 The Urban Airshed Model , a regional forecast model for the effects of air pollution and acid rain , was developed by a private company in the USA in 1970 . Development of this model was taken over by the Environmental Protection Agency and improved in the mid to late 1970s using results from a regional air pollution study . While developed in California , this model was later used in other areas of North America , Europe and Asia during the 1980s . The Community Multiscale Air Quality model ( CMAQ ) is an open source air quality model run within the United States in conjunction with the NAM mesoscale model since 2004 . The first operational air quality model in Canada , Canadian Hemispheric and Regional Ozone and NOx System ( CHRONOS ) , began to be run in 2001 . It was replaced with the Global Environmental Multiscale model - Modelling Air quality and Chemistry ( GEM @-@ MACH ) model in November 2009 . 
