System and method for removing molecular contaminants from an air stream are disclosed. The system includes first, second and third filter. The first filter removes organic contaminants from an air stream passing through the first filter. The second filter is downstream of the first filter, is physically and chemically exchangeable with the first filter and removes organic contaminants from the air stream output of the first filter. The third filter, downstream of the second filter, is not exchangeable with the first filter or the second filter. The first position filter can be replaced by the second filter in the second position when the first filter in the first position becomes depleted as detected. A new filter in the second filter position is inserted. Replacing the depleted first filter with the second downstream filter reduces costs and waste while inserting the new filter in the second position ensures removing organic contaminants.