Youfan Chen

China is a global hotspot for reactive nitrogen (N_r) emissions driven by its large livestock sector, which contribute to air pollution, climate change, and biodiversity losses. Despite their importance, current emission inventory development efforts often address singular N_r species, lacking a comprehensive presentation of all N_r species together and their interconnected features. This may jeopardize China's achievements of carbon neutrality and clean air. In this study, we developed a high-resolution (0.1° × 0.1°) inventory of monthly N_r emissions from livestock manure in China for 23 livestock types from 2005 to 2022. Based on a unified dataset, our inventory provides detailed estimates of multiple N_r emissions from livestock, including ammonia, nitrogen oxides, and nitrous oxide. The inventory can serve as a valuable resource for atmospheric modelling and support integrated nitrogen management strategies in response to China's evolving agricultural landscape, facilitating future decision-making to tackle environmental challenges associated with the agriculture sector.

This study evaluates atmospheric reactive nitrogen deposition to the global ocean from 2010 to 2019 using the GEOS‐Chem model, quantifying the contributions of key anthropogenic and natural sources and examining the impacts of emissions and meteorological changes on interannual variations (IAVs). The average global oceanic nitrogen deposition is 40.7 Tg N yr ⁻¹ , with 78% deposited in the open ocean. Reduced nitrogen (NH _x ) and oxidized nitrogen (NO _y ) contribute equally predominantly through wet deposition (62%). Of the total nitrogen deposition to oceans, 39% originates from natural emissions, 33% from fuel combustion including shipping and aviation (11%), and 22% from agricultural activities. Transportation and agriculture are the major contributors in the Northern Hemispheric mid‐high latitude and Coastal biomes, whereas natural emissions are dominant in Trades and Southern Hemispheric biomes. Both wet and dry NO _y deposition decreases in the Northern Hemisphere mid‐high latitudes but increases in tropical biomes, whereas NH _x shows opposing changes in wet and dry deposition. Anthropogenic emissions drive over 60% of IAVs of oceanic nitrogen deposition except for the NH _x deposition over tropical biomes. Changes in anthropogenic emissions from combustion sources not only influence NO _y deposition through nitrogen oxides (NO _x ) emissions from fuel combustions but also lead to opposing trends in wet and dry NH _x deposition due to nonlinear chemistry of secondary inorganic aerosol formations. These findings highlight the need for integrated management strategies targeting multiple pollutants, including NO _x , ammonia (NH ₃ ), and sulfur dioxide (SO ₂ ) along with international regulations on shipping and aviation to effectively control nitrogen deposition over the ocean.

The adverse effects of the transportation of O₃ and its precursors on local air quality under certain meteorological conditions has long been recognized. Previous studies covered the effects of their transport without distinguishing specific forms (direct transport, via air pollutants originating from emissions outside the target regions; indirect transport, via air pollutants generated from chemical reactions between local and outside precursors) and processes (chemical and physical). This study aimed to figure out the effects of different scales of emissions on O₃ pollution in the Guanzhong basin (GZB) by quantifying the forms and processes of transport using the CAMx model. The results showed that the emissions on different scales had various pathways for influencing O₃ formation under two polluted, synoptic circulation types (southeast high and northeast ridge). Under the southeast high type, the meteorological conditions favored the chemical production of O₃, which led to the highest local O₃ contributions from the GZB. The prominent cross-regional transport was positive for indirect transport from south Shaanxi, implying the synergistic impacts of biogenic VOCs and urban pollutants in the GZB. With the southerly winds in the GZB, the downwind cities of Xi’an were impacted by positive direct and indirect transport from the emissions of Xi’an. These impacts occurred through the processes of gas-phase chemistry (especially O₃P + O₂ and O₃ + NO) and vertical advection. For the northeast ridge type, positive direct transport from the emissions of Henan Province was important for O₃ pollution in the GZB, as there were remarkable easterly airflows. From the east to the west of the GZB, the impacts from the emissions from Henan Province on cities in the GZB were reduced, which occurred through the processes of horizontal advection and vertical dispersion. This work highlights significant differences in the forms and processes of O₃ formation in downwind areas impacted by the emissions from different-scale emissions, and advances our knowledge of atmospheric pollutant transport and its impact on O₃ pollution.

Ammonia (NH₃) is critical to the nitrogen cycle and PM_2.5 formation, yet a great deal of uncertainty exists in its urban emission quantifications. Model-underestimated NH₃ concentrations have been reported for cities, yet few studies have provided an explanation. Here, we explore reasons for severe WRF-Chem model underestimations of NH₃ concentrations in Beijing in August 2018, including simulated gas-particle partitioning, meteorology, regional transport, and emissions, using spatially refined (3 km resolution) NH₃ emission estimates in the agricultural sector for Beijing-Tianjin-Hebei and in the traffic sector for Beijing. We find that simulated NH₃ concentrations are significantly lower than ground-based and satellite observations during August in Beijing, while wintertime underestimations are much more moderate. Further analyses and sensitivity experiments show that such discrepancies cannot be attributed to factors other than biases in NH₃ emissions. Using site measurements as constraints, we estimate that both agricultural and non-agricultural NH₃ emission totals in Beijing shall increase by ∼5 times to match the observations. Future research should be performed to allocate underestimations to urban fertilizer, power, traffic, or residential sources. Dense and regular urban NH₃ observations are necessary to constrain and validate bottom-up inventories and NH_x simulation.

