Nitrate Deposition Research Articles

Fabrication of tricobalt tetraoxide thinfilm photocatalyst from cobalt nitrate deposition by a novel spark method

Tricobalt tetraoxide (Co3O4) thinfilm was successfully deposited for the first time by a novel sparking method through a two-step process, which includes cobalt nitrate deposition and subsequent thermal treatment at 300 °C. The formation mechanism of Co3O4 deposition by sparking process from highly pure cobalt wire is elucidated in detail. Deposited Co3O4 thinfilms under different spark repetition rates were intensely characterized and employed as an effective photocatalyst for degradation of organic dye. Notably, the maximum degradation of organic dye was observed for the catalytic thinfilm deposited at low repetition rate owing to its low band gap and porous morphology with smaller size grains, which may lead to the contribution of more charge carriers in the photocatalytic reaction.

Changes in source composition of wet nitrate deposition after air pollution control in a typical area of Southeast China

In recent years, China has adopted numerous policies and regulations to control NOx emissions to further alleviate the adverse impacts of NO3−-N deposition. However, the variation in wet NO3−-N deposition under such policies is not clear. In this study, the southeastern area, with highly developed industries and traditional agriculture, was selected to explore the variation in NO3−-N deposition and its sources changes after such air pollution control through field observation and isotope tracing. Results showed that the annual mean concentrations of NO3−-N in precipitation were 0.67 mg L−1 and 0.54 mg L−1 in 2014–2015 and 2021–2022, respectively. The average wet NO3−-N depositions in 2014–2015 and 2021–2022 was 7.76 kg N ha−1 yr−1 and 5.03 kg N ha−1 yr−1, respectively, indicating a 35% decrease. The δ15N–NO3− and δ18O–NO3− values were lower in warm seasons and higher in cold seasons, and both showed a lower trend in 2021–2022 compared with 2014–2015. The Bayesian model results showed that the NOx emitted from coal-powered plants contributed 53.6% to wet NO3−-N deposition, followed by vehicle exhaust (22.9%), other sources (17.1%), and soil emissions (6.4%) during 2014–2015. However, the contribution of vehicle exhaust (33.3%) overpassed the coal combustion (32.3%) and followed by other sources (25.4%) and soil emissions (9.0%) in 2021–2022. Apart from the control of air pollution, meteorological factors such as temperature, precipitation, and solar radiation are closely related to the changes in atmospheric N transformation and deposition. The results suggest phased achievements in air pollution control and that more attention should be paid to the control of motor vehicle exhaust pollution in the future, at the same time maintaining current actions and supervision of coal-powered plants.

Knowing your limits: Patterns and drivers of nutrient limitation and nutrient–chlorophyll relationships in US lakes

AbstractAlthough understanding nutrient limitation of primary productivity in lakes is among the oldest research priorities in limnology, there have been few broad‐scale studies of the characteristics of phosphorus (P)‐, nitrogen (N)‐, and co‐limited lakes and their environmental context. By analyzing 3342 US lakes with concurrent P, N, and chlorophyll a (Chl a) samples, we showed that US lakes are predominantly co‐limited (43%) or P‐limited (41%). Majorities of lakes were P‐limited in the Northeast, Upper Midwest, and Southeast, and co‐limitation was most prevalent in the interior and western United States. N‐limitation (16%) was more prevalent than P‐limitation in the Great Basin and Central Plains. Nutrient limitation was related to lake, watershed, and regional variables, including Chl a concentration, watershed soil, and wet nitrate deposition. N and P concentrations interactively affected nutrient–chlorophyll relationships, which differed by nutrient limitation. Our study demonstrates the value of considering P, N, and environmental context in nutrient limitation and nutrient–chlorophyll relationships.

