EPA regulations require engines to meet existing emission standards.  Poor emissions are not only in violation of EPA standards, they are also an indication of incorrect engine performance, incorrect voltage output, and other problems such as excessive fuel consumption, oil burning, engine fatigue, and coolant leaks into the block.  Periodic emission testing can help identify minor problems before they become major ones.  Even subtle problems common to standby generators, such as “wet stacking”, can be identified and corrected during emission tests.