Wet Fluxes Research Articles

Fluxes and sources of metals deposited in dew in Changchun, China

Because of the recent expansion of industrialization and urbanization, the concentration of metals in the atmosphere has significantly increased. Considering the threats of wet metal deposition to the water and soil quality, many studies have primarily focused on wet metal deposition in rain or snow, but there are few reports considering dew. As an important factor of wet deposition, dew cannot be ignored when assessing wet metal deposition. To analyze the fluxes and sources of metals deposited on Hemiptelea davidii (Hance) Planch via dew, dew samples were collected over six months in Changchun from May to October 2021, and the concentrations of 12 metals were measured. The order of both the volume-weighted mean (VWM) concentrations and fluxes of the measured metals were Ca > Na > Mg > K > Al > Fe > Zn > Pb > As > Mn > Cu > Ni. Ca was the most abundant metal, with a VWM concentration and wet flux of 6156.74 ± 1807.69 μg/L and 218.87 mg/m2·y, respectively, which were 3 orders of magnitude higher than those of Pb, As, Mn, Cu, and Ni. Based on correlation and principal component analysis, the metals in dew originated from both natural sources (Ca, Na, Mg, Al, Mn, Fe, and K) and anthropogenic activities (Cu, Ni, Pb, Zn, and As). Combined with the analysis of air mass trajectories, fire maps and microstructure characteristics of particles within dew, it was determined that the metals in dew were mainly sourced from crustal dust, straw burning, vehicle exhaust and coal combustion. Additionally, the determined metals could be attributed to a mixture of long range transport and local sources.

A novel liquid-shielded welding solution for diffusible hydrogen content restriction and metal transfer controlling in underwater FCAW condition

Hydrogen produced by water decomposition caused high diffusible hydrogen content in deposited metal, but also produced numerous spatter and unstable fragments which were considered as the main reason that deteriorated the weld formation during underwater wet flux cored welding (FCAW). Drawn inspiration from onshore gas shielded welding, in this paper, a liquid shielded welding method was invented. As a by-product of biodiesel, glycerol was chosen as liquid protectant. The results suggested that the diffusible hydrogen content in deposited metal was reduced by 62.4% with glycerol shielded due to its higher decomposition threshold and less hydrogen in decomposition products. Arc bubbles were attached to the molten pool surface and their expansion rate and rising velocity were slowed down resulted in more stable droplet transfer process and less spatter owing to high viscosity glycerol protectant. Almost porosity-free joints were obtained and the mechanical properties of the welded joints were also improved.

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.

Rainwater chemistry in a subtropical high-altitude mountain site, South China: Seasonality, source apportionment and potential factors

Long-term and frequent observation of rainwater chemistry provides an opportunity to explore the evolution of air pollutant emissions and the effectiveness of the emission control measures. This study presents variations in rainwater chemistry, possible sources of air pollutant emissions, and wet deposition fluxes of ionic species in the rainfall samples during 2018–2020 at Mt. Lushan located in South China. Results showed that the annual volume-weighted mean (VWM) pH of rainwater was 5.8. Moreover, the VWM of 87.7% rainwater samples had pH values above 5.6, which indicated that the atmospheric pollution at Mt. Lushan had less effect during the study period. The polytonic nitrate ion (NO3−), the doubly charged positive calcium ion (Ca2+) and the ammonium ion (NH4+) were the dominant ions in rainwater where Ca2+ and NH4+ were the main neutralizing ionic species for rainwater acidity. The highly seasonal variability of ionic concentrations in rainwater was observed among different ionic species, which is closely associated with meteorological conditions and anthropogenic emissions present in the various seasons. Annual wet deposition flux showed an increasing trend during the entire periods. Hence, the wet flux of NO3− (76.3 kg ha−1 yr−1) was three times higher than the annual wet deposition flux of sulfate (SO42−, 21.7 kg ha−1 yr−1), which points to the fact that acid deposition is still a severe environmental issue in the Mt. Lushan region. Positive matrix factorization (PMF) and correlation matrix were used to identify five sources for ionic species, including aging sea salt, fossil fuel combustion, agriculture, dust, and biomass burning. These findings could be helpful in establishing emission control policies to protect and manage pollution control in the eco-environment in South China.

