Wet Deposition Fluxes Research Articles

Estimating dry deposition of atmospheric aerosols to urban surfaces by rain washoff

Atmospheric aerosols accumulate onto urban surfaces by dry deposition and are subsequently washed off by rain. If there is a sufficiently long period of dry weather, it may be possible to estimate the dry deposition rate of a chemical species by measuring its concentration in runoff from the surface and its concentration in fresh rain. This hypothesis was tested for horizontal surrogate surfaces exposed to the atmosphere in Syracuse, New York. In each experiment, two flat disks 1 m diameter with 2.54 cm rims and two disks of similar size but without rims were exposed to the atmosphere on the roof of Hinds Hall at Syracuse University to collect dry deposition of aerosol fluoride, chloride, sulfate, potassium, calcium, and strontium. Airborne concentrations were measured simultaneously to calculate dry deposition velocities. Dry deposited material on the flat disks was removed using a Teflon scraper after a few days of exposure, just prior to a rainstorm. In the subsequent storm, sequential samples of runoff from the rimmed disks and fresh rain were collected. The concentrations in fresh rain were subtracted from the concentrations in the runoff to calculate dry deposition fluxes, which were compared to fluxes measured by scraping the flat disks prior to rain. Results showed that sufficient removal of dry deposited material was possible to estimate dry deposition fluxes. Ratios of the mean dry deposition flux onto the rimmed disks to the mean dry deposition flux onto the flat disks had an overall average of 0.89 for all chemical species. This ratio mean and standard deviation was 0.94±0.30 for fluoride, 0.59±0.54 for chloride, 1.0±0.10 for sulfate, 0.80±0.28 for potassium, 1.0±0.03 for calcium, and 0.93±0.12 for strontium. However, some dry deposition fluxes to the rimmed disks were smaller than those to the flat disks in cases where the wet deposition flux was at least one half of the contribution to the total flux. This suggests the importance of having antecedent dry periods of at least several days to use this method to estimate dry deposition of aerosols and to minimize the role of contaminants in the fresh rain contributing significantly to the total concentration in the runoff samples. Future work includes testing this method on rooftops and other horizontal urban surfaces, which may enable reliable estimates of dry deposition rates to urban areas.

Concentrations, sources, fluxes, and absorption properties of carbonaceous matter in a central Tibetan Plateau river basin

Carbonaceous matter (CM) (such as water-insoluble organic carbon (WIOC), black carbon (BC), and water-soluble organic carbon (WSOC)) has a significant impact on the carbon cycle and radiative forcing (RF) of glacier. Precipitation samples and glacier's snow/ice samples (snowpit, surface snow, and granular ice) (Xiao dongkemadi Glacier) were collected at the Dongkemadi River Basin (DRB) in the central Tibetan Plateau (TP) between May and October 2016 to investigate the characteristics and roles of CM in the TP River Basin. WIOC, BC, and WSOC concentrations in precipitation were relatively higher than that in snowpit, but lower than that in surface snow/ice, with the wet deposition fluxes of 0.10 ± 0.002, 0.04 ± 0.001, and 0.12 ± 0.002 g C m−2 yr−1 at DRB, respectively. The positive matrix factorization model identified four major sources (biomass burning source, secondary precursors, secondary aerosol, and dust source) of CM in precipitation at DRB. Two source areas (South Asia and the interior of TP) contributing to the pollution at DRB were identified using a potential source contribution function model, a concentration-weighted trajectory method, and the back-trajectory model. Moreover, the light-absorption by WSOC in the ultraviolet region was 23.0%, 12.1%, and 3.4% relative to the estimated total light-absorption in precipitation, snowpit, and surface snow/ice, respectively. Optical indices analysis revealed that WSOC in snowpit samples presented higher molecular weight, while presented higher aromatic and higher molecule sizes in surface snow/ice and precipitation samples, respectively. RF by WSOC relative to that of BC was estimated to be 17.6 ± 17.6% for precipitation, 10.9 ± 5.8% for snowpit, and 10.7 ± 11.6% for surface snow/ice, respectively, during the melt season in the central TP River Basin. These results help us understand how CM affects glaciers, and they can be utilized to create policies and recommendations that efficiently reduce emissions.

