Wet Nitrogen Deposition Research Articles

Quantifying the wet deposition of reactive nitrogen over China: Synthesis of observations and models

Accurate estimation on reaction nitrogen (Nr) deposition is highly demanded for assessing the impacts on the environment and human beings. This study investigated the wet deposition of inorganic nitrogen (IN) in mainland China by measurements from over 500 sites from five observational networks/databases and ensemble results of eleven chemical transport models (CTMs). Each data source has its focus and limitations and together formed a comprehensive view over China. But the inconsistency among different sources may hinder the appropriate usage of data. Model evaluation results demonstrated the models' deficiency in simulating the wet NO3− deposition over Southeast China (40 % underestimation) and showed an overall underestimation of wet NH4+ deposition over the hotspot regions (5–60 % underestimation). A synthesis of this study and twelve reference studies was conducted to quantify the national amount of wet IN deposition. The estimations by CTMs ranged 2.4–3.9 Tg(N) yr−1 for wet NOy deposition and 4–6.7 Tg(N) yr−1 for wet NHx deposition, after adjusting the results with 10–19 % underestimations in wet NOy deposition and 1–40 % underestimations in wet NHx deposition. The estimations by ground observations ranged 7.1–9 Tg(N) yr−1 for wet NOy deposition and 8–13.1 Tg(N) yr−1 for wet NHx deposition, which were 20–275 % higher than the estimation by CTMs, but the results were strongly influenced by the abundances and representative of measurements. Studies using statistical techniques to interpolate site observations predicted 3–5.5 Tg(N) yr−1 for wet NOy deposition and 3.9–7.2 Tg(N) yr−1 for wet NHx deposition. This approach benefited from high accuracy and good robustness of the statistical models, but the uncertainty in the interpolation methods could be a potential drawback.

Characteristics of Heavy Metals and Other Elements in Atmospheric Dry and Wet Deposition and Health Risk Assessment of a Typical Industrial and Mining City in Central Yunnan

In order to study the characteristics of atmospheric dry and wet deposition elements and the health risks of typical industrial and mining cities in central Yunnan, the atmospheric dry and wet depositions collected from June 2019 to July 2020 in Anning city were selected as the research object and measured. The contents of the 11 indexes TN, F, Cr, Ni, Cu, Zn, Cd, Pb, P, As, and Hg were determined, the annual atmospheric deposition flux was calculated, and the exposure risk model was used to assess the risk to human health. The results showed that:1 In addition to Cr, Ni, and As in the atmospheric dry sediments, the average contents of the elements F, Cu, Zn, Cd, Pb, and Hg were significantly higher than those of the surface soil in Anning City, which were 5.82, 3.00, 28.27, 57.53, 2.83, and 1.08 times higher, respectively. The average contents of F and total nitrogen in wet deposition exceeded the standard value of surface water V-class water. 2 The annual atmospheric deposition flux of total nitrogen was the highest, and the annual deposition flux of eight heavy metal elements from smallest to largest was Hg<Ni<As<Cr<Cd<Cu<Pb<Zn. According to DZ/T 0295-2016, except for the point DQ-11 located near a chemical industrial plant, the atmospheric environmental quality and geochemical grades of other points were all first-class. 3 Hand-to-mouth ingestion was the most important avenue of exposure to atmospheric heavy metals, and the exposure dose and non-carcinogenic health risks to children were far greater than those to adults; the atmospheric As, Cd, and Pb in the study area especially caused certain non-carcinogenic health risks to children. Cr, Cd, As, and Ni carcinogenic risk indexes were lower than 10-6, thus, there was little or no carcinogenic risk. Therefore, it is necessary to strengthen the strict control of atmospheric heavy metal emissions from industrial and mining enterprises in this region.

Influence of nitrogen wet deposition on nitrogen output in a typical watershed in the Three Gorges Reservoir Area

Influence of nitrogen wet deposition on nitrogen output in a typical watershed in the Three Gorges Reservoir Area

Morphological characteristics of amino acids in wet deposition of Danjiangkou Reservoir in China's South-to-North Water Diversion Project.

