Showing papers by "James Walega published in 2008"
TL;DR: In this article, the authors present an overview of some recent studies and developments using this approach that were presented at the 2007 Field Laser Applications in Industry and Research (FLAIR) conference in Florence, Italy.
Abstract: Tunable infrared laser-based instruments on airborne platforms have provided invaluable contributions to atmospheric studies over the past several decades. This paper presents an overview of some recent studies and developments using this approach that were presented at the 2007 Field Laser Applications in Industry and Research (FLAIR, http://www.inoa.it/flair/) conference in Florence, Italy. The present overview only covers select in situ absorption-based instruments that were presented in the airborne session at this conference. In no case are comprehensive details presented. These details can be found in the numerous references given. Additional approaches based upon cavity-enhanced and photoacoustic measurements, which are also making invaluable contributions in airborne atmospheric studies, are not discussed in this brief overview.
48 citations
TL;DR: A tunable diode laser absorption spectrometer (TDLAS) was operated on the NASA DC-8 aircraft during the summer INTEX-NA study to acquire ambient formaldehyde (CH2O) measurements over North America and the North Atlantic Ocean from ∼0.2 km to ∼12.5 km altitude spanning 17 science flights as discussed by the authors.
Abstract: [1] A tunable diode laser absorption spectrometer (TDLAS) was operated on the NASA DC-8 aircraft during the summer INTEX-NA study to acquire ambient formaldehyde (CH2O) measurements over North America and the North Atlantic Ocean from ∼0.2 km to ∼12.5 km altitude spanning 17 science flights. Measurements of CH2O in the boundary layer and upper troposphere over the southeastern United States were anomalously low compared to studies in other years, and this was attributed to the record low temperatures over this region during the summer of 2004. Formaldehyde is primarily formed over the southeast from isoprene, and isoprene emissions are strongly temperature-dependent. Despite this effect, the median upper tropospheric (UT) CH2O mixing ratio of 159 pptv from the TDLAS over continental North America is about a factor of 4 times higher than the median UT value of 40 pptv observed over remote regions during TRACE-P. These observations together with the higher variability observed in this study all point to the fact that continental CH2O levels in the upper troposphere were significantly perturbed during the summer of 2004 relative to more typical background levels in the upper troposphere over more remote regions. The TDLAS measurements discussed in this paper are employed together with box model results in the companion paper by Fried et al. to further examine enhanced CH2O distributions in the upper troposphere due to convection. Measurements of CH2O on the DC-8 were also acquired by a coil enzyme fluorometric system and compared with measurements from the TDLAS system.
39 citations
National Center for Atmospheric Research1, Langley Research Center2, Rice University3, Florida State University4, University of California, Berkeley5, Goddard Space Flight Center6, University of Rhode Island7, Slippery Rock University of Pennsylvania8, United States Naval Academy9, Pennsylvania State University10, University of California, Irvine11, Ames Research Center12, University of Hawaii at Manoa13, Georgia Institute of Technology14, University of Minnesota15, Harvard University16
TL;DR: In this paper, measurements of CH2O from a tunable diode laser absorption spectrometer (TDLAS) were acquired onboard the NASA DC-8 during the summer 2004 INTEX-NA (Intercontinental Chemical Transport Experiment - North America) campaign to test our understanding of convection and production mechanisms in the upper troposphere (UT, 6-12km) over continental North America and the North Atlantic Ocean.
Abstract: Measurements of CH2O from a tunable diode laser absorption spectrometer (TDLAS) were acquired onboard the NASA DC-8 during the summer 2004 INTEX-NA (Intercontinental Chemical Transport Experiment - North America) campaign to test our understanding of convection and production mechanisms in the upper troposphere (UT, 6-12-km) over continental North America and the North Atlantic Ocean. Point-by-point comparisons with box model calculations, when MHP (CH3OOH) measurements were available for model constraint, resulted in a median CH2O measurement/model ratio of 0.91 in the UT. Multiple tracers were used to arrive at a set of UT CH2O background and perturbed air mass periods, and 46% of the TDLAS measurements fell within the latter category. At least 66% to 73% of these elevated UT observations were caused by enhanced production from CH2O precursors rather than direct transport of CH2O from the boundary layer. This distinction is important, since the effects from the former can last for over a week or more compared to one day or less in the case of convective transport of CH2O itself. In general, production of CH2O from CH4 was found to be the dominant source term, even in perturbed air masses. This was followed by production from MHP, methanol, PAN type compounds, and ketones, in descending order of their contribution. In the presence of elevated NO from lightning and potentially from the stratosphere, there was a definite trend in the CH2O discrepancy, which for the highest NO mixing ratios produced a median CH2O measurement/model ratio of 3.9 in the 10-12-km range. Discrepancies in CH2O and HO2 in the UT with NO were highly correlated and this provided further information as to the possible mechanism(s) responsible. These discrepancies with NO are consistent with additional production sources of both gases involving CH3O2 + NO reactions, most likely caused by unmeasured hydrocarbons.
32 citations
17 Mar 2008
TL;DR: In this article, the airborne application of a difference frequency laser-based absorption spectrometer is discussed. But the authors focus on the application of the spectrometers to the detection of pollution over Houston, Texas.
Abstract: We present the airborne application of a difference frequency laser based absorption spectrometer, discuss important instrument functions and requirements, present examples of airborne measurements and its preliminary interpretation toward understanding the pollution over Houston, Texas.
TL;DR: In this paper, mid-infrared lasers based on quasi-phase matched bulk PPLN crystals have been implemented on airborne atmospheric research platforms and enabling a detectable fractional absorbance of about 5E-7, which equates to single digit part-per-trillion detectable concentrations for many atmospherically important trace gases.
Abstract: Tunable, mid-infrared lasers based on quasi-phase matched bulk PPLN crystals have successfully been implemented on airborne atmospheric research platforms and enabling a detectable fractional absorbance of about 5E-7, which equates to single digit part-per-trillion detectable concentrations for many atmospherically important trace gases. Emerging development of ridge waveguide type PPLN crystals show promising performance characteristics, including 100 times better conversion efficiency and good beam quality, which enable more compact system designs. In addition, the flexibility afforded by QPM structured materials to generate coherent mid-infrared radiation, permit unique multi-wavelength operation and detection techniques.