When the Chicago area was required to come into compliance with the ozone ambient standard by 2007, Illinois adopted the Emissions Reduction Market System (ERMS), an emissions trading program that would reduce overall Volative Organic Matter (VOM) emissions in the Chicago area.

The ERMS program only controls emissions from May 1 through September 30, the months when VOM emissions are likely to contribute to the formation of ozone. Each participant is given a baseline emissions allotment, corresponding to an overall area-wide reduction of 12%, according to what they were actually emitting in previous years. The program allows trading among participating sources as long as the specified cap on overall emissions is not exceeded.

This was the first emissions trading program to focus on controlling volatile organic materials. A proposed earlier effort to use emissions trading in the Los Angeles area to limit VOC emissions had never been implemented. Implementing emissions trading for VOM is especially complex. VOM sources not only include a wide array of very different types of emitters, many of them small, but volatile organics represent a class of pollutants, not a single pollutant. To make matters even more difficult that class contains substances that have designated as hazardous air pollutants due to the danger they pose to human health. Clearly not all VOM reductions would have the same environmental impact.