Carboxylic monoacids in the air of mayombe forest (Congo): Role of the forest as a source or sink

In the tropical rain forests of the Congo during the dry season, from June to September 1987, carboxylic acid partial pressures (P _gas) in the air above the canopy, at ground level, and at the boundary layer, were estimated from water samples such as fog and rainwater. The concentrations of these acids were also measured in the sap of tree leaves. Tree leaves act as a sink or as a source if the acid P _gas is greater of lower than the acid concentrations in molecular form in sap. For each of these soluble gases, there is a value of P _gas where the exchange is nul. This is called the compensation point. Values of the compensation point for some tree leaves were evaluated according to Henry's law. Henry's law coefficients at ppm levels were redetermined for formic (HCOOH), acetic (CH₃COOH), propionic (CH₃CH₂COOH), and isobutyric (CH₃CH(CH₃)COOH) acids.By comparison of P _gas and compensation points, it is concluded that the forest was a potential source for these acids. The soil-or the litter-acts as a significant source of a carboxylic acid of C₃ or C₄ atoms in the aliphatic chain. This carboxylic acid, not yet fully characterized, could play an important role in the rain acidity in forested zones of the equatorial areas.The direct emission of these carboxylic acids by vegetation was the main source in the boundary layer above the forest. The average emissions were 3.1×10⁹, 7.8×10⁹, and 8.4×10⁹ molecules cm^-2 s^-1 for HCOOH, CH₃COOH, and CH₃CH₂COOH, respectively. The savanna is an exogenous source of HCOOH and CH₃CH₂COOH during moderately rainy days for 30% of the time. The ozonolysis of isoprene seems to be a small source of HCOOH.     

小试金光谱法同时测定地质样品中超痕量铂钯金

用小试金光谱法同时测定地质样品中低至0·x×10~(-9)级Pt、Pd和Au,包括先用小试金熔炼和灰吹预富集10g样品中的Pt、Pd和Au于1mg的银合粒中,然后把银合粒装入石墨电极同锇-锑合金(ω(Os)=0.06)一起激发,以发射光谱法同时测定它们的含量。小试金法类同经典火试金,但采用纯化过的2PbCO_3·Pb(OH)_2(Pt、Pd和Au的含量皆<0.05 ×10~(-9)代替商品PbO,并且用50ml高铝坩埚在950℃进行熔炼。方法的检出限是Pt0.2×10~(-9),Pd和Au均为0.1×10~(-9)。对于3×10~(-9)的含量,全过程的相对标准偏差(％)是Pt15,Pd11,Au9。此法快速、简便,适用于地质物料的分析。     

破裂岩石的电子发射与压缩原子模型

本文根据压缩原子模型提出岩石在高压及破裂过程中产生自由电子的一种可能机制。根据这种机制可在半定量水平上较为满意地解释岩石破裂中的电子发射、光辐射和岩石的爆炸式破裂。     

Anomalous hydrogen emissions from the San Andreas fault observed at the Cienega Winery,central California

We began continuous monitoring of H₂ concentration in soil along the San Andreas and Calaveras faults in central California in December 1980, using small H₂/O₂ fuel-cell sensors. Ten monitoring stations deployed to date have shown that anomalous H₂ emissions take place occasionally in addition to diurnal changes. Among the ten sites, the Cienega Winery site has produced data that are characterized by very small diurnal changes, a stable baseline, and remarkably distinct spike-like H₂ anomalies since its installation in July 1982. A major peak appeared on 1–10 November 1982, and another on 3 April 1983, and a medium peak on 1 November 1983. The occurrences of these peaks coincided with periods of very low seismicity within a radius of 50 km from the site. In order to methodically assess how these peaks are related to earthquakes, three H₂ degassing models were examined. A plausible correlational pattern was obtained by using a model that (1) adopts a hemicircular spreading pattern of H₂ along an incipient fracture plane from the hypocenter of an earthquake, (2) relies on the FeO–H₂O reaction for H₂ generation, and (3) relates the accumulated amount of H₂ to the mass of serpentinization of underlying ophiolitic rocks; the mass was tentatively assumed to be proportional to the seismic energy of the earthquake.     

Tropospheric methane in the mid-latitudes of the Southern Hemisphere

Results of more than 800 new measurements of methane (CH₄) concentrations in the Southern Hemisphere troposphere (34–41° S, 130–150° E) are reported. These were obtained between September 1980 and March 1983 from the surface at Cape Grim, Tasmania, through the middle (3.5–5.5 km) to the upper troposphere (7–10 km). The concentration of CH₄ increased throughout the entire troposphere over the measurement period, adding further support to the view that CH₄ concentrations are currently increasing on a global scale. For data averaged vertically through the troposphere the rate of increase found was 20 ppbv/yr or 1.3%/yr at December 1981. In the surface CH₄ data a seasonal cycle with a peak to peak amplitude of approximately 28 ppbv is seen, with the minimum concentration occurring in March and the maximum in September–October. A cycle with the same phase as that seen at the surface, but with a significantly decreased amplitude, is apparent in the mid troposphere but no cycle is detected in the upper tropospheric data. The phase and amplitude of the cycle are qualitatively in agreement with the concept that the major sink for methane is oxidation by hydroxyl radicals. Also presented is evidence of a positive vertical gradient in methane, with a suggestion that the magnitude of this gradient has changed over the period of measurements.     

