A mass transfer model is proposed to estimate the rates of chemical emissions from aqueous solutions spilled on hard surfaces inside buildings. The model is presented in two forms: a set of four ordinary differential equations and a simplified exact solution. The latter can be implemented in a spreadsheet. User input includes ten parameters, which represent either the properties of the source or those of the building. All of them can be readily obtained. The proposed model is tested against and in good agreement with the measurements of simulated spill events in a room-sized environmental chamber. This model can be used by emergency response planners to estimate the time history of contaminant concentrations in indoor air. (c) 2007 Elsevier B.V. All rights reserved.