Carbon monoxide is the most abundant of the criteria pollutants. High concentration of Carbon monoxide generally occurs in areas with heavy traffic congestion. There are adverse effects on Human health due to high concentration of CO in the atmosphere. The metropolitan cities are facing such type of problems a lot. In a given signal (data of average CO per day, observed by DPCC Anand Vihar, Delhi), trend is the most important part and also slowest part of a signal. In wavelet analysis terms this corresponds to the greatest scale value. Symlet wavelet is orthogonal and compactly supportive and therefore, it is useful for multiresolution analysis of a CO data. Approximation and Detailed coefficients have been determined using Sym4 wavelet transforms.