Development and intercomparison of condensed isoprene oxidation mechanisms for global atmospheric modeling

A new condensed isoprene oxidation mechanism for global atmospheric modeling (MIM) was derived from a highly detailed master chemical mechanism (MCM). In a box model intercomparison covering a wide range of boundary layer conditions the MIM was compared with the MCM and with five other condensed mechanisms, some of which have already been used in global modeling studies of nonmethane hydrocarbon chemistry. The results of MCM and MIM were generally in good agreement, but the other tested mechanisms exhibited substantial differences relative to the MCM as well as relative to each other. Different formation yields, reactivities and degradation pathways of organic nitrates formed in the course of isoprene oxidation were identified as a major reason for the deviations. The relevance of the box model results for chemistry transport models is discussed, and the need for a validated reference mechanism and for an improved representation of isoprene chemistry in global models is pointed out.