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 (NH_x) 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 NH_x, the NH₄⁺ wet deposition increased by 0.75 Tg N yr⁻¹ with large interannual variations driven by precipitation. Different from NH_x, the oxidized nitrogen (NO_y) 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 (NO_x) emissions. Based on the national scale emission‐deposition relationship estimated from model sensitivity experiments, we find that future emission control would reduce the NO_y 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 NH_x deposition in China from 2015 to 2030. The decrease in NO_x and SO₂ emissions under future scenarios would enhance the NH_x 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.

The accurate estimation of ammonia emission is essential for quantifying secondary inorganic aerosol formation and reactive nitrogen deposition. During the last decades, both fertilizer type and the total amount of nitrogen fertilizer in China have changed, while the resulting changes in ammonia emissions and their spatio-temporal variations are unclear. In this study, we compile a long-term (2005–2020) high-resolution ammonia emission inventory for synthetic fertilizer in China with bottom-up method. We parameterized emissions factors (EFs) considering the impacts of soil properties, method of fertilizer application, fertilizer type, crop type, ambient temperature and wind speed. Meanwhile, the monthly nitrogen fertilizer application is calculated by detailed information on crop-specific fertilizer application practices. For the spatial distribution, the ammonia emissions from fertilizer mostly concentrate in eastern and southwestern China, coincident with the high density of agriculture activity and population in these regions. For the seasonal variation, the ammonia emissions from fertilizer application peak in spring and summer because of dense fertilizer application and high ambient temperature. For the long-term trend, we estimate that the emissions from synthetic fertilizer increased from 5.38 Tg in 2005 to 5.53 Tg in 2008 and remained nearly unchanged during 2008–2012, then decreased to 3.96 Tg in 2020. Urea, ammonium bicarbonate (ABC) and nitrogenous compound fertilizer are major fertilizer types used in China. Despite the increased use of nitrogen fertilizer, ammonia emissions remained stable throughout 2008–2012 with the declined use of ABC. This stable period also reflects ammonia emission increases in western China, offsetting the decreases in eastern China. Furthermore, our emission inventory provides a monthly estimation at a spatial resolution of 0.1 degrees, which can be applied to global and regional atmospheric chemistry model simulations.

Seven scenarios were designed to study the national environmental benefits of ULE in coal-fired power plants (CPPs), ULE in industrial coal burning (ICB) and NH₃ emission reduction by using the GEOS-Chem model. The results showed that although the CPPs have achieved the ULE transformation target, the PM_2.5 concentration across the country has decreased by 4.8% (1.4 μg/m³). Due to the complex non-linear chemical competition mechanism among nitrate and sulfate, the average concentration of nitrate in the country has increased by 1.5% (0.1 μg/m³), which has reduced the environmental benefits of the power plant emission reduction. If the ULE technology is applied to the ICB to further reduce NO_x and SO₂, although the PM_2.5 concentration can be reduced by 10.1% (2.9 μg/m³), the concentration of nitrate will increase by 2.7% (0.2 μg/m³). Based on the CPPs-ULE, NH₃ emissions reduced by 30% and 50% can significantly reduce the concentration of ammonium and nitrate, so that the PM_2.5 concentration is decreased by 11.5% (3.3 μg/m³) and 16.5% (4.7 μg/m³). Similarly, based on the CPPs-ICB-ULE, NH₃ emissions can be reduced by 30% and 50% and the PM_2.5 concentration reduced by 15.6% (4.4 μg/m³) and 20.3% (5.8 μg/m³). The CPPs and ICB use the ULE technology to reduce NO_x and SO₂, thereby reducing the concentration of ammonium and sulfate, causing the PM_2.5 concentration to decline, and NH₃ reduction is mainly achieved through reducing the concentration of ammonium and nitrate to reduce the concentration of PM_2.5. In order to better reduce the concentration of PM_2.5, NO_x, SO₂ and NH₃ emission reduction control measures should be comprehensively considered in different regions of China. By comprehensively considering the economic cost and environmental benefits of ULE in ICB and NH₃ emission reduction, an optimal haze control scheme can be determined.

Shifting towards more meat-intensive diets may have indirect health consequences through environmental degradation. Here we examine how trends in dietary patterns in China over 1980–2010 have worsened fine particulate matter (PM_2.5) pollution, thereby inducing indirect health impacts. We show that changes in dietary composition alone, mainly by driving the rising demands for meat and animal feed, have enhanced ammonia (NH₃) emissions from Chinese agriculture by 63% and increased annual PM_2.5 by up to ~10 µg m^–3 (~20% of total PM_2.5 increase) over the period. Such effects are more than double that driven by increased food production solely due to population growth. Shifting the current diet towards a less meat-intensive recommended diet can decrease NH₃ emission by ~17% and PM_2.5 by 2–6 µg m^–3, and avoid ~75,000 Chinese annual premature deaths related to PM_2.5.