<p>Wastewater treatment plants (WWTPs) are major sources of gaseous nitrogen (N) emissions. The nitrous oxide (N₂O) emissions have been extensively studied, however, how ammonia (NH₃) emissions contribute to N₂O emissions, soil acidification and particulate matter (PM_2.5) formation, have been largely overlooked. This study quantified NH₃ and N₂O emissions from a sludge drying pan (SDP), using inverse-dispersion modelling coupled with open-path Fourier infrared spectroscopic techniques. Here we show low N₂O emissions (&lt;0.001 g m⁻² h⁻¹) and mean NH₃ emissions that are much higher in summer (0.293 g m⁻² h⁻¹) than in winter (0.060 g m⁻² h⁻¹). A mechanistic process model, correlating NH₃ emissions with wind speed and temperature, predicts total NH₃ emissions over the SDP cycle (634 days) at 43 t of NH₃‒N. This represents 30% of total N in the SDP and 6–9% of total N in the WWTPs influent. This study highlights that the use of SDPs by WWTPs is a substantial NH₃ emission source, offering new perspectives for mitigating global N emissions.</p>