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Micro-AirCore: Spatial Mapping of Atmospheric Species
Oral Presentation
Prepared by K. Favela1, P. Tans2, T. Jaeckle3, W. Williamson4
1 - Southwest Research Institute, 6220 Culebra Road, San Antonio, TX, 78238
2 - National Oceanic and Atmospheric Administration, 325 Broadway, Boulder, CO, 80305
3 - Southwest Research Institute, 6220 Culebra Road, San Antonio, TX, 78238
4 - Southwest Research Institute, 6220 Culebra Road, San Antonio, TX, 78238
Contact Information: kristin.favela@swri.org; 210-522-4209
ABSTRACT
Micro-AirCore is a simple, effective, reusable, innovative, and low cost sampler with the ability to provide temporal and spatial resolution of a continuous air sample. When coupled with MS, the resulting time-resolved 3-D profiling can be used to rapidly create chemical maps with a limited number of samples, greatly reducing time, effort and cost. The original NOAA-developed device consists of a long stainless steel tube pre-filled with calibrated gas and allowed to ascend on a weather balloon. During ascent, the device is evacuated as it equilibrates with the decreasing atmospheric pressure. During descent, the tube is filled with atmospheric gas in an ordered manner. Diffusion inside the tube is slow enough that the collected gas remains ordered. Here is described a miniaturization of the NOAA-developed device; the large, stainless steel tube was replaced with Hydroguard fused silica tubing (0.53 mm x 30 m) and two lightweight valves having a total mass of less than 28 grams. Given the minute volumes, cavity-ring down spectroscopy was no longer feasible and a benchtop GC/MS was modified for accurate profiling. This micro-AirCore device was deployed on the SwRI-developed unmanned SkyWisp glider. As a proof-of-concept, carbon dioxide was profiled in the atmosphere up to approximately 20,000 m. A laboratory-based validation system was used for evaluating the micro-AirCore function, including accuracy and precision, for carbon dioxide. The diffusion profiles of carbon dioxide, argon, oxygen and methane were also investigated. Overall, the micro-AirCore device demonstrated an accuracy error of 2% (12CO2) and minimal diffusion over a period of 16 hours (peak width increased by a factor of 1.6). Hold-time tests were performed with lightweight gases (oxygen, carbon dioxide, methane and argon) representing the worst-case scenario for diffusion. However, even after 63 hours, mixing of the gases inside the tube was not complete. A triplet of micro-AirCore devices were deployed on the SkyWisp glider yielding a relative standard deviation of 0.08%, or 0.3 ppm, for CO2. The profile collected resulted in observation of the boundary layer with elevated CO2 levels, a region in the free troposphere with relatively constant CO2 mole fraction, and a gradual decrease in CO2 above 10,000 m. This micro-device has broad applications extending beyond vertical profiling, as fitting the device with a metering device enables horizontal collection of gases. As a proof-of-concept, the micro-AirCore was demonstrated for select EPA TO-15 compounds (1 ppm each of chloroform, benzene, hexane, and toluene). Using the laboratory-based validation system, 2 minute intervals of test gas separated by 10 minutes of nitrogen were delivered to the micro-AirCore device. After holding the gas in the tube, the contents were analyzed and the pattern of gases retained. In summary, the micro-AirCore system has enormous potential for both vertical and horizontal profiling of trace volatile chemicals, enabled by the ability of the mass spectrometer to sample minute quantities of gas in a continuous manner. This technique is applicable to many functions including chemical plume profiling for model verification and the identification of toxic chemical sources; since the system is extremely lightweight it is easily incorporated into unmanned vehicles.
Oral Presentation
Prepared by K. Favela1, P. Tans2, T. Jaeckle3, W. Williamson4
1 - Southwest Research Institute, 6220 Culebra Road, San Antonio, TX, 78238
2 - National Oceanic and Atmospheric Administration, 325 Broadway, Boulder, CO, 80305
3 - Southwest Research Institute, 6220 Culebra Road, San Antonio, TX, 78238
4 - Southwest Research Institute, 6220 Culebra Road, San Antonio, TX, 78238
Contact Information: kristin.favela@swri.org; 210-522-4209
ABSTRACT
Micro-AirCore is a simple, effective, reusable, innovative, and low cost sampler with the ability to provide temporal and spatial resolution of a continuous air sample. When coupled with MS, the resulting time-resolved 3-D profiling can be used to rapidly create chemical maps with a limited number of samples, greatly reducing time, effort and cost. The original NOAA-developed device consists of a long stainless steel tube pre-filled with calibrated gas and allowed to ascend on a weather balloon. During ascent, the device is evacuated as it equilibrates with the decreasing atmospheric pressure. During descent, the tube is filled with atmospheric gas in an ordered manner. Diffusion inside the tube is slow enough that the collected gas remains ordered. Here is described a miniaturization of the NOAA-developed device; the large, stainless steel tube was replaced with Hydroguard fused silica tubing (0.53 mm x 30 m) and two lightweight valves having a total mass of less than 28 grams. Given the minute volumes, cavity-ring down spectroscopy was no longer feasible and a benchtop GC/MS was modified for accurate profiling. This micro-AirCore device was deployed on the SwRI-developed unmanned SkyWisp glider. As a proof-of-concept, carbon dioxide was profiled in the atmosphere up to approximately 20,000 m. A laboratory-based validation system was used for evaluating the micro-AirCore function, including accuracy and precision, for carbon dioxide. The diffusion profiles of carbon dioxide, argon, oxygen and methane were also investigated. Overall, the micro-AirCore device demonstrated an accuracy error of 2% (12CO2) and minimal diffusion over a period of 16 hours (peak width increased by a factor of 1.6). Hold-time tests were performed with lightweight gases (oxygen, carbon dioxide, methane and argon) representing the worst-case scenario for diffusion. However, even after 63 hours, mixing of the gases inside the tube was not complete. A triplet of micro-AirCore devices were deployed on the SkyWisp glider yielding a relative standard deviation of 0.08%, or 0.3 ppm, for CO2. The profile collected resulted in observation of the boundary layer with elevated CO2 levels, a region in the free troposphere with relatively constant CO2 mole fraction, and a gradual decrease in CO2 above 10,000 m. This micro-device has broad applications extending beyond vertical profiling, as fitting the device with a metering device enables horizontal collection of gases. As a proof-of-concept, the micro-AirCore was demonstrated for select EPA TO-15 compounds (1 ppm each of chloroform, benzene, hexane, and toluene). Using the laboratory-based validation system, 2 minute intervals of test gas separated by 10 minutes of nitrogen were delivered to the micro-AirCore device. After holding the gas in the tube, the contents were analyzed and the pattern of gases retained. In summary, the micro-AirCore system has enormous potential for both vertical and horizontal profiling of trace volatile chemicals, enabled by the ability of the mass spectrometer to sample minute quantities of gas in a continuous manner. This technique is applicable to many functions including chemical plume profiling for model verification and the identification of toxic chemical sources; since the system is extremely lightweight it is easily incorporated into unmanned vehicles.