Measurement of Carbon Dioxide, Methane, Nitrous Oxide, Sulfur Hexafluoride and Halocarbons in Ambient Air at an Industrial Park in Huntington Beach, California

摘要

The ability to report concurrently the full complement of long-lived greenhouse gases permits complete assessment of possible sources and their effects on global warming. Just an examination of one or two components cannot provide an adequate evaluation of all potential impacts on our environment. Data and discussions presented demonstrate that ambient levels of all long-lived greenhouses gases can be measured with enough precision and stability to pick up changes in ambient concentrations over extended sampling intervals. These influences over one day can often be overwhelmed by the inherent imprecisions of both ECD and FID detectors, but become important over long-term monitoring or during dramatic changes in the barometer. Ambient pressure has little effect with the measurement of halocarbons due to the use of a mass flow controller to measure sample volumes. Detection limits are not necessarily a determining factor in the measurement of nitrous oxide, methane and carbon dioxide, as these have minimum ambient levels well above established detection limits and are not likely to be lowered soon. More important considerations relate to the reproducibility and accuracy of results, as concentration trends are the essential consideration. Variations in concentrations are an important aspect of monitoring these gases, and precision of results must be minimized to detect subtle variations. A novel addition of internal standards to the every chromatographic run greatly improves the reproducibility by self-correcting for changes in chromatographic conditions and for variations in injection loop temperatures and barometric pressures due to environmental surroundings of the instrument. Ambient pressure and temperature changes have little effect with the measurement of halocarbons due to the employment of a mass flow controller to measure sample volumes. Hourly measurements of the complete list of long-lived greenhouse gases permit assessments of transient releases of these contaminants. By positioning the analyzer downwind of potential sources, any discharge of these gases can be possibly assigned to that nearby location. Averages over a wider time interval can be easily generated by simple computation of the norm of hourly readings over that interval.