Preparation of automobile organic emission surrogates for photochemical model validation

Irradiation chamber studies of the photochemistry of motor vehicle emissions generally use relatively simple surrogates (often fewer than 30 compounds) of complex emissions (often greater than 250 compounds). The question is often asked: Can the photochemistry of complex organic mixtures be adequately simulated by chamber studies using simple surrogate mixtures? The complexity of the compositional profile of motor vehicle organic emissions results in large part from the complexity of the fuel (i.e., the combustion derived compounds are relatively small in number). An experimental protocol is described by permitting preparation of representative complex (greater than 250 compounds) emission surrogates adding a small number (fewer than 30) of selected compounds to the vehicle fuel. Irradiation chamber runs of actual motor vehicle exhaust samples are contrasted with similar runs of associated complex mixture emission surrogates demonstrating the accuracy with which the exhaust photochemistry can be simulated using the surrogate. Time-resolved profiles of NO, NOx–NO, and ozone concentrations, and selected 12.5 h product concentrations, are presented as examples of the comparability of the exhaust and surrogate photochemistry. The observed exhaust and surrogate concentration profiles product distributions are very similar.