Analysis of the ground level ozone concentration is vital for the purpose of forecasting and in identifying the changes and impacts that are very crucial for an agro-based economy like the capital city of Tamil Nadu. Six months data of Ground level Ozone concentration of south Chennai is used to determine the decomposition method. The objective of this study is to analyse the behaviour of Ground level ozone concentration of metropolitan city of Tamil Nadu using decomposition method. The Decomposition techniques are used to identify salient features of a time series such as trend seasonality and cyclical patterns. The weekly behaviour of ground level ozone concentration in south Chennai is tabulated.