PROPOSAL FOR AN IN-SITU MEASUREMENT OF THE ATMOSPHERIC METHANE CONCENTRATION USING A HIGH-RESOLUTION QUADRUPOLE MASS-SPECTROMETER

An in situ, real time measurement of the methane (CH4) concentration i n the earth's atmosphere using a high-resolution quadrupole mass spect rometer (QMS) has been proposed. CH4 is a strong greenhouse gas that c auses warming of the earth's surface. Therefore, the measurement of th e atmospheric CH4 concentration is essential. The high-resolution QMS is equipped with normal and high resolution modes. In the normal mode, the Mass 15/Mass 14 peak ratio was measured for the CH4 concentration of 0-0.08% in volume to obtain the calibration curve and the measured curve showed good linearity and traceability. In addition, in the hig h resolution mode, the measurement of the CH3+/N-15(+) peak ratio was proposed to evaluate the CH4 concentration lower than approximately 0. 02% with a wide dynamic range. The CH3+ (15.0235 u) peak has been succ essfully separated from a N-15(+) (15.0001 u) peak that is a gathering of minor isotropic ions of nitrogen. An overall CH4 concentration ran ge we can measure is predicted to 0.001-30% by using the normal and hi gh resolution modes. Copyright (C) 1996 Elsevier Science Ltd