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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

A Gas Chromatograph/Mass Spectrometer System for UltraLow-Emission Combustor Exhaust Studies

A gas chromatograph (GC)/mass spectrometer (MS) system that allows the speciation of unburnt hydrocarbons in the combustor exhaust has been developed at the NASA Lewis Research Center. Combustion gas samples are withdrawn through a water-cooled sampling probe which, when not in use, is protected from contamination by a high-pressure nitrogen purge. The sample line and its connecting lines, filters, and valves are all ultraclean and are heated to avoid condensation. The system has resolution to the parts-per-billion (ppb) level.

Brabbs, Theodore A.↗
NASA NTRS1995

Subminiaturization for ERAST instrumentation (Environmental Research Aircraft and Sensor Technology)

We are focusing on the Argus as an example to demonstrate our philosophy on miniaturization of airborne analytical instruments for the study of atmospheric chemistry. Argus is a two channel, tunable-diode laser absorption spectrometer developed at NASA for the measurement of nitrogen dioxide (N2O) (4.5 micrometers) and ammonia (CH3) (3.3 micrometers) at the 0.1 parts per billion (ppb) level from the Perseus aircraft platform at altitudes up to 30 km. Although Argus' mass is down to 23 kg from the 197 kg Atlas, its predecessor, our goal is to design a next-generation subminiaturized instrument weighing less than 1 kg, measuring a few cm(exp 3) and able to eliminate dewars for cooling. Current designs enable use to make a small,inexpensive, monolithic spectrometer without the required sensitivity range. Further work is on its way to increase sensitivity. We are continuing to zero-base the technical approach in terms of the specifications for the given instrument. We are establishing a check list of questions to hone into the best micromachining approach and to superpose on the answers insights in scaling laws and flexible engineering designs to enable more relaxed tolerances for the smallest of the components.

Madou, Marc↗
NASA NTRS1997

Automated Test Systems for Toxic Vapor Detectors

The NASA Toxic Vapor Detection Laboratory (TVDL) at the Kennedy Space Center (KSC), Florida, has been using Personal Computer based Data Acquisition and Control Systems (PCDAS) for about nine years. These systems control the generation of toxic vapors of known concentrations under controlled conditions of temperature and humidity. The PCDAS also logs the test conditions and the test article responses in data files for analysis by standard spreadsheets or custom programs. The PCDAS was originally developed to perform standardized qualification and acceptance tests in a search for a commercial off-the-shelf (COTS) toxic vapor detector to replace the hydrazine detectors for the Space Shuttle launch pad. It has since become standard test equipment for the TVDL and is indispensable in producing calibration standards for the new hydrazine monitors at the 10 part per billion (ppb) level. The standard TVDL PCDAS can control two toxic vapor generators (TVG's) with three channels each and two flow/temperature/humidity (FIFH) controllers and it can record data from up to six toxic vapor detectors (TVD's) under test and can deliver flows from 5 to 50 liters per minute (L/m) at temperatures from near zero to 50 degrees Celsius (C) using an environmental chamber to maintain the sample temperature. The concentration range for toxic vapors depends on the permeation source installed in the TVG. The PCDAS can provide closed loop control of temperature and humidity to two sample vessels, typically one for zero gas and one for the standard gas. This is required at very low toxic vapor concentrations to minimize the time required to passivate the sample delivery system. Recently, there have been several requests for information about the PCDAS by other laboratories with similar needs, both on and off KSC. The purpose of this paper is to inform the toxic vapor detection community of the current status and planned upgrades to the automated testing of toxic vapor detectors at the Kennedy Space Center.