Improvement and Uncertainties of Global Simulation of Sulfate Concentration and Radiative Forcing in CESM2

AbstractSulfate is a major atmospheric pollutant and radiative forcing (RF) factor that influences air quality, cloud microphysics, and climate. Therefore, a better evaluation of sulfate concentrations and RF patterns is essential for policy‐making and the management of air pollution and climate change. This study comprehensively estimates the global distribution of sulfate concentrations and RFs and analyzes the sources of uncertainty in the Community Earth System Model version 2 and the Parallel Offline Radiative Transfer model. Compared with the observations, the incorporation of detailed in‐cloud aqueous‐phase chemistry and the enhanced wet deposition (WD) flux of sulfate significantly improved the simulations of sulfur species both near the ground and at high altitudes, which is beneficial for a more accurate estimation of the global RF of sulfate. The improved simulated RF of sulfate from 1850 to 2015 is −0.502 Wˑm−2. This study finds that WD is the key process governing both the horizontal and vertical distributions of sulfate concentrations. The overestimation of surface sulfate and the underestimation of high‐altitude sulfate made by the model are essential uncertainty factors of the sulfate RF estimation. This study emphasizes the importance of improving the simulation of global sulfate distribution as well as its RF, which may strongly pressure the near‐future warming potential when witnessing a rapid transition to a carbon neutral world that is phasing out fossil fuel. A more accurate assessment of sulfate levels and radiation effects will play a remarkable guiding role in the formulation of global emission reduction‐related policies in the future.

A long-term overview of nitrogen in tropical rainwater and wet deposition fluxes in southern Brazil

This work reports inorganic and organic nitrogen concentrations in rainwater and estimates wet deposition fluxes in an agro-industrial region of São Paulo State (Brazil) impacted by biomass burning and vehicular public policies, spanning the period from 2005 to 2020. The overall volume weighted mean (VWM) concentration of nitrate in rainwater was 13.1 ± 0.5 μmol L−1 (n = 696). Despite decreasing vehicular emissions of NOx over the study period, there was no clear trend of nitrate concentrations in rainwater, possibly due to biomass burning emission sources. The overall ammonium VWM concentration was 24.3 ± 1.1 (n = 696). In contrast to nitrate, there was a 94% increase of ammonium in 16 years, attributed to increased emissions from vehicles and fertilizer use, together with variable biomass burning emissions. Dissolved organic nitrogen (DON) concentrations in individual samples ranged from 0.2 to 153 μmol N L−1, corresponding to between 1 and 73% of the total dissolved nitrogen, with VWM of 18.9 ± 0.9 μmol N L−1 (n = 377). Amino acids corresponded, on average, to 15% of the DON. For the majority of the years, the VWM concentrations of nitrate, ammonium, and DON were higher for the pool of samples collected during the dry season, compared to the wet season. These results highlighted the importance of biomass burning sources of reactive nitrogen in drier months, when wildfires are common. The wet deposition flux of total dissolved nitrogen was ∼12 kg N ha−1 yr−1, with ammonium corresponding to 43%, followed by DON (33%) and nitrate (23%). These results demonstrated the importance of including DON when modeling the biogeochemical cycle of nitrogen, especially in a world where wildfires may become more frequent and intense.

Atmospheric wet deposition serves as an important nutrient supply for coastal ecosystems and fishery resources: Insights from a mariculture area in North China

To determine the ecological effects of atmospheric wet deposition of dissolved nutrients on the coastal waters around the Yangma Island, rain and snow samples were collected and analyzed at a shore-based site for one year. The wet deposition fluxes of dissolved inorganic nitrogen and phosphorus (DIN and DIP) and dissolved organic nitrogen and phosphorus were 69.2, 0.136, 13.3 and 0.143 mmol m −2 a −1 , respectively. In summer, the new production fueled by wet deposition accounted for 19.3 % of that in seawater and 16.4 % of the amount of particulate organic carbon ingested by the scallops cultivated in the study area, indicating the potential contribution of wet deposition to fishery resources. Meanwhile, precipitation increased the seasonal average DIN/DIP ratios in surface seawater by 17.7 %, 16.3 %, 23.4 % and 6.5 % in spring, summer, autumn and winter, respectively, which could change the composition of ecological community and cause obvious negative impact on the ecosystem and mariculture. • The annual wet deposition flux of DIN contributed to 34.4 % of the DIN load. • Wet deposition may exacerbate the unbalance of DIN and DIP in coastal waters. • Wet deposition could support 19.3 % of the new production of the study area in summer. • Wet deposition could serve as an important source for fishery resources in summer. • Summer deoxygenation was partly related to excessive N input by wet deposition.

