Among agricultural activities, animal husbandry is one of the main sources of atmospheric pollutant emissions : 15% of the greenhouse gases and 80% of the ammonia emissions come from this sector.Today, at the international level, a major political objective is to decrease the emissions of greenhouse gases (Kyoto Conference) and also of ammonia (Göteborg Conference). It seems therefore necessary that the farmers become aware of the impact of their practices, especially of farmyard manure management, on air quality. The development of assessment tools would be useful to farmers. The aim of this study is to set up an assessment method for the impacts of farmers' practices on air quality. This method is based on three indicators, which assess the emissions of ammonia (NH3), methane (CH4), and nitrous oxide (N20). These gases are emitted during intestinal fermentation of livestock, housing, storing of farmyard manure (and composting), grazing, and manure spreading. The ammonia emission indicator (INH3) is presented in detail. It is calculated by assessing the impact of each practice on gas emission, and then combining the results to assess the global risk at the farm level. The final score lies between 0 (high risk) and 10 (lowest risk), thus assessing the emission of NH3 from the totality of practices concerning farmyard manure management. The methane emission indicator (ICH4) and the nitrous oxide indicator (IN2O) are calculated in the same way. Lastly, we show that the calculation of these indicators on two dairy farms makes it possible not only to diagnose their impacts on air quality, but also to highlight which of the polluting practices can be improved.