Abstract: This study conducted long-term monitoring of the emission fluxes and ambient air concentrations of volatile aldehydes and ketones released from each treatment unit of an A/O process urban wastewater treatment plant in Beijing, evaluated the emission characteristics of four typical aldehydes and ketones on the spatial scale, and calculated the exposure risk values of each process unit to assess the hazards of aldehydes and ketones to the staff and the neighbourhood residents. Results show that the emission fluxes of volatile aldehydes and ketones compounds in the wastewater treatment plant are, in descending order: aerobic tank section 1 > aerobic tank section 2 > aerobic tank section 3 > anoxic tank > primary sedimentation tank > secondary sedimentation tank. The BAF is the treatment unit with the largest percentage of daily emissions of aldehydes and ketones among the treatment units, with more than 57.81% of the four aldehydes and ketones gases. The ambient concentrations of aldehydes and ketones in the ambient air of each treatment unit also varies, with the total concentration varying from 30.44 to 1 230.79 μg/m³, of which formaldehyde has the lowest concentration content, ranging from 2.46 to 71.36 μg/m³, and acetaldehyde has the highest concentration, ranging from 59.32 to 1 454.44 μg/m³. There is a carcinogenic risk of acetaldehyde emitted from each treatment unit.