Mattson, C. B.↗
NASA NTRS1997

Automated Test Systems for Toxic Vapor Detectors

The NASA Toxic Vapor Detection Laboratory (TVDL) at the Kennedy Space Center (KSC), Florida, has been using Personal Computer based Data Acquisition and Control Systems (PCDAS) for about nine years. These systems control the generation of toxic vapors of known concentrations under controlled conditions of temperature and humidity. The PCDAS also logs the test conditions and the test article responses in data files for analysis by standard spreadsheets or custom programs. The PCDAS was originally developed to perform standardized qualification and acceptance tests in a search for a commercial off-the-shelf (COTS) toxic vapor detector to replace the hydrazine detectors for the Space Shuttle launch pad. It has since become standard test equipment for the TVDL and is indispensable in producing calibration standards for the new hydrazine monitors at the 10 part per billion (ppb) level. The standard TVDL PCDAS can control two toxic vapor generators (TVG's) with three channels each and two flow/ temperature / humidity (FTH) controllers and it can record data from up to six toxic vapor detectors (TVD's) under test and can deliver flows from 5 to 50 liters per minute (L/m) at temperatures from near zero to 50 degrees Celsius (C) using an environmental chamber to maintain the sample temperature. The concentration range for toxic vapors depends on the permeation source installed in the TVG. The PCDAS can provide closed loop control of temperature and humidity to two sample vessels, typically one for zero gas and one for the standard gas. This is required at very low toxic vapor concentrations to minimize the time required to passivate the sample delivery system. Recently, there have been several requests for information about the PCDAS by other laboratories with similar needs, both on and off KSC. The purpose of this paper is to inform the toxic vapor detection community of the current status and planned upgrades to the automated testing of toxic vapor detectors at the Kennedy Space Center.

Mattson, C. B.↗
NASA NTRS1997

Permeation Resistance of Personal Protective Equipment Materials to Monomethyhydrazine

Permeation resistance was determined by measuring the breakthrough time and time-averaged vapor transmission rate of monomethylhydrazine (MMH) through two types of personal protective equipment (PPE). The two types of PPE evaluated were the totally encapsulating ILC Dover Chemturion Model 1212 chemical protective suit with accessories, and the FabOhio polyvinyl chloride (PVC) splash garment. Two exposure scenarios were simulated: (1) a saturated vapor exposure for 2 hours (h), and (2) a brief MMH 'splash' followed by a 2-h saturated vapor exposure. Time-averaged MMH concentrations inside the totally-encapsulating suit were calculated by summation of the area-weighted contributions made by each suit component. Results show that the totally encapsulating suit provides adequate protection at the new 10 ppb Threshold Limit Value Time-Weighted Average (TLV-TWA). The permeation resistance of the PVC splash garment to MMH was poorer than any of the totally encapsulating suit materials tested. Breakthrough occurred soon after initial vapor or 'splash' exposure.

Waller, J. M.↗
NASA NTRS1994

Petrology of Impact-Melt Rocks at the Chicxulub Multiring Basin, Yucatan, Mexico

Compositions and textures of melt rocks from the upper part of the Chicxulub structure are typical of melt rocks at other large terrestrial impact structures. Apart from variably elevated iridium concentrations (less than 1.5 to 13.5 +/- 0.9 ppb) indicating nonuniform dissemination of a meteoritic component, bulk rock and phenocryst compositions imply that these melt rocks were derived exclusively from continental crust and platform-sediment target lithologies. Modest differences in bulk chemistry among samples from wells located approximately 40 km apart suggest minor variations in relative contributions of these target lithologies to the melts. Subtle variations in the compositions of early-formed pyroxene and plagioclase also support minor primary differences in chemistry between the melts. Evidence for pervasive hydrothermal alteration of the porous mesostasis includes albite, K-feldspar, quartz, epidote, chlorite, and other phyllosilicates, as well as siderophile element-enriched sulfides, suggesting the possibility that Chicxulub, like Sudbury, may host important ore deposits.

Schuraytz, Benjamin C.↗
NASA NTRS1997

Distributions of Beryllium 7 and Lead 210, and Soluble Aerosol-Associated Ionic Species Over the Western Pacific: PEM West B, February - March 1994

Aerosol sampling for the determination of the concentrations of soluble ionic species and the natural radionuclides Be-7 and Pb-210 was conducted from the NASA DC-8 over the western Pacific as part of GTE/PEM-West B during February - March 1994. Concentrations of most soluble ionic species in the free troposphere were higher in samples collected on flights originating from Hong Kong and Japan than those collected further east over the open ocean. In both regions the measured concentrations were higher than those found during PEM-West A (fall 1991). Activities of Pb-210, a tracer of air masses influenced by sources on the Asian continent, showed the same patterns. These data indicate the effect of stronger continental outflow from Asia over the western Pacific during the spring compared to fall season. For readily scavenged aerosol-associated species and soluble acidic gases the strongest indications of Asian outflow were restricted to altitudes below 6 km. The distribution of the continental tracer Pb-210 was also compared to those of a large number of gas phase species measured on the DC-8. Relatively strong correlations were found with O3, and peroxyacetylnitrate (PAN), but only during the flights over the remote Pacific. During PEM-West A, similar correlations were seen, but they were stronger near Asia. We believe that correlations are a signature of continental air that has been processed by deep wet convection over land before being advected over the ocean. One flight over the Sea of Japan provided the opportunity to sample upper troposphere/lower stratosphere air in and around a tropopause fold. Concentrations of Be-7 reached 7 pCi/cu m STP, and peak O3, mixing ratios of 480 ppb were encountered at 10.7 km. The Be-7 data are used to estimate the fraction of stratospheric air mixed down into the troposphere by circulation in the fold.

