The automotive clean-air catalyst system from Engelhard Corporation (PremAir™) consists of a catalyst-coated vehicle radiator and air-conditioning condenser designed to catalytically remove ground-level ozone and carbon monoxide (CO) from ambient air. Although initial on-road testing of the PremAir™ system showed reasonably high ozone conversion activity and satisfactory catalyst durability during the course of relatively low mileage accumulation, the long-term durability of the catalyst coating, its potential negative impact on cooling efficiency and corrosion characteristics, and incompatibility with the existing radiator manufacturing process remain among the issues of some concern. This paper describes an alternative approach to the problem of on-road pollutant destruction, which involves placing a thin catalytic monolith brick immediately behind the uncoated vehicle radiator. The ozone and CO conversion performance of the alternative clean-air catalyst system was evaluated on a Delphi-Harrison Thermal Systems' dissipator and compared with that of catalyst-coated radiator cores. The tests show the superior ozone conversion performance of the catalytic monoliths (but at the expense of higher pressure drop) compared to the catalyzed radiator cores. A simple mathematical analysis of the ozone conversion data indicates that the ozone conversion reaction over both the catalytic monoliths and catalyzed radiators occurs under the influence of significant mass transfer limitations, and that the ozone destruction performance advantage of the catalytic monoliths can be attributed to their higher gas-solid mass transfer rate. The CO conversion efficiencies observed with both types of catalyst samples were too low (< 10 %) to draw definite conclusions about the impact of catalyst system configuration on CO conversion performance.