The composition of the tropical atmosphere and its changes over time is of significant importance for global climate. Currently large uncertainties in the budgets of many trace gases in the tropics exist, mainly due to a lack of measurements. To fill this gap we have recently installed FTIR instrument supplied by IMK-FZK (Institute of Metrology and climate research center), Germany. In this book there will be a discussion on source and sink of atmospheric CO for each atmospheric layer especially the upper troposphere and lower troposphere. In addition, the detailed working principle of FTIR spectrometer is given. The data obtained from the spectrometer are retrieved using software based on the equation derived in the “Retrieval Theory” section. There also other topics discussed which are useful for the data analysis. The analysis should help people working on atmospheric research especially those using ground-base instruments for data collection on atmospheric gases, or anyone else who is using spectroscopic measurements can use this thesis to see how the data is analyzed. In addition, people working on space borne atmospheric research can also use it for comparison.