Technical Abstract: Animal agriculture, and manure in particular, is a major source of ammonia emissions, and numerous models have been developed for predicting ammonia emission from manure. However, even the most comprehensive models are often inaccurate. Ammonia emission is complicated by volatilization of carbon dioxide, which raises manure pH through kinetically-limited reactions, and therefore affects ammonia speciation and emission rate. We developed a chemical speciation and transport model that includes equilibrium and kinetically-limited reactions for predicting manure pH and carbon dioxide and ammonia emission from manure. Model predictions and emission measurements confirm that carbon dioxide emission influences ammonia emission, and provide quantitative estimates of the effect of manure composition, temperature, and mass transfer coefficient on emission. The relationships identified in this work provide insight into the processes controlling ammonia emission, and can be incorporated into simpler models for predicting ammonia emission from manure.