Author: houston

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.

 

D. Michelle Bailey and J. Houston Miller

Geophysical Research Abstracts Vol. 20, EGU2018-7401, 2018

Due to its ability to influence global climate change, it is imperative to continually monitor carbon dioxide emission levels. Although high-precision sensors are commercially available, these are not cost effective for mapping a large spatial area. A goal of this research is to build out a network of sensors that are accurate and precise enough to provide a valuable data tool for accessing carbon emissions from large, urban or remote areas. This greenhouse gas dataset can be used in numerous environmental assessments and as validation for remote sensing products. Each of our sensors (referred to as “Luftsinn” sensors) utilizes a non-dispersive infrared (NDIR) sensor for the detection of carbon dioxide along with a combination pressure/temperature/humidity sensor and a real-time clock. The sensors communicate using serial and I2C interfaces with a Raspberry Pi ARM-based, microcontroller. Laboratory characterization of the Luftsinn sensors shows ∼1% accuracy when evaluated with gas standards. For field deployment, solar-powered sensors, supporting a 5 W power burden, have been developed.

Two applications are discussed here. First, Luftsinn sensors are being deployed as a part of an innovative opennetworking platform being installed on LED street lights in Washington, DC. In this application, where internet access via WiFi or LoRa is readily available, each Luftsinn unit is connected to a website that leverages recent developments in open source GIS tools. In this way, data from individual sensors can be followed individually or aggregated to provide real-time, spatially-resolved data of CO₂ trends across a broad area. Alternatively, these sensors have been deployed in remote Alaska to evaluate carbon dioxide emissions above thawing permafrost. Data from these deployments are manually retrieved and posted onto the same webpage retroactively. A developing project will combine data collected from these unique environments and incorporate K-12 students residing above and below the 60th parallel to allow them to engage directly with the data and disseminate their findings to peers across the country.

D. Michelle Bailey, Erin M. Adkins, and  J. Houston Miller

Appl. Phys. B (2017) 123:245

We have developed a low-power, open-path, near-infrared (NIR) tunable diode laser sensor for the measurement of near ground-level concentrations of greenhouse gases. Here, we report on instrument design, characterization, and initial measurements of carbon dioxide concentrations during deployment to a thermokarst collapse scar bog near Fairbanks, AK (USA). The optics “launch-box” portion of the instrument couples radiation from an NIR, distributed feedback diode laser operating near 1572 nm with a visible laser for alignment purposes. The outgoing beam is directed through a 3.2-mm hole in a parabolic mirror and the launchbox is oriented using a two axis, altitude-azimuth telescope mount such that the beam strikes a retroreflector target at a set distance downfield. The beam then retraces the path back to the launch-box where the light is collected on the surface of the parabolic mirror and focused onto a multimode fiber that transfers the radiation to an InGaAs detector. Sweeps over a ~1.6 cm^-1 spectral region were collected at a rate of 500 scans per second and were typically stored as 10 s sweep averages. These averaged sweeps could be individually spectrally fit for CO₂ concentration or averaged  into a single spectrum for fitting (after correction for slight frequency drift). Field data reported here was averaged for 2.5 min and was found to follow trends in diurnal cycles of CO₂ concentration cycles reported by sensors located nearby in the field site.

Erin M. Adkins  and  J. Houston Miller

Phys. Chem. Chem. Phys., 2017,19, 28458-28469

Trends linking the topological characteristics of polynuclear aromatic hydrocarbons (PAH) to their electronic properties are reported. TD-DFT electronic spectra computations, using the 6-31G* basis set and B3LYP exchange correlation functional, were calculated for a series of PAH, allowing for the HOMO–LUMO gaps to be reported. Clar structures provide an avenue to link the physical structure and the aromaticity of the molecule; which, when extended by bond length and harmonic oscillator model of aromaticity analysis, provide powerful tools to understand the link between electronic and physical structure. These results lead to the conclusion that all PAH structures show a decrease in HOMO–LUMO gap as a function of size, but the rate of that decrease is directly related to the topology of the molecules. A PAH taxonomy was developed that categorizes PAH into categories with similar topological properties, which allows for modelling of changes in the HOMO–LUMO gap with PAH size. An atom-pair minimization algorithm was used to calculate the binding energy (BE) of homogeneous dimers of the studied PAH. The BE per carbon atom increases with the overall size of the structure to an asymptotic limit, but as with the HOMO–LUMO gap, topology plays a critical secondary factor. Previously published, experimentally determined optical band gaps (OBG) from Tauc/Davis–Mott analysis of extinction spectra in various laminar, non-premixed flames produced a correlation between the HOMO–LUMO gaps of high-symmetry, nearly circular D_2h symmetry molecules to molecular size. The work presented here provides a much more nuanced and predictive evaluation of how OBG depends on structure and size.

Erin M.Adkins, Jennifer A.Giaccai, and  J. HoustonMiller

Proceedings of the Combustion Institute

Maria Botero, Erin M. Adkins, Silvia Gonzalez Calera, Houston Miller, and Markus Kraft

Combustion and Flame 164, 250-258, (2016)

Soot particles formed in a system of non-premixed liquid fuel flames supported on a wick-fed, smoke point test burner (ASTM D1322-08) were characterised by in-situ visible light extinction and thermophoretically-sampled high-resolution transmission electron microscopy measurements, HRTEM. The fuels studied were heptane, toluene and their iso-volumetric mixture (H50T50), given their relevance as surrogate fuels. Extinction measurements were used to calculate the soot volume fraction, Fv, and determine the optical band gap (OBG) as a function of flame position. The OBG was derived from the near-edge absorption feature using Tauc/Davis-Mott analysis. For the HRTEM analysis, soot samples were collected at different locations in the flame using thermophoretic sampling and a fast-insertion technique. The images were then analysed using a `lattice-fringe' algorithm, to determine important parameters such as the fringe length. Polycyclic aromatic hydrocarbon (PAH) sizes were estimated from conjugation length obtained from OBG measurements and fringe lengths from HRTEM measurements. Across all studied flames, the peak Fv ranged from 3.8 ppm in the heptane flame to 18.0 ppm in the toluene flame. Despite this wide range, the average OBG across the different flames only varied from 1.99 eV in the H50T50 to 2.06 eV in the heptane flames, which is consistent with molecule lengths of between 0.98 nm and 1.02 nm. Lattice fringe analysis yielded slightly lower average fringe lengths between 0.85 - 0.96 nm throughout the different flames. This work provides experimental support to the model of soot formation where the transition from chemical to physical growth starts at a modest molecular size; about the size of circumpyrene.

GB Clarke, EL Wilson, JH Miller, HR Melroy

Presented here is a sensitivity analysis for the miniaturized laser heterodyne radiometer. This passive, ground-based instrument measures carbon dioxide (CO₂) in the atmospheric column and has been under development at NASA/GSFC since 2009. The goal of this development is to produce a low-cost, easily-deployable instrument that can extend current ground measurement networks in order to (1) validate column satellite observations, (2) provide coverage in regions of limited satellite observations, (3) target regions of interest such as thawing permafrost, and (4) support the continuity of a long-term climate record. In this paper an uncertainty analysis of the instrument performance is presented and compared with results from three sets of field measurements. The signal-to-noise ratio (SNR) and corresponding maximum uncertainty for a single scan are calculated to be 329.4 ± 1.3 by deploying error propagation through the equation governing the SNR. Reported is an absorbance noise of 0.0024 for six averaged scans of field data, for an instrument precision of 0.14 ppmv for CO₂.