Disclosed is a method for sharply reducing diurnal
breathing loss emissions from automotive evaporative emissions control systems by providing multiple
layers, or stages, of adsorbents. On the fuel source-side of an emissions
control system canister, high
working capacity carbons are preferred in a first canister (adsorb) region. In subsequent canister region(s) on the vent-side, the preferred adsorbent should exhibit a flat or flattened adsorption isotherm on a volumetric basis and relatively lower capacity for
high concentration vapors as compared with the fuel source-side adsorbent. Multiple approaches are described for attaining the preferred properties for the vent-side canister region. One approach is to use a filler and / or voidages as a volumetric
diluent for flattening an adsorption isotherm. Another approach is to employ an adsorbent with the desired adsorption isotherm properties and to process it into an appropriate shape or form without necessarily requiring any special provision for
dilution. The improved combination of high
working capacity carbons on the fuel source-side and preferred lower
working capacity adsorbent on the vent-side provides substantially lower diurnal
breathing emissions without a significant loss in working capacity or increase in flow restriction compared with known adsorbents used in canister configurations for
automotive emissions control systems.