Dibb, J. E.↗
NASA NTRS1997

Distributions of Beryllium 7 and Lead 210, and Soluble Aerosol-Associated Ionic Species Over the Western Pacific: PEM West B

Aerosol sampling for the determination of the concentrations of soluble ionic species and the natural radionuclides Be-7 and Pb-210 was conducted from the NASA DC-8 over the western Pacific as part of GTE/PEM-West B during February - March 1994. Concentrations of most soluble ionic species in the free troposphere were higher in samples collected on flights originating from Hong Kong and Japan than those collected further east over the open ocean. In both regions the measured concentrations were higher than those found during PEM-West A (fall 1991). Activities of Pb-210 tracer of air masses influenced by sources on the Asian continent, showed the same patterns. These data indicate the effect of stronger continental outflow from Asia over the western Pacific during the spring compared to fall season. For readily scavenged aerosol-associated species and soluble acidic gases the strongest indications of Asian outflow were restricted to altitudes below 6 km. The distribution of the continental tracer Pb-210 was also compared to those of a large number of gas phase species measured on the DC-8. Relatively strong correlations were found with O3 and peroxyacetylnitrate (PAN), but only during the flights over the remote Pacific. During PEM-West A, similar correlations were seen, but they were stronger near Asia. We believe that these correlations are a signature of continental air that has been processed by deep wet convection over land before being advected over the ocean. One flight over the Sea of Japan provided the opportunity to sample upper troposphere/lower stratosphere air in and around a tropopause fold. Concentrations of Be-7 reached 7 pCi/cu m STP, and peak O3, mixing ratios of 480 ppb were encountered at 10.7 km. The Be-7 data are used to estimate the fraction of stratospheric air mixed down into the troposphere by circulation in the fold.

Didd, J. E.↗
NASA NTRS1995

Analysis of Ultra-Pure Gases by Ion Mobility Spectrometry

Work has continued with the evaluation of the Ion Mobility Spectrometer (IMS) for the analysis of gases having low parts-per-billion (10(exp -9)) water concentration. A modified PCP, inc. MMS-160 Mobility Mass Spectrometer System was used for the analysis of ultra-pure argon and nitrogen. The MMS-160 system permits the mass-identification of unique reactant and product ions observed in the reduced-water host gases. When the water is removed to low ppb levels, higher energy reactant ions are observed. In nitrogen, distinct odd- and even-numbered nitrogen cluster ion mobility peaks are observed, as well as adduct ion peaks from the trace contaminants in the gas. Argon also produces a cluster ion mobility peak and adduct ion peaks from trace components in the gas. Levels of contaminants in these ultra-pure gases can be determined from the ion mobility spectra. A calibrated source was used to provide variable known quantities of water to the pure gas supply of the IMS.

