Zhiping Zhu

The mitigation of methane (CH₄) emissions from livestock production is crucial to China’s carbon neutrality. Here we established a high-spatiotemporal-resolution dataset of the country’s livestock CH₄ emissions from 1990 to 2020 using four large-scale national livestock greenhouse gas inventory surveys. We estimate CH₄ emissions to be 14.1 ± 2.0 Mt in 2020 and to increase by 13% until 2030 despite CH₄ intensity per kg animal protein having decreased by 55% in the past 30 years. Approximately half of the emissions come from 13% of all Chinese counties. The technical CH₄ mitigation potential is projected to be 36 ± 8% (4.4–6.9 Mt CH₄) in 2030, and reducing food loss and waste could mitigate an additional 1.6 Mt of CH₄. Overall, most CH₄ mitigation could be achieved by increasing animal productivity and coverage of lagoon storage at carbon prices below US$100 tCO₂e⁻¹, being more cost-effective than livestock nitrous oxide mitigation in China.

The size of livestock production in farming is an important factor influencing management strategies, and ultimately affects nitrogen use efficiency (NUE) and nitrogen emissions. Here, by using data from 390,000 farms covering four major livestock animal types across China in 2017, we investigate the relationship between the NUE, nitrogen losses and livestock farm size. Our results show that NUE increases with farm size for all livestock types, while nitrogen losses and manure recycling ratios vary between different livestock types, highlighting the need for tailored management strategies. By optimizing farm size through consolidation or splitting of farms for the specific livestock species at the county scale, while maintaining a constant level of feed supply, China would increase manure recycling to croplands by 6%, increase livestock production by 3% and reduce nitrogen losses by 259,000 tonnes (14%), which could bring notable benefits to environmental protection and food security.

Atmospheric ammonia (NH3) has multiple impacts on the environment, climate change and human health. China is the largest emitter of NH3 globally, with the dynamic inventory of NH3 emission remaining uncertain. Here, we use the high-resolution secondary national pollution survey, integrated satellite data, 15N isotope source apportionment and multiple models to better understand those key features of NH3 emissions and its impacts in China. Our results show that the total NH3 emissions were estimated to be 12.3 Tg yr-1 in 2017 with three emission peaks in April, June and October. NH3 emissions have contributed approximately 23% to secondary PM2.5 formation, a 19.7% increase in nitrogen loading of surface waters, while ammonium deposition led to a decrease in soil pH by 0.0035 units and an increase in the terrestrial carbon sink by 48.8 Tg C yr-1. Reducing agricultural NH3 emissions in China would contribute to the mitigation of air and water pollution challenges, saving damage costs estimated at around 22 billion US dollars due to avoided human and ecosystem health impacts.

Atmospheric ammonia (NH3) has multiple impacts on the environment, climate change and human health. China is the largest emitter of NH3 globally, with the dynamic inventory of NH3 emission remaining uncertain. Here, we use the high-resolution secondary national pollution survey, integrated satellite data, 15N isotope source apportionment and multiple models to better understand those key features of NH3 emissions and its impacts in China. Our results show that the total NH3 emissions were estimated to be 12.3 Tg yr-1 in 2017 with three emission peaks in April, June and October. NH3 emissions have contributed approximately 23% to secondary PM2.5 formation, a 19.7% increase in nitrogen loading of surface waters, while ammonium deposition led to a decrease in soil pH by 0.0035 units and an increase in the terrestrial carbon sink by 83.4 Tg C yr-1. Reducing NH3 emissions in China would contribute to the mitigation of air and water pollution challenges, saving damage costs estimated at around 22 billion US dollars due to avoided human and ecosystem health impacts.

Nearly one quarter of global meat production occurs in China, but a lack of detailed spatial livestock production data hinders ongoing pollution mitigation strategies. Here we generate high-resolution maps of livestock systems in China using over 480,000 farm surveys from 2007 to 2017, finding that China produced more livestock protein with fewer animals and less total pollution impact through better breeding, feeding and manure management in large-scale livestock farms. Hotspots of production can be observed across the North China Plain, Northeastern China and the Sichuan Basin. The Clean Water Act reduced manure nutrient losses to water by one third, but with limited changes to methane and ammonia emissions. Integrated production and consumption abatement measures costing approximately US$6 billion could further reduce livestock pollution by 2050, realizing benefits of up to US$30 billion due to avoided human health and ecosystem costs.

Media depth (MD) and moisture content (MC) are two important factors that greatly influence biofilter performance. The purpose of this study was to investigate the combined effect of MC and MD on removing ammonia (NH₃), hydrogen sulfide (H₂S), and nitrous oxide (N₂O) from swine barns. Biofiltration performance of different MDs and MCs in combination based on a mixed medium of wood chips and compost was monitored. A 3 × 3 factorial design was adopted, which included three levels of the two factors (MC: 45%, 55%, and 67% [wet basis]; MD: 0.17, 0.33, and 0.50 m). Results indicated that high MC and MD could improve NH₃ removal efficiency, but increase outlet N₂O concentration. When MC was 67%, the average NH₃ removal efficiency of three MDs (0.17, 0.33, and, 0.50 m) ranged from 77.4% to 78.7%; the range of average H₂S removal efficiency dropped from 68.1–90.0% (1–34 days of the test period) to 36.8–63.7% (35–58 days of the test period); and the average outlet N₂O concentration increased by 25.5–60.1%. When MC was 55%, the average removal efficiency of NH₃, H₂S, and N₂O for treatment with 0.33 m MD was 72.8 ± 5.9%, 70.9 ± 13.3%, and –18.9 ± 8.1%, respectively; and the average removal efficiency of NH₃, H₂S, and N₂O for treatment with 0.50 m MD was 77.7 ± 4.2%, 65.8 ± 13.7%, and –24.5 ±12.1%, respectively. When MC was 45%, the highest average NH₃ reduction efficiency among three MDs was 60.7% for 0.5 m MD, and the average N₂O removal efficiency for three MDs ranged from –18.8% to –12.7%. In addition, the pressure drop of 0.33 m MD was significantly lower than that of 0.50 m MD (p < 0.05). To obtain high mitigation of NH₃ and H₂S and avoid elevated emission of N₂O and large pressure drop, 0.33 m MD at 55% MC is recommended. Implications: The performances of biofilters with three different media depths (0.17, 0.33, and 0.50 m) and three different media moisture contents (45%, 55%, and 67% [wet basis]) were compared to remove gases from a swine barn. Using wood chips and compost mixture as the biofilters media, the combination of 0.33 m media depth and 55% media moisture content is recommended to obtain good reduction of NH₃ and H₂S, and to simultaneously prevent elevated emission of N₂O and large pressure drop across the media.