tailieunhanh - Organic compound alteration during hypervelocity collection of carbonaceous materials in aerogel

The coexisting systemof VOCs is complex. A small change in environmental conditions (., temperature) may result in changes on VOC concentrations, and also some VOCs may be involved in chemical reactions during the trans- portation. Meanwhile, as a consequence of high density of petroleumrefineries, synthetic organic chemical plants, and variousmobile sources, the formation rate and concentration of ozone in theHouston area are extremely high, and propene becomes a dominant reactive hydrocarbon (20). The specific VOC mixture in the Houston area represents a specific air quality problem compared with other metropolitans (21), which makes studies of the air quality in Houston very et al. (22, 23)made some studies on VOC source identification, one. | Meteoritics Planetary Science 44 Nr 1 15-24 2009 Abstract available online at http Organic compound alteration during hypervelocity collection of carbonaceous materials in aerogel M. K. SPENCER1 S. J. CLEMETT2 S. A. SANDFORD3 D. S. McKAY2 and R. N. ZARE1 1 Department of Chemistry Stanford University Stanford California 94305 USA 2NASA Johnson Space Center Houston Texas 77058 USA 3Astrophysics Branch NASA Ames Research Center Moffett Field California 94035 USA Corresponding author. E-mail zare@ Received 29 October 2007 revision accepted 17 July 2008 Abstract-The NASA Stardust mission brought to Earth micron-size particles from the coma of comet 81P Wild 2 using aerogel a porous silica material as the capture medium. A major challenge in understanding the organic inventory of the returned comet dust is identifying unambiguously which organic molecules are indigenous to the cometary particles which are produced from carbon contamination in the Stardust aerogel and which are cometary organics that have been modified by heating during the particle capture process. Here it is shown that 1 alteration of cometary organic molecules along impact tracks in aerogel is highly dependent on the original particle morphology and 2 organic molecules on test-shot terminal particles are mostly preserved. These conclusions are based on two-step laser mass spectrometry L2MS examinations of test shots with organic-laden particles both tracks in aerogel and the terminal particles themselves . INTRODUCTION Low-density aerogel a transparent porous silica material is uniquely suited for the capture of micron-size particles traveling at high velocities Tsou et al. 1990 Barrett et al. 1992 . Recent success of the NASA Stardust mission emphasizes the appeal of aerogel as a capture medium as well as the need for a more thorough understanding of the physical and chemical processes that occur during capture Brownlee et al. 2006 . Specifically inherent residual organic .