Low-temperature NOx reduction over Cu-LTA and SmMnOx composite catalysts

Low-temperature selective catalytic reduction of NOx with ammonia (NH3-SCR) over zeolite catalysts remains a great challenge in diesel exhaust purification. Herein, Cu-LTA zeolite with excellent hydrothermal stability was composited with a small proportion of SmMnOx oxides, the composite catalytic system efficiently resolves the low-temperature activity challenge encountered by Cu-LTA. The promoting pathways revealed the presence of active nitrite intermediates formed on SmMnOx by activating NO, that were able to migrate to the Cu-LTA and can be further decomposed on the Brønsted acid sites. Compared to the continuous deposition of nitrates in Cu-LTA, the presence of SmMnOx in composite catalysts efficiently reduced the accumulation of inert nitrate and improved the nitrate deposition phenomena. This innovative research would provide a rational strategy to break the barrier of limited low-temperature performance faced by zeolite catalysts, effectively promoting the NOx removal in vehicles sources.

A Strategic NH3-Dosing Approach for the Minimization of N2O Production During NH3-SCR Reactions over Cu-SSZ-13 Catalysts

AbstractThe undesired production of N2O during NH3-SCR reactions is investigated over a reference commercial Cu-CHA catalyst. Steady-state experiments performed in the 150–500 °C temperature range exhibit a bimodal trend in the N2O formation profile, confirming the existence of two different reaction mechanisms occurring at low and high temperatures. Focusing on a low-to-medium T-range, N2O production, usually ascribed to NH4NO3 formation and decomposition, increases with the NO2/NOx ratio. However, an excess of NO2 leads to a decrease in the N2O release due to ammonium nitrate deposition and catalyst clogging phenomena. Steady-state and dynamics experiments show the promoting effect of both NH3 feed concentration and NH3 storage on N2O production at T > 200 °C. Surprisingly, N2O decreases with increasing NH3/NOx ratio at lower temperature. A novel approach based on the strategic injection of NH3 is also applied to mitigate the N2O formation while maintaining high deNOx activity. Remarkably, complete NOx conversion and ~ 11% N2O saving are achieved (with inlet NO2/NOx = 0–0.5) at temperatures exceeding 200 °C; in addition, a peculiar behavior is observed in the N2O profile, which increases and decreases when adding and removing NH3 from the feed, respectively. Notably, the opposite trend is observed in the N2O profile at 200 °C. When under Standard SCR conditions, this so far unreported observation challenges the NH4NO3 formation route for N2O and suggests the existence of different controlling phenomena at different temperature regimes: i) the Cu/redox chemistry at T ≤ 200 °C and ii) the NH3 storage at higher temperature, ideally up to 300 °C.

Water Point and Non-Point Nitrogen Pollution Due to Land-Use Change and Nitrate Deposition in China from 2000 to 2020

Water N-NO3− (mg L−1) pollution is attracting global concern in the face of combating climate change and human health risks. However, there have been comparatively few comprehensively researched studies on water N-NO3− pollution with respect to N-NO3− deposition, soil nitrogen, and land-use changes. We collected a total of 7707 published sampling points on N-NO3− surface and groundwater during flooding and non-flooding seasons during 2000–2020 in China. The types of water N-NO3− pollution (>20) can be categorized as point pollution (ΔTN ≤ 0 or > 1.5) and non-point pollution (0 < ΔTN ≤ 1.5), which were then assessed with respect to soil nitrogen (ΔTN g kg−1) and water N-NO3− changes in this study. We found non-point pollution was concentrated in the Huaihe River Basin and Haihe River Basin with higher urbanization (+6%, +4%), cropland (72%, 45%), nitrogen fertilization (g m−2 yr−1) (>10), and increased wet N-NO3− deposition (WND) (kg ha−1 yr−1) (+4.6, +3). The Haihe River Basin was found to have the highest N-NO3− on its surface (306) and in its groundwater (868) and nitrogen fertilization (32). Point pollution was concentrated in the Songhua and Liaohe River Basin with the highest WND (+7.9) but slow urbanization (+1%). N-NO3− increased during the flooding season compared with the no-flooding season in serious pollution areas. N-NO3− increased in the Liaohe River and middle and low Yangtze River but was reduced in the Weihe River. Therefore, stringent criteria and management, especially during the flooding season are urgently required to mitigate the degree of N-NO3− water pollution that occurs due to intensive agriculture and urbanization with increased N-NO3− deposition.

