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The effectiveness of national policies for air pollution control has been demonstrated, but the relative effectiveness of short-term emission reduction measures in comparison with national policies has not. Here we show that short-term abatement measures during important international events substantially reduced PM2.5 concentrations, but air quality rebounded to pre-event levels after the measures ceased. Long-term adherence to strict emission reduction policies led to successful decreases of 54% in PM2.5 concentrations in Beijing, and 23% in atmospheric nitrogen deposition in China from 2012 to 2020. Incentivized by "blue skies" type campaigns, economic development and reactive nitrogen pollution are quickly decoupled, showing that a combination of inspiring but aggressive short-term measures and effective but durable long-term policies delivers sustainable air quality improvement. However, increased ammonia concentrations, transboundary pollutant flows, and the complexity to achieving reduction targets under climate change scenarios, underscore the need for the synergistic control of multiple pollutants and inter-regional action. In response to the rebound of air pollution during large events in China, the authors propose that a combination of ambitious short-term measures and enduring long-term pollution control policies is a sustainable solution for improving air quality. [ABSTRACT FROM AUTHOR]

Elevated atmospheric reactive nitrogen (Nr) emissions and the subsequent nitrogen (N) deposition have negatively impacted the global environment, particularly in China. In order to assess the long-term trends in atmospheric N deposition in the south of China, Taojiang County in Hunan Province was selected as a representative rural area for study. We analyzed interannual variation in atmospheric Nr, including gaseous ammonia (NH3), nitrogen dioxide (NO2), nitrate acid (HNO3) vapor, particulate ammonium (NH4+), and nitrate (NO3−) in air and NH4+-N and NO3−-N in precipitation from 2011 to 2020. The 10-year average atmospheric wet-plus-dry N deposition was 41.9 kg N ha−1 yr−1, which decreased by approximately 24% after 2012, indicating that NH3 and NOx emissions were effectively reduced by emission controls introduced in 2013. Wet deposition accounted for approximately 74% of the total N deposition and was significantly influenced by annual precipitation amount. Reduced N (NH3, pNH4+, and NH4+ in rainwater) was the dominant form, comprising approximately 58% of the total N deposition, while oxidized N (pNO3−, NO2, HNO3, and NO3− in rainwater) accounted for 42% of the total N deposition. Atmospheric HNO3, NO2, and NH3 concentrations and deposition declined by 30–80% over the decade, while particulate NH4+ and NO3− concentrations and deposition remained at relatively stable levels, which suggests that ongoing research and policy should focus on rural particulate pollution. Future strategies must concentrate on the integrated control of NH3 and NOx emissions to mitigate air pollution and protect human health, particularly in rural areas because current abatement efforts are primarily directed toward urban areas and the industrial sector, whereas non-point source NH3 pollution, influenced mainly by agricultural activities, dominates in rural regions. [ABSTRACT FROM AUTHOR]

