Air pollution caused by sulphur dioxide (SO2) and nitrogen oxides (NOx) has negative impacts on forest health and can initiate forest dieback. Long-term monitoring and analysis of these pollution are ...carried out in Białowieża Forest in NE Poland due to the threats from abiotic, biotic and anthropogenic factors. The main objective of our study was to monitor the levels and trends of air pollutant deposition in Białowieża Forest. During a short-term monitoring period over six years (2014–2021), the concentration of SO2 in the air decreased significantly (from 2.03 μg m−3 in December 2015 to 0.20 μg m−3 in July 2016), while the concentration of NO2 in the air showed a non-significant decrease (from 8.24 μg m−3 in December 2015 to 1.61 μg m−3 May 2016). There was no significant linear trend in the wet deposition of S–SO4 anions. Mean monthly S–SO4 deposition varies between 4.54 and 94.14 mg m−2month−1. Wet nitrogen deposition, including oxidized nitrogen (N–NO3) and reduced nitrogen (N–NH4), showed a non-significant increase. Mean monthly precipitation of N–NO3 and N–N H4 ranged from 1.91 to 451.73 mg m−2month−1. Neither did total sulphur deposition nor total nitrogen deposition exceed the mean deposition values for forests in Europe (below 6 ha−1yr−1 and 3–15 ha−1yr−1, respectively). Our results indicate that air pollutants originate from local sources (households), especially from the village of Białowieża, as demonstrated by the level and spatial distribution of air pollutant deposition. This indicates that air pollutants from the village of Białowieża could spread to other parts of Białowieża Forest in the future and may have a negative impact on forest health and can initiate forest dieback. It is therefore important to continue monitoring air pollution to assess the threats to this valuable forest ecosystem.
•Deposition of S in Białowieża Forest didn't exceed deposition for forests in Europe.•Deposition of N in Białowieża Forest didn't exceed the limit for managed forests.•The deposition (S and N) was highest in the Białowieża Glade (central part of BF).•The deposition (S and N) was lowest in the southern part of Białowieża Forest.
Wet deposition has been well recognized to be affected by species concentration and precipitation; nevertheless, the regimes in the controlling factor of concentration or precipitation have not yet ...been clarified. Using a trace element, selenium (Se), with dual effects on human health as a testbed, we first reproduce the spatial distribution of atmospheric Se concentrations and wet deposition fluxes through GEOS-Chem on a global scale, and examine the spatial patterns and relative importance of anthropogenic emissions vs. natural emissions over various regions around the world. We find that over most Northern Hemisphere continental regions, anthropogenic emissions are the dominant source for atmospheric Se concentration and deposition, while it is dominated by natural sources in the other areas. Nested grid simulations covering China and the continental United States are further conducted. The factors (i.e., Se concentration and precipitation) controlling the wet deposition flux of atmospheric Se are analyzed in detail, through the construction of wet deposition-concentration-precipitation (WETD-C-P) diagram for two regions (mainland China and the continental United States) based on the monthly results. The two regions show distinctive features, reflecting the different spatial patterns of Se emissions and precipitation. Both Se emissions and precipitation are higher in the eastern United States than that in the western United States. In contrast, the emissions and precipitation in northern and southern China show dipole features with stronger emissions over the northern side and higher precipitation on the southern side. We further investigate the impacts of future emission changes in China on atmospheric Se deposition and its sensitivity to emissions and precipitation, revealing a modulation of regime shifts, i.e., from the precipitation dominant regime to the concurrent governance of both precipitation and emissions. The proposed WETD-C-P relationship is useful in elucidating the regime and factors governing the spatial and temporal variations in wet deposition.
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•Examine the spatial pattern of atmospheric Se concentration and wet depositions•Reveal the wet deposition-concentration-precipitation relationship of Se•Discover a modulation regime shift of Se wet deposition in the case of SSP1-2.6
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.
