One of the major pathways for dust supply to surface water of the Arabian Sea is via wet deposition, which is significant during southwest Monsoon (June-September). Aeolian dust supplies macro and ...micronutrients, which can impact on several marine biogeochemical processes. Here we report, major elements and rare earth elements (REEs) content as well as mineralogical and Sr-Nd isotopic composition of particulate collected from wet deposition (WDP) during the southwest monsoon period over the Northeastern Arabian Sea (NEAS) (Goa; 15.4° N, 73.8° E) in 2013. The collected WDP samples are classified into three categories based on changing wind regime, namely: (1) beginning of monsoon (BM; June); (2) mid of monsoon (MM; July-August) and (3) end of monsoon (EM; September). Our result highlights a significant temporal variability in REEs pattern showing a decreasing trend of Lan/Ybn and relatively higher Eu*/Eu anomaly during mid of monsoon compared to beginning and end of monsoon period. High palygorskite (P) with moderate smectite (S) is observed for beginning of monsoon and majority of mid monsoon samples, however, high smectite with moderate palygorskite and negligible palygorskite and smectite abundance is observed for few of mid monsoon and end of monsoon samples, respectively, indicating change in dust sources during the southwest monsoon period. We also observed temporal variability in 87Sr/86Sr (0.7090–0.7193) and εNd (−2.3 to −9.1) isotopic compositions wherein less radiogenic 87Sr/86Sr and relatively more positive εNd is exhibited by mid of monsoon samples compared to those observed in beginning and end of monsoon collections. The seasonal variability in geochemical tracers are related to changes in the dust source areas which are identified as (1) the Arabian Peninsula contributing significantly in beginning of monsoon and majority of mid monsoon samples; (2) Northeastern Africa contributing to some of the mid monsoon samples and (3) Southwest Asia and Thar Desert in end of monsoon samples. These source identification using geochemical tracers are corroborated by the satellite images (CALIPSO and aerosol index maps) and back-trajectory analyses.
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•Geochemical characterization of particulate from wet deposition over the Arabian Sea.•Significant temporal variability in dust characteristics during southwest monsoon.•Major contribution from Arabian Peninsula to aeolian dust over the Arabian Sea.•Contribution from Northeast Africa is also observed during SW monsoon.•Southwest Asia and Thar Desert contribution observed at end of SW monsoon.
Rapid development of agriculture and fossil fuel combustion greatly increased US reactive nitrogen emissions to the atmosphere in the second half of the 20th century, resulting in excess nitrogen ...deposition to natural ecosystems. Recent efforts to lower nitrogen oxides emissions have substantially decreased nitrate wet deposition. Levels of wet ammonium deposition, by contrast, have increased in many regions. Together these changes have altered the balance between oxidized and reduced nitrogen deposition. Across most of the United States, wet deposition has transitioned from being nitrate-dominated in the 1980s to ammonium-dominated in recent years. Ammonia has historically not been routinely measured because there are no specific regulatory requirements for its measurement. Recent expansion in ammonia observations, however, along with ongoing measurements of nitric acid and fine particle ammonium and nitrate, permit new insight into the balance of oxidized and reduced nitrogen in the total (wet + dry) US nitrogen deposition budget. Observations from 37 sites reveal that reduced nitrogen contributes, on average, ∼65% of the total inorganic nitrogen deposition budget. Dry deposition of ammonia plays an especially key role in nitrogen deposition, contributing from 19% to 65% in different regions. Future progress toward reducing US nitrogen deposition will be increasingly difficult without a reduction in ammonia emissions.
Atmospheric particulate matter (PM) pollution and soil trace metal (TM) contamination are binary environmental issues harming ecosystems and human health, especially in the developing China with ...rapid urbanization and industrialization. Since PMs contain TMs, the air-soil nexus should be investigated synthetically. Although the PMs and airborne TMs are mainly emitted from urban or industrial areas, they can reach the rural and remote mountain areas owing to the ability of long-range transport. After dry or wet deposition, they will participate in the terrestrial biogeochemical cycles of TMs in various soil-plant systems, including urban soil-greening trees, agricultural soil-food crops, and mountain soil-natural forest systems. Besides the well-known root uptake, the pathway of leaf deposition and foliar absorption contribute significantly to the plant TM accumulation. Moreover, the aerosols can also exert climatic effects by absorption and scattering of solar radiation and by the cloud condensation nuclei activity, thereby indirectly impact plant growth and probably crop TM accumulation through photosynthesis, and then threat health. In particular, this systematic review summarizes the interactions of PMs-TMs in soil-plant systems including the deposition, transfer, accumulation, toxicity, and mechanisms among them. Finally, current knowledge gaps and prospective are proposed for future research agendas. These analyses would be conducive to improving urban air quality and managing the agricultural and ecological risks of airborne metals.