Amino acids are an important constituent in organic nitrogen deposition, and changes in the content of their components have a direct impact on the nitrogen input to the ecosystem. From December 2018 to November 2019, 176 precipitation samples were collected at Danjiangkou Reservoir, the source of the middle line of the South-to-North Water Diversion Project, and the variation characteristics of dissolved free amino acids (DFAA) and dissolved combined amino acids (DCAA) were analyzed. The volume-weighted value concentration ranges of DFAA and DCAA were 0.159-1.136μmol/L and 1.603-7.044μmol/L, respectively, and amino acids were dominated by DCAA in wet deposition. Our results showed that glutamic acid (Glu), glycine (Gly), and aspartic acid (Asp) were the dominant amino acids in both DFAA and DCAA. The concentration of DFAA was highest in winter, while the concentration of DCAA was in autumn. Dissolved total amino acids (DTAA) were insignificantly correlated with DFAA, whereas they were linearly correlated with DCAA, indicating a significant influence of agricultural activities on DTAA. The analysis of the backward trajectory of air masses showed that amino acids were mainly influenced by proximity inputs around the reservoir. The bioavailability of organic matter was higher in the southeastern of the reservoir than in the northwestern. The wet deposition flux of TDN was 14.096kgN/ha/year, and the potential ecological impact on water bodies cannot be ignored. This study was conducted to clarify the variation characteristics of amino acids fractions in wet deposition and to provide parameters for regional assessment of amino acids wet deposition. The ecological impact of nitrogen wet deposition on water bodies will be explored to provide a basis for nitrogen pollution control and water quality protection in the middle line of the South-to-North Water Diversion Project.

Wet nitrogen (N) deposition to urban Latin America: Filling in the gaps with GEOS-Chem

In Latin America, atmospheric deposition is a major vector of nitrogen (N) input to urban systems. Yet, measurements of N deposition are sparse, precluding analysis of spatial patterns, temporal trends, and ecosystem impacts. Chemical transport models can be used to fill these gaps in the absence of dense measurements. Here, we evaluate the performance of a global 3-D chemical transport model in simulating spatial and interannual variation in wet inorganic N (NH4–N + NO3–N) deposition across urban areas in Latin America. Monthly wet and dry inorganic N deposition to Latin America were simulated for the period 2006–2010 using the GEOS-Chem Chemical Transport Model. Published estimates of observed wet or bulk inorganic N deposition measured between 2006 and 2010 were compiled for 16 urban areas and then compared with model output from GEOS-Chem. Observed mean annual inorganic N deposition to the urban study sites ranged from 5.7 to 14.2 kg ha−1 yr−1, with NH4–N comprising 48–90% of the total. Results show that simulated N deposition was highly correlated with observed N deposition across sites (R2 = 0.83, NMB = −50%). However, GEOS-Chem generally underestimated N deposition to urban areas in Latin America compared to observations. Underestimation due to bulk sampler dry deposition artifacts was considered and improved bias without improving correlation. In contrast to spatial variation, the model did not capture year-to-year variation well. Discrepancies between modeled and observed values exist, in part, because of uncertainties in Latin American N emissions inventories. Our findings indicate that even at coarse spatial resolution, GEOS-Chem can be used to simulate N deposition to urban Latin America, improving understanding of regional deposition patterns and potential ecological effects.

Seasonal variation of transport pathways and potential source areas at high inorganic nitrogen wet deposition sites in southern China

