The POCP ranges indicate large differences in O 3 production between individual VOCs, which justifies the use of this ranking scale instead of treating all VOCs as a homogeneous group of species in abatement strategies.Both the average O 3 production over 96 hr and the maximum contribution to the O 3 concentration were studied. The most efficient O 3 producers were found to be isoprene, 2-methyl-2-butene, and acrolein. As a group, the alkenes are the most potent O 3 producers, followed by higher alkanes and then the aromatics. The calculated values show a good agreement with previously calculated POCP values under northern European conditions.