A Surface Acoustic Wave Thermometer

Bulk and surface acoustic wave devices have been studied as temperature sensors since the early 1960s. Advantages of acoustic temperature sensors are a high resolution, frequency output, and ease of integration with other acoustic sensors. A disadvantage is the need for hermetic packaging which slows sensor response time and increases cost, but is necessary to prevent sensor contamination. Surface skimming bulk wave (SSBW) devices have more recently been studied for signal processing applications and have been found to be less sensitive to aging and much less sensitive to surface contamination than other acoustic devices. Although they have temperature coefficients of up to 40 PPM/°C, there have been no studies of SSBW devices as temperature sensors. The objectives of this work were to study the temperature characteristics and contamination sensitivity of a 150 MHz quartz SSBW device as a temperature sensor, as well as calibration methods. Calibration procedures are an important concern in applications where the temperature sensor must be located close to its electronics and where the electronics are not subject to the temperature being measured. The SSBW ATS was found to have very low sensitivity to contamination as compared to SAW or APM devices. Microscopic levels of contamination should produce temperature deviations of less than 0.01 °C. The temperature coefficient of frequency was found to be 32 PPM/°C with a deviation from a second order curve fit of about 0.2 °C while the 3 Hz short term stability of the SSBW oscillator could provide a temperature resolution of about 0.001 °C. Although the ATS was successfully calibrated with two of the techniques where the ATS was remotely located with extension cables, removing the cables required single point re-calibration. When the cables were coiled up with the sensor electronics, errors of about 1 °C resulted due to the movement of the cables. These results suggest that \u27non-hermetically sealed SSBW devices could be used as temperature sensors where integration with another sensor or a digital output is desired. An in-situ calibration procedure is needed to eliminate the need for single point re-calibration after the ATS is placed in its application

Light absorption by biomass burning source emissions

h i g h l i g h t s Two distinct types of biomass smoke were identified by the MAE vs. OC/EC dependence. They also differed with respect to artifacts in the filter-based b abs measurement. Present assessments of biomass burning BC emissions might be largely overestimated. Biomass burning emissions with high OC/EC ratios may include some liquid-like OM. These liquid-like organic components can complicate filter-based b abs measurements. Black carbon (BC) aerosol has relatively short atmospheric lifetimes yet plays a unique and important role in the Earth's climate system, making it an important short-term climate mitigation target. Globally, biomass burning is the largest source of BC emissions into the atmosphere. This study investigated the mass absorption efficiency (MAE) of biomass burning BC generated by controlled combustion of various wildland fuels during the Fire Laboratory at Missoula Experiments (FLAME). MAE values derived from a photoacoustic spectrometer (~7.8 m 2 /g at a wavelength of 532 nm) were in good agreement with those suggested for uncoated BC when the emission ratios of organic carbon (OC) to elemental carbon (EC) were extremely low (i.e., below 0.3). With the increase of OC/EC, two distinct types of biomass smoke were identified. For the first type, MAE exhibited a positive dependence on OC/EC, while the overestimation of the light absorption coefficient (b abs ) by a filter-based method was less significant and could be estimated by a nearly constant correction factor. For the second type, MAE was biased low and correlated negatively with OC/EC, while the overestimation of b abs by the filter-based method was much more significant and showed an apparent OC/EC dependence. This study suggests that BC emission factors determined by the commonly used thermal-optical methods might be sustantially overestimated for some types of biomass burning emissions. Our results also indicate that biomass burning emissions may include some liquid-like organics that can significantly bias filter-based b abs measurements

Emissions from the laboratory combustion of wildland fuels: Particle morphology and size

[1] Time-resolved optical properties of smoke particles from the controlled laboratory combustion of mid-latitude wildland fuels were determined for the first time using advanced techniques, including cavity ring-down/cavity enhanced detection (CRD/CED) for light extinction and two-wavelength photoacoustic detection for light absorption. This experiment clearly resolves the dependence of smoke properties on fuel and combustion phase. Intensive flaming combustion during ponderosa pine wood (PPW) burning produces particles with a low single scattering albedo of 0.32 and a specific mass extinction efficiency of 8.9 m 2 g À1 . Burning white pine needles (WPN) features a prolonged smoldering phase emitting particles that are not light-absorbing and appear much larger in size with an extinction efficiency %5 m 2 g À1 . A Mie scattering model was formulated, which estimates the black carbon fraction in the PPW and WPN smoke particles at 66% and 12%, respectively. These observations may refine the current radiative forcing estimates for biomass burning emissions. Citation

