Critical Loads Of Nitrogen Research Articles

Atmospheric deposition patterns in bulk open field precipitation and throughfall in Aleppo pine forest and black pine forest on the eastern Adriatic coast

The Mediterranean region, with its unique ecological characteristics, is particularly sensitive to global environmental changes, including climate change and impact of air pollution.Although Aleppo pine and black pine forests are the most abundant on the eastern Adriatic coast, atmospheric deposition in these forests is poorly studied. Changes in the chemical composition of precipitation as it passes through the tree canopy can lead to soil and groundwater eutrophication, and soil acidification, which affects plant vitality. In this study, the dynamics of ion deposition in Aleppo pine forest (Pinus halepensis Mill.) and black pine forest (Pinus nigra Arnold) on the eastern Adriatic coast are investigated, focusing on throughfall and bulk open field depositions.The aim of our research was to fill the gaps in understanding the influence of tree canopies on deposition fluxes in two different Mediterranean pine stands and to compare total inorganic nitrogen loads with critical loads. Over a period of two years, bulk open field precipitation and throughfall were sampled, measured and analysed using the ICP Forest methodology.The results indicate significant differences in ion deposition between bulk open field and throughfall, with throughfall showing higher values for almost all ions. The highest enrichment ratio was determined for K+. The comparison of the actual inorganic nitrogen load with the critical nitrogen load for Mediterranean pine forests revealed that the inorganic nitrogen load exceeded the critical load in the Aleppo pine forest. Ion deposition increased in the throughfall compared to bulk precipitation, which can be attributed to the seasonality of precipitation, including leaching and long dry periods. These findings enhance our understanding of ion deposition fluxes in vulnerable Mediterranean pine ecosystems and emphasize the need for long-term research on this topic in the actual changing environmental conditions.

Spatial Distribution of Ammonia Concentrations and Modeled Dry Deposition in an Intensive Dairy Production Region.

Agriculture generates ~83% of total US ammonia (NH3) emissions, potentially adversely impacting sensitive ecosystems through wet and dry deposition. Regions with intense livestock production, such as the dairy region of south-central Idaho, generate hotspots of NH3 emissions. Our objective was to measure the spatial and temporal variability of NH3 across this region and estimate its dry deposition. Ambient NH3 was measured using diffusive passive samplers at 8 sites in two transects across the region from 2018-2020. NH3 fluxes were estimated using the Surface Tiled Aerosol and Gaseous Exchange (STAGE) model. Peak NH3 concentrations were 4-5 times greater at a high-density dairy site compared to mixed agriculture/dairy or agricultural sites, and 26 times greater than non-agricultural sites with prominent seasonal trends driven by temperature. Annual estimated dry deposition rates in areas of intensive dairy production can approach 45 kg N ha-1 y-1, compared to <1 kg N ha-1 y-1 in natural landscapes. Our results suggest that the natural sagebrush steppe landscapes interspersed within and surrounding agricultural areas in southern Idaho receive NH3 dry deposition rates within and above the range of nitrogen critical loads for North American deserts. Finally, our results highlight a need for improved understanding of the role of soil processes in NH3 dry deposition to arid and sparsely vegetated natural ecosystems across the western US.

Wet deposition of sulfur and nitrogen in the Jiuzhaigou World Heritage Site, China: Spatial variations, 2010–2022 trends, and implications for karst ecosystem conservation

Excessive sulfur and nitrogen deposition is a threat to natural ecosystems. This study investigated the spatio-temporal changes of wet sulfur and nitrogen deposition in Jiuzhaigou to understand the responses of wet deposition chemistry to local and national air pollutant emission changes and to assess relevant ecological risks. The results show that local emission sources (e.g., tourism, post-earthquake reconstruction, and vegetation damages) largely elevated the concentrations of SO42−, NO3−, NH4+, and Ca2+ at the non-background sites during 2021–2022; However, the gaps of annual sulfur and nitrogen wet deposition fluxes among the background, semi-background, and non-background sites were reduced by annual precipitation. The pH was also higher at the non-background sites due to stronger acid neutralization capacities from crustal dust there, and acid precipitation (pH < 5.6) was not detected at all the sites. During the 2010 to 2022 period, the wet deposition of SO42− and TIN (i.e. total inorganic nitrogen) and the equivalent ratio of SO42−: NO3− generally presented a declining trend at the background and semi-background sites, as a result of regional and national emission reductions. The TIN reduction from 2015 to 2016 to 2021–2022 at the background site was more from wet NH4+ deposition and the site's NO3− concentrations and fluxes were relatively stable. Compared to the critical loads (CLs) of sulfur and nitrogen for acidification and eutrophication, the annual wet and wet+dry deposition fluxes of sulfur and nitrogen were lower in almost the entire watershed, except for the CLmin of nitrogen for acidification in considerable areas. However, all the wet deposition samples were calcite-unsaturated and had annual TIN concentrations higher than the national environmental standard of total nitrogen for surface water. More field investigations are needed to better assess the ecological risks.

