Measurement of carbon dioxide fluxes in the Amazon basin and the design, development and testing of two new carbon dioxide detectors

In order to improve our understanding of the global carbon budget and the potential for future climate change resulting from carbon dioxide emissions to the atmosphere, it is necessary to quantify the sources and sinks of atmospheric carbon dioxide (CO2). It is especially important to measure the carbon dioxide exchange between the atmosphere and different components of the biosphere. Flux measurement techniques used to quantify these exchanges include the chamber method, the eddy correlation and eddy accumulation techniques, and mixed layer techniques such as the convective boundary layer gradient method and the budget method.; The budget method was used to determine carbon dioxide fluxes to and from the forest canopy in the Peruvian Amazon from data obtained in a field experiment conducted during the summer of 1996. Measurements of CO2 exchange with forests are of particular interest due to the possibility that the magnitude of the carbon dioxide sink due to the terrestrial biosphere is increasing. Daytime and nocturnal samples were collected by flask sampling at different altitudes within and above the convective boundary layer from a balloon platform. Carbon dioxide concentrations were determined off-site by non-dispersive infrared spectroscopy. The fluxes that were subsequently calculated from these flask samples (--0.373 +/- 0.063 m ppmv CO 2 s--1, daytime; +0.128 +/- 0.024 m ppmv CO 2 s--1, nocturnal) agreed with previous experiments conducted in the Brazilian Amazon that concluded that this region is a net carbon dioxide sink.; These fluxes were determined from a very limited data set, which is one of the inherent disadvantages of the flask sampling technique. This thesis presents the development of two carbon dioxide detectors which can collect data continuously in the field. They are portable and inexpensive, and can be miniaturized for use with kite or balloon platforms. Both detectors incorporate the use of hollow fiber membranes. The carbon dioxide detector based on conductivity operates on the principle that the conductance of water is dependent on the concentration of carbon dioxide in a surrounding air stream. This detector exhibits a 1/e response time of ∼30 s and a precision (RSD) of 0.1%. A colorimetric detector monitors the equilibrium shift between the acid and base forms of an indicator dye in response to a change in the gaseous carbon dioxide concentration. Preliminary results using two different modes of detection are presented, but future work is required to fully characterize the sensitivity, response time and precision. The absorbance instrument is more easily miniaturized and could be readily modified for the measurement of other trace gases such as sulfur dioxide, carbon monoxide and ammonia.