Assessing the performance of combination particulate and gaseous contaminant air filters

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Assessing the performance of combination particulate and gaseous contaminant air filters

Tronville, Paolo / Rivers, Richard

In recent years, several manufacturers have offered filters formed from media which are intended to remove both aerosols and gaseous contaminants. These 'combo' filters have been supplied for both general-ventilation use and for vehicle cabin climate control systems. The performance of two filters of this type designed for vehicles has been analyzed. The analysis of performance is limited to their removal of volatile organic contaminants (VOCs) by activated carbons which have not been impregnated with additional chemicals. Inlet concentrations of VOCs were estimated from published values for the concentration of gaseous contaminants found in highway and street traffic. Published expressions for determining the retentivity of activated carbons, include the effects of contaminant type and concentration, filter flow rate and carbon bed characteristics were developed for much higher inlet concentrations than exist in even the most polluted street situations, and give impossible (negative-value) retentivities. An alternate analysis valid for VOC concentrations at the microgram-per-cubic-meter level is presented. Retentivity and breakthrough time for benzene and acetaldehyde (typical VOCs) are calculated and compared to published test data on similar filters. The breakthrough times are short enough to raise questions regarding the usefulness of these filters with their very thin beds of activated carbon.