Some theoretical results concerning O 3 ‐NO x ‐VOC chemistry and NO x ‐VOC indicators

A series of model results is shown pertaining to ozone, reactive nitrogen (NO y ), and peroxides in polluted regions. The results focus on ratios such as O 3 /NO y and H 2 O 2 /HNO 3 that have been proposed as indicators for O 3 ‐NO x ‐VOC sensitivity. These ratios are shown to correlate with predicted NO x ‐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 NO x ‐VOC transition values for indicators appear to be valid for moderately polluted conditions with 80–150 ppb O 3 . Changes in indicator behavior are linked to odd hydrogen chemistry and in particular to changes in the ratio of O 3 to primary radical production. Changes in indicator behavior are also correlated with the values of a test ratio, O 3 /(2H 2 O 2 +NO z ) which can be evaluated against measurements. Ratios of the form ΔO 3 /ΔNO y , representing differences relative to background values, are proposed for analyzing NO x ‐VOC sensitivity in individual urban plumes. Comparisons are made to extent‐of‐reaction parameters, which have been proposed for evaluating NO x ‐VOC sensitivity.