Revealing the two distinctive roles of HY zeolite in enhancing the activity and durability of manganese oxide-zeolite hybrid catalysts for low-temperature NH3-SCR

Recently, metal oxide-zeolite hybrid systems have shown promise in enhancing catalytic performance in low-temperature selective catalytic reduction (SCR), but not much is known as to mechanistic details. The purpose of this study is to examine fluctuations in low-temperature activity contingent upon the presence or absence of zeolite and to elucidate a dual functional mechanism of mixed zeolite in improving the catalytic performance of MnOx, which is closely related to inter-particle diffusion of nitrite and nitrate species from MnOx to zeolite. Firstly, strong Brønsted acid sites on zeolite demonstrate a significantly faster reduction of diffused nitrite species compared to Brønsted/Lewis acid sites on MnOx. More importantly, we discovered that zeolite prevents ammonium nitrate deposition by absorbing and decomposing diffused nitrate species from MnOx. Such distinct interaction between zeolite and both nitrite and nitrate species clarified here will be of great promise in designing future hybrid catalytic materials for low-temperature NH3-SCR reactions.

Electrochemical polymerization of PEDOT:PSS with graphene oxide and silver nanoparticles for antibacterial coating and SERS detection

This study involved the use of electrochemical polymerization to coat poly(3,4-ethylenedioxythiophene) (PEDOT), polystyrene sulfonate (PSS) and graphene oxide (GO) onto SUS316L stainless steel substrates, aiming to produce PEDOT:PSS and GO@PEDOT:PSS films. Following this, Ag@PEDOT:PSS and GO/Ag@PEDOT:PSS films were developed through the electrochemical deposition of silver nitrate. Electrochemical impedance spectroscopy (EIS) indicated that adding GO increased the impedance of film, while AgNPs deposition decreased it, thereby enhancing conductivity. Films with AgNPs showed surface enhanced Raman scattering (SERS) effects, as assessed using malachite green (MG). Compared to films without GO, the GO/Ag@PEDOT:PSS films exhibit enhanced conductivity and SERS detection performance due to the negatively charged functional groups on the GO surface forming a continuous layer of AgNPs. Moreover, antibacterial capabilities were evaluated through bacterial attachment and inhibition zone assays. Both Ag@PEDOT:PSS and GO/Ag@PEDOT:PSS films were effective in inhibiting bacterial adhesion, achieving up to 99.4 % and 99.0 % inhibition, respectively. In the inhibition zone assays, the GO/Ag@PEDOT:PSS film showed a 1.33 times increase in antibacterial efficacy compared to Ag@PEDOT:PSS. Furthermore, the effectiveness of electrodepositing antibiotics on these substrates was investigated, confirming optimal antibacterial performance. This efficacy is attributed to the synergistic interaction between silver nanoparticles and antibiotics, potentially reducing the need for antibiotics. The findings of this study highlight its significant potential for applications in antibacterial treatments and biomedical detection.

Research progress on nitrate isotope coupled multi-tracer tracing groundwater nitrate pollution

Nitrate pollution in groundwater has become a global concern. One of the most important issues in controlling the nitrate pollution of groundwater is to identify the pollution source quickly and accurately. In this review, we firstly summarized the isotopic background values of potential sources of nitrate pollution in groundwater in 17 provinces (cities, autonomous regions) and 29 study areas in China, which could provide the fundamental database for subsequent research. Secondly, we reviewed the research progress of nitrate isotopes combined with multiple tracers for tracing nitrate in groundwater, and discussed their applicable conditions, advantages, and disadvantages. We found that halides and microorganisms combined with nitrate isotopes could accurately trace the pollution sources of domestic sewage, excrement and agricultural activities. The combination of Δ17O and nitrate isotopes could effectively distinguish the source of atmospheric deposition of nitrate in groundwater. The combination of groundwater age and nitrate isotopes could further determine the time scale of nitrate pollution. In addition, we summarized the application cases and compared the characteristics of mass balance mixing model, IsoSource model, Bayesian isotope mixing model, and EMMTE model for quantitative identification of nitrate pollution in groundwater. For the complexity and concealment of groundwater pollution sources, the coupling of nitrate isotopes with other chemical and biological tracing methods, as well as the application of nitrate isotope quantitative models, are effective tools for reliably identifying groundwater nitrate sources and transformation processes.