Global food loss and waste embodies unrecognized harms to air quality and biodiversity hotspots.

Global food loss and waste (FLW) undermines the resilience and sustainability of food systems and is closely tied to the United Nation's Sustainable Development Goals on climate, resource use and food security. Here we reveal strong yet under-discussed interconnections between FLW and two other Sustainable Development Goals of Human Health and Life on Land via the nitrogen cycle. We find that eliminating global FLW in 2015 would have reduced anthropogenic NH3 emissions associated with food production by 11.4 Tg (16%), decreased local PM2.5 concentrations by up to 5 μg m-3 and PM2.5-related years of life lost by 1.5 million years, and mitigated nitrogen critical load exceedances in global biodiversity hotspots by up to 19%. Halving FLW in 2030 will reduce years of life lost by 0.5-0.8 million years and nitrogen deposition by 4.7-6.0 Tg N per year (4%) (range for socioeconomic pathways). Complementary to near-term NH3 mitigation potential via technological measures, our study emphasizes incentivizing FLW reduction efforts from air quality and ecosystem health perspectives.

Standardized naming convention and classification system for critical loads of nitrogen and sulfur deposition

AbstractCritical loads (CLs) of atmospheric deposition have been used for multiple decades to assess the impacts of air pollutants on terrestrial and aquatic ecosystems. However, these CLs have been developed by different researchers, at different times, using different methods, and are named in different ways with varying levels of information and levels of specificity. In this study, we identified the elements that describe CLs and used them to develop and test a standardized CL naming convention and a complementary CL classification system applicable to all CLs. The CL naming convention consists of: the form of deposition; the biological receptor, response, and threshold; and chemical criterion and threshold, thereby clearly communicating what the CL is and what it protects. The CL classification system contains all the elements that define and describe a CL, but the CL classes are not fixed and are therefore, defined by the user. The application of the CL naming convention and classification system to an existing US CL database and national forest was successful, demonstrating not only the utility of the naming convention and classification system, but how both can also be used to guide future CL science.

High-resolution maps of critical loads for sulfur and nitrogen in China

The critical load concept is an important scientific guideline for acid deposition control. It was not only a crucial scientific basis to determine the emission reduction targets in Europe, but also used in China’s air pollution control, especially the designation of two control zones. Currently, critical loads of sulfur and nitrogen are still exceeded in Europe, America, and East Asia (mainly in China), and need to be continuously updated to meet the demands of further emission reductions. Critical loads of China were calculated and mapped in the 2000s, but are not sufficiently accurate due to methodological and data limitations. Here we present the latest high-quality critical loads for China, based on high-resolution basic data on soil, vegetation, and atmospheric base cations deposition, and up-to-date knowledge on important parameters. Our data, which is going to be included in GAINS-China, can be used to assess the ecological benefits of nitrogen and sulfur reductions in China at a regional or national scale, and to develop mitigation strategies in the future.

The cumulative impacts of droughts and N deposition on Norway spruce (Picea abies) in Switzerland based on 37 years of forest monitoring

Norway spruce is one of the most important tree species in Central Europe, however, it is facing major problems with recent droughts. In this study we present 37 years (1985–2022) of long-term forest observation data on 82 different forest sites across Switzerland including 134′348 tree observations. The sites consists of managed spruce or mixed forest stands with beech (Fagus sylvatica) and comprise large gradients in altitude (290–1870 m), precipitation (570–2448 mm a−1), temperature (3.6–10.9 °C) or total nitrogen deposition (8.5–81.2 kg N ha−1 a−1).Long-term tree mortality has increased more than fivefold due to the multiple drought years 2019, 2020 and 2022, which is more than double the increase following the 2003 drought. We used a Bayesian multilevel model including three years of lagged drought indicator to predict spruce mortality. Besides stand age, the most important factors were drought and N deposition. Especially under drought conditions spruce mortality was increased on sites with high N deposition. Moreover, N deposition increased the imbalance of foliar phosphorus concentrations, with negative impacts on tree mortality. Mortality was increased by a factor of 1.8 in spruce compared to mixed beech and spruce stands. Stands with high mortality rates showed previously an increased proportion of trees with damaged crowns, especially after the droughts of 2003 and 2018.Taken together, we found evidences of an increase in spruce mortality droughts amplified under high N depositions. The perennial drought of 2018–2020 resulted in a cumulative spruce mortality of 12.1 % (564 dead trees in 82 sites) in only three years. With a Bayesian change-point regression framework we estimated a critical empirical load for nitrogen of 10.9 ± 4.2 kg N ha−1 a−1, which is in line with current thresholds, above which future plantings of spruce in Switzerland may not be a sustainable option due to the observed interaction between drought and nitrogen deposition.