Stimac, Robert M.↗
NASA NTRS1999

Chemical Sensors Based on IR Spectroscopy and Surface-Modified Waveguides

Sol-gel processing techniques have been used to apply thin porous films to the surfaces of planar infrared (IR) waveguides to produce widely useful chemical sensors. The thin- film coating serves to diminish the concentration of water and increase the concentration of the analyte in the region probed by the evanescent IR wave. These porous films are composed of silica, and therefore, conventional silica surface modification techniques can be used to give the surface a specific functional character. The sol-gel film was surface-modified to make the film highly hydrophobic. These sensors were shown to be capable of detecting non-polar organic analytes, such as benzonitrile, in aqueous solution with detection limits in the ppb range. Further, these porous sol-gel structures allow the analytes to diffuse into and out of the films rapidly, thus reaching equilibrium in less than ten seconds. These sensors are unique because of the fact that their operation is based on the measurement of an IR absorption spectrum. Thus, these sensors are able to identify the analytes as well as measure concentration with high sensitivity. These developments have been documented in previous reports and publications. Recently, we have also targeted detection of the polar organic molecules acetone and isopropanol in aqueous solution. Polar organics are widely used in industrial and chemical processes, hence it is of interest to monitor their presence in effluents or decontamination process flows. Although large improvements in detection limits were expected with non-polar organic molecules in aqueous solutions using very hydrophobic porous sol-gel films on silicon attenuated total reflectance (Si ATR) waveguides, it was not as clear what the detection enhancements might be for polar organic molecules. This report describes the use of modified sol-gel-coated Si ATR sensors for trace detection and quantitation of small polar organic molecules in aqueous solutions. The detection of both acetone and isopropanol molecules in aqueous solution has been previously reported for chalcogenide fiber optic sensors. The sol-gel film was produced using a mixture of ethyltriethoxysilane and tetraethoxysilane and the surface modification was carried out using trimethylchlorosilane. We have demonstrated that this film concentrates the target polar analytes from aqueous solution in the region probed by the evanescent wave to improve detection limits by as much as a factor of 450.

Lopez, Gabriel P.↗
NASA NTRS1971

Design and Performance of a Gas Chromatograph for Automatic Monitoring of Pollutants in Ambient Air

In recent years, interest in air pollution constituents has focused on carbon monoxide and hydrocarbons as prime components of polluted air. Instrumental methods have been developed, and commercial instruments for continuous monitoring of these components have been available for a number of years. For the measurement of carbon monoxide, non-dispersive infrared spectroscopy has been the accepted tool, in spite of its marginal sensitivity at low parts-per-million levels. For continuously monitoring total hydrocarbons, the hydrogen flame ionization analyzer has been widely accepted as the preferred method. The inadequacy of this latter method became evident when it was concluded that methane is non-reactive and cannot be considered a contaminant even though present at over 1 ppm in the earth's atmosphere. Hence, the need for measuring methane separately became apparent as a means of measuring the reactive and potentially harmful non-methane hydrocarbons fraction. A gas chromatographic method for the measurement of methane and total hydrocarbons which met these requirements has been developed. In this technique, methane was separated on conventional gas chromatographic columns and detected by a hydrogen flame ionization detector (FID) while the total hydrocarbons were obtained by introducing a second sample directly into the FID without separating the various components. The reactive, or non-methane hydrocarbons, were determined by difference. Carbon monoxide was also measured after converting to methane over a heated catalyst to render it detectable by the FID. The development of this method made it possible to perform these measurements with a sensitivity of as much as 1 ppm full scale and a minimum detectability of 20 ppb. Incorporating this technique, criteria were developed by APCO for a second generation continuous automatic instrument for atmospheric monitoring stations.

Villalobos, R.↗
NASA NTRS1999

Hydrazine Detection with a Tunable Diode Laser Spectrometer

Several instruments have been developed to measure low concentrations of hydrazine but none completely meet the sensitivity requirements while satisfying additional criteria such as quick response, stable calibration, interference free operation, online operation, reasonable cost, etc. A brief review is presented of the current technology including the electrochemical cell, the ion mobility spectrometer, the mass spectrometer, and the gas chromatograph. A review of the advantages and disadvantages of these instruments are presented here. The review also includes commercially unavailable technology such as the electronic nose and the Tunable Diode Laser (TDL) IR Spectrometer. It was found that the TDL could meet the majority of these criteria including fast response, minimum maintenance, portability, and reasonable cost. An experiment was conducted to demonstrate the feasibility of such a system using an existing (non-portable) instrument. A lead-salt tunable diode laser, cooled to 85 degrees Kelvin was used to record direct absorption and second-derivative spectra of Hydrazine at several pressures to study the sensitivity to low levels of Hydrazine. Spectra of NH3 and CO2 were used for wavelength identification of the scanned region. With a pathlength of 80 m, detection sensitivities of about 1 ppb were achieved for hydrazine in dry nitrogen at a cell pressure of 100 mbar. For spectroscopic detection of Hydrazine, spectral regions including strong Ammonia or Carbon Dioxide lines must be avoided. Strong Hydrazine absorption features were identified at 940/cm showing minimal contribution from Ammonia interferences as suitable candidates for Hydrazine gas detection. For the studies reported here, the particular laser diode could only cover the narrow regions near 962/cm and 965/cm where strong Ammonia interferences were expected. However, the high resolution (0.001/cm) of the TDL spectrometer allowed individual lines of Hydrazine to be identified away from interferences from either Ammonia or Carbon Dioxide, especially at lower pressures. A Hydrazine line was identified at 961.75/cm which was free from Ammonia absorption and would be suitable to monitor hydrazine levels. This paper also shows data on the degradation of the detectivity of Hydrazine with increasing pressure. Several design options for a portable unit are presented, including designs with near IR and Quantum Cascade laser components which do not require liquid nitrogen cooling.

