Acidification of livestock manure can reduce emission of the greenhouse gases methane (CH₄) and nitrous oxide (N₂O), as well as ammonia (NH₃). We examined the relation between emission of these gases and transformation of organic matter as affected by acidification. Liquid cattle manure was acidified with sulfuric acid to pH 5.5 at a pilot scale (100 L), and we measured effects on CH₄, N₂O, CO₂ and NH₃ emissions and on transformation of pH buffer components and organic matter. Acidification reduced NH₃ emissions by 62% (47 d) and emission of CH₄ by 68% (57 d). Emissions of N₂O were negligible, probably due to the absence of a surface crust. Reductions in NH₃ and CH₄ emission were highest at the start but declined over time concomitantly with a gradual increase in the stored liquid manure pH. Acidification did not significantly affect CO2 emissions. Emission of CO₂ was high, fiveto ten-fold of CH₄ emissions, until Day 16 of storage, after which the CO₂ emission rate declined to around twice the CH₄ emission rate; consequently, the majority of C loss during the early stages of storage was CO₂. Cumulative emission of C in CO₂ and CH₄ closely matched depletion of dissolved organic carbon (DOC), suggesting that DOC may be a predictor for CH₄ emission from dilute slurries. volatile fatty acid and total ammoniacal nitrogen concentrations in surface layers were substantially higher than at the center of stored liquid manure, perhaps resulting from microbial activity at the surface. This pattern deserves attention when predicting NH₃ emission from stored slurry.