Thermal effects on dispersion of secondary inorganic aerosols in an urban street canyon

The surface heating in complex urban areas affects concentration of secondary inorganic aerosol (SIA) via flow and chemical environment changes. Previous studies on heating effects on pollutants have focused on effect of dispersion change. However, the heating of buildings also affects SIA concentration via chemical environmental changes, such as reaction rate and thermodynamic equilibrium changes. Accordingly, we investigated the effect of heating, by not only flow changes but also chemical environment changes, on SIA using a coupled chemistry-computational fluid dynamics (CFD) model. We investigated the change of temperature and wind in each scenario to separately identify the effects caused by the chemistry and dynamics of thermal heating on reactive aerosols. We found that both the chemical and dynamical effects reduce SIA concentration. The effect of heating caused by chemical environment changes on SIA was 49.4% larger than that of flow changes, suggesting the importance of chemical reactions in aerosol calculations in urban microscale aerosol simulations, which are not considered in most CFD-based models. We conclude that chemical speciation and detailed aerosol chemistry calculations, including an inorganic aerosol thermodynamic equilibrium model, should be considered for accurately accounting for the effect of heating on urban areas.