Soil structure and soil moisture dynamics inferred from time-lapse electrical resistivity tomography

The semi-arid sagebrush steppe in the western United States faces pressures from the agriculture industry, recreation use, invasive grasses, and a changing climate. A key to facilitating the healthy management of this ecosystem is understanding the distribution and behavior of soil moisture in the vadose zone in both natural and agricultural settings. Within unsaturated environments, soil moisture is spatially and temporally heterogeneous, and changes in porosity and permeability within arid soils complicate characterization of soil hydrologic properties. Importantly, accumulations of ‘caliche’ or pedogenic calcium carbonate in arid soils can greatly limit permeability; however, observing the role that caliche plays in the hydrologic process is difficult because the installation of in situ instruments disturbs the soils and only provides information at a single point. To investigate vadose zone processes on a broad temporal and spatial scale, we installed a 7x8m2 electrical resistivity tomography (ERT) array at the Reynolds Creek Critical Zone Observatory in southwestern Idaho. Existing soil moisture observations show that infiltration is limited to depths less than 60 cm at this site, as compared to at least 90 cm at other sites in the watershed. To capture the seasonal wetting and drying of the soils, as well as the soils’ response to rainfall events, we monitored the site bi-weekly during the spring, summer, and fall of 2015 and 2016. A time-lapse ERT array was placed adjacent to coaxial impedance dielectric reflectometry (CIDR) probes so that the time-lapse ERT data could be referenced to precise measurements of volumetric water content. In addition to the measurements provided by the ERT array and CIDR probes, soil texture analysis and soil profile descriptions from a near-by soil pit show typical arid soil morphology, with accumulations of clays and calcium carbonate in the B horizon. The resulting ERT inversions show the following soil structure: (1) a high-resistivity top layer corresponding with minor amounts of pedogenic calcium carbonate; (2) a low-resistivity intermediate layer at depths corresponding with substantial accumulations (stage IV) of carbonate; and (3) a high-resistivity deep saprolite. The resistivity of the top layer varies seasonally with changes in precipitation, while the intermediate carbonate soil layer does not. This agrees well with the changes in soil moisture with depth measured by the CIDR probes and suggests that the top of the carbonate soil layer limits infiltration. However vertical structure and cracks within the carbonate soil layer create vertical preferential flow paths; resistivity within these flow paths responds to large precipitation events and seasonal changes in soil moisture. This implies that the preferential flow paths are a conduit for soil moisture flow that is not captured by the CIDR probes. From the combined interpretation of the ERT and CIDR we conclude that soil structure and the presence of calcic soil horizons inhibits soil moisture infiltration during both the summer dry months and the winter wet flux period; however, preferential flow paths provide an important vertical connection between the deep and shallow portions of the critical zone.

A synthesis review on atmospheric wet deposition of particulate elements: scavenging ratios, solubility, and flux measurements

Atmospheric dry and wet deposition of particulate matter controls its lifetime in air and contributes to the environmental burden of toxic pollutants and thus has important implications on human and ecosystem health. This synthesis review focuses on atmospheric wet deposition of particulate elements and analyzed their scavenging ratios (i.e., ratio of concentration in precipitation to that in ambient air), solubility, and wet deposition flux measurements based on published studies in the literature, aiming to gather updated knowledge that can be used for modeling their wet deposition. Our analysis finds that scavenging ratios of a specific element have a narrow range. Overall, elemental scavenging ratios for snow are approximately three times higher than those for rain. Elements that are bound to coarse (PM2.5–10) particles have larger scavenging ratios than those bound to fine (PM2.5) particles, except for Fe and Si. Solubility of elements in rainwater ranges from 8% (Fe) to 94% (Ca). Solubility is moderately correlated with scavenging ratio, possibly explaining the lower scavenging ratios of Fe and Si compared with other elements with similar fine fractions. Data collected from North America, Europe, the Middle East, and Asia show that the wet fluxes of Al and Fe are orders of magnitude greater than those of routinely monitored anthropogenic elements (Zn, Pb, Cu, Ni, Cd, Cr). Wet deposition fluxes of particulate elements in the Middle East exceed those in other regions, likely due to regional transport of dust and soil resuspension. Fluxes from all regions are a factor of two to three times greater in industrialized and urban locations than in rural and remote locations because of industrial, vehicular, and soil and mineral dust emissions. Dry deposition fluxes are usually greater than wet deposition fluxes, although to varying degrees according to co-located measurements. Based on the relationships between scavenging ratio and the elemental PM2.5 fraction under rain and snow conditions, we derived regression equations for estimating scavenging ratios of particulate elements for which measurements are limited. Such knowledge and data improve the quantification of atmospheric deposition fluxes for an expanded list of metals and metalloids and the understanding of pathways contributing to ecological risk.

Underwater Pulse-Current FCAW - Part 1: Waveform and Process Features

The typical metal transfer mode in conventional underwater wet flux cored arc welding (FCAW) delivers large droplet repulsive transfer with low frequency. The process stability and the weld quality are seriously deteriorated with significant spatter and frequent arc extinctions. It is thought the repulsive forces applied on droplets can be reduced by rapidly decreasing the welding current, making the droplets sag and oscillate. A novel underwater pulsecurrent FCAW was proposed to periodically regulate the forces applied on droplets. The experimental system was developed with specially designed pulse current and reliable arc length control. Visual and electrical signals were collected simultaneously to study the process features. It was found that the maximum droplet diameter decreased to less than 5 mm; the temporary arc-extinguishing frequency decreased significantly; there was almost no short-circuit transfer and surface-tension transfer; and the stability of the welding process was significantly improved.