This study attempts to identify the dominant transport pathways, potential source areas, and their seasonal variation at sites with high inorganic nitrogen (IN) wet deposition flux in southern China. This is a long-term study (2010–2017) based on continuous deposition measurements at the Guangzhou urban site (GZ) and the Dinghushan Natural Reserve site (DHS) located in the Pearl River Delta (PRD) region. A dataset on monthly IN concentration in precipitation and wet deposition flux were provided. The average annual fluxes measured at both sites (GZ: 33.04±9.52, DHS: 20.52±10.22 kg N/(ha∙year)) were higher, while the ratios of reduced to oxidized N (GZ: 1.19±0.77, DHS: 1.25±0.84) were lower compared with the national mean level and the previous reported level throughout the PRD region. The dominant pathways were not always consistent with the highest proportional trajectory clusters. The transport pathways contributing most of deposition were identified in the north and north-northeast in the dry season and in the east-southeast, east, and south-southwest in the wet season. A weighted potential source contribution function (WPSCF) value >0.3 was determined reasonably to define the potential source area. Emission within the PRD region contributed the majority (≥95% at both sites) of the IN deposition in the wet season, while the contribution outside the region increased significantly in the dry season (GZ: 27.86%, DHS: 95.26%). Our results could help create more effective policy to control precursor emissions for IN fluxes, enabling reduction of the ecological risks due to excessive nitrogen.

Influence of Nitrogen Wet Deposition on Watershed Nitrogen Output in a Typical Watershed in the Three Gorges Reservoir Area

Influence of Nitrogen Wet Deposition on Watershed Nitrogen Output in a Typical Watershed in the Three Gorges Reservoir Area

Twenty years of nitrogen deposition to Norway spruce forests in Sweden

The yearly, total (dry+wet) deposition of inorganic nitrogen (inorg-N) to Norway spruce forests was estimated with a full spatial coverage over Sweden for a twenty-year period, 2001–2020, based on combined measurements with Teflon string samplers, throughfall deposition and bulk deposition to the open field. The results were based on a novel method to apply estimates of the dry deposition based on measurements at a limited number of sites, to a larger number of sites with only bulk deposition measurements, in turn based on the existence of a strong geographical gradient in the dry deposition of inorg-N from southwest to northeast Sweden. The method should be applicable for other geographical regions where gaseous NH3, NO2 and HNO3 are not main drivers of N dry deposition and where geographical gradients in dry deposition could be defined. It was shown that Norway spruce forests in south Sweden receive more N from deposition than has been previously estimated, based on modelling. Clear time trends were demonstrated for decreased deposition of inorg-N to Norway spruce forests in all parts of Sweden. The decreases were somewhat larger than what could be expected from the decrease in the reported emissions of inorg-N from Europe. The results emphasize that estimates of the total deposition are necessary in order to map levels and follow the development of N deposition in forests.

The Development and Application of Machine Learning in Atmospheric Environment Studies

Machine learning (ML) plays an important role in atmospheric environment prediction, having been widely applied in atmospheric science with significant progress in algorithms and hardware. In this paper, we present a brief overview of the development of ML models as well as their application to atmospheric environment studies. ML model performance is then compared based on the main air pollutants (i.e., PM2.5, O3, and NO2) and model type. Moreover, we identify the key driving variables for ML models in predicting particulate matter (PM) pollutants by quantitative statistics. Additionally, a case study for wet nitrogen deposition estimation is carried out based on ML models. Finally, the prospects of ML for atmospheric prediction are discussed.

Characteristics of Atmospheric Inorganic Nitrogen Wet Deposition in Coastal Urban Areas of Xiamen, China

To evaluate the impact of increasing atmospheric nitrogen deposition input to the coastal ecosystem, measurements were conducted to analyze the inorganic nitrogen wet deposition to Xiamen Island during April to August in 2014. Using ion chromatography and shown to contain main nine water-soluble ions—including Na+, NH4+, K+, Mg2+, Ca2+, Cl−, NO−, NO3−, and SO42−—we analyzed the composition of the wet deposition sample and verified the contribution of different ions to the different sources. The results showed that the mean NO3−-N and NH4+-N concentration in rainfall for five months was 4.55 ± 5.15 mg·L−1 (n = 31) and 1.20 ± 1.16 mg·L−1 (n = 33), respectively. Highest NO3−-N (74.65 mg·N·L−1) and NH4+-N (16.06 mg N·L−1) values were both observed in May. Maximum NO3−-N deposition (507.5 mg·N·m−2) was also in May, while the highest NH4+-N deposition (99.8 mg·N·m−2) was in June. The total inorganic wet nitrogen flux during sampling period was 11.1 kg·N·ha−1. The HYSPLIT backward air masses trajectory and USEPA PMF model was used, as the composition of the air masses passing over the sample area were impacted from three sources: fertilizers and biomass combustion, formation of secondary aerosol, and Marine aerosols. The concentration ratio of SO42− and NO3− in ranged between 0.5 and 3 in rainfall samples with an average of 1.34, suggesting that the contribution from vehicle exhaust to air pollution in the sample area is increasing. Long-term continuous monitoring of wet deposition in this region needs to be expanded to fully understand the impacts of human activity on air quality and to quantify N deposition to local marine ecosystems.

