System and method for removing airborne molecular contaminants from gas streams

A method of replacing filters in a stack of replaceable filters comprising a first filter in a first position, a second filter in a second position downstream of the first filter, and third filter in a third position downstream of the second position comprising:

• i) passing an air stream through the filter stack, wherein the first filter comprises a media layer that removes airborne contaminants from the air stream, the second filter is physically and chemically exchangeable with the first filter and comprises a media layer that removes airborne contaminants from an air stream output from the first filter;
• and the third filter is not physically and chemically exchangeable with the first filter or the second filter and comprises a media layer that is capable of removing a base from an air stream output from the second filter;
• ii) detecting breakthrough of an airborne organic contaminant from the air stream downstream of the first filter indicating a depleted first filter;
• iii) removing the depleted first filter from the first position in the stack and replacing the depleted first filter with the second filter in the second position in the stack;
• and
• iv) inserting a replacement second filter in the second position, downstream of the second filter now in the first position in the stack, that is physically and chemically exchangeable with the second filter now in the first position in the stack.