A series of model results is shown pertaining to ozone, reactive nitrogen (NOy), and peroxides in polluted regions. The results focus on ratios such as O3/NOy and H2O2/HNO3 that have been proposed as indicators for O3-NOx-VOC sensitivity. These ratios are shown to correlate with predicted NOx-VOC sensitivity for a variety of zero-dimensional (0-D) and 3-D models, but the correlation varies in situations ranging from relatively clean to highly polluted. The previously identified NOx-VOC transition values for indicators appear to be valid for moderately polluted conditions with 80--150 ppb O3. Changes in indicator behavior are linked to odd hydrogen chemistry and in particular to changes in the ratio of O3 to primary radical production. Changes in indicator behavior are also correlated with the values of a test ratio, O3/(2H2O2+NOz) which can be evaluated against measurements. Ratios of the form ΔO3/ΔNOy, representing differences relative to background values, are proposed for analyzing NOx-VOC sensitivity in individual urban plumes. Comparisons are made to extent-of-reaction parameters, which have been proposed for evaluating NOx-VOC sensitivity.