Investigation of Real Car Exhaust in Environmental Simulation Chambers: Results from the INFORMATEX and DIFUSO Projects

摘要

It has been demonstrated that atmospheric simulation chambers offer the unique possibility for studying the impact of real car exhaust under almost real-world conditions on tropospheric photosmog formation. The experiments performed in the EUPHORE smog chamber were simulated using a simple box model, including gas-phase chemistry only. The model described all experiments with high accuracy. Sensitivity analyses were carried out in order to explain the observations. The addition of diesel exhaust to a well-defined simple VOC mixture caused a significant increase of the ozone formation after irradiation, in comparison to smog experiments with a similar VOC/NO_x ratio in the absence of exhaust gas. The increase of ozone observed in the exhaust runs was mainly caused by the high initial concentrations of nitrous acid and formaldehyde emitted by the diesel engine. Higher aldehydes were of minor importance. The ozone formation was not dependent on the formulation of the diesel fuel. Differences in ozone formation rates for the single experiments were due to deviations in initial start concentrations as well as photolysis conditions. Further studies within the DIFUSO project studies exhibited that the influence of diesel soot on the ozone formation is negligible under the conditions of the smog chamber experiments performed. The present simulations using a simple gas-phase model leading to good agreement of experimental and calculated data confirmed this observation. For the future, detailed measurements of NO_x, HONO and aldehydes in diesel exhaust for typical motor conditions should be considered. The use of such data as input parameters for the calculation of ozone formation potentials (e.g. incremental reactivities by the method of Carter et al. 1995) can contribute to a better estimation of the influence of diesel exhaust on tropospheric ozone formation.