Monitoring air quality in the municipal wastewater treatment plants is an initial stage in preventing several problems related to air emissions. This study measured 103 volatile organic compounds (VOCs), total VOC (TVOC), and some prominent air pollutants (CO, CO2, NH3, H2S, PM1, PM2.5, PM7, PM10, TSP) in the municipal wastewater treatment plant X located in the north of Taiwan. Thirty-three VOCs were identified, which categorized as alkane, aromatic, alkene, ester, ether, haloalkane and ketone. Five dominant factors were determined from principal component analysis (PCA). The first factor involves indoor activities (such as particulate matter resuspension), and outdoor activities (such as vehicles exhausts), which explained 32.42% of total variance. Factor 2 was paint applications and domestic wastewater decomposition, with an explained variance of 17.23%. Factor 3 was solvent use, with an explained variance of 14.26%. Factor 4 was solvent use and road dust, with an explained variance of 8.54%. Factor 5 was a byproduct of the chlorination treatment process, with an explained variance of 6.92%. The five factors explained 79.37% of total variance. By applying absolute principal component scores (APCS), source apportionments were obtained having 35.21%, 26.04%, 16.13%, 7.03%, and 15.59% for factors 1, 2, 3, 4, and 5, respectively. Toluene had the highest ozone formation potential (OFP).