Precipitation scavenging of beryllium-7 (7Be): Observation results and parameterization

This study aims to develop a 1D model that makes it possible to calculate the daily total 7Be wet deposition flux. For this purpose, long-term (2015–2021), high-frequency (daily) and time-synchronized series of observations of 7Be wet deposition flux and its atmospheric activity concentration are analyzed in this paper. Daily mean 7Be activity concentration in the atmosphere, daily total 7Be wet deposition flux and mean 7Be activity concentration, washout ratio, deposition velocity and scavenging coefficient with individual precipitation events lie in the range of 0.1–17 mBq m−3, 0.8–117.2 Bq m−2 d−1, 0.4–11.3 Bq L−1, 331–3799, 0.2–24.7 cm s−1 and (0.8–35.6) × 10−5 s−1, respectively. Quantitative estimates of the influence of precipitation parameters (amount, intensity and duration) on the daily total 7Be wet deposition flux, mean 7Be activity concentration in precipitation, washout ratio, deposition velocity and scavenging coefficient with individual precipitation events have been obtained using correlation analysis. It has been found that precipitation amount has the greatest influence on 7Be deposition flux and deposition velocity, precipitation intensity has the greatest influence on washout ratio and scavenging coefficient, and precipitation duration has the greatest influence on 7Be activity concentration in precipitation. The relationships between these parameters have been parameterized. Based on these parameterizations, five 1D models that calculate the daily total 7Be wet deposition flux have been introduced and validated against the observation data. It has been revealed that the model, which is based on deposition velocity parameterization and uses the data on 7Be activity concentration in the atmosphere and the daily amount of precipitation as predictors, reproduces the highest fraction of the observational data (88%) with the lowest average calculation error (32%) compared to the other four models.

Assessment of aeolian dust concentration, elemental composition, and their wet and dry deposition fluxes over the Northeast Arabian Sea

ABSTRACT Atmospheric aerosol over the Arabian Sea is significantly impacted by the long-range transported mineral dust from the surrounding continents. This transported mineral dust is hypothesized and tested during several studies to see the impacts on the surface ocean biogeochemical processes and subsequently to the Carbon cycle. It is, thus important to quantify dust contributions and their fluxes to the Arabian Sea. Here we assess temporal variability of dust concentration, their elemental characteristics as well as quantify their dry and wet deposition fluxes over the North-eastern Arabian Sea. The dust concentrations were found to vary from 59 to 132 µg m−3 which accounts for 50% to 90% of total mass during dusty days. However, its contribution during pre and post dust storms ranges between 6% and 60%. Relatively higher dust dry deposition flux of 28 ± 7 mg m−2 day−1 (range: 20–44) is estimated for dusty days compared to pre and post dusty days (range: 0.4–22 mg m−2 day−1). In contrast to dry deposition fluxes, significantly higher fluxes are estimated from wet deposition, averaging around 240 ± 220 mg m−2 day−1. These values are five times higher than those reported from cruise samples collected over the Arabian Sea. The contribution of dust to aerosol mass is further ascertained using elemental composition, wherein a significant correlation was observed between Fe and Al (r2 = 0.77) for samples collected during the dusty period, highlighting their similar crustal sources. Our estimation of dust flux over this region has implications for the supply of nutrients associated with natural dust to the surface water of the Arabian Sea. Implications: The Arabian Sea, one of the productive oceanic regions among the global oceans, has been identified as a perennial source of atmospheric CO2. This basin is heavily impacted by atmospheric dust deposition/inputs owing to its geographical location being surrounded by arid and semi-arid regions. It has been hypothesized that aeolian dust plays a significant role in modulating surface water biogeochemical processes including primary productivity, in the Arabian Sea. Furthermore, modelling studies have highlighted on the role of dust (containing Fe) in fueling and enhancing primary productivity in the Arabian Sea. However, quantification of dust deposition fluxes (wet and dry) on seasonal time scale is missing in the literature. This paper aims to partially fulfil this research gap by providing a long-term data of wet and dry deposition fluxes over the northeastern Arabian Sea. We have also discussed their seasonal variability and factors affecting this flux. Thus, this study will be valuable contribution to the aeolian research community and have significant implication toward the role of aeolian deposition to the surface water biogeochemical processes in the Arabian Sea.

