Isoprene, the most emitted non-methane hydrocarbon, is known to influence ozone (O3) formation in urban areas rich with biogenic emissions. To keep up with the recent advance on isoprene oxidation chemistry including the identification of isoprene epoxydiols (IEPOX) as a precursor to secondary organic aerosol (SOA), Xie et al. (2013) updated the SAPRC (Statewide Air Pollution Research Center)-07 chemical mechanism. It is currently unknown how the Xie modification of SAPRC07T impacts the ability of the model to predict O3. In this project we will evaluate the Xie mechanism with simulations of 24 isoprene experiments from the UNC gas-phase chamber. Our results suggest that the new mechanism increases NOX (nitrogen oxides) inter-conversion and produces more O3 than SAPRC07 for all experiments. In lower NOX experiments, the new mechanism worsens O3 performance towards the wrong direction, increasing bias from 8.9% to 15.8%. We found increased NOX recycling from NOZ (oxidized NO2) accounts for that. These results underline the importance of further studies on characterizing the NOX recycling rate from isoprene nitrates.Master of Science in Environmental Engineerin
