The ability of air biofilters to remove carbon monoxide (CO), a priority pollutant that harms human and environmental health was investigated. Environmental accounting of biofilters was performed using emergy analysis to compare resource requirements of biofilters to catalytic converters. Cylindrical PVC biofilters were filled with pebbles or compost, inoculated with soil slurries and loaded with either bottled CO or engine exhaust CO. In batch experiments, compost and pebble biofilters exhibited exponential decrease in CO over time with compost removing 90% of 1000 ppm-bottled CO and pebble biofilters removing 80% CO in 24 hours. In continuous flow experiments, compost biofilter exposed to 1000 ppm-CO generated from a gasoline engine was able to reduce CO levels (45%) at efficiency commensurate to a bottled CO source. In the range of 500-1000 ppm-CO, biofilters used less total environmental and energy resources to remove CO (12E9 solar emjoules) than conventional catalytic converters (40E9 solar emjoules).