To accredit an exhaust emission control device whose installation costs exceed the statutory limits for mandatory devices it must be shown that such a device can reduce the emissions of each of at least two of the three pollutants, hydrocarbons, carbon monoxide, and oxides of nitrogen, without increasing the third pollutant, by a minimum of twenty percent below the emission levels obtained with the mandatory accredited or approved device. The State Board may permit the installation of a device in lieu of an approved, certified, or accredited device.

The test procedures for determining compliance with these standards are set forth in “California Exhaust Emission Criteria and Test Procedures for Accrediting Emission Control Devices Sold on a Non-Mandatory Basis,” dated February 13, 1974.