Signatures of Indian endosulfan usage in China's environment

Endosulfan, as an organochlorine pesticide (OCPs), was widely used in agriculture. As the largest endosulfan user country in the world and adjacent to China, it is interesting to know to what extent the endosulfan usage of India could affect the environment in China. In this study, we established gridded endosulfan usage, atmospheric emission, and soil residue inventories in 2010 based on its application in different crops in China and India. We employed an atmospheric transport model CanMETOP to simulate atmospheric and soil concentrations, as well as dry and wet deposition flux of α- and β-endosulfan. Results were used to assess the signatures of Indian endosulfan usage in the China's environment. In 2010, endosulfan usage, atmospheric emissions, and highest soil residue in China were 3083.9, 1312.7, and 587.5 tonnes, and 3204.8, 1441.4, and 463.7 tonnes in India, respectively. The spatial distribution of modeled atmospheric and soil concentrations, and dry deposition fluxes of endosulfan were in line with its usage but wet deposition fluxes were mainly identified in Southern China and Sichuan basin with heavy rainfall, especially for α-endosulfan. Endosulfan tended to transport from India to Tibetan plateau, Yunnan-Kweichow Plateau, and some provinces in southern China under the Indian Summer Monsoon regime. Due to its stronger volatility, α-endosulfan posed a more significant impact on China's environment via the atmospheric transport from India compared to β-endosulfan. Although rainfall during Indian Summer Monsoon reduced endosulfan levels in the air during its journey from India to China, it was observed that Indian endosulfan usage in 2010 contributed more than 50% of atmospheric concentrations and 30% of soil concentrations of α-endosulfan in some regions in Tibetan plateau.

Deposition Characteristics of Water-soluble Inorganic Nitrogen and Organic Nitrogen in Atmospheric Precipitation in the Northern Suburbs of Nanjing

Based on atmospheric precipitation collected in the northern suburbs of Nanjing from 2019 to 2020, the pH, conductivity, and chemical components of precipitation were analyzed. The seasonal variation in pH and conductivity of atmospheric precipitation in the northern suburbs of Nanjing were studied. The pollution levels and deposition characteristics of water-soluble inorganic nitrogen (WSIN) and organic nitrogen (WSON) in precipitation were also analyzed. The frequency of acid rain (pH<5.6) in atmospheric precipitation in the northern suburbs of Nanjing reached 37.18% during the observation period. Precipitation acidification was more serious in autumn and winter, and the pH value showed a variation trend of spring>summer>autumn>winter. The average conductivity of precipitation was 29.49 μS·cm-1; high pH and conductivity in spring were related to the high dust content in the atmosphere. The seasonal difference between WSIN and WSON in precipitation was significant. The highest and lowest concentrations of NO3--N and NH4+-N appeared in spring and summer, respectively. The concentration of WSON was the highest in autumn (2.63 mg·L-1). The average concentration ratio of WSON to water-soluble total nitrogen (WSTN) in precipitation was approximately 0.47, indicating that WSON played an important role in the study of total nitrogen. The average wet deposition fluxes of WSIN and WSON were 12.10 kg·(hm2·a)-1 and 11.13 kg·(hm2·a)-1, respectively, in which the inorganic nitrogen deposition was mainly NH4+-N.

Biogeochemical properties and fate of dissolved organic matter in wet deposition: Insights from a mariculture area in North Yellow Sea

To address the potential roles of atmospheric wet deposition in carbon cycling in coastal waters, a comprehensive study of the biogeochemical properties of dissolved organic matter (DOM) in precipitation and the resulting implication in a mariculture area in North Yellow Sea was conducted. The annual mean concentrations of dissolved organic carbon (DOC), chromophoric and fluorescent dissolved organic matter (CDOM and FDOM) were 1.52 ± 1.52 mg C L−1, 0.36 ± 0.66 m−1 and 0.38 ± 0.35 QSU, respectively. The concentrations of most DOM proxies exhibited significant negative correlations with the corresponding precipitation amount (R2 = 0.15–0.40, P < 0.01), but the dilution effects became less significant when the precipitation amount exceeded 10.2, 10.7, 10.2 and 2.4 mm for DOC, CDOM, highly‑oxygenated and hypoxic structured humic-like substances, respectively. Seasonally, the dominant precipitation type in winter was snowfall, in which the DOM contained more high-molecular-weight compounds with higher aromaticity and humification degree, while the characteristics of DOM in intensive rainfall in summer were contrary to those in winter. The wet deposition flux of DOC to this region was estimated to be 6.31 × 108 g C a−1, which was 3.3 and 1.4 times that of the dry deposition and local riverine input, thereby contributing to 4.0 % of the DOC storage in the study area. In summer, the intensive input of DOC through wet deposition (0.43 g C m−2) to surface seawater could enrich its bioavailable DOC by 10.7 μmol L−1, the complete aerobic decomposition of which would cause an obvious dissolved oxygen depletion in the surface seawater by 21.4 μmol L−1, demonstrating the influence of wet deposition on summer deoxygenation in coastal waters.

