Evaluating Isoprene Oxidation Chemistry in Gas-Phase Mechanisms Using in Situ Observations of Formaldehyde

Oxidation of isoprene by OH can significantly impact atmospheric composition; however, the driving chemistry is extremely complex and not fully understood. As a result, isoprene oxidation schemes vary widely among gas-phase mechanisms used in air quality models (AQMs) and chemical transport models (CTMs). We use the Framework for 0-D Atmospheric Modeling (F0AMv3) to simulate isoprene chemistry using five different gas-phase mechanisms: CB05 and CB6r2 of the Carbon Bond mechanism, GEOS-Chem version 9-02, and Master Chemical Mechanism versions 3.2 and 3.3.1. Mechanisms are evaluated with respect to formaldehyde (HCHO), a high-yield product of isoprene oxidation. As a basis for comparison, we utilize in situ observations of HCHO from the SENEX and SEAC⁴RS aircraft campaigns, which took place in the Southeast US in 2013. We also intercompare mechanisms in terms of HCHO production rates and offer suggestions for improving isoprene oxidation in the mechanisms that support AQMs and CTMs. Results are extended to consider the impact of improved isoprene oxidation chemistry on ozone production.