CO2 causes the greenhouse effect and consequent natural disruption of the environment. Therefore, it needs to develop technologies for the sequestration and reduction of CO2. On the other hand, some diseases with the chronic intake of metals at low concentration will possibly become a problem in the future, which means that it is required to develop accurate analytical methods for metals at even lower concentration. Based on these circumstances, the electrochemical or photocatalytic reduction of CO2 released to the environment, and atomic spectrometry for environmental samples were investigated. First, in the electrochemical reduction of CO2 in methanol, the reduction products could be controlled by the selections of supporting electrolytes and cathode materials. Furthermore, the photocatalytic CO2 reduction reaction could proceed in liquid and supercritical CO2 media. Next, a sensitive and accurate analytical method of specific trace metals, such as cobalt, silver and rhodium, in environmental samples by electrothermal atomization atomic absorption spectrometry with a metal tube atomizer was developed. Moreover, a direct determination method of elemental content in individual dried biological cells and particulates by ICP-AES or ICP-MS was investigated. These determination methods may play a significant role in various fields, such as environmental science, pharmacy and biochemistry.