Characteristics of atmospheric inorganic nitrogen wet deposition in coastal urban areas of Xiamen, China

Characteristics of atmospheric inorganic nitrogen wet deposition in coastal urban areas of Xiamen, China

Wet deposition of atmospheric inorganic reactive nitrogen (Nr) across an urban-industrial-rural transect of Nr emission hotspot (India)

Wet deposition of atmospheric inorganic reactive nitrogen (Nr) across an urban-industrial-rural transect of Nr emission hotspot (India)

High atmospheric wet nitrogen deposition and major sources in two cities of Yangtze River Delta: Combustion-related NH3 and non-fossil fuel NOx

High ammonia (NH3) and nitrogen oxide (NOx) emissions are related to serious air pollution in urban areas and the negative impacts of excessive reactive nitrogen (N) deposition on many ecosystems. However, whether there is a relationship between N deposition rates and their sources with urbanization or not remains unclear in many areas. Here, we investigated the deposition rates of ammonium (NH4+), nitrate (NO3−), dissolved organic N, and water-insoluble particular N from July 2017 to June 2018 at two urban and two suburban sites in the Yangtze River Delta (YRD). The δ15N values of precipitation NH4+ and NO3− were measured, and major sources were analyzed using a Bayesian isotope mixing model. Wet N deposition rates were higher in Yangzhou (developing city, 20.3–22.7 kg N ha−1 yr−1) than those in Nanjing (developed city, 19.4–20.5 kg N ha−1 yr−1), and were higher at urban sites (20.4–22.5 kg N ha−1 yr−1) than those at suburban sites (18.7–20.3 kg N ha−1 yr−1). δ15N values of precipitation NH4+ increased with an increase in precipitation pH because ambient acidity affects the equilibrium isotope fractionation between NH3 and NH4+ and wet scavenging coefficients of NH3 and particulate NH4+. For NH4+, combustion-related NH3 sources (62%–65% with 5.5–6.4 kg N ha−1 yr−1, including coal combustion, vehicle exhaust, and biomass burning) contributed more than volatilization NH3 sources (35%–38% with 2.9–3.9 kg N ha−1 yr−1, including fertilizer application and waste volatilization). For NO3−, non-fossil fuel NOx sources (50%–63% with 3.4–4.1 kg N ha−1 yr−1, including biomass burning and microbial N cycle) were comparable to fossil fuel NOx sources (37%–50% with 2.4–3.4 kg N ha−1 yr−1, including coal combustion and vehicle exhaust). This study evidenced high N deposition rates and the importance of combustion-related NH3 emissions and non-fossil fuel NOx emissions in city areas of the YRD.

Wet deposition of total dissolved nitrogen in Indo-Gangetic Plain (India)

Very limited information on the magnitude and environmental impacts of both inorganic and organic forms of nitrogen (N) wet deposition is available in India. Molar concentrations of inorganic (NH4+ and NO3-) and organic N in rainwater were monitored at three different land use sites in Indo-Gangetic Plain (IGP) during the monsoon period (June-September) of 2017. It has been observed that dissolved organic N (DON) contributed significantly to the total dissolved N (TDN) ranging from 5 to 60%. Dissolved inorganic N (DIN = NH4+ + NO3-) concentration was recorded as high as 221.0 μmol L-1 at urban site to as low as 65.9 μmol L-1 at the rural site. A similar pattern was also observed for DON. NH4+ contribution to TDN had the order urban megacity (65%) > urban (70%) > rural (75%). Agriculture and animal husbandry are the primary sources of NH4+ emissions in the rural site. However, NO3- has shown a contrasting trend at these sites (25%, 15%, and 8%, respectively). Wet deposition fluxes of atmospheric TDN were observed to be higher at urban sites. This can be attributed to a variety of local sources such as vehicular emission, microbial emissions, biomass burning, human excreta due to higher population density, and transportation from surrounding areas, as observed from concentration weighted trajectories (CWT) model and cluster analysis. Upwind region of IGP has experienced major influence of air mass transported from agriculturally rich northwest part of India. However, both the downwind sites have experienced by-and-large the influence of south-westerly air masses originated over the Arabian Sea. This study has found that the DON contributes significantly to TDN, and therefore, its inclusion for nitrogen budget assessment in South Asia is emphasized.

