Seasonal characteristics on the ammonia emissions of a typical large-scale pig farm in the Yangtze River Delta, China

Ammonia (NH 3 ) is a key PM 2.5 precursor that significantly contributes to haze formation and air quality degradation. Livestock farming accounts for more than 50 % of China's annual NH 3 emissions, and large-scale pig farms represent a major anthropogenic source. However, the current systematic knowledge of NH 3 emissions characteristics from large-scale pig farms is still deficient, and there are insufficient studies localized for China. We conducted year-round intensive monitoring of NH 3 emissions from a representative large-scale pig farm in the Yangtze River Delta to quantify the interactions between growth stage and season. In terms of seasonal variation, NH 3 emissions peaked in summer at 3.95 kg NH 3 ·year −1 ·head −1 and were lowest in winter at 1.53 kg NH 3 ·year −1 ·head −1 . For the growth stages, we found that the average annual emission factors for piglet houses, nursery houses, fattening houses, gestation houses, and farrowing houses (with some piglets included) were 0.24, 0.84, 1.83, 3.55, and 5.61 kg NH 3 ·year −1 ·head −1 . In addition, this study found that temperature was the key driver of NH 3 emissions (mean Spearman's r = 0.66, P < 0.001), whereas the overall correlation for humidity was weaker, with emissions significantly suppressed only in winter when ventilation was inadequate (average r = 0.49, P < 0.001). Based on local conditions, the farm-level annual NH 3 emission factor was determined to be 2.45 kg NH 3 ·year −1 ·head −1 , highlighting the critical summer period for targeted mitigation. These findings provide a scientific basis for refining regional emission inventories and for developing stage- and season-specific abatement strategies that support PM2.5 control and the sustainable transformation of intensive pig production in the Yangtze River Delta. • A year-round NH 3 emission study on large-scale pig farm in Yangtze River Delta. • NH 3 emissions vary seasonally, highest in summer and lowest in winter. • NH 3 emissions vary by pig types, highest in farrowing sows and lowest in piglets. • Temperature drives NH 3 emissions; humidity effect is ventilation-dependent. • Localized annual emission factor established: 2.45 kg NH 3 ·year −1 ·head −1 .