Atmospheric dry deposition of nitrogen and phosphorus in Lake Qinghai, Tibet Plateau

To investigate the fluxes and potential sources of the atmospheric dry deposition (ADD) of nitrogen (N) and phosphorous (P) in the Lake Qinghai area, atmospheric deposition dusts were collected monthly at the eastern coast of Lake Qinghai from October 2017 to September 2018. N and P species in the dusts were determined. Results indicated that the annual ADD flux (ADDF) of dusts was 215.64 g m−2 yr−1, 48% of which occurred in March and April. The annual ADDF of N was 7.98 kg ha−1 yr−1, 49% of which was water-soluble total nitrogen, including 23%, 16%, and 10% of water-soluble NH4+-N, NO3−-N, and organic N, respectively. The annual ADDF of the total P was 1.72 kg ha−1 yr−1, only 6% of which was water-soluble. The dusts as well as the N and P in the dusts primarily originated from western Inner Mongolia and northern Gansu, driven by the winter monsoon. However, relatively high concentrations of N and P in the dusts in summer might be related to the southeast Asian monsoon from southern Gansu and northern Sichuan. Overall, the ADDF of the total N was about half of the atmospheric wet deposition flux (AWDF) of N, while the ADDF of the total P was approximately equal to the AWDF of P. However, most of the P in the dusts was not water-soluble and thus not readily bioavailable. Therefore, N and P wet deposition provides most of the readily available nutrients to phytoplankton in Lake Qinghai.

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.

Earth system modeling of mercury using CESM2 – Part 1: Atmospheric model CAM6-Chem/Hg v1.0

Abstract. Most global atmospheric mercury models use offline and reanalyzed meteorological fields, which has the advantages of higher accuracy and lower computational cost compared to online models. However, these meteorological products need past and/or near-real-time observational data and cannot predict the future. Here, we use an atmospheric component with tropospheric and stratospheric chemistry (CAM6-Chem) of the state-of-the-art global climate model CESM2, adding new species of mercury and simulating atmospheric mercury cycling. Our results show that the newly developed online model is able to simulate the observed spatial distribution of total gaseous mercury (TGM) in both polluted and non-polluted regions with high correlation coefficients in eastern Asia (r=0.67) and North America (r=0.57). The calculated lifetime of TGM against deposition is 5.3 months and reproduces the observed interhemispheric gradient of TGM with a peak value at northern mid-latitudes. Our model reproduces the observed spatial distribution of HgII wet deposition over North America (r=0.80) and captures the magnitude of maximum in the Florida Peninsula. The simulated wet deposition fluxes in eastern Asia present a spatial distribution pattern of low in the northwest and high in the southeast. The online model is in line with the observed seasonal variations of TGM at northern mid-latitudes as well as the Southern Hemisphere, which shows lower amplitude. We further go into the factors that affect the seasonal variations of atmospheric mercury and find that both Hg0 dry deposition and HgII dry/wet depositions contribute to it.

Wet deposition of atmospheric selenium and sensitivity to emission and precipitation patterns

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.

Chemical Composition Characteristics and Source Contributions of Precipitation in Typical Cities on the North Slope of Tianshan Mountain in Xinjiang during 2010–2019