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•Atmospheric dry and wet deposition input metals into soil-plant system.•Urban tree leaves remove atmospheric particulates and trace metals.•Foliar absorption of some airborne metals more than crop root uptake.•Aerosols impact solar radiation for plant photosynthesis and crop production.•Long-range atmospheric transport of trace metals impact mountain ecosystems.
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•Concentrations of Cu in rainwater and Zn in particulate were the highest among TEs.•Forest soils had higher Pb, Ni concentrations and lower Cd, Hg concentrations.•The Zn, Ni, Pb, and ...Cu have accumulated in forest vegetation and tissues.
The biogeochemical cycling of trace elements (TEs) in forest ecosystems is important because it plays a role in providing essential nutrients to plants and soils and because it can potentially have toxic effects. In this study, we investigated the concentration of TEs in atmospheric wet deposition, vegetation and soil in Qinghai spruce (QS) and Qilian juniper (QJ) forests of the Qilian Mountains. Our results show that the average concentrations of Cu in rainwater in QS and QJ forests were 10.30 and 5.35 μg L−1, respectively, the highest concentrations of all TEs in these environments. We suggest that the particulate matter present in the air was the main contributor of TEs in atmospheric wet deposition, which is affected by element specificity, regional factors, and the scavenging process during rainfall events. Most vegetation and tissues had high concentrations of Zn, Ni, Pb, and Cu, suggesting that these elements have accumulated in plants. The Zn, Pb, and Ni levels in forest plants may be correlated with those in forest soils. Our study highlights the role that atmospheric wet deposition can play in affecting TEs cycling across forest ecosystems. Managers need to further reduce TEs levels in emissions from surrounding sources and improve long-term observation of TEs in forest ecosystems.
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•Atmospheric wet deposition fluxes of TEs to forest were analyzed in Qilian Mountains.•Similarities and differences of wet deposition were discussed in two forest stands.•Potential ...influencing factors of TEs in wet deposition were investigated.•Three major sources were identified for particulate matter.•Industrial activities and waste incineration were the largest contributors of PM.
Atmospheric deposition is the main pathway by which trace elements (TEs) enter the terrestrial ecosystems, but few studies have investigated atmospheric TE deposition in remote forests. To understand the concentration, fluxes, influencing factors, and sources of TEs in atmospheric wet deposition, 104 samples from 13 rainfall events in two forest stands of the Qilian Mountains between July and September 2018 were collected and analyzed for eight TEs. The order of volume-weighted mean (VWM) concentration of TEs was Cu > Pb > Ni > Cr > Cd > As > Hg. Cu was the most abundant TE, with VWM concentrations of 6.33–10.90 μg L−1 in Qinghai spruce (PiceacrassifoliaKom.) forest and 3.21–7.48 μg L−1 in Qilian juniper (Juniperus przewalskii Kom.) forest, which were 2 or 3 orders of magnitude higher than those of Hg, respectively. The wet deposition fluxes of TEs in Qinghai spruce forest were larger than those in Qilian juniper forest. The rainfall amount, rainfall intensity, rainfall duration, relative humidity, and wind speed were found to be important factors influencing atmospheric TE deposition. Based on correlation analysis, Principal Component Analysis (PCA) and Positive Matrix Factorization (PMF) modeling, three major sources of particulate matter (PM) were identified, namely industrial activities and waste incineration, traffic emissions and coal combustion, and biomass burning. Industrial activities and waste incineration were the dominant contributors, accounting for 79% of PM mass. Our results confirm that long-range transport of TEs has a significant impact on remote forest ecosystems in the Qilian Mountains.
