Assessing ultrafine particle concentrations in the Rotterdam region using modelling and measurements

Population in urbanized areas is consistently exposed to elevated concentrations of ultrafine particles (UFP). Due to limited UFP measurement data, a modelling approach can help fill the gaps in both spatial and temporal coverage of the observation network. This study utilizes the LOTOS-EUROS model and measurements to characterize UFP concentrations within the urban area of Rotterdam, The Netherlands. Rotterdam is a particularly interesting location as it contains a variety of UFP sources (shipping, industry, traffic, airport).The LOTOS-EUROS model is extended with the SALSA2 module for particle dynamics. Currently nucleation is not taken into account in LOTOS-EUROS and measurements are used to provide background conditions for the 1x1 km2 resolution model domain. Within the domain, a new UFP emission inventory for this area is used. The model results are compared with measurements obtained from a 1-month summer campaign from the Rijnmond Central Environmental Management Service (DCMR) and from the Ruisdael Observatory. Measurement locations include Veldkersweg (urban background with influence of road and airport) and Nieuwe Maas (urban background, influenced by shipping) and the rural Cabauw observatory.We will provide a joint analysis of measurements and model results that provides valuable insight in the behaviour of UFP in the Rotterdam region. As expected, both urban locations, Veldkersweg and Nieuwe Maas, exhibit consistently higher PNC compared to the more remote Cabauw observatory. Model results clearly show the large contributions from shipping in the area. Comparison with observations reveal that background values are modelled reasonably well but that the model can currently not represent the higher values of two urban observation stations measuring UFP. Further model development is needed to include nucleation. In addition, more research is needed to quantify the competing effects of coagulation and deposition close to the source, which relates to the questions how emissions as reported in the emission inventory can be used in a model like LOTOS-EUROS, where instant dilution applies.