General Motors has built an environmental chamber at its Milford Proving Ground to run emission tests at controlled atmospheric conditions. This chamber was designed using constant speed fans and dampers to simulate altitudes between sea level and Denver, which is approximately 5000 ft above sea level. The chamber can also control temperatures within a range of 45-100°F at humidities of 9-100 gr H2O/lb dry air.With this chamber, environmental conditions can be changed to desired levels very quickly to measure the vehicle sensitivity to the change. It is also possible to hold the environment constant and run controlled comparison studies on emission-related components to determine the effect of different distributors, carburetors, etc., relative to emission values.Past test experience has proved that vehicle emissions change with changing environment. However, the degree of change is different from one vehicle to another.