Final Report for SERDP Project RC-1649: Advanced Chemical Measurements of Smoke from DoD-prescribed Burns

Objectives: Project RC-1649, “Advanced Chemical Measurement of Smoke from DoD-prescribed Burns” was undertaken to use advanced instrumental techniques to study in detail the particulate and vapor-phase chemical composition of the smoke that results from prescribed fires used as a land management tool on DoD bases, particularly bases in the southeastern U.S. The statement of need (SON) called for “(1) improving characterization of fuel consumption” and “(2) improving characterization of air emissions under both flaming and smoldering conditions with respect to volatile organic compounds, heavy metals, and reactive gases.” The measurements and fuels were from several bases throughout the southeast (Camp Lejeune, Ft. Benning, and Ft. Jackson) and were carried out in collaboration and conjunction with projects 1647 (models) and 1648 (particulates, SW bases). Technical Approach: We used an approach that featured developing techniques for measuring biomass burning emission species in both the laboratory and field and developing infrared (IR) spectroscopy in particular. Using IR spectroscopy and other methods, we developed emission factors (EF, g of effluent per kg of fuel burned) for dozens of chemical species for several common southeastern fuel types. The major measurement campaigns were laboratory studies at the Missoula Fire Sciences Laboratory (FSL) as well as field campaigns at Camp Lejeune, NC, Ft. Jackson, SC, and in conjunction with 1648 at Vandenberg AFB, and Ft. Huachuca. Comparisons and fusions of laboratory and field data were also carried out, using laboratory fuels from the same bases. Results: The project enabled new technologies and furthered basic science, mostly in the area of infrared spectroscopy, a broadband method well suited to biomass burn studies. Advances in hardware, software and supporting reference data realized a nearly 20x improvement in sensitivity and now provide quantitative IR spectra for potential detection of ~60 new species and actual field quantification of several new species such as nitrous acid, glycolaldehyde, α-/β-pinene and D-limonene. The new reference data also permit calculation of the global warming potential (GWP) of the greenhouse gases by enabling 1) detection of their ambient concentrations, and 2) quantifying their ability to absorb IR radiation

Emissions of trace gases and aerosols during the open combustion of biomass in the laboratory

We characterized the gas- and speciated aerosol-phase emissions from the open combustion of 33 different plant species during a series of 255 controlled laboratory burns during the Fire Laboratory at Missoula Experiments (FLAME). The plant species we tested were chosen to improve the existing database for U.S. domestic fuels: laboratory-based emission factors have not previously been reported for many commonly-burned species that are frequently consumed by fires near populated regions and protected scenic areas. The plants we tested included the chaparral species chamise, manzanita, and ceanothus, and species common to the southeastern US (common reed, hickory, kudzu, needlegrass rush, rhododendron, cord grass, sawgrass, titi, and wax myrtle). Fire-integrated emission factors for gas-phase CO{sub 2}, CO, CH{sub 4}, C{sub 2-4} hydrocarbons, NH{sub 3}, SO{sub 2}, NO, NO{sub 2}, HNO{sub 3} and particle-phase organic carbon (OC), elemental carbon (EC), SO{sub 4}{sup 2-}, NO{sub 3}{sup -}, Cl{sup -}, Na{sup +}, K{sup +}, and NH{sub 4}{sup +} generally varied with both fuel type and with the fire-integrated modified combustion efficiency (MCE), a measure of the relative importance of flaming- and smoldering-phase combustion to the total emissions during the burn. Chaparral fuels tended to emit less particulate OC per unit mass of dry fuel than did other fuel types, whereas southeastern species had some of the largest observed EF for total fine particulate matter. Our measurements often spanned a larger range of MCE than prior studies, and thus help to improve estimates for individual fuels of the variation of emissions with combustion conditions