Dominant contribution of nitrogen compounds in precipitation chemistry in the Lake Victoria catchment (East Africa)

This work provides a complete chemical characterization of rains collected in the tropical rural site of Mbita (Kenya) on the shores of Lake Victoria (annual rainfall 1259.3 mm). We present a wet nitrogen deposition budget including inorganic and organic dissolved nitrogen in relation with atmospheric sources of gases and particles, precipitation rate and air mass transport. A unique 2 yr monitoring data set (2017–2019), providing 183 rain samples was collected and analyzed according to international standards (WMO/GAW). Considering that precipitation represents the largest contributor of water to the Lake Victoria (80%), this study gives new insights in the seasonality of nutrients wet deposition (WD) inputs in the unique natural resource represented by Lake Victoria and its catchment. Four main contributions to the chemical composition of precipitation, were identified: (a) a 28% terrigenous contribution related to crustal and biomass sources, (b) a 14% marine contribution related to Indian ocean air masses intrusion, (c) a 15% organic contribution due to volatile organic carbon emissions from biomass burning and vegetation and (d) a predominant nitrogenous contribution of 39% due to livestock and fertilizers, biomass burning and neighboring agricultural fires. Ammonium and nitrate volume weighed mean concentrations are 36.75 and 8.88 μeq l−1, respectively. Rain in Mbita is alkaline (pH = 5.8) highlighting neutralization by heterogeneous chemistry. Total nitrogen WD is 8.54 kgN ha−1 yr−1, 58 760 tN yr−1 for the entire lake, with 26% attributed to dissolved organic nitrogen. A total atmospheric deposition of 15 kgN ha−1 yr−1 is estimated taking into account dry deposition estimate from literature, showing that the Lake Victoria ecosystem is exposed to eutrophication. An extensive and regular monitoring of wet and dry nitrogen deposition is highly recommended both in-shore and off-shore to help improving the efficiency of nitrogen use in agricultural areas and reduce nitrogen losses around Lake Victoria.

Atmospheric deposition of sulfur and nitrogen in the West China rain zone: Fluxes, concentrations, ecological risks, and source apportionment

The West China Rain Zone (WCRZ; 25,000 km2) is a broad mountainous ecotone between the urbanized Sichuan Basin (SCB) and the rural Qinghai-Tibetan Plateau (QTP). The WCRZ is rich in biodiversity and may be influenced by the air pollutants transported from the SCB towards the QTP. As air pollution can cause adverse effects on ecosystem health, this study investigated the fluxes, ecological risks, and sources of sulfur and nitrogen deposition by using a source-oriented community multiscale air quality (CMAQ) model for the entire WCRZ and its constituent national nature reserves in 2015. Results indicate that for sulfur (75%) and nitrogen (70%), the majority of the WCRZ area had annual total deposition fluxes higher than their critical loads. In addition, the annual volume-weighted mean (VWM) total inorganic nitrogen (TIN) wet deposition concentrations in almost the entire WCRZ exceeded the standard for total nitrogen of surface water in protected areas (0.2 mg N L−1). This exceedance is detrimental for the headwater watersheds that have precipitation as their sole water source. In each of the national nature reserves (NNRs), the average annual total deposition fluxes ranged between ~12–38 (sulfur) and ~ 15–38 kg S(N) ha−1 a−1 (nitrogen). About 40–100% (sulfur) and 5–85% (nitrogen) of the areas have annual total fluxes higher than the corresponding critical loads. Furthermore, the average VWM TIN concentration of wet deposition in each WCRZ NNR is higher than 0.2 mg N L−1. Therefore, sulfur and nitrogen deposition likely pose severe risks to some important natural ecosystems in the WCRZ. Based on the source apportionment results, to reduce sulfur and nitrogen deposition in the WCRZ, both SCB and non-SCB emissions should be controlled. In addition, the agricultural NH3 emissions and the industrial and power plant SO2 and NOx emissions should be reduced by larger extents than that of other sectors. This study provides a basis for future atmospheric and ecological observations in the WCRZ.

