The North China Plain has been identified as a significant hotspot of ammonia (NH 3 ) due to extensive agricultural activities. Satellite observations suggest a significant increase of about 30 % in tropospheric gas-phase NH 3 concentrations in this area during 2008–2016. However, the estimated NH 3 emissions decreased slightly because of changes in Chinese agricultural practices, i.e., the transition in fertilizer types from ammonium carbonate fertilizer to urea, and in the livestock rearing system from free-range to intensive farming. We note that the emissions of sulfur dioxide (SO 2 ) have rapidly declined by 60 % over recent few years. By integrating in situ measurement datasets, multi-year NH 3 emission inventories, and chemical transport model simulations, we demonstrate that the increases in NH 3 can be almost entirely attributable to this rapid SO 2 emission reduction. The annual average sulfate concentrations decreased by about 50 %, which significantly weakened the formation of ammonium sulfate and increased the average proportions of gas phase NH 3 within the total NH 3 column concentrations from 26 % (2008) to 37 % (2016). Both the decreases in sulfate and increases in NH 3 concentrations show highest values in summer, possibly because the formation of sulfate aerosols is more sensitive to SO 2 emission reductions in summer than in other seasons.