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A follow on paper to the "The Molecular Composition of Soot" paper published in Angewandte Chemie has been accepted for publication in the Proceedings of the Combustion Institute.   Group co-authors include Shellie Golden, Jennifer Giaccai, Andrew Kamischke, and Houston Miller.  Other GW authors include Akos Vertes and Andrew Korte. Here, we expand on the application of Chemical Graph Theory to isomer enumeration and validate our findings with group additivity and DFT thermodynamic calculations.

A collaboration between GW Chemistry's Miller and Vertes labs has led to a recent accepted article which is available online in the journal Angewandte Chemie International Edition, a publication of the German Chemical Society.

Abstract: Soot (sometimes referred to as Black Carbon) is produced when hydrocarbon fuels are burned. Our hypothesis is that polynuclear aromatic hydrocarbon (PAH) molecules are the dominant component of soot, with individual PAH molecules forming ordered stacks that agglomerate into primary particles (PP). Here we show that the PAH composition of soot can be exactly determined and spatially resolved by low-fluence laser desorption ionization, coupled with high-resolution mass spectrometry imaging. This analysis revealed that PAHs of 239-838 Da, containing few oxygenated species, comprise the soot observed in an ethylene diffusion flame. As informed by chemical graph theory (CGT), the vast majority of species observed in the sampled particulate matter may be described as  benzenoids, consisting of only fused 6-membered rings. Within that limit, there is clear evidence for the presence of radical PAH in the particulate samples. Further, for benzenoid structures the observed empirical formulae limit the observed isomers to those which are nearly circular with high aromatic conjugation lengths for a given aromatic ring count. These results stand in contrast to recent reports that suggest higher aliphatic composition of primary particles

 

Accepted in the journal Applied Optics

Experimental PHOCS spectra and retrieval fit.  Shown above is an oxygen feature at 7815.67 cm-1 and a water feature at 7816.74 cm-1.  Plotted above the spectrum are fit residuals.

 

Abstract: We describe the development of a near-infrared laser heterodyne radiometer (LHR):  Precision Heterodyne Oxygen-Calibration Spectrometer (PHOCS). The prototype instrument is equipped with two heterodyne receivers for oxygen and water (measured near 1278 nanometers) and carbon dioxide (near 1572 nanometers) concentration profiles, respectively. The latter may be substituted by a heterodyne receiver module equipped with a laser to monitor atmospheric methane near 1651 nanometers.). Oxygen measurements are intended to provide dry gas corrections and – more importantly – determine accurate temperature and pressure profiles that, in turn, improve the precision of the CO2 and H2O column retrievals. Vertical profiling is made feasible by interrogating the very low-noise absorption lines shapes collected at »0.0067 cm-1 resolution. PHOCS complements results from the Orbiting Carbon Observatory (OCO-2), Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS), and ground-based Fourier transform spectrometers. In this manuscript we describe the development of the instrument by Mesa Photonics and present the results of initial tests in the vicinity of Washington, D.C.

 

A collaboration between Stanford University, the University of Connecticut, the University of Toronto, and George Washington University published in the journal Fuel.

Chiara Saggese, Ajay V. Singh, Xin Xue, Carson Chu, Mohammad Reza Kholghy, Tongfeng Zhang, Joaquin Camacho, Jennifer Giaccai, J. Houston Miller, Murray J. Thomson, Chih-Jen Sung, Hai Wang,

Abstract Real jet fuels are complex mixtures of many organic components, some of which are aromatic compounds.Towards the high-temperature end of the distillation curve, some of the fuel components are multi-ring com-pounds. A small amount of these high molecular weight species in the fuel could impact soot nucleation in practical engines especially when the fuel is injected as a spray. This work aims to highlight the variation of the sooting propensity of jet fuels as a function of distillate fractions and to examine the validity of a surrogate fuel in emulating soot production from real fuels. Particle size distribution functions and soot volume fractions are studied in a series of laminar premixed stretch-stabilized ethylene flames doped with Jet A, its various distillate fractions, and the 2nd generation MURI surrogate. Soot formation as a result of doping real jet fuel and its distillate fractions is also investigated in counterflow and coflow diffusion flames. The results show that the higher-boiling distillates mostly influence soot nucleation and produce substantially more soot in nucleation controlled flames than the light molecular fraction and jet fuel as received, while such an effect is seen to be small in flames where soot production is controlled by surface growth. The potential impact of distillate fractions on soot nucleation propensities is discussed