Nitrogen compounds at Mexican and USA coasts on the Gulf of Mexico

In recent decades, anthropogenic emissions in the Gulf of Mexico have caused a deterioration in air quality in surrounding areas, mainly due to particulate matter, sulfur dioxide and nitrogen dioxide. Over this period, interest in reactive nitrogen compounds has increased due to their relationships to air quality and ecosystem impacts associated with atmospheric deposition. In this study we summarize air concentrations of nitrogen dioxide in ambient air and wet atmospheric deposition of nitrate and ammonium along the southern coast of the United States of America and eastern Mexico over the period 2017 to 2020. The highest concentrations of ammonium and nitrate were observed in precipitation at Texas and sites in Mexico, although the highest rates of atmospheric deposition were observed in Florida and Louisiana. The ratio between ammonium and nitrate in precipitation was higher at Mexican stations than in studied sites in the United States, influenced by meteorological factors, atmospheric emissions, and characteristic air mass transport in the region. Back trajectory modeling showed the importance of the seasonality of the wind in the transport of nitrogen compounds of local and regional origin that affect Veracruz.

A comprehensive observation of organic and inorganic nitrogen in gases, particulate matter and precipitation in the northern suburb of Nanjing, East China, with an emphasis on size-resolved particulate nitrogen

China is considered one of the nitrogen deposition hotspots in the world. Measurements to date have focused mainly on inorganic nitrogen, organic nitrogen and the size distribution of particulate nitrogen has yet to be studied. Lack of dry deposition observations imposes a reliance on models, resulting in a much larger uncertainty relative to wet deposition which is routinely measured. In this study, dry and wet organic and inorganic nitrogen deposition were comprehensively measured in Nanjing in 2019, and nitrogen species in size-segregated particles were investigated. Total annual nitrogen deposition flux was up to 29.96 kg N ha−1 yr−1 in Nanjing, with wet deposition contributed slightly more (51.90%) to total deposition than dry deposition (48.10%). Observations revealed that reduced nitrogen (NHx = NH3 + NH4+) contributed 65.49% of the total inorganic nitrogen deposition budget, which implied that the control of reduced N in urban environments is needed to improve local air quality. Dry deposition of ammonia played an especially key role in dry deposition, contributing from 18.17% to 55.91% in different seasons. The deposition flux of water-soluble organic nitrogen (WSON) dominated by wet deposition, with the wet WSON about 4.6 times higher than that of dry deposition and contributed 41.18% of the wet nitrogen deposition. The wet N deposition in summer was significantly higher than in the other three seasons. The seasonal patterns in dry deposition were driven mostly by seasonal concentration patterns. The highest deposition of ammonia occurred in summer, while the deposition of nitrogen dioxide, particulate ammonium and nitrate peaked in winter. The maximum dry and wet WSON deposition appeared in autumn. Higher NH4+ concentration almost distributed in each size bin and centered in ranges of 0.18–1.0 μm, while higher NO3− concentration scattered in particle size ranges of 1.8–5.6 μm and 0.18–1.0 μm.

Finite sample corrections for average equivalence testing.

Average (bio)equivalence tests are used to assess if a parameter, like the mean difference in treatment response between two conditions for example, lies within a given equivalence interval, hence allowing to conclude that the conditions have "equivalent" means. The two one-sided tests (TOST) procedure, consisting in testing whether the target parameter is respectively significantly greater and lower than some pre-defined lower and upper equivalence limits, is typically used in this context, usually by checking whether the confidence interval for the target parameter lies within these limits. This intuitive and visual procedure is however known to be conservative, especially in the case of highly variable drugs, where it shows a rapid power loss, often reaching zero, hence making it impossible to conclude for equivalence when it is actually true. Here, we propose a finite sample correction of the TOST procedure, the -TOST, which consists in a correction of the significance level of the TOST allowing to guarantee a test size (or type-I error rate) of . This new procedure essentially corresponds to a finite sample and variability correction of the TOST procedure. We show that this procedure is uniformly more powerful than the TOST, easy to compute, and that its operating characteristics outperform the ones of its competitors. A case study about econazole nitrate deposition in porcine skin is used to illustrate the benefits of the proposed method and its advantages compared to other available procedures.

