The Indoor Environment Department (IED) at Lawrence Berkeley National Laboratory (LBL) in Berkeley, CA (USA) is a world class research group in indoor air pollution, pollutant dynamics, pollutant dispersion, ventilation, and air flow modeling. One of the lab's main goals is "...understanding human exposures to environmental pollutants found in indoor and outdoor air." Many of the IED's publications are available for download

OpenFOAM is a sophisticated open-source framework for performing computational fluid dynamics (CFD) simulations.

From the website: "The OpenFOAM (Open Field Operation and Manipulation) CFD Toolbox can simulate anything from complex fluid flows involving chemical reactions, turbulence and heat transfer, to solid dynamics, electromagnetics and the pricing of financial options. OpenFOAM is produced by OpenCFD Ltd, is freely available and open source, licensed under the GNU General Public Licence."