Houseman, John↗
NASA NTRS1999

A Review of Hydrazine Sensors: The State of the Art

Several types of sensors have been developed over the past few years that quantify the vapor concentrations of the hydrazines. These sensors are able to detect concentrations as low as 10 parts per billion (ppb) up to several parts per million (ppm). The scope of this review will be focused on those sensors that are most current in the marketplace as either leak detectors or personnel monitors. Some technical information on the theory of operations of each hydrazine detector will also be included. The review will highlight current operations that utilize hydrazine sensors including the Kennedy Space Center (KSC), the United States Air Force (USAF) at Cape Canaveral Air Station (CCAS), USAF F-16 facilities. The orientation of the review will be towards giving users usable practical information on hydrazine sensors.

Meneghelli, B. J.↗
NASA NTRS1999

The Mars Environmental Compatibility Assessment (MECA) Wet Chemistry Experiment on the Mars 2001 Lander

The Mars Environmental Compatibility Assessment (MECA) is an instrument suite that will fly on the Mars Surveyor 2001 Lander Spacecraft. MECA is sponsored by the Human Exploration and Development of Space (HEDS) program and will evaluate potential hazards that the dust and soil of Mars might present to astronauts and their equipment on a future human mission to Mars. Four elements constitute the integrated MECA payload: a microscopy station, patch plates, an electrometer, and the wet chemistry laboratory (WCL). The WCL consists of four identical cells, each of which will evaluate a sample of Martian soil in water to determine conductivity, pH, redox potential, dissolved C02 and 02 levels, and concentrations of many soluble ions including sodium, potassium, magnesium, calcium and the halides. In addition, cyclic voltammetry will be used to evaluate reversible and irreversible oxidants present in the water/soil solution. Anodic stripping voltammetry will be used to measure concentrations of trace metals including lead, copper, and cadmium at ppb levels. Voltammetry is a general electrochemical technique that involves controlling the potential of an electrode while simultaneously measuring the current flowing at that electrode. The WCL experiments will provide information on the corrosivity and reactivity of the Martian soil, as well as on soluble components of the soil which might be toxic to human explorers. They will also guide HEDS scientists in the development of high fidelity Martian soil simulants. In the process of acquiring information relevant to HEDS, the WCL will assess the chemical composition and properties of the salts present in the Martian soil.

Grannan, S. M.↗
NASA NTRS1999

Biomass Burning Influences on the Composition of the Remote South Pacific Troposphere: Analysis Based on Observations from PEM Tropics-A

Airborne, in-situ measurements from PEM-Tropics-A (September/October 1996) are analyzed to show the presence of distinct pollution plumes in the middle-tropical troposphere of the remote South Pacific (10-30degS). These elevated plumes cause a relative maximum at about 5-7km attitude in the vertical distribution of primary and secondary species characteristic of fuel combustion and biomass burning (CO, C2H2, C2H6, CH3Cl, PAN, O3). Similar plumes were also observed at mid-latitudes in the middle troposphere during three flights east of New Zealand (40-45degS). In all, pollution plumes with CO larger than 100 ppb were observed 24 times on 7 separate flight days south of the equator. The observed plumes were generally embedded in very dry air. Ten-day back trajectory analysis supports the view that these originated from the biomass burning regions of South Africa (and South America) and were transported to the South Pacific along long-distance subsiding trajectories. The chemical composition of the southern Pacific troposphere analyzed from the PEM-Tropics-A data is compared with data from the tropical regions of the northern Pacific (PEM-West-A) and southern Atlantic (TRACE-A) during the same Sept/Oct time period. Sizable perturbations in the abundance of ozone and its key precursors, resulting from the transport of pollution originating from biomass burning sources, are observed in much of the Southern Hemispheric troposphere.

