Bryan R. Bzdek
Graduate Student
Department of Chemistry and Biochemistry
University of Delaware
Newark, DE 19716
Tel./Fax: (302) 831-4265/(302) 831-6335
Email: bbzdek@udel.edu
Research Interests
My research interests involve using mass spectrometry to better understand atmospheric chemistry, with specific focus on the chemistry of ambient nanoparticles. Atmospheric aerosols negatively impact human health and global climate. In terms of global climate, the dominant effect is cooling, either directly through the scattering of solar radiation or indirectly by serving as cloud condensation nuclei (CCN, the seeds for clouds), which increase the amount of sunlight scattered by clouds and influence precipitation patterns. While we have a firm understanding of the climatic effects of greenhouse gases, comparatively little is understood about aerosol climatic effects, especially the light scattering effects due to clouds. This effect is called the aerosol indirect effect. One reason that the aerosol indirect effect is poorly understood is due to difficulty in predicting CCN concentrations under varying conditions. Although the ability of particles to serve as CCN may depend on several parameters, most particles >100 nm diameter may serve as CCN. There are two classes of particles that may serve as CCN. The first consists of primary particles, which are emitted directly into the atmosphere by both natural and anthropogenic processes. The second class consists of particles that arise from new particle formation processes. New particle formation occurs when gas-phase species condense to form new particles in the low nanometer size range. These particles then grow into the CCN size range over time. Recent models suggest that new particle formation may account for up to ~50% of global CCN. However, it is difficult to quantify the effect due to new particle formation, in part because particle formation and growth mechanisms are poorly understood.
The predominant mechanism for forming new particles in the troposphere is thought to be a ternary mechanism involving sulfuric acid, water, and a third species that effectively lowers the nucleation barrier. Ammonia has generally been considered to be that third species because it is ubiquitous, having many natural and anthropogenic sources. However, both particle nucleation and particle growth rates appear to be much higher than those predicted by theory, suggesting that some other species are involved in these processes. Recently, focus has turned to amines as potentially significant contributors to particle formation and growth. Amines are emitted from many of the same sources as ammonia, although they are emitted at much lower levels. While atmospheric amine concentrations are relatively low–as much as two to three orders of magnitude below that of ammonia–mounting evidence suggests they have a disproportionately large impact on particle formation and growth. The overarching goal of my thesis research is to understand the role of amines in particle formation and growth.
Relevant Publication:
B. R. Bzdek and M. V. Johnston, “New Particle Formation and Growth in the Troposphere,” Analytical Chemistry, 2010, 82, 7871-7878.
Composition and Reactivity of Ambient Nuclei
This project involves performing kinetics experiments that aim to elucidate the most likely (most favorable) composition of the smallest ambient clusters (~1 nm diameter). These experiments utilize Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), which provides high resolving power and high accuracy mass-to-charge (m/z) measurements, allowing for the assignment of unique elemental formulae to reactant and product ions. For these experiments, an individual ammonium salt cluster is exposed to an amine gas that is leaked in at constant pressure. A reaction results whereby the amine sequentially displaces the ammonia in the cluster. Because ions can be held in the instrument for varying lengths of time, the progress of the reaction can be monitored. The data are then fit to kinetic models to quantitatively determine the reaction rate for each step. This type of analysis on a wide range of cluster compositions (ammonium bisulfate, ammonium nitrate, and ammonium methanesulfonate) and cluster sizes has indicated that displacement of ammonia by amine is collision-limited if the ammonium ion is on the surface of the cluster. However, at large cluster sizes, an ammonium ion can be essentially trapped in the core of the cluster, rendering the exchange more difficult (slower). In addition to the displacement reaction, we have also observed that the amine can add to a cluster and neutralize remaining acid. When taking into account the measured rates of both of these pathways and by comparing them to rates of reaction with ammonia, it appears that amine chemistry may compete favorably with ammonia chemistry under typical atmospheric conditions.
Relevant Publications:
J. W. DePalma, B. R. Bzdek, D. J. Doren, and M. V. Johnston, “Structure and Energetics of Nanometer Size Clusters of Sulfuric Acid with Ammonia and Dimethylamine,” Journal of Physical Chemistry A, 2012, 116, 1030-1040.
B. R. Bzdek, D. P. Ridge, and M. V. Johnston, “Amine Reactivity with Charged Sulfuric Acid Clusters,” Atmospheric Chemistry and Physics, 2011, 11, 8735-8743.
B. R. Bzdek, D. P. Ridge, and M. V. Johnston, “Reactivity of Methanesulfonic Acid Salt Clusters Relevant to Marine Air,” Journal of Geophysical Research – Atmospheres, 2011, 116, D03301, doi: 10.1029/2010JD015217.
B. R. Bzdek, D. P. Ridge, and M. V. Johnston, “Size-Dependent Reactions of Ammonium Bisulfate Clusters with Dimethylamine,” Journal of Physical Chemistry A, 2010, 114, 11638-11644.
B. R. Bzdek, D. P. Ridge, and M. V. Johnston, “Amine Exchange into Ammonium Bisulfate and Ammonium Nitrate Nuclei,” Atmospheric Chemistry and Physics, 2010, 10, 3495-3503.
Ambient Observations of New Particle Formation
Another research focus involves field campaigns to determine the composition of ambient nanoparticles both during and before/after new particle formation. During these campaigns, we utilize our home-built Nano Aerosol Mass Spectrometer (NAMS), which can quantitatively characterize the composition of 7-30 nm diameter particles in the air. We have performed field campaigns to examine nanoparticle composition during new particle formation events in Lewes, DE, a rural/coastal environment as well as in Wilmington, DE, an urban environment. We have observed during these studies that nanoparticle composition shifts to a more inorganic composition during the events. We have also been able to link quantitatively gas-phase sulfuric acid concentrations to particle-phase sulfur. Recently, NAMS was deployed to a field station in Hyytiälä, Finland, a remote boreal environment. Analysis of the individual particle spectra from this campaign is currently underway.
Relevant Publications:
B. R. Bzdek, C. A. Zordan, M. R. Pennington, G. W. Luther III, and M. V. Johnston, “Quantitative Assessment of the Sulfuric Acid Contribution to New Particle Growth,” Environmental Science and Technology, 2012, Just Accepted Manuscript, doi: 10.1021/es204556c.
B. R. Bzdek, C. A. Zordan, G. W. Luther III, and M. V. Johnston, “Nanoparticle Chemical Composition During New Particle Formation,” Aerosol Science and Technology, 2011, 45, 1041-1048.
(on the method) S. Wang, C. A. Zordan, and M. V. Johnston, “Chemical Characterization of Individual, Airborne Sub-10 nm Particles and Molecules,” Analytical Chemistry, 2006, 78, 1750-1754.
Links
Department of Chemistry & Biochemistry
Delaware Environmental Institute (DENIN)
Last update: 03/2012