The monitoring air, water, soil, or biota is the practice of sampling systematically these environmental elements. Thus, in the Environmental Sciences, the data monitoring denotes the data obtained by sampling systematically the environment. The primary purposes of data monitoring are, among others, the detection of levels of air pollutants, the detection of trends, and the elaboration of spatial and temporal summaries. Additional purposes include the estimation of the indexes of air quality or the support of a database for the application of environmental policies and regulations.