The nitrogen crisis in the Netherlands has raised wide attention and heated debate in recent years. Human activities have increased the losses of reactive nitrogen to the environment, which puts human and ecosystem health at risk and causes soil acidification, eutrophication, and subsequent biodiversity loss. Additionally, nitrogen deposition may magnify the effects of climate change by influencing vegetation growth and carbon exchange during droughts. However, as the main drivers of reactive nitrogen deposition, ammonia emissions are challenging to estimate. This Ph.D. study aims to refine agricultural ammonia emission estimates in space and time by combining and refining existing datasets and models and assimilating remote sensing. The emission estimates were validated using various measurements from ground-based stations and satellites.