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Simulations using seven chemical mechanisms are intercompared against O-3, NOx and hydrocarbon data from photooxidation experiments conducted at the University of North Carolina outdoor smog chamber. The mechanisms include CB4-2002, CB05, CB05-TU, a CB05 variant with semi-explicit aromatic chemistry (CB05RMK), SAPRC07, CS07 and MCMv3.1. The experiments include aromatics, unsaturated dicarbonyls and volatile organic compound (VOC) mixtures representing a wide range of urban environments with relevant hydrocarbon species. In chamber simulations the sunlight is characterised using new solar radiation modelling software. A new heterogeneous chamber wall mechanism is also presented with revised chamber wall chemical processes. Simulations from all mechanisms, except MCMv3.1, show median peak O-3 concentration relative errors of less than 25% for both aromatic and VOC mixture experiments. Although MCMv3.1 largely overpredicts peak O-3 levels, it performs relatively better in predicting the peak NO2 concentration. For aromatic experiments, all mechanisms except CB4-2002, largely underpredict the NO-NO2 crossover time and overpredict both the absolute NO degradation slope and the slope of NO2 concentration rise. This suggests a major problem of a faster and earlier NO to NO2 oxidation rate across all the newer mechanisms. Results from individual aromatic and unsaturated dicarbonyl experiments illustrate the unique photooxidation chemistry and O-3 production of several aromatic ring-opening products. The representation of these products as a single mechanism species in CB4-2002, CB05 and CB05-TU is not adequate to capture the O-3 temporal profile. In summary, future updates to chemical mechanisms should focus on the chemistry of aromatic ring-opening products.