Ammonia　(NH3)　emitted　from　motor　vehicles　is　a　by-product　of　measures　taken　to　reduce　emissions　of　other　pollutants　(e.g.　NOx　and　CO)　and　has　potentially　important　environmental　impacts.　NH3　levels　can　be　impacted　by　various　emission　standards.　However,　there　is　a　lack　of　investigations　of　the　influences　from　the　implementation　of　different　vehicular　emission　standards　on　long-term　changes　in　NH3　emissions.　To　fill　this　gap,　we　estimated　the　inter-annual　NH3　emissions　of　light-duty　gasoline　vehicles　(LDGVs)　under　different　emission　standards　(State　0　to　State　V)　from　1999　to　2017　and　investigated　the　emission　change　characteristics　under　the　rapidly　developing　Chinese　economy.　Results　showed　that　the　NH3　emissions　from　LDGVs　had　a　sharp,　42-fold　increase　(from　1.8　Gg　to　77.9　Gg).　However,　NH3　emissions　per　capita　have　begun　to　decrease　with　increases　in　socioeconomic　development,　presenting　an　inverted　U-shaped　tendency　as　a　function　of　per　capita　GDP.　Further　exploration　indicated　that　the　decline　in　emission　factors,　as　determined　by　upgrades　in　emission　standards,　was　the　decisive　factor　in　promoting　the　downward　trend　in　per　capita　emissions.　This　suggests　that　continuously　upgrading　emission　standards　has　offset　the　increase　in　NH3　emissions　due　to　the　rapid　growth　of　motor　vehicles.　Quantitative　scenario　analysis　showed　a　two-stage　impact　of　emission　standards　on　NH3　emissions:　emissions　would　decrease　77%　(48%-90%　for　different　years)　if　State　I　and　State　II　were　not　implemented;　while　if　none　of　standards　were　upgraded　(State　III　to　State　V),　NH3　emissions　would　increase　118%　(13%-224%　for　different　years),　2-6　times　the　impacts　from　the　growth　of　vehicle　population　and　the　decline　of　vehicle　kilometres　traveled.　The　data　and　findings　in　this　study　can　provide　scientific　support　for　understanding　air　pollution　in　urban　areas　and　for　formulating　further　vehicle　pollution　mitigation　measures　in　China　and　other　countries.　(C)　2019　Elsevier　B.V.　All　rights　reserved.