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
Rainwater chemistry of extreme rain events is not well characterized. This is despite an increasing trend in intensity and frequency of extreme events and the potential excess loading of elements to ...ecosystems that can rival annual loading. Thus, an assessment of the loading imposed by hurricane/tropical storm (H/TS) can be valuable for future resiliency strategies. Here the chemical characteristics of H/TS and normal rain (NR) in the US from 2008 to 2019 were determined from available National Atmospheric Deposition Program (NADP) data by correlating NOAA storm tracks with NADP rain collection locations. It found the average pH of H/TS (5.37) was slightly higher (p < 0.05) than that of NR (5.12). On average, H/TS events deposited 14% of rain volume during hurricane season (May to October) at affected collection sites with a maximum contribution reaching 47%. H/TS events contributed a mean of 12% of Ca2+, 22% of Mg2+, 18% of K+, 25% of Na+, 7% of NH4+, 6% of NO3−, 25% of Cl− and 11% of SO42− during hurricane season with max loading of 77%, 62%, 94%, 65%, 39%, 34%, 64% and 60%, respectively, which can lead to ecosystems exceeding ion-specific critical loads. Four potential sources (i.e., marine, soil dust, agriculture and industry/fossil fuel) were indicated by PCA. The positive matrix factorization (PMF) suggested Mg2+, Na+ and Cl− were primarily marine-originated in both event types, while 36% more sea-salt Ca2+ and 33% more sea-salt SO42− were deposited during H/TS. Agriculture and industry/fossil fuel were the main sources of NH4+ and NO3−, respectively, in both rain event types. However the NH4+ contribution from industry/fossil fuel increased by 13% during H/TS indicating a potential vehicle source associated with emergency evacuations. This work provides a comprehensive assessment of the rainwater chemistry of H/TS and insight to expected ecosystem loading for future extreme events.
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•H/TS can contribute large rain amount and ion depositions within hours.•The large ion deposition can help exceed potential critical load of ecosystem.•Mg2+, Ca2+ and SO42− are more correlated with Na+ and Cl− during H/TS•H/TS can entrain more marine materials and deposit more sea-salt ions.•An increased NH4+ emission from industry/fossil fuel was observed during H/TS.
In order to investigate the wet and dry deposition fluxes of the water-soluble organic carbon (WSOC) and water-insoluble organic carbon (WIOC) and to clarify the factors influencing them, a ...simultaneous observation of the WSOC and WIOC in both the wet and dry deposition and in the aerosols was conducted for 2 years at an urban site in central Japan. The average deposition fluxes of the WSOC and WIOC by the wet process were 3.514 and 1.719 mgC m−2 day−1, respectively, and those by the dry process were 0.346 and 0.822 mgC m−2 day−1, respectively. About 82% of the organic carbon (OC) that is the sum of the WSOC and WIOC was deposited by the wet process. A large contribution of the wet process to the atmospheric deposition was found not only for the WSOC but also for the WIOC; the contribution of the wet process to the atmospheric deposition was about 91% for the WSOC and about 68% for the WIOC. About 67% of the OC in the wet deposition was explained by the WSOC, whereas about 70% of the OC in the dry deposition was by the WIOC. The WSOC in the coarse aerosols (d = 2.0–10 μm) in the surface atmosphere had a significant impact on the wet deposition flux of the WSOC. In addition, the length of the rainy period also strongly influenced the wet deposition flux of the WSOC. On the other hand, the WIOC in the wet deposition would be influenced by its concentration not only in the ground surface aerosols but also in the upper atmospheric aerosols. The dry deposition fluxes of the WSOC and WIOC were significantly affected by their concentrations in the aerosols with the diameters larger than 10 μm (PM>10). The dry deposition of the PM>10 aerosols in the surface atmosphere had a significant impact on the OC deposition by the dry process.
•The wet process occupies 91% and 68% of the WSOC and WIOC deposition, respectively.•About 67% of the OC in the wet deposition was explained by the WSOC.•About 70% of the OC in the dry deposition was explained by the WIOC.•Wet deposition of the WSOC is affected by the coarse aerosols and rainfall duration.•Dry deposition of the WSOC and WIOC is significantly affected by the PM>10 aerosols.
