Browsing by Author "Liang, Mao-Chang"

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Absorption cross sections of NH3, NH2D, NHD2, and ND3 in the spectral range 140-220 nm and implications for planetary isotopic fractionation
(2006-08-20)
Cheng, Bing-Ming
;
Lu, Hsiao-Chi
;
Chen, Hong-Kai
;
Bahou, Mohammed
;
Lee, Yuan-Pern
Cross sections for photoabsorption of NH3, NH2D, NHD2, and ND3 in the spectral region 140-220 nm were determined at similar to 298 K using synchrotron radiation. Absorption spectra of NH2D and NHD2 were deduced from spectra of mixtures of NH3 and ND3, of which the equilibrium concentrations for all four isotopologues obey statistical distributions. Cross sections of NH2D, NHD2, and ND3 are new. Oscillator strengths, an integration of absorption cross sections over the spectral lines, for both A X and B X systems of NH3 agree satisfactorily with previous reports; values for NH2D, NHD2, and ND3 agree with quantum chemical predictions. The photolysis of NH3 provides a major source of reactive hydrogen in the lower stratosphere and upper troposphere of giant planets such as Jupiter. Incorporating the measured photoabsorption cross sections of NH3 and NH2D into the Caltech/JPL photochemical diffusive model for the atmosphere of Jupiter, we find that the photolysis efficiency of NH2D is lower than that of NH3 by as much as 30%. The D/H ratio in NH2D/NH3 for tracing the microphysics in the troposphere of Jupiter is also discussed.
Dust transport from non-East Asian sources to the North Pacific
(2012-06-26)
Hsu, Shih-Chieh
;
Huh, Chih-An
;
Lin, Chuan-Yao
;
Chen, Wei-Nai
;
Mahowald, Natalie M.
It is generally thought that East Asia dominates the supply of eolian dust to the North Pacific. Here we show the first data-based evidence of dust primarily from non-East Asian sources even during March 2010 when a super dust storm from East Asia struck the western Pacific. Chemical characteristics of aerosol samples collected at a high-mountain site in Taiwan show variable inputs from eolian dust and biomass burning. From backward trajectory analyses, satellite observation and model simulation, dust origins can be traced to the Middle East and North Africa, suggesting an integrated source from the global dust belt. Our global model results demonstrate that dust deposition in the North Pacific is primarily contributed by non-East Asian sources with an eastward decrease along the Westerlies. Citation: Hsu, S.-C., et al. (2012), Dust transport from non-East Asian sources to the North Pacific, Geophys. Res. Lett., 39, L12804, doi:10.1029/2012GL051962.
Isotopic fractionation of nitrogen in ammonia in the troposphere of Jupiter
(2007-03-10)
Liang, Mao-Chang
;
Cheng, Bing-Ming
;
Lu, Hsiao-Chi
;
Chen, Hong-Kai
;
Alam, M. S.
Laboratory measurements of the photoabsorption cross section of (NH3)-N-15 at wavelengths between 140 and 220 nm are presented for the first time. Incorporating the measured photoabsorption cross sections of (NH3)-N-15 and (NH3)-N-14 into a one-dimensional photochemical diffusive model, we find that at 400 mbar, the photolytic efficiency of (NH3)-N-15 is about 38% greater than that of (NH3)-N-14. In addition, it is known that ammonia can condense in the region between 200 and 700 mbar, and the condensation tends to deplete the abundance ratio of (NH3)-N-15 and (NH3)-N-14. By matching the observed ratio of (NH3)-N-15 and (NH3)-N-14 at 400 mbar, the combined effect of photolysis and microphysics produces the ratio of (2.42 +/- 0.34) x 10(-3) in the deep atmosphere, in excellent agreement with the Galileo spacecraft measurements. The usefulness of the isotopic composition of ammonia as a tracer of chemical and dynamical processes in the troposphere of Jupiter is discussed.