Precipitation samples collected at a remote high elevation site (i.e., Nam Co Station, 4730 m a.s.l.) in the southern Tibetan Plateau were analyzed for total mercury (HgT) between July 2009 and 2011, ...particulate-bound mercury (HgP) between July 2010 and 2011 and methylmercury (MeHg) from July through August of 2009. The volume-weighted mean (VWM) concentrations and wet deposition fluxes of HgT and MeHg in precipitation were 4.8 ng L⁻¹ and 1.75 μg m⁻² yr⁻¹, 0.031 ng L⁻¹ and 0.01 μg m⁻² yr⁻¹, respectively. VWM HgT concentration was approximately two times higher during the non-monsoon season than during the monsoon season, while 83% of the HgT wet deposition fluxes occurred during the monsoon season. The HgT and MeHg concentrations are comparable to the reported data for some of the most remote alpine and polar regions worldwide (e.g., Churchill), but the wet deposition fluxes of HgT and MeHg were among the lowest in the world. Analysis of Hg speciation has presented that HgP and MeHg concentrations are high, making up 71.2% and 1.82% of the HgT on average (VWM), respectively. The high HgP%, as well as a significantly positive between HgT and HgP (R² = 0.91; n = 44; p < 0.001), confirmed that atmospheric deposition of Hg in the Tibetan Plateau was occurring in the form of HgP. A decreasing trend in HgT concentrations with increasing amount of precipitation (R² = 0.08; N = 101; p < 0.005) was found at Nam Co Station, indicative that scavenging of HgP from the atmosphere was an important mechanism contributing Hg to precipitation. The precipitation amount, rather than HgT concentration, was found to be the governing factor affecting HgT wet deposition flux. Moreover, a comparison between measured wet deposition flux of Hg at Nam Co Station and the estimates from environmental records indicated that both snowpits and lake sediments appear to be reliable archives for estimating historical Hg accumulation rates over the Tibetan Plateau.
Lake Erhai is a potentially phosphorus (P)-limited lake and its water quality may have been affected by atmospheric P deposition. However, there have been few studies on atmospheric P deposition in ...this lake. In this study, we established five wet deposition monitoring sites and two dry deposition monitoring sites around Lake Erhai to quantify the wet and dry deposition of total phosphorus (TP), including dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP) and particulate phosphorus (PP) from July 2022 to June 2023. Wet deposition fluxes of P species were collected by automatic rainfall collection instrument, and dry deposition fluxes were estimated using airborne concentration measurements and inferential models. The results reveal that among the different P components, DOP had the highest contribution (50%) to wet TP deposition (average all sites 12.7 ± 0.7 mg P m2/yr), followed by PP (40%) and DIP (10%). Similarly, DOP (51%) was the major contributor to dry TP deposition (average two sites 2.4 ± 0.9 mg P m2/yr), followed by DIP (35%) and PP (14%). Wet deposition dominated the annual total TP deposition (wet plus dry), accounting for approximately 83%. The key seasons for dry deposition were spring and autumn, which accounted for 64% of the annual total dry TP deposition. In comparison, wet deposition was significantly higher in the summer, accounting for 73% of the annual total wet TP deposition. The results of the potential source contribution function and concentration-weighted trajectories analysis indicate that local source emission and long-range transport from surrounding cities jointly exerted a substantial influence on aerosol P concentrations, particularly in the eastern and northwestern regions of the lake. These findings provide a comprehensive understanding of the different P components in atmospheric deposition, which is beneficial for developing effective strategies to manage the P cycle in Lake Erhai.
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•Wet and dry fluxes of P were 12.7 and 2.4 mg P/m2/yr in Lake Erhai, respectively.•DOP contributed 50% and 51% of total wet and dry P deposition fluxes, respectively.•Wet deposition peaked in summer, while dry deposition peaked in autumn or spring.•Total TDP deposition flux accounted for approximately 7% of the riverine TDP inputs.•Local emission sources and regional transport jointly affected P deposition.
The temporal and spatial patterns of nitrogen wet deposition were investigated in the Pearl River Delta (PRD) under different weather types. The study was carried out in 27 monitoring sites with ...reliable meteorological data from 2010 to 2017. Large spatial variation data showed that both annual volume weighted mean (VWM) concentrations and fluxes were higher in the central PRD while lower in the outer area. The annual mean concentrations and fluxes were in the range of 0.8–1.3 mg N L−1 and 10.9–20.6 kg N ha−1 yr−1, respectively. The monthly mean concentrations and fluxes ranged from 0.1 to 0.2 mg N L−1 and 0.4 to 2.4 kg N ha−1, respectively. Further the study data revealed that the ratio of NH4+/NO3− was 1.1 which was much lower than the ratio reported in other regions like Northern China, Sichuan Basin, the US and Europe. The flux of NH4+ in urban sites was comparable to rural sites, implying that potential non-agricultural NH3 emissions were likely to be high in the PRD. The top three weather types were E, C and SE, with the total contribution of more than a half to the flux. Multiple linear regression was used to set up an equation to predict the variation of annual fluxes under the changes in weather conditions. The result hints that the variation on annual fluxes in the PRD tends to be stable in the next 30 years. Considering the increasing impact on the ecosystem, more effort should be exerted to reduce nitrogen wet deposition in the future.
