Evaluation of CMAQ parameterizations for SOA formation from the photooxidation of α-pinene and limonene against smog chamber data

A set of experiments carried out at the EUPHORE smog chamber have been simulated using a simplified version of the Community Multiscale Air Qualtity model version 4.7 (CMAQv4.7). First, the terpene parameterizations included in the model have been tested against the experimental data, showing a general overprediction of the aerosol mass formed. Experimental differences between the experiments presented here and those from which the model parameters were obtained, such as the NO:NO2 ratio and the type of OH-initiator seem to be the reason of the overprediction observed. In the second part of the work, new parameterizations have been calculated for the two different set of conditions defined: CALTECH conditions, based on the experiments by Griffin et al. (1999) and Hoffmann et al. (1997) (low NO:NO2 ratio and propene as OH-inititator) and EUPHORE conditions, based on the experiments of this work (high NO:NO2 ratio and HONO as OH-initiator). We have estimated increases of 11% and 82% in the stoichiometric coefficients αi of the surrogate semivolatile products when the conditions change from EUPHORE to CALTECH conditions. Finally, the parameterizations are tested against an independent set of experiments published by Li et al. (2007). Results indicate that the parameters derived for the EUPHORE conditions simulate well experiments carried out under similar conditions. However, the parameters tend to overpredict SOA formation under high NOx conditions.