Exploration of the Mn-O coordination regulated reaction stability of manganese oxides in NH3-SCR: Effect of deposited ammonium nitrates

Manganese oxide-based catalysts exhibit excellent low-temperature denitration efficiency, making them potential candidates for application. Herein, the relationship between reaction stability and phase structure for MnO2, Mn2O3 and Mn3O4 was disclosed. The NO conversion for Mn2O3 drastically reduced after 120 h reaction, while minor decline was detected for MnO2 and Mn3O4. Based on dedicate qualitative and quantitative analyses on the deposits over catalyst surface, deactivation trigged by ammonium nitrate (AN) deposition was confirmed. Different from penta-coordinated Mn4+ on MnO2 (110) and tri-coordinated Mn2+, penta-coordinated Mn4+ on Mn3O4 (101), the unique tetra-coordinated Mn3+ on Mn2O3 (200) could stabilize the nitrates and make it difficult to be removed via decomposition or reaction and accumulate continuously, which resulted in the significant deactivation. This research could not only unveil the poisoning mechanism of MnOx based catalysts, but also provide new insights into the relationship between the catalytic stability and surface Mn-O microstructure.

Estimating atmospheric nitrogen deposition within a large river basin using moss nitrogen and isotope signatures

Assessing flux and primary sources of the atmospheric nitrogen (N) deposition with high spatial resolution remained challenging. The epilithic moss is considered a suitable biological monitor to explore N deposition. Our study presented a detailed analysis of flux and major source contributions of ammonium (NH4+) and nitrate (NO3−) deposition using N and δ15N signatures of epilithic moss collected densely from the Yangtze River basin. The results showed a more negative δ15N and higher N concentration of the moss in cropland and urban area than in forest and grassland of the basin. A gradient of the estimated N deposition (9.6–34.0 kg ha−1 yr−1) occurred from the Tibetan Plateau to lower reaches, with amount of NH4+ was approximately three times higher than NO3− deposition. The contribution from volatilization to NH4+ deposition (33.28 ± 8.10%) was less than the contribution from combustion (66.72 ± 8.10%), inconsistent with the traditional findings that N fertilizer and livestock waste are the principal sources of NH3 emissions. Fossil fuel was the dominant sources of NO3− deposition, accounted for 70.22 ± 18.67%. From 2006 to 2019, the source contribution of N deposition in forest remained unchanged, while NH3 volatilization and fossil fuel emitted NOx in urban areas have increased. Our findings highlighted the importance of combustion sources to N deposition in the Yangtze River basin.

Patterns and drivers of atmospheric inorganic nitrogen deposition in Northeast Asia

Elevated nitrogen (N) deposition due to intensified emissions of NH3 and NOx is a global problem with profound consequences on living organisms and the environment. Although N emission rates are currently considered to be high in East Asia, reports on the current N deposition level and composition are still limited, especially in northeastern China, where official N deposition monitoring sites are unavailable. This limits our understanding of the spatio-temporal N deposition patterns and their influencing factors at regional to continental scales. Here, we used data collected mostly during 2019 at 38 sites, comprising 7 sites in northeastern China and 31 EANET (Acid Deposition Monitoring Network in East Asia) sites in middle and east Russia, Mongolia, central and southern China, South Korea and Japan to explore the spatial-seasonal variations and drivers of ammonium and nitrate deposition across the Northeast Asia. Total bulk inorganic N (TIN) deposition was 3.7–24.5 kg N ha−1 yr−1 and NH4+-N/NO3−-N ratio in the TIN was 0.8–2.8 in northeastern China. The bulk/wet TIN deposition averaged 7.5 kg N ha−1 yr−1 (predominantly in the form of ammonium-N: NH4+-N/NO3−-N = 1.4) over the Northeast Asia region, with the highest rates being observed in northeastern China (11.6), as well as central and southern China (10.7), followed by east Russia, South Korea and Japan (5.6), and the lowest in middle Russia and Mongolia (1.5). This regional bulk/wet TIN deposition level is about twice of the wet TIN deposition level in Europe and the United States. The TIN deposition in summer and spring was 45–467% higher than in autumn and winter. Out of the ten land uses considered, only agricultural and urban land uses significantly positively correlated with NH4+-N and NO3−-N deposition rates across all monitored sites. This study suggests that the ongoing agricultural and urban expansions are likely to enhance N deposition and its associated effects across global ecosystems.