Development of science and policy related to acid deposition in East Asia over 30years.

Scientific and public interest in acid deposition and its ecological impacts have increased throughout 1990s in East Asia (Northeast and Southeast Asia). After being established in 2001, the Acid Deposition Monitoring Network in East Asia (EANET) celebrates the 20th anniversary in 2021, and is now being expanded in scope reflecting the shifting social concern from acid deposition to broader air quality and climate change in recent years. This paper reviews the past 30years of development of scientific research and policy related to acid deposition in East Asia. Since the onset of the twenty-first century, East Asia has had the highest SO2 and NOx emissions in the world by continents, with substantial economic developmental inequality among countries. An overview of studies on sulfur and nitrogen deposition, the acidification of inland water and forest soil, and forest decline reveal that although limited acidification of inland water and forest soils have been documented, no decline in the populations of fish and other aquatic biota has been reported in East Asia. After a review of policy-oriented modeling studies on source receptor relationships and the critical loads of sulfur and nitrogen in East Asia, the history of EANET and its success and challenges are discussed. Finally, the importance of epistemic communities as the interface between science and policy in the region is discussed. Regional governance and cooperation are essential for reducing the emission of greenhouse gases, especially short-lived climate pollutants and atmospheric pollutants to realize the co-benefits of global climate change mitigation and improved air quality.

Nitrogen Critical Loads: Critical Reflections on Past Experiments, Ecological Endpoints, and Uncertainties.

Nitrogen Critical Loads (NCL), as purported ecological dose-response outcomes for nitrogen deposition from anthropogenic sources, play a central role in environmental policies around the world. In the Netherlands, these NCL are used to assess, via calculations using the model AERIUS, to what extent NCL are exceeded for different habitats as a result of different sources such as industry, agriculture, traffic. NCL are, however, not well defined, and are subject to hitherto unrecognized forms of uncertainty. We will address this with reference to a number of key studies that forms the basis for several NCL. We will subsequently propose amendments that could be applicable to future nitrogen studies and their enhanced relevancy in decision making.

Hierarchical change-point regression models including random effects to estimate empirical critical loads for nitrogen using Bayesian Regression Models (brms) and JAGS

The concept of critical loads is used in the framework of the Convention on Long-range Transboundary Air Pollution (UNECE) to define thresholds below which no damaging effects on habitats occur based on the latest scientific knowledge. Change-point regression models applied in a Bayesian framework are useful statistical tools to estimate critical empirical loads. While hierarchical study designs are common in ecological research, previous methods to estimate critical loads using change-point regression did not allow to analyse data collected under such a design. This method update provides an implementation of hierarchical data structure by including random effects such as study sites or as in this example tree species within the Bayesian approach of change-point regression models using two different approaches. The example data set is an European wide gradient study of the impact of climate change and air pollution on forest tree health assessed by foliar nutrient status of nitrogen (N) to phosphorus (P) from 10 different conifer tree species originated from 88 forest sites and 9 countries covering 22 years (1995-2017). Both modelling approaches using JAGS and Bayesian Regression Models using ‘Stan’ (brms) resulted in reasonable and similar estimations of the critical empirical load for nitrogen (CLempN) for temperate forests. These methodological examples of using different approaches of Bayesian change-point regression models dealing with random effects could prove useful to infer CLempN for other ecosystems and long-term data sets.•Hierarchical change-point regression models are suitable for estimating critical empirical loads.•The Bayesian framework of these models provides the inclusion of the current critical load and various confounding or modifying variables.•Here we present two ways of implementing hierarchical data sets in Bayesian change-point regression models using JAGS and brms.

Nitrogen Critical Loads: Critical Reflections on Past Experiments, Ecological Endpoints and Uncertainties.