Long-term application of manure reduced nutrient leaching under heavy N deposition

Little is known about the importance of long-term fertilization in crop production and nutrient leaching under heavy wet nitrogen (N) deposition from the atmosphere (WNDA) in tropical and subtropical soils. Thus, a 15-year (2004–2018) field experiment was established on a yellow soil (Orthic Arisols) near Zunyi, Southwest China, to compare the effects of fertilization on maize yields and nutrient leaching in a rotation system of summer maize-winter wheat-summer flue-cured tobacco (or sometimes sweet potato). All crops in this system received no fertilizers (CK), only chemical fertilizers (CF), or manure plus chemical fertilizers (MCF). MCF achieved higher yield and economic efficiency of fertilizers than CF after the first four maize cropping seasons. These results suggested a positive interaction between manure and chemical fertilizers. Maize plants used residual nutrients in the soil from the previous fertilizer management, which may interfere with manure efficiency. MCF alleviated soil acidification and increased soil organic matter (OM), available nutrients, microbial biomass, and enzyme activities (urease and phosphatase compared with CK and invertase and catalase compared with CF). The stimulation of microbial growth and activities may lead to OM depletion in the CF soil, while OM added into the soil in the MCF treatment may exceed microbial OM consumption. During the maize growing season, MCF decreased N and K leaching losses compared with CF. WNDA accounted for 10–12% of N fertilized to maize and 32–69% of maize N uptake in the unfertilized soil. WNDA may thus be an important N source of maize in N-poor soils.

Long-term atmospheric inorganic nitrogen deposition in West African savanna over 16 year period (Lamto, Côte d’Ivoire)

We present a long term assessment trend of atmospheric inorganic nitrogen deposition in Sub Saharan Africa (2000–2015) using observational and model data. This work proposes a compilation of International Network to study Deposition and Atmospheric chemistry in Africa wet and dry nitrogen deposition fluxes collected at the wet savanna site of Lamto (Côte d’Ivoire). Total deposition calculation takes in account: (a) gaseous (NO2, NH3, HNO3) dry deposition fluxes estimated by considering nitrogen compound concentrations at the monthly scale and modeling average monthly dry deposition velocities, (b) particulate PM10 (pNO3 −, pNH4 +) dry deposition fluxes calculated using the same inferential method and (c) wet deposition (WD) fluxes including ions concentration measurements (NO3 −, NH4 +) in rainwater combined with rainfall amount. We demonstrate for the first time the monthly and annual decreasing trends for dry nitrogen deposition of N-NO2 (−2.33% month−1 and −2.54% yr−1) and N-NH3 (−2.55% month−1 and −2.89% yr−1), but increasing trends for dry deposition of N-HNO3 (+1.00% month−1) and WD of N-NO3 − (+1.67% month−1 and +2.13% yr−1) and N-NH4 + (+2.33% month−1 and +3.36% yr−1). Dry season N-NO2 deposition flux decline shows agreement with long term trend in NOx emissions by biomass burning. Increasing trends for wet N deposition signals a gradual increase of nitrogen fertilizers use in agricultural practices in the Lamto area. Results also show no significant trend in total N deposition over the 16 year study period explained by the compensation of decreasing and increasing trends for dry and wet N deposition, respectively. However, at the annual scale, the mean total N deposition flux is estimated to 10.3 ± 1.2 kgN ha−1 yr−1 over the 16 year period, indicating an increase of 8% compared to the period 2000–2007.

