Engineering topics

Wennberg, Paul O.

Publications and source records attributed to Wennberg, Paul O..

23 records · Page 2

NASA NTRS2005

SCIAMACHY and FTS CO2 Retrievals Using the OCO Retrieval Algorithm

The Orbiting Carbon Observatory (OCO) mission will make the first global, space-based measurements of atmospheric C02 with the precision and coverage needed to characterize C02 sources and sinks on regional scales. OCO will make spectrally and spatially highly resolved measurements of reflected sunlight in the 02A -band and two near-infrared C02 bands. To test the OCO retrieval algorithm, SCIAMACHY and ground-based Fourier Transform Spectrometer (FTS) measurements at Park Falls, Wisconsin have been analyzed. Good agreement between SCIAMACHY and FTS C02 columns has been found with SCIAMACHY showing a much larger scatter than FTS measurements. Both SCIAMACHY and FTS overestimate the surface pressure by a few percent which significantly impacts retrieved C02 columns.

remote sensing↗

NASA NTRS2002

Laboratory Studies of the Photochemistry of Peroxynitric Acid

Observations of odd hydrogen radicals at high SZA in the lower stratosphere have demonstrated that our understanding of the HO(x) chemistry is incomplete [Wennberg et al., 1994a; Salawitch et al., 1994; Wennberg et al., 1999]. In particular, the concentrations of the HO(x) radicals are significantly larger than expected under weak photolytic conditions. Donaldson et al. [1997] have speculated that excitation of overtones of the OH stretching frequency in molecules such as HNO3 and HO2NO2 may be significant sources of HO(x) under these conditions. Although weak, vibrationally mediated photolysis may be important because it occurs in the near IR and visible and can provide energy in excess of the dissociation energy (D(o)): HONO2 + hv yields OH + NO (D(o) approx. 600 nm) and HOONO2 + hv yields OH + NO3 (D(o) approx. 735 nm) HOONO2 + hv yields HO2 + NO2 (D(o) approx. 1250 nm). In this project we developed instrumentation to characterize the photodissociation yields of hydroxyl containing compounds in the visible and near IR. This effort has involved coupling a tunable photolysis optical parametric oscillator (OPO) laser system with precise determination of the hydroxyl radical. The OPO system [Wu et al., 1997] was developed with support from the NSF Major Research Instrumentation Fund in a proposal entitled "Development of Novel, Compact Light Sources for Advanced Spectroscopy in Atmospheric Science and Materials Research" (Geoffrey A. Blake, P.I. California Institute of Technology).

Wennberg, Paul O.↗

NASA NTRS2002

Photodissociation of Peroxynitric Acid in the Near-IR

Temperature-dependent near-IR photodissociation spectra were obtained for several vibrational overtone transitions of peroxynitric acid (HNO4) with a tunable OPO photolysis/OH laser-induced-fluorescence system. Band-integrated photodissociation cross-sections (definity integral of sigma(sub diss)), determined relative to that for the 3nu(sub 1), OH stretching overtone, were measured for three dissociative bands. Assuming unit quantum efficiency for photodissociation of 3nu(sub 1), we find 2nu(sub 1) + nu(sub 3)(8242/cm) = (1.21 x 10(exp -20) (independent of temperature), 2nu(sub 1) (6900/cm) = 4.09 x 10(exp 18) * e(sup (-826,5/T)) (295 K greater than T greater than 224 K), and nu(sub 1) + 2nu(sub 3) (6252/cm) = 1.87 x 10(exp -19) * e(sup (- 1410.7/T)) (278 K greater than T greater than 240 K) sq cm/molecule cm. The photodissociation cross-sections are independent of pressure over the range 2 to 40 Torr. Temperature-dependent quantum yields (phi) for these transitions were obtained using integrated absorption cross-sections (definity integral of sigma(sub abs)) of HNO4 overtone vibrations measured with a FTIR spectrometer. In the atmosphere, photodissociation in the infrared is dominated by excitation of the first overtone of the OH stretching vibration (2nu((sub 1)). Inclusion of all dissociative HNO4 overtone and combination transitions yields a daytime IR photolysis rate of approximately 1 x 10(esp -1)/s. This process significantly shortens the estimated lifetime of HNO4 in the upper troposphere and lower stratosphere.

Roehl, Coleen M.↗

NASA NTRS2002

Atmospheric CO2 retrieved from ground-based near IR solar spectra

The column-averaged volume mixing ratio (VMR) of CO2 over Kitt Peak, Arizona, has been retrieved from high-resolution solar absorption spectra obtained with the Fourier transform spectrometer on the McMath telescope. Simultaneous column measurements of CO2 at approx.6300/cm and O2 at approx.7900/cm were ratioed to minimize systematic errors. These column ratios were then scaled by the mean O2 VMR (0.2095) to yield column- averaged vmrs of CO2. These display similar behavior to the Mauna Loa in situ surface measurements. During the period 1977- 1995, the column-averaged mixing ratio of CO2 increased at an avenge rate of 1.49 +/- 0.04 ppmv/yr with seasonal variations of approx.7 ppmv peak-to-peak. Our retrievals demonstrate that this remote technique is capable of precisions better than 0.5%.

Yang, Zhong-Hua↗

NASA NTRS1994

Harvard ER-2 OH laser-induced fluorescence instrument

The Harvard ER-2 OH instrument is scheduled to be integrated into the NASA ER-2 high altitude aircraft ozone payload in August 1992. Design and fabrication is presently underway. This experiment is a descendant of a balloon borne instrument designed and built in the mid-1980s. The ER-2 instrument is being designed to measure OH and HO2 as part of the NASA ozone payload for the investigation of processes controlling the concentration of stratospheric ozone. Although not specifically designed to do so, it is hoped that valid measurements of OH and HO2 can be made in the remote free troposphere with this instrument.

Wennberg, Paul O.↗