Nitrogen Critical Loads: Critical Reflections on Past Experiments, Ecological Endpoints and Uncertainties.

A food tax only minimally reduces the N surplus of Swiss agriculture

CONTEXTMost Western-European countries exceed the critical loads for nitrogen (N) losses. High nitrogen (N) inputs make agriculture one of the largest contributors to N pollution. There might be a potential to reduce this losses with an output tax on animal products, as they have low N use efficiency and a tax has the potential to reduce the consumption of this products. OBJECTIVEWe want to assess the potential of a food tax on animal products to reduce the N surplus of Swiss agriculture. METHODSWe implemented a tax on meat and a tax on milk and meat in the agent-based model SWISSland. The model combines an agent-based model with a microeconomic model at the farm scale. To better understand the low response of the food tax, we applied in a second step a robust two-step global sensitivity analysis of abatement costs of individual model agents. RESULTS AND CONCLUSIONSImposing a tax led to an N surplus reduction of 2.1% where only meat was taxed and 2.3% where both milk and meat were taxed. The sensitivity analysis showed that distinct agents reacted non-uniformly to changing prices, so that the effect of the tax was sometimes even cancelled out. This calls for more differentiated policies to reduce the negative impact of N losses. SIGNIFICANCEThe overall impact of the food tax was minor as the distinct agents react not uniformly to lower producer prices.

Lichen-based critical loads for deposition of nitrogen and sulfur in US forests

Critical loads are thresholds of atmospheric deposition below which harmful ecological effects do not occur. Because lichens are sensitive to atmospheric deposition, lichen-based critical loads can foreshadow changes of other forest processes. Here, we derive critical loads of nitrogen (N) and sulfur (S) deposition for continental US and coastal Alaskan forests, based on nationally consistent lichen community surveys at 8855 sites. Across the eastern and western US ranges of 459 lichen species, each species' realized optimum was the N or S atmospheric deposition value at which it most frequently occurred. The mean of optima for all species at a site, weighted by their abundances, was defined as a community “airscore” indicative of species’ collective responses to atmospheric deposition. To determine critical loads for adverse community compositional shifts, we then modeled changes in airscores as a function of deposition, climate and forest habitat predictors in nonparametric multiplicative regression. Critical loads, indicative of initial shifts from pollution-sensitive toward pollution-tolerant species, occurred at 1.5 kg N ha−1 y−1 and 2.7 kg S ha−1 y−1. Importantly, these critical loads remain constant under any climate regime nationwide, suggesting both simplicity and nationwide applicability. Our models predict that preventing excess N deposition of just 0.2–2.0 kg ha−1 y−1 in the next century could offset the detrimental effects of predicted climate warming on lichen communities. Because excess deposition and climate warming both harm the most ecologically influential species, keeping conditions below critical loads would sustain both forest ecosystem functioning and climate resilience.

Sphagnum response to nitrogen deposition and nitrogen critical load: A meta-analysis

Sphagnum plants are sensitive to nitrogen deposition changes. However, previous literature is inconclusive on the response of Sphagnum to nitrogen deposition, little is known about the nitrogen critical load for Sphagnum growth, and the factors that influence the response of Sphagnum plant growth to nitrogen deposition are still unclear. Therefore, we conducted a meta-analysis of 60 experiments with different gradients of nitrogen application to Sphagnum plants in 14 countries around the world, and the results showed that excess nitrogen reduces Sphagnum production. Mixed-effects models were established to analyze the nutrient, environmental and climatic factors that may affect the response of Sphagnum plants to nitrogen deposition, and the results indicated that the water table and cumulative nitrogen were the most important influencing factors. We compared AICc values to select an optimal model set. We used a meta-analysis combined with general additive models (GAMs) to estimate the nitrogen critical load for Sphagnum, and we concluded that this load in the mid- to high-latitude region is in the range of 5–40 kg ha−1yr−1.

