<Table> <Tr> <Th> Source </Th> <Th> Percentage </Th> </Tr> <Tr> <Td> Electric Generation * </Td> <Td> 34% </Td> </Tr> <Tr> <Td> Industry * </Td> <Td> 15% </Td> </Tr> <Tr> <Td> Large Non-Agricultural Methane Sources * </Td> <Td> 5% </Td> </Tr> <Tr> <Td> Light -, Medium -, and Heavy - Duty Vehicles * </Td> <Td> 22% </Td> </Tr> <Tr> <Td> Other Transport </Td> <Td> 7% </Td> </Tr> <Tr> <Td> Commercial and Residential Heating </Td> <Td> 7% </Td> </Tr> <Tr> <Td> Agriculture </Td> <Td> 7% </Td> </Tr> <Tr> <Td> HFCs </Td> <Td> 2% </Td> </Tr> <Tr> <Td> Other </Td> <Td> 1% </Td> </Tr> </Table> <Tr> <Th> Source </Th> <Th> Percentage </Th> </Tr> <Tr> <Td> Electric Generation * </Td> <Td> 34% </Td> </Tr> <Tr> <Td> Industry * </Td> <Td> 15% </Td> </Tr>

The clean air act mandated setting standards for what secondary pollutant