Ammonia (NH.sub.3) emissions have large impacts on air quality and nitrogen deposition, influencing human health and the well-being of sensitive ecosystems. Large uncertainties exist in the "bottom-up" NH.sub.3 emission inventories due to limited source information and a historical lack of measurements, hindering the assessment of NH.sub.3 -related environmental impacts. The increasing capability of satellites to measure NH.sub.3 abundance and the development of modeling tools enable us to better constrain NH.sub.3 emission estimates at high spatial resolution. In this study, we constrain the NH.sub.3 emission estimates from the widely used 2011 National Emissions Inventory (2011 NEI) in the US using Infrared Atmospheric Sounding Interferometer NH.sub.3 column density measurements (IASI-NH.sub.3) gridded at a 36 km by 36 km horizontal resolution. With a hybrid inverse modeling approach, we use the Community Multiscale Air Quality Modeling System (CMAQ) and its multiphase adjoint model to optimize NH.sub.3 emission estimates in April, July, and October. Our optimized emission estimates suggest that the total NH.sub.3 emissions are biased low by 26 % in 2011 NEI in April with overestimation in the Midwest and underestimation in the Southern States. In July and October, the estimates from NEI agree well with the optimized emission estimates, despite a low bias in hotspot regions. Evaluation of the inversion performance using independent observations shows reduced underestimation in simulated ambient NH.sub.3 concentration in all 3 months and reduced underestimation in NH4+ wet deposition in April. Implementing the optimized NH.sub.3 emission estimates improves the model performance in simulating PM.sub.2.5 concentration in the Midwest in April. The model results suggest that the estimated contribution of ammonium nitrate would be biased high in a priori NEI-based assessments. The higher emission estimates in this study also imply a higher ecological impact of nitrogen deposition originating from NH.sub.3 emissions.