Ammonia emissions and their key influencing factors from naturally ventilated dairy farms

Ammonia (NH₃) contributes several adverse impacts to the environment, especially the crucial role of PM_2.5 precursors. In China, approximately 13.5% of the total NH₃ emissions from agricultural activities are related to dairy cows farming. The goals of this study were to define NH₃ emissions, localize emission factors, and clarify relationships between NH₃ emissions and potential influencing factors from dairy farms. The measurements were carried out in three typical naturally ventilated dairy farms with different scales, floor materials and manure managements over four seasons. Results showed that NH₃ emission rate from all areas changed in the range of 0.01-2.96 mg min^-1 m^-2 in the three farms. NH₃ emission factors ranged from 5.21 to 38.10 kg a^-1 cow^-1 with the outdoor exercise area as the largest contributor. The variation of NH₃ emissions in the three farms was consistent and positively related to ambient temperature (R² > 0.8, p < 0.01). Strong relationships (p < 0.01) between NH₃ emissions and relative humidity were found only in outdoor exercise and sedimentation tank of Farm A and manure storage of Farm B. The NH₃ emission rates were dependent on floor material and the frequency of manure collection. However, the effect of manure collection methods on NH₃ emissions was insignificant. Results from this study provide accurate data to improve the atmospheric pollutant emission inventories, and clarify the impact of different influencing factors on NH₃ emissions from livestock farms.