Black carbon modelling in urban areas: investigating the influence of resuspension and non-exhaust emissions in streets using the Street-in-Grid (SinG) model.

Black carbon (BC) is a primary and inert pollutant often used as a traffic tracer. Even though its concentrations are generally low at regional scale, BC presents very high concentrations in streets (local scale), potentially causing important effects on human health and environment. modelling studies of BC concentrations usually underestimate BC concentrations, because of uncertainties in both emissions and modelling. Both exhaust and non-exhaust traffic emissions present uncertainties, but those on non-exhaust emissions, such as tyre, brake and road wear and particle resuspension, are particularly high. In terms of modelling, the street models do not always consider the two-way interactions between the local and regional scales, i.e. the influence of the high BC concentrations observed in streets on the urban background concentrations, which can enhance the BC concentrations in streets. This study uses the multi-scale Street-in-Grid model (SinG) to simulate BC concentrations in a Paris suburb street-network, taking into account the two-way coupling between local and regional scales. The BC concentrations in streets proved to have an important influence on urban background concentrations. The two-way dynamic coupling leads to an increase in BC concentrations in large streets with high traffic emissions (with a maximal increase of about 48 %), and a decrease in narrow streets with low traffic emissions and low BC concentrations (with a maximal decrease of about 50 %). A new approach to estimate particle resuspension in streets is implemented, strictly respecting the mass balance on the street surface. The resuspension rate is calculated from the available deposited mass on the street surface, which is estimated based on a particle deposition and wash-off parametrizations adapted to street-canyon geometries. The simulations show that particle resuspension presents a low contribution to black carbon concentrations, as the deposited mass is not significant enough to justify high resuspension rates. Non-exhaust emission, such as brake and tyre and road wear, largely contribute to BC emissions, with a contribution equivalent to exhaust emissions. Here, emission factors of tyre, brake and road wear are calculated based on the literature, and a sensitivity analysis of these emission factors on BC concentrations in streets is performed. The model to measurement comparison shows that tyre-emission factors usually used in Europe are probably under-estimated, and tyre-emission factors coherent with some studies of the literature and the comparison performed here are proposed. [ABSTRACT FROM AUTHOR]