We present a model analysis that quantifies the influence of anthropogenic emission variations on the recent (2005–2015) and future (2030) changes in national scale nitrogen deposition in China and the interacting relationships between their emissions and depositions. We find that the 0.39 Tg N yr−1 increase in the dry deposition of reduced nitrogen (NHx) during 2007–2015 is dominated by the decrease in sulfur dioxides (SO2) emissions, which reduces the formation of ammonium (NH4+) aerosols from gas‐phase ammonia (NH3). Although the decrease in SO2 emissions led to conversion from wet to dry deposition of NHx, the NH4+ wet deposition increased by 0.75 Tg N yr−1 with large interannual variations driven by precipitation. Different from NHx, the oxidized nitrogen (NOy) deposition increased by 1.6 Tg N yr−1 from 2005 to 2011 and decreased by 1.1 Tg N yr−1 from 2011 to 2015, following the changes in nitrogen oxides (NOx) emissions. Based on the national scale emission‐deposition relationship estimated from model sensitivity experiments, we find that future emission control would reduce the NOy deposition by 2.4 ± 0.08 to 3.4 ± 0.12 Tg N yr−1 (49%–73%), but only lead to small decreases of 0.93 ± 0.05 to 1.2 ± 0.06 Tg N yr−1 (9%–14%) in NHx deposition in China from 2015 to 2030. The decrease in NOx and SO2 emissions under future scenarios would enhance the NHx dry deposition over domestic China, diminishing the effectiveness of the NH3 emission control. The results emphasize that stricter strategies for controlling agricultural NH3 emissions should be taken to alleviate the adverse environmental impacts from atmospheric nitrogen deposition. Plain Language Summary: China is a hotspot of atmospheric nitrogen deposition over the world due to rapid industrialization and intensified agricultural production. Based on the atmospheric chemistry model experiments, we quantify the response of nitrogen deposition in China to recent and future changes in anthropogenic emissions. We find that from 2007 to 2015, the increase in NHx dry deposition is dominated by the reduction in sulfur dioxides (SO2) emissions, while the increase in ammonium (NH4+) wet deposition is due to the increase in precipitation. Different from NHx, the NOy deposition peaked around 2011 and then decreased following the nitrogen oxide (NOx) emission reductions. Based on the future emission scenarios, we estimate that the future emission control in China can effectively reduce the NOy deposition by more than 49% but would only lead to a small decrease in NHx deposition in 2030 compared to 2015. This study highlights the importance of stricter strategies for controlling agricultural ammonia (NH3) emissions to alleviate the adverse environmental impacts from atmospheric nitrogen deposition in the future. Key Points: The decrease in SO2 emissions dominated the increase in NHx dry deposition flux from 2007 to 2015 in ChinaThe NOy deposition in China peaked around 2011 and then decreased following the NOx emission reductionsThe future emission control in China would effectively reduce the NOy deposition but only lead to small decrease in NHx deposition in 2030 [ABSTRACT FROM AUTHOR]

Aims: Litter decomposition is a crucial component of nutrient recycling. Short-term nitrogen (N) deposition has been shown to influence litter decomposition in temperate steppe with significant variability due to differences in atmospheric N deposition, species identity, and experimental duration. Therefore, the effect of N addition, especially long-term, on litter decomposition in alpine grassland still needs further investigation. Methods: To address these knowledge gaps, we examined the influence of long-term N addition on litter decomposition, taking advantage of a field experiment with five N addition levels (0, 10, 30, 90, and 150 kg N ha−1 yr−1) with a meta-analysis, which has been running for 11 years in an alpine grassland, Northwest China. Results: Long-term N addition consistently decreased litter decomposition rates, and N negative effect became stronger with the increasing N addition rates. Reduced litter decomposition rates were related to lower soil enzymes activities. Litter decomposition rates were strongly correlated with litter quality, but weakly correlated with soil quality, but which suggested that litter quality and soil quality played important role in regulating litter decomposition. Furthermore, a regional meta-analysis revealed that N addition accelerated litter decomposition when all data were averaged. Although N addition indirectly increased litter decomposition, it had no direct effect on decomposition. However, the direction and degree of the direct effect of N on litter decomposition were regulated by N addition rate, experimental duration and form of N fertilizer. Conclusions: Overall, these results demonstrated that long-term N addition decreased litter decomposition and N negative effect increased over time. [ABSTRACT FROM AUTHOR]