Atmospheric wet deposition of major ionic constituents and inorganic nitrogen in Bangladesh: Implications for spatiotemporal variation and source apportionment

The quantitative and qualitative characterization of ions and inorganic nitrogen in precipitation assists in understanding the accompanying sources and chemistry of regional precipitation. A total of 212 event-based precipitation samples were collected from four sites in Bangladesh in 2017 to investigate the physicochemical characteristics, sources, and deposition of atmospheric ionic constituents and inorganic nitrogen. During the entire monitoring period, 5.7% of the total samples were acidic (i.e., pH < 5.6), indicating that Bangladesh does not suffer severely from acid rain. The electrical conductivity (EC) and total dissolved solids (TDS) values indicate the inverse relationship between the amount of precipitation on the spatiotemporal scale. Ca2+ was the dominant neutralizing factor at four sites, which was demonstrated by the equivalent ratio of the neutralization potential to the acidifying potential and fractional acidity. Moreover, it had the highest volume-weighted mean concentration of all the sites, validating the calcareous nature of the soil aerosolized into the atmosphere. Distinct seasonality was observed for the majority of the ions with higher concentrations in the non-monsoon climate. Sea salt species displayed the pattern of Satkhira > Cox's Bazar > Dinajpur > Sylhet, whereas the anthropogenic species exhibited the order of Dinajpur > Satkhira > Sylhet > Cox's Bazar, underlining the local and regional impacts of these species in Bangladesh. Based on the source apportionment, the sources were categorized as marine (Na+ and Cl−), terrigenous (Ca2+, Mg2+, and HCO3−), fossil fuel combustion (NO3− and SO42−), agriculture (NH4+), and biomass burning (K+). The Cl− in Sylhet and Satkhira suggests additional sources associated with anthropogenic activities. The back-trajectory analyses and the National Centers for Environmental Prediction's final (NCEP FNL) datasets illustrate the presence of significantly diverse air masses with contributions from various sources in the monsoon and non-monsoon climates. Both the amount of precipitation and the ionic quantity governs the fluxes in Bangladesh. The Na+ % and SAR lie under the safe category suggesting a good precipitation water quality for agriculture and soil in Bangladesh, while the deposition of inorganic nitrogen has resulted in a value above the threshold line (10 kg ha−1 y−1). Thus, this study conveys a comprehensive picture of the ionic composition, providing a baseline dataset to assess the atmospheric environment in this lowland region.

Wet Inorganic Nitrogen Deposition at the Daheitin Reservoir in North China: Temporal Variation, Sources, and Biomass Burning Influences

Atmospheric nitrogen deposition is of great concern to both air quality and the ecosystem, particularly in northern China, which covers one-quarter of China’s cultivated land and has many heavily air polluted cities. To understand the characteristics of wet N deposition at rural sites in northern China, one-year wet deposition samples were collected in the Daheitin reservoir region. Due to the intense emissions of gaseous nitrogen compounds from heating activities during cold seasons and distinct dilution effects under different rainfall intensities and frequencies, the volume weighted mean concentrations of wet N deposition showed higher levels in dry seasons but lower levels in wet seasons. In contrast, the wet N deposition rates varied consistently with precipitation, i.e., high during the wet season and lower during the dry season. The annual wet deposition rate of total inorganic ions (the sum of NO3−–N and NH4+–N) at the rural site in North China from July 2019 to June 2020 was observed at 18.9 kg N ha−1 yr−1, still remained at a relatively high level. In addition, biomass burning activities are ubiquitous in China, especially in northern China; however, studies on its impact on wet N deposition are limited. Non-sea salt potassium ion (nss-K+) was employed as a molecular tracer to investigate the characteristics of biomass burning activities as well as their impact on the chemical properties of wet N deposition. Three precipitation events with high nss-K+ levels were captured during the harvest season (June to July). The variations in the patterns of nss-K+, deposited N species, and ratios of nss-K+ to nitrogen species as well as their relationships all indicated that biomass burning emissions contributed remarkably to NO3−–N but had a minor influence on NH4+–N.