Hybrid Ceramic Self-Healing Coatings for Corrosion Protection of Al Alloys in 3% NaCl Solution

This work focuses on the development of sol–gel self-healing coatings for corrosion protection of Al alloys. The use of this method will help to reduce the costs associated with the coating as well as their environmental impact. Coatings were made of a titania matrix loaded with microparticles of poly(vinyl-alcohol) (PVA) containing cerium nitrate as an inhibitor. The PVA particles dissolve in water, so that the cerium nitrate deposits on the Al surface subjected to corrosion. The PVA microspheres were made via the emulsion method, and then loaded with cerium nitrate. The amount of cerium nitrate loaded in the microspheres was evaluated using UV–Vis. As a second step, the titania coating with embedded PVA microspheres loaded with cerium nitrate was deposited on an AA6082 substrate via a sol–gel route. The corrosion resistance of the coated samples was tested in NaCl solution. The coating microstructure, before and after the corrosion tests, was analysed with the use of an SEM (scanning electron microscope) and EDS (energy dispersive spectroscopy), while the corrosion resistance was investigated by EIS (electrochemical impedance spectroscopy). The results showed that the coatings were uniform and compact. They also showed the ability of the hybrid TiO2-based coating to provide protection for the AA6082 from corrosion. The coatings with an induced defect (scratch) were also analysed, and the EIS analysis of the coatings over time showed an increase in resistance, confirming the ability of the coating to heal itself.

Impact of Air Refreshing and Cloud Ice Uptake Limitations on Vertical Profiles and Wet Depositions of Nitrate, Ammonium, and Sulfate

AbstractThe impacts of cloud mixing and uptake on wet scavenging are not adequately resolved in global models which can lead to an overestimation of the removal of water‐soluble gases and aerosols from the atmosphere. To address this issue, we develop and implement novel parameterizations to consider the impacts of these processes. Our analysis of vertical profiles of nitric acid, inorganic nitrate, ammonium, and sulfate concentrations during the Atmospheric Tomography Mission periods indicates that air refreshing limitation has a significant impact above 800 hPa, while cloud ice uptake limitation plays an important role above 500 hPa. Incorporating these two processes resulted in a reduction of wet depositions of these species across source regions and a slight increase in their downwind regions. Wet depositions of nitrate, ammonium, and sulfate were reduced in source regions by 22.7%, 8.4%, and 8.3%, respectively and increased in downwind regions by 10.1%, 7.0%, and 4.3%, respectively.

A distinctive latitudinal trend of nitrogen isotope signature across urban forests in eastern China.

Rapid urbanization has greatly altered nitrogen (N) cycling from regional to global scales. Compared to natural forests, urban forests receive much more external N inputs with distinctive abundances of stable N isotope (δ15 N). However, the large-scale pattern of soil δ15 N and its imprint on plant δ15 N remain less well understood in urban forests. By collecting topsoil (0-20 cm) and leaf samples from urban forest patches in nine large cities across a north-south transect in eastern China, we analyzed the latitudinal trends of topsoil C:N ratio and δ15 N as well as the correlations between tree leaf δ15 N and topsoil δ15 N. We further explored the spatial variation of topsoil δ15 N explained by corresponding climatic, edaphic, vegetation-associated, and anthropogenic drivers. Our results showed a significant increase of topsoil C:N ratio towards higher latitudes, suggesting lower N availability at higher latitudes. Topsoil δ15 N also increased significantly at higher latitudes, being opposite to the latitudinal trend of soil N availability. The latitudinal trend of topsoil δ15 N was mainly explained by mean annual temperature, mean annual precipitation, and atmospheric deposition of both ammonium and nitrate. Consequently, tree leaf δ15 N showed significant positive correlations with topsoil δ15 N across all sampled plant species and functional types. Our findings reveal a distinctive latitudinal trend of δ15 N in urban forests and highlight an important role of anthropogenic N sources in shaping the large-scale pattern of urban forest 15 N signature.

