Municipal wastewater treatment processes have the function of removing harmful pollutants in the wastewater. However, there are probably several problems of air emissions related to these processes, especially for residents who live near a wastewater treatment plant. Volatile organic compounds exposure increases the risk of cancer. Thus, the health risk of residents to ambient volatile organic compounds exposure is essential to be conducted. One hundred and three volatile organic compounds (VOCs), total volatile organic compounds (TVOCs), and some prominent air pollutants (CO, CO2, NH3, H2S, PM1, PM2.5, PM7, PM10, TSP) were investigated at the surface of an underground wastewater treatment plant in Taipei City during four different seasons. Twenty four VOCs were identified, some of which were categorized as carcinogenic to humans (Group 1) and possibly carcinogenic to humans (Group 2B) according to the International Agency for Research on Cancer. The mean values of CO, CO2, PM1, PM2.5, PM7, PM10 and TSP were found to be 0.64 ppm, 293.68 ppm, 1.37 µg m–3, 3.20 µg m–3, 10.74 µg m–3, 13.48 µg m–3, and 16.90 µg m–3, respectively. NH3 and H2S were not detected in the present study. The health risk for residents was estimated following the method from United States Environmental Protection Agency (U.S. EPA). The cumulative of carcinogenic risk was 3.48 × 10–5 and categorized as a possible risk. In addition, the result was also possibly affected by traffic nearby. The magnitude for non-carcinogenic risk index was less than 1.