How to filter out sulfur dioxide
Just add your gas mix in a container with NaOH solution and shake well or bubble it continuously through the solution. SO2 dissolves in water to form H2SO3 (and H2SO4 in the atmosphere when it rains resulting in what we call acid rain) which will be neutalized by NaOH to give dissolved Na2SO3. Your air should be freed of most SO2. This is how it is done in the industry. There are many other ways as well but most rely in neuralizing the SO2. Google Flue-gas desulfurization for more details.