The SHED Simulator is a computer-controlled device that uses a mass flow controller to inject a known quantity of sample gas into a SHED. The timed injections may be performed as a single shot or as multiple shots on an hourly basis for a 24-, 48-, or 72-hour diurnal test. The injections may vary in length from hour to hour and may also vary in rate with each injection. The actual injection will be within 0.5% of the intended injection on a mass flow basis. Additionally, the MFC is capable of up to 14 separate gas calibrations.