No abstract

The concentration of methane has been measured in tropospheric air samples collected in remote locations between 55°N and 53°S during six collection periods between November 1977 and November 1980. The observed concentrations of CH4 have increased in each of six latitude locations by an average of 0.052±0.005 ppmv between January 1978 and January 1980. This (1.4±0.2)×1014 gram increase in the total atmospheric burden of CH4 corresponds to 35±12% of the yearly flux of (4.0±1.3)×1014 grams needed to maintain the CH4 concentration in steady‐state at its recent level of about 1.6 ppmv. The 1978‐1980 excess of about 0.7×1014 grams per year of sources over sinks for CH4 could arise from either an increase in biogenic releases or from a decrease in the average OH radical concentration in the lower troposphere, or from both.

Iridium-modified, boron-doped diamond electrodes fabricated by an ion implantation method have been developed for electrochemical detection of arsenite (As(III)). Ir+ ions were implanted with an energy of 800 keV and a dose of 10(15) ion cm(-2). An annealing treatment at 850 degrees C for 45 min in H2 plasma (80 Torr) was required to rearrange metastable diamond produced by an implantation process. Characterization was investigated by SEM, AFM, Raman, and X-ray photoelectron spectroscopy. Cyclic voltammetry and flow injection analysis with amperometric detection were used to study the electrochemical reaction. The electrodes exhibited high catalytic activity toward As(III) oxidation with the detection limit (S/N = 3), sensitivity, and linearity of 20 nM (1.5 ppb), 93 nA microM(-1) cm(-2), and 0.999, respectively. The precision for 10 replicate determinations of 50 microM As(III) was 4.56% relative standard deviation. The advantageous properties of the electrodes were its inherent stability with a very low background current. The electrode was applicable for analysis of spiked arsenic in tap water containing a significant amount of various ion elements. The results indicate that the metal-implanted method could be promising for controlling the electrochemical properties of diamond electrodes.