China’s Nitrogen Deposition Falls, Yet Farm Emissions Now Drive the Damage

China’s skies have been quietly changing. For decades, the country’s breakneck industrial growth loaded the atmosphere with reactive nitrogen, a family of compounds that includes nitrogen oxides from smokestacks and tailpipes and ammonia from farms and livestock. When that nitrogen settles back to Earth through rain, snow, and the direct uptake of gases and particles by surfaces, it acts as an unintended and often harmful fertilizer, acidifying soils, choking waterways, and reshaping plant communities. A comprehensive new review published in Nature Reviews Earth & Environment now draws together the full arc of this four-decade story, and it reveals both a genuine policy success and a stubborn, growing problem rooted in agriculture.

The synthesis, led by Lei Liu and Xuejun Liu of China Agricultural University together with an international team spanning more than twenty institutions, compiles evidence from national monitoring networks and atmospheric chemistry models to reconstruct how reactive nitrogen deposition across China has shifted since 1980. The headline finding is striking: deposition climbed relentlessly for three decades, peaking at 16.4 teragrams of nitrogen per year during 2010 to 2012, before turning a corner. By 2020, total deposition had fallen 14 percent to 13.3 teragrams per year, a decline the authors attribute overwhelmingly to stringent industrial controls on nitrogen oxide emissions.

The mechanics of that turnaround deserve attention. Nitrogen oxides are produced when fossil fuels burn at high temperatures, in power plants, factories, cement kilns, and vehicle engines. Once emitted, they transform in the atmosphere into nitric acid and nitrate aerosols that are scavenged by precipitation or deposited dry onto canopies and soils. Beginning in the early 2010s, China rolled out aggressive emission reduction programs, including ultra-low emission standards for the power sector and tightening vehicle regulations. Satellite observations of nitrogen dioxide columns documented steep drops in pollution hotspots, and the deposition record followed. The review reports that oxidized nitrogen deposition declined by 34 percent, accounting for nearly all of the observed national reduction.

But here is the twist that gives the review its urgency: while oxidized nitrogen fell, reduced nitrogen, the ammonia and ammonium compounds largely traced to agriculture, kept rising. Reduced nitrogen now constitutes 60 to 70 percent of total deposition across China, a share that has transformed the chemistry of the problem. Ammonia escapes from fertilized fields, manure heaps, and livestock operations, and unlike nitrogen oxides it has faced almost no targeted regulation. Adding to the complexity, declining sulfur dioxide emissions have reduced the formation of ammonium sulfate aerosols, which in turn leaves more free ammonia in the atmosphere and can even enhance ammonia and ammonium deposition, a feedback known as the ammonia compensating effect.

The ecological consequences of this agricultural dominance are documented in sobering detail. Widespread soil acidification is depleting base cations such as calcium and magnesium from croplands and forests, with long-term measurements across Chinese forest ecosystems showing significant pH declines. Freshwater systems are suffering too; atmospheric nitrogen input to lakes such as Taihu contributes measurably to eutrophication, fueling algal blooms that degrade drinking water supplies. Biodiversity is under pressure as nutrient enrichment favors fast-growing species over the specialized plants of grasslands and other nutrient-poor habitats, with experimental nitrogen addition studies in Chinese grasslands and tropical forests documenting species losses and shifts in community composition.

The review quantifies the scale of the policy challenge with a critical loads analysis, the standard framework for assessing how much nitrogen an ecosystem can absorb before harm occurs. As of 2020, roughly 15 percent of China’s land area still receives reactive nitrogen deposition exceeding the critical load for eutrophication, meaning ecosystems in those zones are being over-fertilized beyond their capacity to cope. The authors warn that climate change will make matters worse, because warming and intensified precipitation extremes are projected to reduce ecosystem resilience, thereby expanding the terrestrial area where deposition exceeds critical loads even if emissions remain flat.

To put China’s situation in global perspective, the team calculated what reductions would be needed to match the average nitrogen deposition levels currently experienced in the United States and Western Europe, regions that themselves wrestled with and partially tamed this problem over recent decades. The answer is dramatic: China would need to cut ammonia deposition by 56 to 76 percent and nitrogen oxide deposition by 53 to 60 percent. Those numbers underscore that despite genuine progress, Chinese ecosystems remain bathed in nitrogen at rates several times higher than their Western counterparts, with the gap driven primarily by the unrestrained agricultural ammonia component.

Why has ammonia escaped regulation for so long? Part of the answer is practical. Agricultural ammonia emissions come from millions of smallholder farms spread across vast territories, making them far harder to monitor and control than a few hundred power plants. Fertilizer overuse remains endemic in parts of Chinese agriculture, and manure management is often rudimentary. Yet the review notes that cost-effective mitigation options exist, from optimized fertilizer application and enhanced-efficiency products to improved livestock housing and manure storage. Research on smallholder ammonia mitigation campaigns has shown that air quality can improve while cereal yields are maintained, and economic analyses suggest the societal benefits of halving agricultural ammonia emissions in China far exceed the abatement costs.

The authors argue that the way forward requires integrating agricultural ammonia management into the broader architecture of climate and air quality policy, rather than treating it as a separate agricultural issue. This means connecting nitrogen policy to food system reform, including improvements in nitrogen use efficiency across the entire chain from fertilizer production to livestock feed to human diets. It also means anticipating the interactions between pollution control and climate, since a warmer, wetter future will alter both the emissions of ammonia from soils and livestock and the atmospheric processes that deposit nitrogen back to the surface. The review’s framework positions nitrogen deposition abatement as inseparable from the sustainability of China’s food systems.

For the world beyond China, the study offers both a template and a warning. The 34 percent drop in oxidized nitrogen deposition proves that determined industrial emission control can bend the curve on one of the most stubborn forms of air pollution, a lesson relevant to rapidly developing economies across Asia and Africa where nitrogen oxide emissions are still climbing. But the simultaneous rise in reduced nitrogen shows that solving the industrial half of the problem while ignoring agriculture simply shifts the burden. As global food demand grows and nitrogen fertilizer use expands, the Chinese experience makes clear that comprehensive nitrogen management, spanning smokestacks, tailpipes, fields, and barns alike, is the only route to protecting ecosystems while feeding a nation.

Subject of Research: Drivers, trends and ecological impacts of atmospheric reactive nitrogen deposition in China

Article Title: Drivers, trends and impacts of nitrogen deposition in China

Article References: Liu, L., Liu, X., Wang, X., Xu, W., Tang, A., Du, E., Duan, L., Pan, Y., Zhang, L., Shen, J., Song, L., Li, K., Zhou, X., Lu, X., Zhao, Y., Yu, Q., Li, M., Zhang, X., Wen, Z., … Zhang, F. (2026). Drivers, trends and impacts of nitrogen deposition in China. Nature Reviews Earth & Environment. https://doi.org/10.1038/s43017-026-00830-x

Image Credits: AI Generated

DOI: 10.1038/s43017-026-00830-x

Keywords: nitrogen deposition, reactive nitrogen, ammonia emissions, nitrogen oxides, soil acidification, eutrophication, critical loads, China, air quality, agriculture, ecosystem health, emission controls