The Himalayan–Tibetan Plateau is a typical remote region with sparse air pollution. However, air pollution in cites of the inner Himalayan–Tibetan Plateau is relatively serious due to emissions from ...local residents. Carbonaceous aerosols are not only an important component of air pollutants that affect the health of local residents but also an important trigger of climate change. In this study, the annual wet and dry deposition rates of carbonaceous particles were investigated in Lhasa—a typical city in the Himalayan–Tibetan Plateau, by collecting precipitation and dry deposition samples and analyzing with a thermal-optical measurement protocol. The results showed that the in-situ annual wet deposition rates of water-insoluble organic carbon (WIOC) and black carbon (BC) were 169.6 and 19.4 mg m−2 yr−1, respectively, with the highest and lowest values occurring in the monsoon and non-monsoon periods, respectively. Both precipitation amounts and concentrations of WIOC and BC contributed to wet deposition rates. The dry deposition rates of WIOC and BC in Lhasa had an opposite seasonal variation to that of wet deposition, with annual average deposition rates of 2563.9 and 165.7 mg m−2 yr−1, respectively, which were much higher than those of the nearby glacier region and remote area. These values were also much higher than the results from modeling and empirical calculations, indicating that Lhasa is a high pollution point that cannot capture by models. The results in this study have significant implications for the transport of local emissions in Lhasa to the nearby remote and glacier regions.
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•High in-situ black and organic carbon deposition rates were reported in Lhasa.•High deposition rates were mainly resulted from local emissions in Lhasa.•Dry deposition is more important than wet deposition in Lhasa particle scavenging.
To determine the seasonal variations in the removal efficiency of fine aerosols (PM2.5) in the Northeast Asia, we analyzed 7Be data collected for the surface air and precipitation over 20 years in ...Korea. The 7Be activity concentrations in the surface air were relatively higher in spring owing to tropopause folding but lower in summer owing to efficient removal by precipitation. The monthly 7Be concentrations decreased as the precipitation amounts increased showing a negative correlation (r2 = 0.34) against the precipitation amount. These results indicate that the concentrations of 7Be and fine aerosols are mainly controlled by the same washout effect, although the sources are different. The mean depositional velocities of fine aerosols, based on the 7Be mass balance model, showed a large seasonal variation, with its maximum value (1.9 cm s−1) in July and minimum value (0.22 cm s−1) in March. The 7Be depositional velocity reflects the net deposition of fine aerosols excluding moisture effects. Thus, the concentrations of fine aerosols can occur as high as five-fold in the dry season, if the input terms of fine aerosols remain the same. Our results imply that precipitation plays a critical role in the seasonal changes in the concentrations of fine aerosols, providing much clean air in the summer monsoon season in the Northeast Asia.
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•The highest 7Be activities were observed in spring due to large stratospheric air inputs.•The lowest 7Be activities were observed in summer due to larger removal by precipitation.•The deposition velocity of fine aerosols was maximum in summer due to large precipitations.•The residence time of fine aerosols in winter is 5-fold longer than that in summer.
The Congo River supplies vast quantities of trace metals (TMs) to the South Atlantic Ocean, but TM budgets for the Congo plume derived using radium isotopes for GEOTRACES cruise GA08 suggest ...additional input other than the river outflow. Considering the tight correlations between most dissolved TMs and salinity in the plume and the high rainfall during the wet season over the Congo shelf, we hypothesized that wet atmospheric deposition is a TM source to the Congo plume. Observed TM concentrations in rainwaters across the Congo shelf were mostly comparable to values from previous work in the North Atlantic and Mediterranean Sea. Wet deposition contributed the equivalent of 43% dCd, 21% dCu, 20% dPb and 68% dZn of the Congo River fluxes. Our findings show an important role of wet deposition in supplying TMs to the South Atlantic overlapping with the region that receives substantial TM fluxes from the Congo River.
