Economic and social projections indicate that during next several decades there will be major geographical redistribution of surface emissions of O3 precursors, such as NO(x), CH4 and CO. A net decrease in their emissions from northern hemispheric mid-latitudes will be accompanied by substantial increases from the tropics. We have investigated a hypothetical scenario of currently underway transition of such emission patterns using a global two-dimensional photochemical model. With overall O3 precursor releases held constant, a simultaneous transfer of their emissions by 25% from the latitude belt 75°N-35°N to 5°S-35°N increases tropospheric oxidizing capacity such that the methane global lifetime and concentrations fall by more than 3%. Seasonally dependent changes in surface O3 concentrations are also calculated. In influencing OH concentration, redistribution of surface NO(x) emissions is 2-3 orders of magnitude more efficient per unit mass than CO emissions. Shifts in methane sources have insignificant effects on global photochemistry, but lead to a decrease in its interhemispheric gradient.

The atmospheric distributions of CH4, C2H6, C3H8, C2H2, and C2Cl4 and their annual chemical removal rates in steady state are determined versus latitude using a modified version of the Oslo two-dimensional global tropospheric photochemical model. A photochemically calculated hydroxyl radical distribution, which has been validated with methylchloroform data, and seasonally varying surface measurements of the title species are used to compute their respective global annual surface source strengths and steady state lifetimes. Computed annual surface source strengths of CH4, C2H6, C3H8, C2H2, and C2Cl4 are 490, 10.4, 8.4, 3.1 Tg (1 Tg = 1012 g), and 432 kT (1 kT = 109 g), respectively. The calculated annual chemical removal rates of these compounds show distinct latitudinal distributions. Because their steady state global lifetimes are less than the model interhemispheric exchange time (about 1 year), the calculated north to south ratios of the deduced surface emission strengths of C2H6, C3H8, C2H2, and C2Cl4 probably reflect the locations of their sources. Within the limits of previously estimated industrial emissions of C2Cl4 (3-4 kT) for the southern hemisphere, our calculations indicate that about 47 kT of additional southern hemispheric source of C2Cl4 is required for 1989-1990 to attain steady state mass balance in this region. There are two possibilities for this needed source: either other industrial sources are missing, or there are unidentified natural sources of C2Cl4. So far, oceans have been suggested as a natural source. Normalization of monthly varying ratios of hemispherically averaged calculated surface mixing ratios of C2H6, C3H8, and C2H2 and their respective observed mixing ratios with respect to those for C2Cl4 indicates that the sources of these hydrocarbons are seasonal in nature. It is also shown that convective transport effectively redistributes these short-lived species but their calculated surface source strengths are relatively independent of this transport process. Copyright 1998 by the American Geophysical Union.

We report CH4 mixing ratios and δ13C of CH4 values for remote air at two ground-based atmospheric sampling sites for the period December 1994 to August 1998 and similar data from aircraft sampling of air masses from near sea level to near tropopause in September and October of 1996 during the Global Tropospheric Experiment Pacific Exploratory Mission (PEM)-Tropics A. Surface values of δ13C-CH4 ranged from -47.02 to -47.52‰ at Niwot Ridge, Colorado (40° N, 105° W), and from -46.81 to -47.64‰ at Montaña de Oro, California (35° N, 121° W). Samples for isotopic analysis were taken from 2° to 27° S latitude and 81° to 158° W longitude and from sea level to 11.3 km in altitude during the PEM-Tropics A mission. They represent the first study of 13CH4 in the tropical free troposphere. At ∼11 km, δ13C-CH4 was ∼1‰ greater than surface level values. Methane was generally enriched in 13C as altitude increased and as latitude increased (toward the South Pole). Using criteria to filter out stratospheric subsidence and convective events on the basis of other trace gases present in the samples, we find evidence of a vertical gradient in δ13C-CH4 in the tropical troposphere. The magnitude of the isotopic shifts in atmospheric CH4 with altitude are examined with a two-dimensional tropospheric photochemical model and experimentally determined values for carbon kinetic isotope effects in chemical loss processes of CH4 Model-calculated values for δ13C-CH4 in both the troposphere and lower stratosphere significantly underpredict the enrichment in 13CH4 with altitude observed in our measurement data and data of other research groups. Copyright 1999 by the American Geophysical Union.

Background Human reproduction depends on the fusion of a mature oocyte with a sperm cell to form a fertilized egg. The genetic events that lead to the arrest of human oocyte maturation are unknown. Methods We sequenced the exomes of five members of a four-generation family, three of whom had infertility due to oocyte meiosis I arrest. We performed Sanger sequencing of a candidate gene, TUBB8, in DNA samples from these members, additional family members, and members of 23 other affected families. The expression of TUBB8 and all other β-tubulin isotypes was assessed in human oocytes, early embryos, sperm cells, and several somatic tissues by means of a quantitative reverse-transcriptase-polymerase-chain-reaction assay. We evaluated the effect of the TUBB8 mutations on the assembly of the heterodimer consisting of one α-tubulin polypeptide and one β-tubulin polypeptide (α/β-tubulin heterodimer) in vitro, on microtubule architecture in HeLa cells, on microtubule dynamics in yeast cells, and on spindle assembly in mouse and human oocytes. Results We identified seven mutations in the primate-specific gene TUBB8 that were responsible for oocyte meiosis I arrest in 7 of the 24 families. TUBB8 expression is unique to oocytes and the early embryo, in which this gene accounts for almost all the expressed β-tubulin. The mutations affect chaperone-dependent folding and assembly of the α/β-tubulin heterodimer, disrupt microtubule behavior on expression in cultured cells, alter microtubule dynamics in vivo, and cause catastrophic spindle-assembly defects and maturation arrest on expression in mouse and human oocytes. Conclusions TUBB8 mutations have dominant-negative effects that disrupt microtubule behavior and oocyte meiotic spindle assembly and maturation, causing female infertility. (Funded by the National Basic Research Program of China and others.).