Lake Erhai is a potentially phosphorus (P)-limited lake and its water quality may have been affected by atmospheric P deposition. However, there have been few studies on atmospheric P deposition in this lake. In this study, we established five wet deposition monitoring sites and two dry deposition monitoring sites around Lake Erhai to quantify the wet and dry deposition of total phosphorus (TP), including dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP) and particulate phosphorus (PP) from July 2022 to June 2023. Wet deposition fluxes of P species were collected by automatic rainfall collection instrument, and dry deposition fluxes were estimated using airborne concentration measurements and inferential models. The results reveal that among the different P components, DOP had the highest contribution (50%) to wet TP deposition (average all sites 12.7 ± 0.7 mg P m2/yr), followed by PP (40%) and DIP (10%). Similarly, DOP (51%) was the major contributor to dry TP deposition (average two sites 2.4 ± 0.9 mg P m2/yr), followed by DIP (35%) and PP (14%). Wet deposition dominated the annual total TP deposition (wet plus dry), accounting for approximately 83%. The key seasons for dry deposition were spring and autumn, which accounted for 64% of the annual total dry TP deposition. In comparison, wet deposition was significantly higher in the summer, accounting for 73% of the annual total wet TP deposition. The results of the potential source contribution function and concentration-weighted trajectories analysis indicate that local source emission and long-range transport from surrounding cities jointly exerted a substantial influence on aerosol P concentrations, particularly in the eastern and northwestern regions of the lake. These findings provide a comprehensive understanding of the different P components in atmospheric deposition, which is beneficial for developing effective strategies to manage the P cycle in Lake Erhai. [Display omitted] • Wet and dry fluxes of P were 12.7 and 2.4 mg P/m2/yr in Lake Erhai, respectively. • DOP contributed 50% and 51% of total wet and dry P deposition fluxes, respectively. • Wet deposition peaked in summer, while dry deposition peaked in autumn or spring. • Total TDP deposition flux accounted for approximately 7% of the riverine TDP inputs. • Local emission sources and regional transport jointly affected P deposition. [ABSTRACT FROM AUTHOR]

Global changes in precipitation and atmospheric N deposition affect the geochemical cycle of the element and its hydrological cycle in the ecosystem. It may also affect the relationship between plant water use efficiency (WUE) and nutrients, as well as the relationship between plant nutrients. Desert ecosystems are vulnerable to global changes. Haloxylon ammodendron is the dominant species in the Asian desert. Revealing the variations in these relationships in H. ammodendron with precipitation and N deposition will enhance our understanding of the responses of plants to global change in terms of trade-off strategies of nutrient absorption, water and element geochemical cycles in desert ecosystems. Thus, we conducted field experiments with different amounts of water and N. This study showed that WUE of H. ammodendron was not correlated with nitrogen content (N), phosphorus content (P), and potassium content (K) when water and N supply were varied (p > 0.05 for WUE vs. N, P, and K), suggesting lack of coupling between water use and nutrient economics. This result was associated with the lack of correlation between plant nutrients and gas exchang in H. ammodendron. However, water addition, N addition and the interaction between both of them all played a role in the correlation between plant N, P and K owing to their different responses to water and N supplies. This indicates that global changes in precipitation and N deposition will affect N, P and K geochemical cycles in the Asian deserts dominated by H. ammodendron, and drive changes in the relationships between plant nutrients, resulting in changes in the trade-off strategy of plant absorption of N, P, and K. [ABSTRACT FROM AUTHOR]

The study of emissions and depositions of atmospheric reactive nitrogen species (N r s) in a region is important to uncover the sources and sinks of atmospheric N r s in the region. In this study, atmospheric total N r s depositions including both wet-only and dry deposition were monitored simultaneously across major land-use types in a 105 km2 catchment called Jinjing River Catchment (JRC) in subtropical central China from 2015 to 2016. Based on activity data and emission factors for the main N r s emission sources, ammonia (NH 3) and nitrogen oxides (NO x) emission inventories for the catchment were also compiled. The estimated total N r s deposition in JRC was 35.9 kg N ha−1 yr−1, with approximately 49.7 % attributed to reduced compounds (NH x), and 40.5 % attributed to oxidized (NO y). The total N r s emission rate in JRC was 80.4 kg N ha−1 yr−1, with 61.5 and 18.9 kg N ha−1 yr−1 from NH 3 and NO x emissions, respectively. Livestock excretion and fertilization were the two main contributing emission sources for NH 3 , while vehicle sources contributed the bulk of NO x emissions. The net atmospheric budgets of N r s in paddy field, forest, and tea field were +3.7, −36.1, and +23.8 kg N ha−1 yr−1, respectively. At the catchment scale, the net atmospheric budget of N r s was +47.7 kg N ha−1 yr−1, with +43.7 kg N ha−1 yr−1 of NH x and +4.0 kg N ha−1 yr−1 of NO y , indicating that the subtropical catchment was net sources of atmospheric N r s. Considering that excessive atmospheric N r emissions and deposition may cause adverse effects on the environment, effects should be conducted to mitigate the N r s emissions from agriculture and transportation, and increasing the area of forest is good for reducing the net positive budget of atmospheric N r s in the subtropical catchments in China. [Display omitted] • Mean atmospheric N r deposition was 36 kg N ha−1 yr−1 in a subtropical catchment in a 2-yr study. • Total N r emissions in catchment were 80 kg N ha−1 yr−1, with 62 kg N ha−1 yr−1 from NH 3 emissions. • The net N r budget showed high emissions due to NH 3 emissions from livestock and fertilization. • Paddy and tea fields were net sources of N r s, while forest was a net strong sink of N r s. Both atmospheric emissions and depositions of Nrs were high, and the net budget showed high emissions in a typical agricultural catchment in subtropical central China. [ABSTRACT FROM AUTHOR]

