(a) In addition to certifying devices which meet the standards set forth in, or established pursuant to, Sections 43602 and 43610, the state board shall adopt standards for certifying exhaust devices which achieve a reduction of the emission of hydrocarbons, carbon monoxide, and oxides of nitrogen from the exhaust of a motor vehicle substantially below the standards for any two pollutants set forth in, or established pursuant to, Section 43602 or 43610. If, however, an exhaust device is shown to substantially reduce the emission of any two of the three pollutants, the state board may certify such a device, so long as the installation of such device in a motor vehicle does not increase the emission of the other pollutant in excess of the emission of that pollutant by the vehicle in the absence of such a device.