The global distribution of methane in the troposphere

Methane has been measured in air samples collected at approximately weekly intervals at 23 globally distributed sites in the NOAA/GMCC cooperative flask sampling network. Sites range in latitude from 90° S to 76° N, and at most of these we report 2 years of data beginning in early 1983. All measurements have been made by gas chromatography with a flame ionization detector at the NOAA/GMCC laboratory in Boulder, Colorado. All air samples have been referenced to a single secondary standard of methane-in-air, ensuring a high degree of internal consistency in the data. The precision of measurements is estimated from replicate determinations on each sample as 0.2%. The latitudinal distribution of methane and the seasonal variation of this distribution in the marine boundary layer has been defined in great detail, including a remarkable uniformity in background levels of methane in the Southern Hemisphere. We report for the first time the observation of a complete seasonal cycle of methane at the South Pole. A significant vertical gradient is observed between a sea level and a high altitude site in Hawaii. Globally averaged background concentrations in the marine boundary layer have been calculated for the 2 year-period May 1983–April 1985 inclusive, from which we find an average increase of 12.8 ppb per year, or 0.78% per year when referenced to the globally averaged concentration (1625 ppb) at the mid-point of this period. We present evidence that there has been a slowing down in the methane growth rate.Presented at the Conference on the Scientific Application of Baseline Observations of Atmospheric Composition (SABOAC), Aspendale, Australia, 7–9 November 1984.     

Termites and global methane—another assessment

New CH₄ emission data from a number of Northern and Southern Hemispheric, tropical and temperate termites, are reported, which indicate that the annual global CH₄ source due to termites is probably less than 15 Tg. The major uncertainties in this estimate are identified and found to be substantial. Nevertheless, our results suggest that termites probably account for less than 5% of global CH₄ emissions.     

广州地区稻田甲烷排放及中国稻田甲烷排放的空间变化

１９９３年在广州地区采用中国科学院大气物理研究所研制的自动采集和分析系统测量了稻田甲烷的排放率，首次获得了占我国２０－２５％左右水稻收获面积的华南地区稻田甲烷排放特征值。从而宏观地使我国五个主要水稻生态区的甲烷排放率都有了实测资料。稻田甲烷排放率的季节变化主要与气温及灌溉水状态的变化的较大关系，日变化规律以下午出现极大为主。本实验田的甲烷排放率低。     

Automated in-situ monitoring of atmospheric non-methane hydrocarbon concentrations and gradients

A fully automated system measuring C2–C6 hydrocarbon concentrations and vertical gradients was installed at Harvard Forest in Petersham, Massachusetts, using a gas chromatograph with dual flame ionization detectors and cryogenic sample preconcentration. Measurements were made simultaneously at two heights above the forest canopy at forty five minute intervals, continuously from July 1992 to the present. Data for concentration gradients were combined with CO₂ flux measured by eddy correlation to determine the rates of production of biogenic hydrocarbons by the forest.     

Estimates of monoterpene and isoprene emissions from the forests in Switzerland

Emission rates of biogenic volatile organic compounds emitted by the forests were estimated for five geographical regions as well as for all Switzerland. Monoterpene and isoprene emissions rates were calculated for each main tree species separately using the relevant parameters such as temperature, light intensity and leaf biomass density. Biogenic emissions from the forests were found to be about 23% of the total annual VOC emissions (anthropogenic and biogenic) in Switzerland. The highest emissions are in July and lowest in January. Calculations showed that the coniferous trees are the main sources of the biogenic emissions. The major contribution comes from the Norway spruce (picea abies) forests due to their abundance and high leaf biomass density. Although broad-leaved forests cover 27% of all the forests in Switzerland, their contribution to the biogenic emissions is only 3%. Monoterpenes are the main species emitted, whereas only 3% is released as isoprene. The highest emission rates of biogenic VOC are estimated to be in the region of the Alps which has the largest forest coverage in Switzerland and the major part of these forests consists of Norway spruce. The total annual biogenic VOC emission rate of 87 ktonnes y^–1 coming from the forests is significantly higher than those from other studies where calculations were carried out by classifying the forests as deciduous and coniferous. The difference is attributed to the high leaf biomass densities of Norway spruce and fir (abies alba) trees which have a strong effect on the results when speciation of trees is taken into account. Besides the annual rate, emission rates were calculated for a specific period during July 4–6, 1991 when a photochemical smog episode was investigated in the Swiss field experiment POLLUMET. Emission rates estimated for that period agree well with those calculated for July using the average temperatures over the last 10 years.