A new indicator is proposed for determining if tropospheric ozone production in a specific area is limited by VOC or NOx. The indicator &THgr;=&tgr;OHVOC/&tgr;OHNOx describes the ratio of the lifetimes of OH against the losses by reacting with VOC and NOx. Whereas &tgr;OHNOx can be obtained by conventional measurements, the new pump and probe OH approach which is described in part one of this publication makes it now possible to obtain also &tgr;OHVOC. Indicator values above a threshold value of 0.2¿50% are representative of NOx-saturated conditions where an increase of NOx emissions causes lower ozone production. For values below 0.01 the ozone production is very insensitive to changes of VOC emissions. The robustness of this indicator against several parameters such as temperature, humidity, photolysis, and initial ozone concentrations is tested in a box model and compared to the robustness of other earlier proposed indicators. In contrast to earlier proposed indicators, this new one is not based on photochemically produced long-lived species but describes the instantaneous regime of an air parcel. Three-dimensional simulation shows that this indicator is quite successful in estimating the impact of increased or reduced emissions on the ozone concentrations for each location in the modeling area. This will make it a very helpful tool for developing ozone abatement strategies. ¿ 2001 American Geophysical Union