The O3 sensor includes an electrochemical concentration cell (ECC), and a non-reactive gas sampling pump. The ECC is comprised of two platinum electrodes in separate anode and cathode chambers. The electrodes are immersed in a potassium iodide solution of different concentrations. As ambient air containing O3 is pumped into the cathode solution, a chemical reaction occurs and generates an electrical current in proportion to the rate at which O3 enters the cell. Preparation of each O3 is conducted over a week as the ECC requires 3-4 days to acclimatize before use.