Hydrogeochemistry Studies in the Oil Sands Region to Investigate the Role of Terrain Connectivity in Nitrogen Critical Loads

Hydrology and geochemistry studies were conducted in the Athabasca Oil Sands region to better understand the water and nitrogen cycles at two selected sites in order to assess the potential for nitrogen transport between adjacent terrain units. A bog—poor fen—upland system was instrumented near Mariana Lakes (ML) (55.899° N, 112.090° W) and a rich fen—upland system was instrumented at JPH (57.122° N, 111.444° W), 100 km south and 45 km north of Fort McMurray, Alberta respectively. LiDAR surveys were initially conducted to delineate the watershed boundaries and topography and to select a range of specific locations for the installation of water table wells and groundwater piezometers. Field work, which included a range of physical measurements as well as water sampling for geochemical and isotopic characterization, was carried out mainly during the thaw seasons of 2011 to 2015. From analysis of the runoff response and nitrogen species abundances we estimate that nitrogen exchange between the wetlands and adjacent terrain units ranged between 2.2 and −3.1 kg/ha/year for rich fens, 0.6 to −1.1 kg/ha/year for poor fens, and between 0.6 and −2.5 kg/ha/year for bogs, predominantly via surface pathways and in the form of dissolved nitrate. A significant storage of dissolved ammonium (and also dissolved organic nitrogen) was found within the pore water of the bog-fen complex at Mariana Lakes, which we attribute to decomposition, although it is likely immobile under current hydrologic conditions, as suggested by tritium distributions. In comparison with the experimental loads of between 5 and 25 kg/ha/year, the potential nitrogen exchange with adjacent terrain units is expected to have only a minor or negligible influence, and is therefore of secondary importance for defining critical loads across the regional landscape. Climate change and development impacts may lead to significant mobilization of nitrogen storages, although more research is required to quantify the potential effects on local ecosystems.

Extensive Estimate of Nitrogen Budget and Critical Loads at the Scale of a Semi-Arid Tropical Grazed Site (Dahra, Senegal)

Extensive Estimate of Nitrogen Budget and Critical Loads at the Scale of a Semi-Arid Tropical Grazed Site (Dahra, Senegal)

大气氮沉降对中亚草地生态系统净初级生产力的影响

氮沉降作为除气候变化、CO₂浓度升高以及土地利用变化之外的第四大主要影响陆地生态系统结构和功能的因素，其对碳循环过程的影响研究相对薄弱，同时也是不确定性最大的环节之一。近年来，由于长期高强度的放牧导致草地生态系统的生产力降低，氮成为典型草地植物生长和生态系统净初级生产力的主要限制因子。据研究，亚洲的氮沉降平均增速极有可能高于全球氮沉降平均增速，成为未来氮沉降增加最快的区域。在此背景下，研究大气氮沉降对于中亚草地生态系统的影响具有重要的意义。利用反硝化-分解模型（DNDC）分析1979-2014年中亚地区草地生态系统净初级生产力（NPP）的时空分异，探讨氮沉降对草地NPP影响。结果表明：（1）1979-2014年间，中亚地区平均草地NPP约为（173.10±31.80） g C m^-2 a^-1，草地NPP时空分异明显，各草地类型的NPP从大到小依次为森林草甸、温带草原和荒漠草原，并且草地NPP以（2.67±1.30） g C m^-2 a^-1的速度逐年增长；（2）当前氮沉降情景总体上促进了中亚地区草地NPP的增长，1979-2014年氮沉降使得中亚草地NPP增加了0.42 Pg C。;Climate change, increased CO₂ concentration, nitrogen deposition and land use change are currently recognized as the main factors affecting the structure and function of ecosystems. Among them, the research on the influence of nitrogen deposition on carbon cycling process is still insufficient with great uncertainty. In recent years, as the productivity of grassland ecosystem is reduced due to long-term intensive grazing, nitrogen has become a limiting factor of typical grassland. The increasing rate of nitrogen deposition in Asia is probably higher than the global average as reported by previous research. In view of this, it is of significant importance to study the effect of atmospheric nitrogen deposition on grassland ecosystem in Central Asia. In this study, Denitrification-Decomposition (DNDC) model was utilized to analyze the temporal and spatial variation of grassland net primary productivity (NPP) in Central Asia from 1979 to 2014, to explore the effects of nitrogen deposition on grassland NPP. The results showed that:(1) During 1979-2014, the annual averaged temperature in Central Asia showed a significant increase trend((0.03±0.01)℃ a^-1, R²=0.40), while the precipitation decreased with the trend of (2.26±1.78)mm a^-1(R²=0.35). (2) from 1979 to 2014, the average NPP of grassland in Central Asia was about(173.10±31.80)g C m^-2 a^-1, and the spatial and temporal differences of grassland NPP were obvious. The highest NPP of grassland was found in forest meadow, followed by temperate grassland, and desert grassland NPP. Moreover, the grassland NPP increased at the rate of(2.67±1.30)g C m^-2 a^-1. (3) The current nitrogen deposition scenario generally benefits the growth of grassland NPP in central Asia, which increases the grassland NPP by 0.42 Pg C in the last 36 years. Based on the existing studies, we cannot determine whether the decrease of NPP in this part of grassland is caused by reaching the critical load of nitrogen, and more in-depth studies are needed.

