Charles T. Chaffin

SO2∶HCl ratios in the plumes from Mt. Etna and Vulcano determined by Fourier Transform Spectroscopy

Volcanic gases have important climatic and environmental effects, and provide insights into magmatic processes. Direct sampling of volcanic gases is inherently difficult and often hazardous. Here, the authors report the results of long path measurements of SO{sub 2} and HCl from Mt. Etna and Vulcano (Italy) obtained by active mode Fourier Transform InfraRed (FTIR) spectroscopy. Spectra recorded in September 1994 over path lengths of up to 2 km indicate SO{sub 2}:HCl ratios of 3-5:1 for Etna, and 0.7-1.4:1 for Vulcano, consistent with their different styles of activity. Combined with contemporaneous Correlation Spectrometer (COSPEC) SO{sub 2} flux measurements, these ratios indicate an HCl flux for Etna of about 1700 t/d (about 16% of the present global anthropogenic flux) and for Vulcano of about 13 t/d. They also report the first remote spectroscopic detection of volcanic SiF{sub 4}. 17 refs., 3 figs., 1 tab.

Remote determination of SiF4 in volcanic plumes: A new tool for volcano monitoring

SiF4 is probably a common trace component of fumarole gases on volcanoes, arising from interactions between magmatic HF and wall rocks. It is not distinguished from HF in conventional analyses. A strong absorption band at 1032 cm−1 makes SiF4 well suited to remote open-path FTIR spectroscopic techniques. We report the first measurements of SiF4 in volcanic gases at Etna and Vulcano (Sicily). SiF4 concentrations were low at Etna, but higher at Vulcano, where the SO2: SiF4 ratio was consistently around 1.7×10−2: 1. Thermodynamic considerations show that the HF : SiF4 ratio increases sharply with increasing temperature. Thus, remote measurements of SiF4 may offer a qualitative way of constraining fumarole temperatures. We use our FTIR measurements of HCl: SiF4 in combination with conventional measurements of HCl: HF to infer an HF :SiF4 ratio for Vulcano of ∼10:1, consistent with gas temperatures in the range 200–450°C.

FT-IR remote sensing of industrial atmospheres for spatial characterization

Two identical Fourier transform infrared (FT-IR) field monitoring systems have been used to investigate differences in apparent plume concentrations as a function of height. The two systems also have been used to monitor the same plume simultaneously at the same height to estimate the precision that can be expected. The data collected suggest that IR beam height may play a significant role in the measured concentrations of plume constituents.

New methods make volcanology research less hazardous

Volcanic gases are important to the scientific community for many reasons: the Earths secondary atmosphere originated through volcanic degassing, and volcanic gases still play a crucial role in the Earth system. Occasional massive eruptions pump such large quantities of acid gas into the stratosphere that the resulting aerosols modify global climate for months or years. Also, volcanic gases escaping from magma bodies act as “messengers” that warn of impending eruptions and convey insight into magma chamber processes. Volcanologists are interested in both the fluxes and the compositions of exhaled gases, but collecting in situ measurements on active volcanoes is hazardous. Several volcanologists were killed by an unexpected eruption of Galeras volcano in Colombia in January 1993, including our colleague Geoff Brown. This tragedy emphasized the need for remote methods for studying volcanoes. Two approaches are being explored: satellite remote sensing and ground-based techniques.

A Method of Predicting Point and Path- Averaged Ambient Air VOC Concentrations, Using Meteorological Data

A method of predicting point and path-averaged ambient air VOC concentrations is described. This method was developed for the case of a plume generated from a single point source, and is based on the relationship between wind directional frequency and concentration. One-minute means of wind direction and wind speed were used as inputs to a Gaussian dispersion model to develop this relationship. Both FTIR spectrometry and a whole-air sampling method were used to monitor VOC plumes during simulated field tests. One test set was also conducted using only whole-air samplers deployed in a closely-spaced network, thus providing an evaluation of the prediction technique free of any bias that might exist between the two analytical methods. Correlations between observed point concentrations and wind directional frequencies were significant at the 0.05 level in most cases. Predicted path-integrated concentrations, based on observed point concentrations and meteorological data, were strongly correlated with observed...

Infrared detection and analysis of vapor plumes using an airborne sensor

An airborne infrared (IR) line-scanner and a Fourier transform infrared (FT-IR) spectrometer operating in the 3- 5micrometers and 8-12micrometers spectral regions provide a rapid wide- area surveillance capability. The IR scene containing target vapors is mapped remotely with the wide fields of view (FOV) multi-spectral IR line-scanner using 14 bands. The narrow FOV FT-IR spectrometer permits remote verification of target vapor plume contents within the IR scene. The IR image and FT-IR interferogram analysis supply a near real-time detection that provides visual monitoring of potential downwind vapor hazards. This capability is demonstrated using the target vapor methanol. An active mono-static FT-IR configuration furnishes ground-truth monitoring for methanol released from an industrial stack and a nearby ground-level area. The airborne and ground-truth results demonstrate the usefulness of this approach in alerting first responders to potential downwind vapor hazards from an accidental release.

Investigation of the effects of resolution on the performance of classical least-squares (CLS) spectral interpretation programs when applied to volatile organic compounds (VOCs) of interest in remote sensing using open-air long-path Fourier transform infrared (FT-IR) spectrometry

Abstract In the last 10 to 15 years, many investigations into the usefulness of multivariate data analysis techniques have been made using various algorithms to both qualify and quantify data obtained using Fourier transform (FT-IR) spectrometry. In the last 5 to 7 years, many investigations into remote sensing of volatile organic compounds (VOCs) in the atmosphere using open-air long-path FT-IR spectrometry have been made. This paper is a progress report of the attempt of our two laboratories to combine the two fields.

Generating well-characterized chemical plumes for remote sensing research

In the interest of remote sensing research, equipment and techniques have been developed to generate heated plumes with controlled and well-characterized temperature and composition profiles. This report describes the construction of a plume generating device as well as the field operations involved in creating and monitoring heated plumes for research purposes. Performance specifications for the plume generator and its components are provided and typical FTIR validation data are included that illustrate the devices capabilities.

Estimation of VOC emission rates from FTIR measurements and whole-air canister data

Methods of estimating VOC emission rates from a point source are being field tested by the University of Kansas, in cooperation with Region VII of the U.S. EPA and Kansas State University. The methods use path-integrated VOC concentrations, meteorological data, and a form of the Gaussian dispersion equation. VOC concentrations were derived both from a whole-air canister sampling method, with subsequent GC analysis, and from open-path FTIR measurements; estimated emission rates produced from the two analytical methods were compared. Canister-derived concentrations provided higher mean estimation accuracies than did FTIR measurements for both 1, 1, 1-Trichloroethane and toluene; however, for a third data set consisting of all other compounds released, FTIR measurements provided higher values. Estimation accuracy also was evaluated as a function of atmospheric stability and downwind distance; accuracy generally increased and variability decreased as stability increased; accuracy was better at longer than at 50 meters.

Using a gas cell to characterize FT-IR air sensor performance

A gas cell is used to characterize the analytical performance of an FTIR sensor collecting air monitoring data in an active sampling configuration. Hardware and data collection techniques are described and example data are presented. Instrument performance is characterized and discussed in terms of accuracy, precision, linearity, drift, and reproducibility.