This work presents the results of a ten-year investigation (2010–2019) on the characteristics and sources of precipitation pollution in typical cities locating in the economic belt on the North Slope of Tianshan Mountain, Xinjiang. The water-soluble ions’ characteristics (Na+, NH4+, K+, Mg2+, Ca2+, F−, Cl−, SO42−, NO3−), neutralizing capacity, wet deposition and sources of precipitation in Urumqi, Karamay and Yining during 2010–2019 were compared and analyzed. The study showed that from 2010 to 2019, the pH value of precipitation in Urumqi, Karamay and Yining varied from 4.18 to 10.55 with a volume-weighted mean (VWM) pH of 6.33, and the pH value showed an upward trend overall. The VWM electrical conductivity (EC) of the precipitation was the highest in Urumqi and the lowest in Yining, indicating that Urumqi was the most polluted and Yining was relatively clean. The most important cation in the precipitation of the three cities was Ca2+, and the most important anion was SO42−. The ratio of SO42−/NO3− indicated that the air pollution in Urumqi and Yining belonged to the typical coal-smoke air pollution, while there was compound pollution in Karamay. As can be seen from the neutralization factor, Ca2+ had the strongest neutralization ability, followed by Na+ and NH4+. Nitrate and sulfate in the atmosphere of Urumqi, Karamay and Yining are likely to exist in the form of NH4NO3, CaSO4 and (NH4)2SO4•CaSO4•2H2O. Wet deposition flux analysis of S and N showed that S pollution of the precipitation in Urumqi showed a decreasing trend, while N pollution showed an increasing trend. S pollution of the precipitation in Karamay gradually decreased, while N pollution of the precipitation in Yining became more and more serious. By analyzing origins of major ions in precipitation, it is concluded that human activities (industry, agriculture, heating, and transportation) are the main sources of ions in precipitation, and natural sources (soil dust) also play an important role.

Saharan Dust Deposition in Central Europe in 2016—A Representative Year of the Increased North African Dust Removal Over the Last Decade

Changes in circulation patterns associated with climate change have led to an increase in the frequency and intensity of Saharan dust events (SDEs) in the Carpathian Basin. The annual number of dust events was 4.2 on average between 1979 and 2010, while in the period of 2011–2018, it has increased to 10.3. This study presents a quantitative assessment of wet deposition of dust particles to Lake Balaton (Central Europe) with mineralogical and particle size distribution measurements. In addition to a comprehensive, systematic SDE identification process, rainwater samples were collected in 2016, and the particles on the filters were characterised using a range of analytical techniques. The atmospheric transport of particulates and moisture was evaluated using HYSPLIT Lagrangian trajectory model. XRD measurements revealed that during these events, the major minerals were quartz, kaolinite and 10-Å phyllosilicates. In addition, mineralogical source markers of arid dust (palygorskite and smectite) were also identified in majority of the analysed samples. Based on the results, wet deposition fluxes of dust particles were estimated for the region. 2016 was a typical and representative year for the decade, with twelve identified dust episodes. The synoptic patterns of the events fit well with the typical meteorological character of the North African dust intrusions with enhanced atmospheric meridionality described earlier. From the twelve episodes of 2016, seven were depositional events when wet deposition could be observed at ground level. Dust material of five episodes was analysed in detail, while particles of the two February wet deposition episodes were only granulometrically characterised. General uncertainties that hinder the characterisation of mineral dust in climate models were also observed in the granulometric and dust flux data of the sampled material. The particle size of the deposited dust was coarser than the upper cut-off level of grain size of the models. In addition, the discrepancies between measured and simulated deposition values clearly demonstrated the incorrect representation of dust flux in numerical simulations (partly due to inaccurate grain size data in the models).

Pah levels in the soil-litter-vegetation-atmosphere system of Atlantic Forest remnants in Southeast Brazil.

Although the Brazilian Atlantic Forest is a hotspot for biodiversity conservation, it is one of the most fragmented biomes in Brazil and also affected by air pollutants such as polycyclic aromatic hydrocarbons (PAHs). The study aimed at measuring the PAH levels in leaf trees, litter, soil, and atmosphere of two Atlantic Forest remnants impacted by air pollutants during summer and winter periods; identifying emission sources; and investigating the relationship among the PAH concentrations in the soil, litter, leaves, and atmosphere. Site 1 is situated in the largest South American city, with rainy summers and dry winters, and characterized by intense urbanization. Site 2 is situated in a large forest continuum and is characterized by wet climate with no defined dry seasons. It is more distant from the anthropogenic urban sources than site 1, but closer to an industrial complex. No differences were detected for PAH amounts (summer + winter) in the particles and wet deposition fluxes between sites. In site 1, the highest concentrations of PAHs in the particles were measured during the winter while in the leaf trees were measured during the summer. PMF model showed that sites 1 and 2 receive PAHs mainly from vehicle emissions and industrial activities, respectively. The accumulation of heavier compounds in soil and leaves via wet deposition was more evident in site 2. PAHs were mainly stored in the soil of site 1, contrasting with site 2, where they were retained in litter, which were attributed to disturbances of decomposer community and reduced decomposition rates.

