Measurements Of Atmospheric Methane Research Articles

Measurements of atmospheric methane at the Japanese Antarctic Station, Syowa

Precise and continuous measurements of the atmospheric CH4 concentration were initiated at Syowa Station, Antarctica in February 1988, using a gas chromatograph equipped with a flame ionization detector. The measurement precision was typically ± 0.07% in a concentration range of 0.5 to 2.5 ppmv. The standard gases were CH4-in-air mixtures and their CH4 concentrations were determined gravimetrically with uncertainties of ± 0.2%. The CH4 concentrations measured at the station were extremely stable, and outliers due to local contamination such as station activities were not found. The diurnal CH4 variation was hardly observable throughout the year. The average seasonal CH4 variation showed minimum and maximum concentrations in early March and late September, respectively, and a peak-to-peak amplitude of 30 ppbv. Annual mean values of the CH4 concentration were 1640 and 1651 ppbv in 1988 and 1989, respectively. A concentration difference of 11 ppbv between the two years may suggest that recent annual increase rate of the CH4 concentration is smaller than previously reported values of about 1% year-1.

Rule-based expert system for evaluating the quality of long-term, in-situ gas chromatographic measurements of atmospheric methane (technical memo)

Methane is an important trace constituent of the earth's atmosphere because it is active both chemically and radiatively. The absorption of infrared radiation by atmospheric methane, and the rapid increase in the global atmospheric burden of methane over the past century combine to raise concerns that continued increases may contribute to global warming and climate change within the next century. The use of a rule-based expert system to assess the integrity of in situ gas chromatographic methane measurements made at the NOAA/CMDL Point Barrow, Alaska and Mauna Loa, Hawaii observatories is presented. The expert system flags ambient samples analyzed during chromatograph system instability and excludes them from further scientific analysis. The development and implementation of the expert system are described in detail. A comparison between data sets flagged by a human expert and by the expert system shows that the expert system can successfully reproduce the efforts of a human when evaluating gas chromatograph system stability. Advantages and limitations of the use of an expert system for the task are also discussed.

Trends of atmospheric methane during the 1960s and 1970s

Sporadic measurements of atmospheric methane, using gas chromatography, have been taken since the early 1960s. We found 188 measurements between 1962 and 1979 reported in various publications with data in 70 of the 216 months. We have analyzed these measurements to estimate the trends of methane between 1960 and 1980. The data were adjusted for differences of absolute calibration and for latitudinal variations, and analyzed by ordinary regression analysis, weighted regression analysis, and nonparametric methods. Our best estimate of the increasing trend during this period is 13±3 ppbv/yr which is similar to, but somewhat less than, the trend of about 17 ppbv/yr over the last decade.

5341. Automated analyzer for aircraft measurements of atmospheric methane and total hydrocarbons: W R Cofer, III and G C Purgold,Rev Sci Instrum;52 (10), 1981, 1560–1564

5341. Automated analyzer for aircraft measurements of atmospheric methane and total hydrocarbons: W R Cofer, III and G C Purgold,Rev Sci Instrum;52 (10), 1981, 1560–1564

Automated analyzer for aircraft measurements of atmospheric methane and total hydrocarbons

An automated methane/total hydrocarbon analyzer was developed and flight tested that produced alternate methane/total hydrocarbon measurements every 7 s, providing the spatial resolution needed for regional hydrocarbon measurements at aircraft speeds. The sensitivity of the analyzer to oxygen and water vapor interference was characterized at appropriate concentrations. A technique to periodically measure atmospheric oxygen was determined to be necessary for accurate hydrocarbon measurements and incorporated into the analyzer. A data collection methodology was developed to minimize errors resulting from changes in flame ionization detector sensitivity at different altitudes (pressures). Selected aircraft data acquired during the 1979 Southeastern Virginia Urban Plume Study are presented to illustrate instrument performance.