Houston urban air composition characterization using a mobile laboratory and measurements of HONO at Moody Tower
| Project Period: | 05/01/2008 - 08/31/2009 |
| Total Budget: | $364,696 |
| Sub-Contractors: | Aerodyne
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Aerodyne will deploy the Aerodyne mobile laboratory for six weeks to several locations in Houston. The mobile laboratory has the essential instrumentation to characterize the composition of continuously sampled air. It was designed to be sufficiently nimble that it can be driven on narrow or congested streets. The strength of having a comprehensive array of analytically defensible measurements makes it an ideal platform for characterizing emission sources. It can only sample, however, where it can drive. Typically, we maneuver downwind from a target source and let the wind advect diluted plumes to our measurement location. The high time response instrumentation yields emission ratios, which for combustion sources can be converted to fuel-based emission indices. In previous campaigns, we have detected and located non-combustion point sources by driving and targeting the location of maximum concentration of the pollutant species in question. For SHARP and FLAIR, the mobile lab will be deployed in support of numerous research groups’ measurements. The array of real-time 1s measurements make it an ideal platform from which to collect whole air samples for later analysis. Collaborators’ instruments can be integrated into the mobile laboratory – an activity we have successfully done in the past with researchers from MIT, Montana State University, Virginia Tech University, Los Alamos national laboratory, and Tufts University.
The mobile laboratory will also transport a HONO spectrometer and at the outset of the campaign that will be deployed at the Moody Tower. The HONO instrument we plan to deploy is part of a collaboration between Aerodyne and Steve Wofsy’s research group at Harvard. This instrument will use a continuous wave QCL device and we anticipate that it will be be ready in time for the SHARP deployment in April 2009. The goals are for this instrument to be capable of HONO measurements with sufficient speed and sensitivity to do flux measurements. We have a commitment from the ARI/Harvard development team that the instrument can be used for these measurements provided it is ready. Any SHARP/HARC funding for the deployment will not be used for development purposes, only for shipping and travel costs. We anticipate that the graduate student (Ben Lee) shepherding this instrument will join Scott Herndon and Ezra Wood for the in-field staffing and post campaign analysis.
A detailed simulation of the transmission spectrum at 1 ppbv of HONO and 0.13% water vapor in the region 1659 cm-1 is shown in the figure to the left. The top half of the figure is the simulated transmission spectrum due to absorption by HONO alone, while the bottom half shows the total transmission for HONO in the presence of ambient H2O. We will use the unique spectral fingerprints for HONO and H2O across the tuning region to ensure separation by simultaneously fitting all the absorption lines across the region. One second spectroscopic data for HONO will be collected, analyzed in real time to compute mixing ratios, and archived. Mixing ratios over suitable intervals to merge with other data streams. Routine post-processing of the data will validate spectroscopic purity, verify the absence of unknown absorbers in the ambient matrix, and quantify fitting statistics. The anticipated 1-minute detection limit (S/N = 2) of this spectrometer is less than 20 pptv.
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