Export of Dissolved Organic Carbon from the Source Region of Yangtze River in the Tibetan Plateau

The carbon release and transport in rivers are expected to increase in a warming climate with enhanced melting. We present a continuous dataset of DOC in the river, precipitation, and groundwater, including air temperature, discharge, and precipitation in the source region of the Yangtze River (SRYR). Our study shows that the average concentrations of DOC in the three end-members are characterized as the sequence of groundwater &gt; precipitation &gt; river, which is related to the water volume, cycle period, and river flow speed. The seasonality of DOC in the river is observed as the obvious bimodal structure at Tuotuohe (TTH) and Zhimenda (ZMD) gauging stations. The highest concentration appears in July (2.4 mg L−1 at TTH and 2.1 mg L−1 at ZMD) and the secondary high value (2.2 mg L−1 at TTH 1.9 mg L−1 at ZMD) emerges from August to September. It is estimated that 459 and 6751 tons of DOC are transported by the river at TTH and ZMD, respectively. Although the wet deposition flux of DOC is nearly ten times higher than the river flux, riverine DOC still primarily originates from soil erosion of the basin rather than precipitation settlement. Riverine DOC fluxes are positively correlated with discharge, suggesting DOC fluxes are likely to increase in the future. Our findings highlight that permafrost degradation and glacier retreat have a great effect on DOC concentration in rivers and may become increasingly important for regional biogeochemical cycles.

Multiproxy probing of anthropogenic influences on the different components of dissolved organic matter in coastal rainwater

In an environment that is tightly linked to humankind, how anthropogenic activity affects the quality and quantity of dissolved organic matter (DOM) in atmospheric depositions is not well understood. In this study, dissolved organic carbon (DOC), UV–vis spectra combined with molecular markers, including formic acid (FA), acetic acid (AA) and dissolved black carbon (DBC), were applied to track the temporal variation and influential factors of rainwater DOM at a coastal site. The ranges of DOC, light absorption at 254 nm (a254), FA, AA and DBC were 23.2–471 μmol L−1, 0.16–10.6 m−1, 0.12–23.5 μmol L−1, 0.44–37.8 μmol L−1 and 0.02–4.8 μmol L−1, respectively. The negative correlations between DOC, a254, AA and precipitation amount revealed a dilution effect. The concentrations of all measured DOM components were statistically different among different seasons with the highest value in spring. Higher DOM concentrations also occurred in the rain with backward trajectories influenced by the land. Compared to the nearby riverine DOM, the DOC-specific UV absorbance (SUVA254) of rainwater was lower, suggesting lower aromaticity of rainwater DOM. Significant correlations among different DOM components suggest that they shared similar sources or were affected by the same processes, while the significant correlations with anions (SO42−, F− and NO3−) and the ratio of FA to AA all suggested that the direct emission and secondary production from anthropogenic emissions (fossil fuel burning, biomass and biofuel burning) played important roles in regulating the level of DOM concentration in rainwater. Correlations with environmental variables (PM2.5, CO and NO2) further confirmed the input from anthropogenic activities. Furthermore, the monthly wet atmospheric deposition fluxes of DOM components (except DBC) can be successfully simulated by monthly precipitation and monthly average values of PM2.5 and NO2. Future studies should examine how atmospheric deposition affects the biogeochemical cycles in coastal regions.

Wet Deposition Fluxes of Mineral Dust and Their Relation With Cold Pools in the Central Sahel

AbstractBased on a large number of in‐situ measurements performed over a 9‐years period in two Sahelian stations, we investigate the drivers of the dust wet deposition in relation to the meteorological situations and the PM10 (Particulate Matter with diameter lower than 10 μm) surface concentrations. Precipitation associated with cold pools (CP) contribute to more than 90% of the precipitation amount associated with the collected wet deposition samples. The wet deposition events associated with these CP control by far the wet deposition, that is, 66% and 81%, depending on the station. The dust washout ratios (WR) corresponding to the most convective events under high level of dust concentrations were found to be in the range of 319–766 while WR of other kind of events are depending on the dilution effect. This range of value are in the lower range of WR previously estimated and used in dust modeling studies (200–2000).