The present work shows the SO2 gas sensing property of SnO2 thin film based sensor prepared by using RF sputtering technique. Different catalysts (MgO and V2O5) in form of nanoclusters having diameter of 600？μm have been loaded on SnO2 surface to detect SO2 gas. The sensing response of all these films towards SO2 is monitored. Microstructural studies have been carried out using XRD and UV-Visible Spectrophotometer and a good correlation has been found between the microstructural and gas sensing properties of these deposited samples. Both catalysts when incorporated with SnO2 film show high selectivity towards SO2 gas at lower operating temperature. MgO gives a sensitivity of 317% at an operating temperature of 280°C towards 500？ppm of SO2 gas whereas V2O5 catalyst gives a sensitivity of 166% at 280°C for the same amount of gas. 1. Introduction Recently, substantial interest has arisen in terms of protecting the environment from various air pollutants generated by combustion exhausts. SO2 is one of the most hazardous atmospheric pollutants because it directly contributes to acid rain. Several studies have shown that repeated exposure to low levels of SO2 (<5？ppm) can cause permanent pulmonary impairment [1]. The long-term and short-term exposure limits for SO2 gas are 2？ppm and 5？ppm, respectively. Therefore, the development of an efficient SO2 gas sensor for environmental monitoring has become a necessary task. There are various techniques for determining the SO2 gas concentration in the atmosphere such as ion chromatography [2], Fourier transform infrared spectrometry [3], optical fiber sensors [4], SAW gas sensors [5], conductometry [6], and electrochemical methods [7]. Amongst all the techniques, conductometric sensors are fast, highly sensitive, reproducible, of low cost, and convenient. Semiconducting tin oxide (SnO2) based conductometric gas sensors have received much attention for more than four decades due to their suitable physical-chemical properties and possibility to detect wide variety of gases with high response [8–11]. SnO2 is naturally nonstoichiometric having a rutile phase that eases the adsorption of oxygen on its surface and thus it is highly sensitive towards many toxic and harmful gases [10, 11]. The main problem with the pure SnO2 thin film based gas sensors is their poor selectivity and high operating temperatures that can be improved to a great extent by using specific catalysts [12, 13]. The aim of this study is to develop a SnO2 thin film based SO2 gas sensor with MgO and V2O5 catalysts having efficient response
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