Table

Some Application Sectors for Chromatographic Analysis of Major Air Components

Atmosphere

Continuous emission monitoring Worker safety/industrial hygiene Indoor air monitoring

Global monitoring network for greenhouse effect

Biological processes

Wastewater effluent monitoring

Earthquake prediction

Volcanic eruption prediction

Ecosystem monitoring

Energy exploration

Geological evaluation

Earthquake prediction

Pollution remedial process feedback

Site investigation

Volcanic eruption prediction

Soil biogenic emission measurement

Environmental forensics

Water

Soil necessary for development of reliable global carbon budget models.61 Certain chromatographic methods have been developed for this purpose that allow large sample numbers to be collected in the field and analyzed rapidly in the laboratory. Stable isotope geochemistry is one of the most powerful methods of CO2 source investigation and can be facilitated by GC-IRMS.39 For example, one study conducted in the East European Russian tundra zone region shows that over the critical value of 14°C, an increase of mean diurnal air temperature in these ecosystems lead to a change in the carbon net flux from sink to source.62 The result is reversed when the temperature is under that critical value. This effect is primarily caused by the increase of gross ecosystem respiration at higher temperatures. This study provides evidence of possible positive feedback between climate warming and carbon emission to the atmosphere on regional and short-term scales.

Another interesting result indicates that anthropogenic and biogenic CO2 have similar isotopic characteristics and polluted and unpolluted sites cannot be distinguished by the 813C-S180 distribution. Further comparison of data from different sampling networks is needed.39

Like carbon dioxide, atmospheric methane has long been considered a major contributor to the greenhouse effect. Measurement of methane concentrations in the atmosphere by GC-FID can help to understand its distribution between global sources and sinks and its growth rate for a period of time. Dlugokencky et al.6 have shown that a strong north-south gradient in methane with an annual mean difference of about 140 ppb between the northernmost and southernmost sampling sites exists. Methane time-series concentrations from the high southern latitude sites have a relatively simple seasonal cycle with a minimum during late summer-early fall, which can be explained by its photochemical destruction during that period. Typical seasonal cycle amplitudes there are about 30 ppb. This figure is almost twice in the high north region, possibly because of a more complex interaction between methane sources and sinks and atmospheric transport. Moreover, from a global perspective, the growth rate for methane has decreased from about 13.5ppb/year in 1983 to 9.3 ppb/year in 1991, while the global burden of atmospheric methane increased at an average rate of 11.1 ± 0.2 ppb/yr. In the northern hemisphere alone, the growth rate of methane was near zero in 1992. The most acceptable reason is that a change in a methane source is influenced directly by human activities, such as fossil fuel production. The atmospheric measurements provide an integrated picture, which is useful in gaining a better understanding of the global methane budget especially when combined with a model of atmospheric transport and chemistry. The information from monitoring programs can be applied in decision-making for policies and regulations.

The fact that natural gas is generated by thermal degradation of sedimentary organic matter has been widely accepted. Because of the complex structure of kerogen, it is not well understood which reactions proceed during thermal gas generation. Gases generated from dry coal-pyrolysis reactions in an open system, such as methane, carbon dioxide, carbon monoxide, propane, etc., can be analyzed by GC coupled with IRMS.46 Experimental results can be used to study the reaction mechanisms, kinetic order of the reactions, signature of the hydrocarbon precursors within the kerogen, and the burial and accumulation history of the kerogen as well. The results also help to provide the basis for an extension of compositional kinetic approaches in natural gas geochemistry to isotope level (isotope-specific kinetics). In light of this, the feasibility of a reaction-kinetic approach for prediction of isotope compositions of natural gas as a function of time-temperature history of the source material becomes achievable. This approach can ultimately be employed in geological petroleum and natural gas exploration.

In order to understand how H2O and CO2 are exchanged between leaf tissues and the air, measurement of the photosynthetic isotope fractionation by open flow gas analysis is conducted in a gas exchange chamber under controlled conditions of temperature, light intensity and humidity, and CF-IRMS and GC are employed.40 When the same method is applied to ecosystem isotope fractionation in a field experiment, the variation in atmospheric CO2 concentrations and 8 13C values primarily reflect variations in net photosynthesis (daytime) and respiration. The 818O and CO2 data also reflect these processes, but with added complications because of oxygen isotope exchanges with soil and leaf water pools.

0 0

Post a comment