A stack of replaceable filters, wherein the stack of replaceable filters is an asymmetrical filter stack, comprising: a first filter comprising two or more media layers (2,2), wherein at least two of the two or more media layers (2,2) of the first filter are capable of removing airborne contaminants from the group consisting of organics and acids from an air stream that passes through the first filter; a second filter downstream of the first filter that has physical and chemical properties that enable it to be exchangeable with the first filter, the second filter comprising two or more media layers (2,2), wherein at least two of the two or more media layers (2,2) of the second filter are capable of removing airborne contaminants from the group consisting of organics and acids from the air stream output from the first filter; and a third filter downstream of the second filter, wherein the third filter is not exchangeable with the first filter or the second filter, the third filter comprises two or more media layers (1,6), and the two or more media layers (1,6) of the third filter differ from the two or more media layers (2,2) of the first and second filters (310, 320), wherein at least one of the two or more media layers (1,6) of the third filter is capable of removing airborne contaminants that are organics or acids or bases output from the second filter and at least one of the two or more media layers (1,6) of the third filter removes basic contaminants including ammonia from the air stream output from the second filter; and an initial capacity of the first filter and an initial capacity of the second filter for a removal of airborne molecular organic contaminants are within +/- 25% as measured in part per billion hours at a same gas flow rate and contaminant input challenge; and the second filter has a capacity for airborne organic contaminants sufficient to permit exchange with a depleted first filter. a first filter comprising two or more media layers (2,2), wherein at least two of the two or more media layers (2,2) of the first filter are capable of removing airborne contaminants from the group consisting of organics and acids from an air stream that passes through the first filter; a second filter downstream of the first filter that has physical and chemical properties that enable it to be exchangeable with the first filter, the second filter comprising two or more media layers (2,2), wherein at least two of the two or more media layers (2,2) of the second filter are capable of removing airborne contaminants from the group consisting of organics and acids from the air stream output from the first filter; and a third filter downstream of the second filter, wherein the third filter is not exchangeable with the first filter or the second filter, the third filter comprises two or more media layers (1,6), and the two or more media layers (1,6) of the third filter differ from the two or more media layers (2,2) of the first and second filters (310, 320), wherein at least one of the two or more media layers (1,6) of the third filter is capable of removing airborne contaminants that are organics or acids or bases output from the second filter and at least one of the two or more media layers (1,6) of the third filter removes basic contaminants including ammonia from the air stream output from the second filter; and an initial capacity of the first filter and an initial capacity of the second filter for a removal of airborne molecular organic contaminants are within +/- 25% as measured in part per billion hours at a same gas flow rate and contaminant input challenge; and the second filter has a capacity for airborne organic contaminants sufficient to permit exchange with a depleted first filter.