Singh, H. B.↗
NASA NTRS2000

The Next Generation MOD: A Microchip Amino Acid Analyzer for Detecting Extraterrestrial Life

The MOD (Mars Organic Detector) instrument which has selected for the definition phase of the BEDS package on the 2005 Mars Explorer Program spacecraft is designed to simply detect the presence of amino acids in Martian surface samples at a sensitivity of a few parts per billion (ppb). An additional important aspect of amino acid analyses of Martian samples is identifying and quantifying which compounds are present, and also distinguishing those produced abiotically from those synthesized by either extinct or extant life. Amino acid homochirality provides an unambiguous way of distinguishing between abiotic vs. biotic origins. Proteins made up of mixed D- and L-amino acids would not likely have been efficient catalysts in early organisms because they could not fold into bioactive configurations such as the a-helix. However, enzymes made up of all D-amino acids function just as well as those made up of only L-amino acids, but the two enzymes use the opposite stereoisomeric substrates. There are no biochemical reasons why L-amino acids would be favored over Damino acids. On Earth, the use of only L-amino acids in proteins by life is probably simply a matter of chance. We assume that if proteins and enzymes were a component of extinct or extant life on Mars, then amino acid homochirality would have been a requirement. However, the possibility that Martian life was (or is) based on D-amino acids would be equal to that based on L-amino acids. The detection of a nonracemic mixture of amino acids in a Martian sample would be strong evidence for the presence of an extinct or extant biota on Mars. The finding of an excess of D-amino acids would provide irrefutable evidence of unique Martian life that could not have been derived from seeding the planet with terrestrial life (or the seeding of the Earth with Martian life). In contrast, the presence of racemic amino acids, along with non-protein amino acids such as alpha-aminoisobutyric acid and isovaline, would be indicative of an abiotic origin, although we have to consider the possibility that the racemic amino acids were generated from the racemization of biotically produced amino acids.

Mathies, R. A.↗
NASA NTRS2001

Analysis of Volatile Organic Compounds in a Controlled Environment: Ethylene Gas Measurement Studies on Radish

Volatile organic compound(VOC), ethylene gas, was characterized and quantified by GC/FID. 20-50 ppb levels were detected during the growth stages of radish. SPME could be a good analytical tool for the purpose. Low temperature trapping method using dry ice/diethyl ether and liquid nitrogen bath was recommended for the sampling process for GC/PID and GC/MS analysis.

Kong, Suk Bin↗
NASA NTRS1998

Making Intercontinental Burning Influences Quantitative: Lessons on Transport and Geochemistry From the 3-D Simulation of CO in PEM-T A and TRACE-A

We report on two aspects of the simulation of global transport of plumes originating from subtropical biomass fires. We use of meteorological assimilation (MM5) at 2-degree resolution with a Grail cloud parameterization and a Blackadar-based planetary boundary layer parameterization. Ames's GRACES model provides emissions, transport, and an appropriate level of simulated chemical transformation. We have worked with passive-tracer CO or linear chemistry. This is appropriate since we find major work to be done in evaluating CO source strengths and transport mechanisms before chemical integrations could be meaningful. First, we present mechanisms by which CO and other pollutants are introduced into the free troposphere, and are then transported with hate dilution from approx. 0 to approx. 180 degrees longitude. One principal conduit for these plumes is the vernal subtropical jet; however the plumes appear at various altitudes and latitudes as they influenced by frontal motions and (most likely) radiative processes. A common, repeated pattern of transport has pollutant plumes arriving in the distant Pacific Ocean from Africa and South America at 25 degrees south and 14 km altitude. Following this, there is then a general appearance of pollution at extending down to 5 kin at more equatorial (10 S) and polar latitudes (to 45 S). Second, we evaluate the quantitative success of our simulation. (Such success requires efforts considerably beyond trajectory analyses, and is necessary for our community to claim an understanding of the effects of biomass burning on global atmospheric chemistry and the planet's trend in oxidizing capacity.) We find that we simulate most pollution episodes sampled by Glenn Sachse's CO instrument and the Blake hydrocarbon analyses during PENT A. We will present our current ideas on why our general levels appear satisfactory when the observations are within 20 ppb of background levels, but substantially miss the variability associated with the most intense biomass burning plumes. As time allows, we will speculate on the origins of a class of plumes that appear in the mid-troposphere, but are missing from our simulations.

Chatfield, Robert↗