Structure and Reactivity of Sub-3 nm Ammonium/Aminium Sulfate Clusters Relevant to Tropospheric New Particle Formation
EMSL Project ID
40013
Abstract
New particle formation (NPF) occurs when gas-phase species condense to form new particles in the low-nanometer size range. These particles can subsequently grow to diameters of about 100 nm, at which point they may serve as cloud condensation nuclei (CCN), which can affect climate by increasing cloud albedo and influencing precipitation patterns. The predominant particle formation mechanism believed to occur in the troposphere is a ternary mechanism involving sulfuric acid, water, and ammonia. However, recent field and laboratory studies have suggested that organic amines may play an important role in NPF and in the growth of newly-formed particles to larger sizes, despite their atmospheric presence at levels that are orders of magnitude lower than that of ammonia. Previous research in our laboratory has shown that when an alkyl amine molecule collides with an ammonium bisulfate nano-cluster, the amine substitutes for ammonia with nearly 100% probability. The high reaction probability suggests that if sub-3 nm diameter particles in the atmosphere are composed of sulfate salts, they are likely to be aminium salts even if they were originally formed as ammonium salts. We propose to study ammonium/aminium bisulfate salt clusters in more detail using the unique capabilities within EMSL. In the first portion of the proposed work, we will study the energetics of ammonium/aminium bisulfate cluster dissociation using an FTICR-MS instrument that was specially designed for this purpose. Each cluster dissociation reaction we will study represents the reverse of a particle growth step in the atmosphere. Therefore, determining the binding energies as a function of cluster size will inform us about the thermodynamics of particle growth, and ultimately permit more accurate predictions of the impact of new particle formation on global climate. In the second portion of the proposed work, computational modeling of the structures of ammonium and aminium bisulfate clusters will be performed. Specifically, we hope to distinguish surface vs. interior (protected) ammonium ions in these clusters to understand why most ammonium ions in an ammonium bisulfate cluster exchange quickly with amine but the last substitution (presumably an interior ammonium ion) can be much slower in 'large' clusters . Additionally, calculation of the formation energies for these clusters will allow us to determine free energy changes for decomposition of a larger cluster into a smaller cluster. The calculated values will be compared to the experimental values obtained by FTICR.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2010-10-12
End Date
2011-10-16
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Bzdek BR, JW Depalma, DP Ridge, J Laskin, and MV Johnston. 2013. "Fragmentation Energetics of Clusters Relevant to Atmospheric New Particle Formation." Journal of the American Chemical Society 135(8):3276-3285. doi:10.1021/ja3124509
Depalma JW, BR Bzdek, DJ Doren, and MV Johnston. 2012. "Structure and Energetics of Nanometer Size Clusters of Sulfuric Acid with Ammonia and Dimethylamine." Journal of Physical Chemistry A 116(3):1030-1040. doi:10.1021/jp210127w