The overall effectiveness of an air cleaner depends on its ability to trap small particles and on the amount of air drawn through it. There are no industry-wide performance standards, but the Association of Home Appliances Manufacturers (AHAM) has developed the Room Air Cleaner Certification Program. This program provides a uniform standard for portable air cleaners called the clean air delivery rate (CADR). The CADR is the amount of clean air measured in cubic feet per minute (cfm) that an air cleaner delivers to a room. AHAM publishes a list of Certified Air Cleaners that meet the standards of the Room Air Cleaners Certification Program. The list contains the CADR ratings for removing dust, tobacco smoke, and pollen by brand name and model number of air cleaners. The CADR ratings vary greatly by the type of pollutant, as well as by brand and model number. For example, if you are concerned about removing pollen from the air (rather than tobacco smoke, for example) then you should choose an air cleaner that is certified by AHAM and has a high CADR for pollen.