Ammonia and methane emissions from two naturally ventilated dairy cattle buildings and the influence of climatic factors on ammonia emissions

► Variation of internal concentrations of NH3, CH4 and CO2 followed the same trend. ► NH3 emission rates varied from 18 to 77 g HPU−1 d−1 for the two buildings. ► Diurnal pattern was found for NH3 and CH4 emission rates. ► A linear relationship existed between NH3 emission and wind speed (P < 0.001). ► A linear relationship was found between NH3 emission and air temperature (P < 0.001).