Articles | Volume 9, issue 4
Methods for assessment of models
11 Apr 2016
Methods for assessment of models |  | 11 Apr 2016

Oligomer formation in the troposphere: from experimental knowledge to 3-D modeling

Vincent Lemaire, Isabelle Coll, Florian Couvidat, Camille Mouchel-Vallon, Christian Seigneur, and Guillaume Siour

Abstract. The organic fraction of atmospheric aerosols has proven to be a critical element of air quality and climate issues. However, its composition and the aging processes it undergoes remain insufficiently understood. This work builds on laboratory knowledge to simulate the formation of oligomers from biogenic secondary organic aerosol (BSOA) in the troposphere at the continental scale. We compare the results of two different modeling approaches, a first-order kinetic process and a pH-dependent parameterization, both implemented in the CHIMERE air quality model (AQM) (, to simulate the spatial and temporal distribution of oligomerized secondary organic aerosol (SOA) over western Europe. We also included a comparison of organic carbon (OC) concentrations at two EMEP (European Monitoring and Evaluation Programme) stations. Our results show that there is a strong dependence of the results on the selected modeling approach: while the irreversible kinetic process leads to the oligomerization of about 50 % of the total BSOA mass, the pH-dependent approach shows a broader range of impacts, with a strong dependency on environmental parameters (pH and nature of aerosol) and the possibility for the process to be reversible. In parallel, we investigated the sensitivity of each modeling approach to the representation of SOA precursor solubility (Henry's law constant values). Finally, the pros and cons of each approach for the representation of SOA aging are discussed and recommendations are provided to improve current representations of oligomer formation in AQMs.

Short summary
Oligomerization is one of the most important identified processes of secondary organic aerosol evolution. We have simulated the formation of oligomers from biogenic precursors, using two different parameterizations implemented in the air quality model CHIMERE. This study shows that oligomer concentration fields are quite sensitive to the way the competition between local formation, evaporation and transport is restituted. The benefits and disadvantages of each approach are discussed in details.