Modelling of road contributions to PM2.5 and particle number concentrations with the LOTOS-EUROS model

Road traffic is a major contributor to ultrafine particles and to PM2.5. The contribution of volatile organic compounds (VOCs), in particular of intermediate (IVOC) and low (SVOC) volatility is still uncertain. One reason is that species are not in emission inventories, another reason is that their pathways to form secondary organic aerosol (SOA) are strongly simplified in chemistry-transport models (CTM). In the framework of the EASVOLEE project, the CTM LOTOS-EUROS is being updated to better account for SOA formation and to better describe particle size and number from road traffic.

To this end, the LOTOS-EUROS model has recently been extended with the CB7 chemistry scheme. This scheme includes more VOC species and more detailed organic chemistry than the operational CBM4 chemistry scheme. This update also allows for the uptake of the developments of Manavi and Pandis (2022, 2024) to efficiently include SOA formation from road transport S/I/VOCs. In addition, the Volatility Basis Set (VBS) scheme was updated to make the model for SOA more accurate and faster. LOTOS-EUROS has adopted the SALSA2 module to model particle size distributions and particle number concentrations. In the near future, the organic vapors from the VBS calculations will be coupled to SALSA2 to investigate the impact of condensable organic vapors to ultrafine particle concentrations and size distributions. The model will then use new road emissions from the EASVOLEE project to represent the contribution of road transport to particle number concentrations and PM2.5. The envisaged model approach and preliminary results will be presented.