We perform a positive matrix factorization (PMF)-based source apportionment by combining GHG measurements with coincident VOC measurements in the San Joaquin Valley of California. Using VOCs as source tracers, we identify dairies and livestock as major sources of CH4 and N2O in the region. Agriculture is a significant source of N2O enhancements too, while vehicle emissions are found to be a negligible source of N2O. The findings are relevant to the state’s GHG inventory verification process.