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•Easterly (E) weather type has the greatest influence on N deposition flux.•The proportion of NO3− was similar to NH4+ both in monthly and annual fluxes.•Sites in the Central Pearl River Delta (PRD) have the higher N deposition.•The trend of wet deposition flux induced by changes of weather tends to be stable.
A quantitative understanding of the roles of rainfall and pollutant concentrations in wet deposition is important because they critically influence terrestrial and aquatic ecosystems. However, their ...relative contributions to wet deposition, which vary across regions, have not yet been identified. We propose two methods that quantitatively separate the contributions of rain and pollutant concentrations to wet deposition: one is based on simplified equations describing the wet scavenging of pollutants and the other is based on random forest models employing SHapley Additive exPlanations. Three-dimensional long-term air quality simulations from 2003 to 2019 are used as inputs for both the physics-based and machine learning models. Remarkably, the results drawn from the explainable machine learning model are consistent with those from the physics-based approach: overall, rain is a more important limiting factor than pollutant concentrations and the relative contribution of rain is larger than that of pollutants by up to a factor of 3–4 in polluted regions. In polluted regions, pollutant concentrations can remain relatively high even in the presence of precipitation owing to continuous and intense emissions; therefore, wet deposition is limited by rainfall. The contribution of rainfall is larger by 1.5–2.5 than that of pollutant concentrations in regions even with low emissions and this considerably large role of rain suggests that regional or transboundary pollutant transport plays a key role in modulating wet deposition. However, in very remote regions, once the rainfall amount exceeds a certain value, rainfall no longer contributes to increasing wet deposition because atmospheric pollutants are readily removed by rain. So, the contributions of the two factors are comparable in pristine regions. Our results can serve as a basis for explaining interannual variations in wet deposition and for future projections of wet deposition under emission control plans and climate change scenarios across regions.
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•A physics-based method is proposed to separate rain-dominant and concentration-dominant wet deposition from total one•Random forest models are trained to predict wet deposition, contributions of rain and concentration are quantified by SHAP•The two methods agree well with each other•Rain is a more important contributor than pollutants in polluted regions by a factor of 3–4•In pristine regions, rain and pollutants have comparable contributions
Recent laboratory studies suggest that secondary organic aerosol (SOA) formation rates are higher than assumed in current models. There is also evidence that SOA removal by dry and wet deposition ...occurs more efficiently than some current models suggest and that photolysis and heterogeneous oxidation may be important (but currently ignored) SOA sinks. Here, we have updated the global GEOS-Chem model to include this new information on formation (i.e., wall-corrected yields and emissions of semi-volatile and intermediate volatility organic compounds) and on removal processes (photolysis and heterogeneous oxidation). We compare simulated SOA from various model configurations against ground, aircraft and satellite measurements to assess the extent to which these improved representations of SOA formation and removal processes are consistent with observed characteristics of the SOA distribution. The updated model presents a more dynamic picture of the life cycle of atmospheric SOA, with production rates 3.9 times higher and sinks a factor of 3.6 more efficient than in the base model. In particular, the updated model predicts larger SOA concentrations in the boundary layer and lower concentrations in the upper troposphere, leading to better agreement with surface and aircraft measurements of organic aerosol compared to the base model. Our analysis thus suggests that the long-standing discrepancy in model predictions of the vertical SOA distribution can now be resolved, at least in part, by a stronger source and stronger sinks leading to a shorter lifetime. The predicted global SOA burden in the updated model is 0.88 Tg and the corresponding direct radiative effect at top of the atmosphere is −0.33 W m−2, which is comparable to recent model estimates constrained by observations. The updated model predicts a population-weighed global mean surface SOA concentration that is a factor of 2 higher than in the base model, suggesting the need for a reanalysis of the contribution of SOA to PM pollution-related human health effects. The potential importance of our estimates highlights the need for more extensive field and laboratory studies focused on characterizing organic aerosol removal mechanisms and rates.
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