Automotive cabin air filters have become increasingly popular as automotive manufacturers recognize the need to provide vehicle occupants with a more comfortable driving experience. Cabin air filters which reduce particulates (e.g. dust, pollen) have been standard on many European models since the late 1980's and have recently become available on several vehicles produced by Ford Motor Company in North America. Market research (focus panels and customer surveys) has shown that consumers expect cabin air filters to reduce both particulates and odors/gases and as a result, future vehicles will offer systems which address both.Test methods and standardized test codes for evaluating these types of filters are currently being drafted. Current methods for testing such gas/odor filters call for part-per-million challenge levels for reasons of analytical simplicity and test speed. However, gases from vehicle exhaust and industrial sources are present in ambient air in part-per-billion (ppb) concentration levels. Questions raised about the differences in filter performance at these two levels can be answered by developing the appropriate test methods for comparison testing.Most cabin air filters designed to reduce gaseous pollutant levels rely on adsorbents such as activated carbon. Under certain conditions some gases will desorb from the carbon. Questions about desorption can be answered by developing appropriate test methods which can be related to ‘real-life’ conditions.This paper will describe the methodology and the results for measuring a cabin air filter's capability to remove ppb level gases and its desorption characteristics.