Quantifying the similarities and differences in atmospheric nitrogen (N) deposition between different ecosystems is important to develop effective measures to reduce air pollution and maintain biodiversity. Here we show that the constitution of N deposition differed significantly between a grassland and a desert ecosystem in Northwestern China. Flux of bulk (wet plus part of dry deposition) and dry (gaseous NH 3 and NO 2) deposition were continuously monitored from 2018 to 2020. The grassland and desert sites had similar amount of total N deposition, being 7.29 and 6.33 kg N ha−1 yr−1, respectively. However, N deposition at the grassland was dominated by the bulk deposition (4.44 kg N ha−1 yr−1, 61% of the total N deposition), whereas that at the desert was dominated by dry deposition (4.20 kg N ha−1 yr−1, 66% of total deposition). The desert had greater ambient concentrations of NH 3 (3.66 μg N m−3) and NO 2 (1.52 μg N m−3) than the grassland (2.73 μg NH 3 –N m−3 and 0.72 μg NO 2 –N m−3). The amount of reduced N deposition (NH 4 + and NH 3) was around 3 times of that of oxidized N deposition (NO 3 − and NO 2) in both ecosystems. The N deposition rates in both ecosystems have exceeded the critical load for the fragile ecosystems (5–10 kg N ha−1 yr−1), highlighting the importance of reducing N emission sources that are related with anthropogenic disturbance. [Display omitted] • The boundary of Tarim Basin and Tibet Plateau has relatively low N deposition. • Bulk and dry deposition dominated in grassland and desert, respectively. • The reduced/oxidized N ratio in N deposition was close to 3 in both ecosystems. • N deposition exceeded the minimum critical load value for sensitive ecosystems. [ABSTRACT FROM AUTHOR]

• The impacts of N deposition and its change on N flow was quantified. • The spatial impacts and the drivers of N deposition were observed. • The indirect N deposition contributed for 12.94% of the river N flow. • The change in N deposition induced the declining river N:P ratio. Atmospheric deposition has a significant impact on the nutritional status and limitations of aquatic ecosystems. However, the impacts have considerable uncertainty due to a lack of quantification of the indirect nitrogen (N) deposition, in terms of atmospheric-land surface-water bodies fluxes. In this study, we combined monitoring N deposition datasets with semi-distributed modeling to characterize the baseline N flow in tributary streams in the Three Gorges Reservoir Region of China, and predicted the varying impacts of indirect N deposition from 2006 to 2015. This study indicated that the indirect N deposition, as an important N source, accounted for 10.47% of the total N flow of tributary streams. The Clean Air Action or Carbon Neutral would induce a reduction of deposition and then reduced the tributary N flux by 0.45 × 104–1.09 × 104 T yr−1. Meanwhile, the declining N deposition would result in the tributary N: phosphorus (P) stoichiometry to 22.04, approaching from P limitation to N limitation. The variation in N/P ratio was smaller in agricultural watersheds than those forest- and grass-dominated watersheds. Our finding indicated that process toward mitigating water quality will be difficult without consideration the indirect impacts of N deposition, and attention should be paid to variations in nutrient limitation and the plankton communities of inland waters due to the variation of regional or global N deposition. [ABSTRACT FROM AUTHOR]