Plain Language Summary
The Congo River has the second largest freshwater discharge volume globally and creates an extensive near‐equatorial plume into the Atlantic Ocean. The Congo plume constitutes an important source of trace metals (TMs) to the ocean, which impacts biogeochemical cycles in the tropical and subtropical ocean. However, existing work suggests a discrepancy within the TM budgets in the Congo plume and points to unknown source other than the Congo River or shelf sediments. Most TM concentrations across the Congo plume remain tightly correlated with salinity, suggesting that any additional sources are likely also freshwater‐derived or enter the ocean at the river mouth coincidently with direct riverine TM inputs. Here, TM concentrations in ocean, river and rainwater collected during the GEOTRACES GA08 cruise are combined to suggest that wet deposition augmented some Congo TM fluxes to the ocean. Fluxes of anthropogenic Cd, Cu, Pb and Zn to the Congo shelf from wet deposition are of the same order of magnitude as the Congo River. Concentrations of these elements in rainwater are similar to prior observations reported for the North Atlantic and Mediterranean Sea, suggesting that a large fraction of the global range of rainwater concentrations over the ocean has been captured in our observations.
Key Points
The Congo River is an important source of trace metals (TMs) to the South Atlantic Ocean revealed by data from GEOTRACES cruise GA08
Wet deposition (rainfall) is identified as an additional TM source to the Congo plume by concurrently considering river and rain data
Rainfall supplies anthropogenic dTMs (Cd, Cu, Pb and Zn) with fluxes equivalent to 20%–68% of those from the Congo River on the Congo shelf
Atmospheric wet deposition (AWD) is an important pathway for anthropogenic and natural pollutants entering aquatic ecosystems. However, the study on the magnitudes and ecological effects of AWD of ...various nutrient species (nitrogen, phosphorus and silicon) on Jiaozhou Bay is scarce. To address these issues, in this study, wet deposition samples were collected at a coastline site along Jiaozhou Bay from June 2015 to May 2016. Dissolved inorganic nitrogen (DIN, including NH4–N, NO3–N and NO2–N), dissolved organic nitrogen (DON), dissolved inorganic phosphorus (DIP, i.e. PO4–P), dissolved organic phosphorus (DOP) and reactive silicate (SiO3–Si) were analyzed. The volume-weighted mean (VWM) concentrations of NH4–N, NO3–N and DON in AWD were higher compared with those of NO2–N, PO4–P, DOP and SiO3–Si. The annual influxes of NH4–N, NO3–N, NO2–N, DON, DIP, DOP, and SiO3–Si via AWD were 92.8, 54.5, 0.427, 47.5, 0.274, 0.448 and 1.73mmol·m−2·yr−1 respectively; NH4–N and DOP were the dominant species for N and P, and the roles of DON and DOP in AWD could not be neglected. Significant seasonal variations were observed in concentrations and fluxes of all nutrient species owing to the effects of rainfall, the intensities of local emission sources and the long-distance transports of natural and anthropogenic pollutants. The major sources of N, Si and P in AWD were agricultural activities, soil dust and a mixing one involving both anthropogenic and natural sources, respectively. Though AWD represents relatively low percentages of external inputs for nutrients and low contribution to primary productivity (PP) of Jiaozhou Bay, large amounts of nutrient inputs originating from sudden heavy rains may enhance PP prominently, as well as aggravate P-limitation and Si-limitation and further affect phytoplankton community structures and size-fractioned structures with the quite high DIN:DIP ratios and extremely low Si:DIN ratios in AWD.
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•Concentrations and fluxes of various nutrient species were analyzed.•The impacting factors of seasonal variations of nutrients in AWD were illustrated.•DON, DOP occupied 24.3% and 62.0% of the AWD fluxes of TDN and TDP, respectively.•AWD would aggravate the P- and Si-limitation of surface waters.•Sudden heavy rains affect PP and community structures of phytoplankton.