Adaptive forest management

Adaptive management is the basic concept of forest ecosystem management strategy in conditions of increased risks. Therefore, there is a need to develop key theories and information on which adaptive forest management is based. Adaptive management of forest resources has become the premise of modern forestry development strategies in Europe, and the main ideas about this method of management have developed primarily on the knowledge of forest ecology. Adaptive management is the monitoring of activities (monitoring) in order to adjust future activities to the desired effects of management. The main causes that have influenced the application of adaptive management in forestry are related to strategic forestry principles and global challenges. Forest ecosystems are exposed to natural and social risks that cause disturbances and adverse effects of management. In order to reduce the risk for the realization of strategic goals in forestry, there is a need to develop management mechanisms for the adaptation of forest ecosystems. Global activities, in addition to the implementation of measures for mitigation (mitigation) of climate change, include measures for adaptation (adaptation) to climate change, especially for underdeveloped countries and developing countries, in order to ensure sustainable development and mitigate the negative consequences for forest ecosystems. It is necessary to go beyond the management framework based mainly on a simplified balance between volume, increment and stature, and to systematically integrate the results of all interventions and external influences on forests in order to improve the condition of forests and adapt to changes. The best indicator of endangerment of species and forest plant communities is the reduction of their range and biodiversity. Most climate models predict large changes within forests due to the high rates of climate change and the limitations of adaptation of many tree species to climatic extremes. Forests are slowly adapting to new conditions, especially due to increasing temperatures, increasing carbon dioxide concentrations and increasing nitrate deposition. The most influential climate variable for forests is the one that determines wind disturbance. The key to forest management in risk conditions lies in increasing the participation of more resistant species adapted to future climatic conditions, ie in promoting the diversity of tree species and their provenances and the heterogeneity of structural forms of forests. To create such forests, it isnecessary to cultivate forests whose characteristics are close to natural and potential forest communities for appropriate habitat conditions and indigenous species. Adaptive forest management implies a multidisciplinary approach and a four-phase cycle of strengthening understanding of complex biophysical, socioeconomic and political systems with constant monitoring (ecosystem control) and acquiring new empirical knowledge whose positive effects are applied in practice. The advantage of adaptive management is that plans and activities are adjusted based on the results of monitoring in the newly created unforeseen conditions.

Nitrate chemistry in the northeast US – Part 1: Nitrogen isotope seasonality tracks nitrate formation chemistry

Abstract. Despite significant precursor emission reductions in the US over recent decades, atmospheric nitrate deposition remains an important terrestrial stressor. Here, we utilized statistical air mass back trajectory analysis and nitrogen stable isotope deltas (δ(15N)) to investigate atmospheric nitrate spatiotemporal trends in the northeastern US from samples collected at three US EPA Clean Air Status and Trends Network (CASTNET) sites from December 2016–2018. For the considered sites, similar seasonal patterns in nitric acid (HNO3) and particulate nitrate (pNO3) concentrations were observed with spatial differences attributed to nitrogen oxide (NOx) emission densities in source contributing regions that were typically ≤ 1000 km. Significant spatiotemporal δ(15N) variabilities in HNO3 and pNO3 were observed with higher values during winter relative to summer, like previous reports from CASTNET samples collected in the early 2000s for our study region. In the early 2000s, δ(15N) of atmospheric nitrate in the northeast US had been suggested to be driven by NOx emissions; however, we did not find significant spatiotemporal changes in the modeled NOx emissions by sector and fuel type or δ(15N, NOx) for the source regions of the CASTNET sites. Instead, the seasonal and spatial differences in the observed δ(15N) of atmospheric nitrate were driven by nitrate formation pathways (i.e., homogeneous reactions of NO2 oxidation via hydroxyl radical or heterogeneous reactions of dinitrogen pentoxide on wetted aerosol surfaces) and their associated δ(15N) fractionation. Under the field conditions of low NOx relative to O3 concentrations and when δ(15N, NOx) emission sources do not have significant variability, we demonstrate that δ(15N) of atmospheric nitrate can be a robust tracer for diagnosing nitrate formation.