Acid wet-deposition modeling sensitivity to WRF-CMAQ planetary boundary layer schemes and exceedance of critical loads over an industrializing coastal valley in northwestern British Columbia, Canada

Computational tools used to implement the critical-load approach of atmospheric deposition impact often do not elucidate modeling uncertainty making it difficult for environmental policy-makers to know how much confidence to put in its results, also hampering aspects that may need improving. This study evaluated acid deposition modeling for various parameterizations of the planetary boundary-layer (PBL) over the Terrace-Kitimat valley, a physiographically complex region of northwestern British Columbia. Of five schemes, simulations with the Mellor-Yamada-Nakanishi-Niino Level 3 and Mellor-Yamada-Janjic PBL schemes best captured weekly wet deposition fluxes of acidifying ions (SO42−, NO3−, NH4+) within a factor of 2 of observations at an industrial fence line station. Alongside the Yonsei University PBL scheme, these two schemes slightly overestimated the chemical species at a station that was distant from major anthropogenic precursor sources in the valley, hence useful for worst-scenario projections of atmospheric deposition on the natural environment. Forest soils in the vicinity of a large aluminum smelter in Kitimat was estimated to be in exceedance of critical load of acidity by 30.1–53.5 kg S ha−1 yr−1. Exceedance of critical load of nutrient nitrogen restricted to the Terrace area (≤ 7 km2), ranged between none and 0.71 kg ha−1 yr−1. This work provides guidance for using PBL schemes in the Weather Research and Forecasting model that is coupled to a deposition model when calculating critical-load exceedance over temperate, rugged, coastal geographies.

Safeguarding Natura 2000 habitats from nitrogen deposition by tackling ammonia emissions from livestock facilities

Nitrogen deposition is one of the main environmental threats to the conservation goals in areas protected by the European Habitats Directive, a problem that is quite pronounced in the livestock-rich region of Flanders, Belgium. Livestock farms are often located close to Natura 2000 areas. Therefore, ammonia emissions from livestock housing and manure storage have a high contribution to the deposition in these nearby protected habitats. In order to control this problem, the Flemish government imposes restrictions on livestock farms that pose a substantial threat to protected habitats nearby. In this paper, we evaluate the effectiveness of this spatially differentiated policy. Using an integrated spatially explicit modeling approach, we were able to show that the effectiveness of this policy is rather limited in terms of reducing the proportion of habitats in exceedance of the critical load for nitrogen. In order to obtain a good status for all sensitive habitats, emission abatement efforts should extend beyond the livestock sector. The effectiveness of the policy is dependent on habitat type and the livestock subsectors contributing to emissions nearby. Furthermore, by means of four different habitat classes, the effectiveness of alternative policy options can be easily assessed on the level of individual habitats.

Atmospheric concentrations and dry deposition of reactive nitrogen in the state of São Paulo, Brazil

Abstract Estimates of nitrogen deposition play a key role in better understanding the human impacts on the nitrogen biogeochemical cycle. This paper examines the concentration of reactive nitrogen (Nr) in the atmosphere and the average dry deposition in the state of Sao Paulo, Brazil. The Nr species that were measured were in the gaseous (NO2, NH3 and HNO3) and particulate phases (NH4+, NO3−). Denuder-based samplers were spatially distributed in six sites to account for different types of land cover and urbanization. Samples were collected over 2 years (2015–2017). The dominant form of inorganic Nr in the atmosphere was the gaseous NO2 at all sampling sites, which represented 79% of the total. The average concentrations of NH3, HNO3, NH4+ and NO3− were 10%, 3%, 6% and 2% of the total Nr, respectively. The average Nr dry deposition in Sao Paulo State was 10.6 kg N ha−1 yr−1. The highest average deposition of Nr was found in the SP sampling site and is related to intense vehicular traffic, waste management and industrial activities. This work suggests that dry deposition of Nr into the Atlantic Forest next to Sao Paulo municipality can exceed the critical nitrogen load suggested for most forests. This implies that human activities in the surrounding areas may be affecting the integrity of one of the most important biodiversity hotspots in South America. These results will contribute to improve Nr budget estimates and to advance Nr deposition modelling approaches.