Transboundary dust storms, fueled by rampant desertification in Mongolia, pose a severe environmental threat to hundreds of millions of people and to sustainable development across East Asia. While ecological restoration is a recognized solution, its potential and cross-boundary benefits remain unquantified at a policy-relevant scale. Here we show that even without large-scale interventions, 67.5% of Mongolia's territory experienced a decrease in desertification severity from 2005 to 2023, yielding a net 23.0% reduction in spring dust emissions by 2023. This natural improvement alone reduced the dust column mass density over North China and Northeast China by 5.4% and 13.3%, respectively. If Mongolia had implemented proven ecological restoration measures similar to those adopted in China's Inner Mongolia during the same period, spring dust emissions could have been substantially reduced by 42.7%. This would in turn reduce spring dust pollution over North China and Northeast China by 10.6% and 18.6%, respectively. Such findings provide rigorous, evidence-based quantification that large-scale ecological restoration in Mongolia is not only a national imperative but also a critical strategy for delivering substantial transboundary air quality co-benefits, underscoring the global value of investing in sustainable land management.