 

a Mechanical Engineering Department, Stanford University, Stanford, CA 94305, USA

b Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269, USA

c. Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Canada

d. Department of Chemistry, The George Washington University, Washington, DC 20052, USA

Jennifer A. Giaccai and J. Houston Miller

Abstract: Interactions of oxygen with polynuclear aromatic hydrocarbons (PAH) can occur both in the flame and during oxidation of soot atmospherically. Past experimental measurements of PAH in soot samples collected either immediately after combustion, from the atmosphere, or in a flame show a variety of oxygen moieties within the PAH structures. This study investigated the electronic structure of oxygen-containing PAH to gain insight into their interaction with light both to better interpret spectroscopic measurements and to recognize the role of oxygen-containing PAH in atmospheric radiative forcing. Our research has shown that oxygen in ethers and hydroxyl moieties on PAH showed little change to the HOMO-LUMO gap (HLG), whereas ketones and aldehydes show a HLG decrease of 0.5 eV. The effect is enhanced when more than one ketone is present on a PAH molecule and further enhanced in subsequent dehydrogenation to a quinone-like structure. The presence of an oxygen-containing PAH with a ketone functional group in a dimer and trimer will substantially lower the HLG of the PAH stack. This may have a significant effect in the interaction of atmospheric soot with solar radiation.

 

Molecular orbitals for ketone-ketone and ketone-parent dimers showing electron density remains on the ketone containing monomer in the HOMO and LUMO orbitals. In the ketone/parent dimer the ketone molecule is the upper molecule. Parent molecule is naphtha[8,1,2-abc]coronene.

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Proceedings of the Combustion Institute,Volume 37, Issue 1, 2019
Pages 903-910

Trump White House quietly cancels NASA research verifying greenhouse gas cuts

Our group developed a collaborative proposal with biologists at GW and the University  of Vermont in early 2017 for this program.  We had an inkling that CMS was in trouble when we were notified that he proposal would not be reviewed.  The Terrestrial Sink is one of the largest "negative feedbacks" for increased carbon dioxide in the atmosphere.  (In plain speak, trees and other terrestrial biomass consume CO2 that fossil fuels add to atmosphere.)  The magnitude of the terrestrial sink is also very uncertain, but evidence over the last decade suggests that it is changing, and not in a good way: less carbon is being sequestered  by terrestrial biomass.

"You can't manage what you don't measure."

"This type of research is likely to continue, but leadership will pass to Europe."

Carbon cycle sources and sinks. From https://eoportal.org/web/eoportal/satellite-missions/content/-/article/oco2.

After several months of preparation both in the classroom and in the laboratory, the first Eco-Equity LuftSinn sensor was installed on the roof of Cardozo High School in Northwest Washington DC.  You can check out data from this and LuftSinn other sensors at our companion site.

 

 

EE-1 sensor installed on roof of Cardozo High School with the Washington Monument in the background.
The AP Environmental Science Class at Cardozo learning about their new sensor.

presented at the Spring Technical Meeting Eastern States Section of the Combustion Institute, March 4-7, 2018 State College, Pennsylvania

Abstract: Carbon-based black pigments have been used extensively in art and cultural heritage objects.  In East Asia particularly, soot has been the primary black pigment in the form of Chinese ink and inksticks.  Valuable information about soot’s chemical morphology can be obtained by Raman spectroscopy.  Analysis of the D and G bands in Raman spectra of carbonaceous materials has long been used to identify the amount of disorder, but a more detailed application of Raman has yet to be applied to artists’ pigments.  In this study, a number of East Asian inksticks and their component soots (soot from pine wood or vegetable oils and, more recently, industrial carbon black) were examined.  The D and G peaks of the Raman spectra were fit with both two-band and five-band peak fitting routines.  The fitting results were used in principal component analysis (PCA) to differentiate between different Chinese ink sources.

