A computational procedure, that takes into account climatic data and produces hourly mobile emissions of pollutants on a fine grid for the Montréal Metropolitan area has been developed for the use of Environment Canada. The procedure computes HC, CO, NO x , CO 2 , SO 2 and NH 3 mobile emissions, as well as 2.5-and 10-µm particles. The mobile emissions are calculated on the highways and main arteries of the Montreal road network. The emissions from parked vehicles are computed as well. A user friendly interface, called GRILLE, has been developed for entering parameters and launching the calculations. GRILLE calls up command files for the MOBILE 6.2C software and EMME/2 macros, which include the calculation procedure. This procedure has two parts. The first, obtains emission rates, and the second part, obtains the vehicle flows on the network and estimates the pollution on a fine grid. Results could be retrieved as simple text format or as graphic output. The emission computations can be done for any day and any hour of the year. Use of the model by Environment Canada is described as well.