Microcollection of gases in a capillary tube: preservation of spatial and temporal resolution.

Researchers at the National Oceanic and Atmospheric Administration (NOAA) have recently developed and reported a novel air collection device for measuring vertical profiles of trace gases in the atmosphere, which has been applied to carbon dioxide and methane so far. The device consists of a long stainless steel tube that is prefilled 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. The diffusion rate inside the tube is slow enough that the collected gas remains ordered. Here is reported a miniaturization of the device described above, in which the stainless steel tube is replaced with Hydroguard fused silica tubing (0.53 mm × 30 m) and two lightweight valves having a total mass of less than 28 g. This micro-AirCore device was deployed on the SwRI-developed unmanned SkyWisp glider. Profiling of carbon dioxide in the atmosphere proceeded via mass spectrometric detection. 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 demonstrated an accuracy error of 2% ((12)CO(2)) and minimal diffusion over a period of 16 h (peak width increased by a factor of 1.6). Even after 63 h, mixing of the gases inside the tube was not complete. A triplet of micro-AirCores was deployed on the SkyWisp glider yielding a relative standard deviation of 0.08%, or 0.3 ppm, for CO(2). The profile collected resulted in observation of the boundary layer with elevated CO(2) levels, a region in the free troposphere with relatively constant CO(2) mole fraction, and a gradual decrease in CO(2) above 10,000 m. This microdevice has broad applications extending beyond vertical profiling. Fitting the device with a metering device could enable horizontal collection of gases.

Dust as a collection media for contaminant source attribution.

Dust was investigated for its ability to retain source attribution profiles (SAPs) after chemical exposure. Three distinct sources of the organophosphate pesticide acephate were investigated as a proof-of-concept model. In addition, attribution profiles were created and tested using compounds related to chemical warfare agents (CWAs), specifically VX and G-series agents: O-ethyl methylphosphonothioate (EMPTA), N,N-diisopropylmethylamine (DIPMA), N,N-diisopropylethylamine (DIEA), diisopropylamine (DIPA), diethyl aniline (DEA), diethyl ethyl phosphonate (DEEP), trimethyl phosphite (TMP), dimethyl hydrogen phosphite (DMHP), diethyl hydrogen phosphite (DEHP), triethyl phosphate (TEP), ethyl methylphosphonate (EMPA), and diisopropyl methylphosphonate (DIMP). Dust was collected from a storage shed, aliquots deposited on carpet and loaded with distinct chemical profiles using an exposure chamber and aerosolizer. After a given period of time (1h, 24h, or 72 h), the dust was extracted and its SAP analyzed by gas chromatography-mass spectrometry (GC-MS) and/or liquid chromatography-tandem mass spectrometry (LC-MS/MS). Principal components analysis (PCA) was used to determine the association of dust exposed to the same and different chemical sources. PCA results demonstrate that dust samples exposed to distinct chemical sources are clearly differentiated from one another across all collection times. Furthermore, dust aliquots exposed to the same source can be clearly associated with one another across all collection times. When the CWA-related compounds were subjected to elevated temperature (90°C) conditions, it was found that the signature was stable at the 1h and 24h collections. At 72 h and elevated temperature, larger deviations from the control were observed for some compounds. Elevated pH (10) affected the profile to a lesser degree than elevated temperature. Overall, dust is found to be an effective media for the in situ collection of source attribution profiles.