DOE Office of Science user facility. 

Publication 

G.W. Vandergrift, et al. “Tethered balloon system and High-Resolution Mass Spectrometry Reveal Increased Organonitrates Aloft Compared to the Ground Level.” Environmental Science & Technology 58, 10060 (2024). [DOI: 10.1021/acs.est.4c02090] 

This article was featured on the cover of Environmental Science & Technology.