 

D. Michelle Bailey and J. Houston Miller

Geophysical Research Abstracts Vol. 20, EGU2018-821, 2018

 

Beyond anthropogenic carbon emissions, the increase in atmospheric carbon from natural feedbacks such as thawing permafrost poses a risk to the global climate as global temperatures continue to increase. Permafrost is formally defined as soil that is continuously frozen for 24 consecutive months. These soils comprise nearly twenty-five percent of the Earth’s terrestrial surface and possess twice the amount of carbon currently in the atmosphere. Continuous collection of carbon dioxide (CO2) and methane (CH4) concentrations is imperative in understanding seasonal and inter-annual variability of carbon feedbacks above thawing permafrost. A multi-year collaborative effort with the University of Alaska – Fairbanks, NASA Goddard Space Flight Center, and our group at George Washington University was undertaken to monitor these feedbacks near Fairbanks, Alaska.

In June 2017, we deployed two open-path tunable diode laser sensors at the Bonanza Long Term Ecological Research Site for measurement of CO2 and CH4 concentrations. The open-path instrument (OPI) is an inexpensive, low-power sensor that collects spatially-integrated measurements of target molecules approximately 1.5 meters above ground level. With a total power burden of 18 W, the sensors ran exclusively on solar power for 15 days in a young thermokarst bog and 3.5 days at a rich fen site. Here we report on initial retrieval of diurnal cycles from each field site and compare our spatially-integrated measurements of CO2 and CH4. For CO2, the magnitude of the diurnal cycles show a strong dependence on daily weather at both field sites. These laser measurements are complemented by point measurements of CO2, temperature, pressure, and humidity made along the laser’s optical path by non-dispersive infrared (NDIR) sensors. Instrument up-time during field campaigns was limited by ground-surface instability resulting in misalignment and loss of laser-return signal. To mitigate against this performance degradation, we also present an auto-alignment scheme for the OPI. By implementing a simplex optimization approach via a custom Python script, the instrument can adjust the alt-azi position of the laser launch box in order to maximize return signal without human intervention. We have demonstrated this alignment protocol over short and long pathlengths and found that the utility of autoalignment is limited by the pointing accuracy of our motorized mount.

 

About this EGU colloquium

The instrumentation and its development play a key role in the advance in research, which makes it possible to offer to the researchers state-of-the-art tools to address scientific "open questions" and to open new fields of research leading to new discoveries.

Since the last decade, atmospheric environmental monitoring has benefited from the development of novel spectroscopic measurement techniques owing to the significant breakthroughs in photonic technology from the UV to the THz domain, which allows opening up new research avenues for observation of spatial and long-term trends in key atmospheric precursors, improving our understanding of tropospheric chemical processes and trends that affect regional air quality and global climate change. Extensive development of spectroscopic instruments for sensing the atmosphere continues to be carried out to improve their performance and functionality, and to reduce their size and cost.

This proposed focus session entitled "Advanced Spectroscopic Measurement Techniques for Atmospheric Science" addresses the latest developments and advances in a broad range of photonic instrumentation, optoelectronic devices and technologies, and also their integration for a variety of atmospheric applications. The objective is to provide an opportunity to get a broad overview of the current state-of-the-art and future prospects in photonic instrumental development for atmospheric sensing. It provides an interdisciplinary forum to enhance interactions between experimentalists, atmospheric scientists, development engineers, as well as R&D and analytical equipment companies to define the needs of the atmospheric scientists to address current atmospheric science issues, and coordinate these needs with the current capabilities of spectroscopic measurement techniques.

Topics for presentation and discussion will include but not be limited to: cavity-enhanced spectroscopy including IBBCEAS, ICOS, CRDS, UAV- or balloon-based measurement techniques, heterodyne radiometry, and aerosol spectroscopy ....; and their applications to in situ photonic metrology (concentration, vertical concentration profile, isotopes, flux, ...) of atmospheric aerosol, radicals & trace gases (HOx, RO2, NO3, HONO, NOx, greenhouse gases, halogens, CH2O, VOCs, BVOCs, light hydrocarbons, ....) in field observation, geological exploration, prospecting and survey, intensive campaigns and smog chamber study.

 

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