Influence of welding speed on weld pool dynamics and welding quality in underwater wet FCAW

The effects of welding speed on the molten pool dynamics, the weld forming and the diffusible hydrogen content in deposited metal during underwater wet flux cored arc welding (FCAW) were studied. The molten pool was elongated with a higher solidification speed, as the welding speed was increased. The faster solidification improved the stability of the molten pool by reducing the bubbles and gas disturbance during FCAW, whereas it caused more hydrogen remaining in the deposited metal and increased the diffusible hydrogen content of the weld. According to the variation coefficient of weld reinforcement, the weld formation was improved at first and then deteriorated with the increasing welding speed. More bulges appeared in the weld at a low welding speed and pits were formed more easily with a high welding speed. The occurrence of the defects was closely related to the molten pool behaviors, which were determined by the pool angles during FACW.

Temporal variation of ethanol in rainwater from the sugar cane belt of São Paulo State (Brazil)

This work presents the first comprehensive assessment of ethanol dissolved in rainwater of São Paulo State's sugar cane belt, considering the period from 2012 to 2017. Ethanol concentrations ranged from 0.25 to 20.9 μmol L−1, with a volume-weighted mean (VWM) of 4.67 ± 0.13 μmol L−1 (n = 410). Despite the increasing use of ethanol fuel in Brazil, during the study period, the ethanol concentration in rainwater showed an average decrease of 0.54 μmol L−1 per year, attributed to technological improvements in vehicular fuel combustion and catalysts. Anthropogenic emissions appeared to overwhelm possible seasonal fluctuations of ethanol in rainwater due to biogenic sources or meteorological conditions such as temperature, solar radiation, rainfall amount, rainfall rate, and air mass origin. Higher VWM concentrations were generally observed in dry months, when the production of ethanol in the distilleries was highest and biomass burning increased. Consideration of ethanol oxidation in aqueous media by OH radicals indicated that secondary formation of highly toxic aldehydes is likely to increase with greater use of this biofuel. Dissolution of gaseous ethanol during cloud formation appeared to be a more important mechanism of atmospheric removal of this alcohol, compared to below-cloud processes. The wet flux of ethanol was ca. 3 kg ha−1 year−1 and there were evidences that atmospheric replenishment of this species was fast. Brazil has used ethanol fuel on a large scale since the 1980s, so better understanding of the behavior of this species in the lower troposphere of the study region can provide valuable information to assist in predicting future worldwide impacts of increasing use of this biofuel.

Four-year Measurements of Wet Mercury Deposition at a Tropical Mountain Site in Central Taiwan

ABSTRACT Rainwater samples were collected between 2010 and 2013 at Lulin Atmospheric Background Station (LABS) to study the distribution and characteristics of wet mercury (Hg) deposition, and possible driving mechanisms. Sample Hg concentrations ranged from 0.8 to 35.1 ng L–1 with an overall volume-weighted mean (VWM) concentration of 9.2 ng L–1. Annual wet Hg deposition fluxes ranged between 24.4 and 48.9 µg m–2 with a mean value of 32.3 µg m–2. This mean annual wet flux was about 1.5–6.0 times the values measured at 15 sites in the U.S. and 4–16 times the values reported from mountain and high-elevation sites in China. Both rainwater Hg concentration and rainfall amount contributed to this geographical difference, but rainfall amount played a more important role. This indicated that tropical mountains in East and Southeast Asia, especially the windward maritime slopes with abundant rainfall, could be hot spots of wet Hg deposition. Wet Hg deposition flux was high in summer because of elevated rainwater Hg concentrations and high rainfall. The seasonal pattern of rainwater Hg concentrations was different from that of the East Asian air pollutant export, indicating other factors, e.g., rainfall type, were also influencing rainwater Hg concentrations. A clear difference in seasonal frequency distribution of rainfall types was observed, with rain events associated with the Pacific high pressure type (PH) occurring more frequently in summer months. PH rainfall type had the highest VWM Hg concentration (13.5 ng L–1), 2.3–6.2 ng L–1 greater than those of the other rainfall types. Because of intense surface heating under summer PH conditions, precipitation systems usually form locally due to strong convection, resulting in afternoon shower. Therefore, the elevated rainwater Hg levels in summer at LABS were likely due to the scavenging of free tropospheric gaseous oxidized Hg (GOM) by deep convection.

Methyl and Total Mercury in Different Media and Associated Fluxes in a Watershed Forest, Southwest China.

Mercury (Hg) deposition in the forest ecosystem is a significant source of input for methyl Hg (MeHg) and total Hg (THg) to the subtropical forest field and downstream aquatic systems. Wet deposition, litterfall, runoff, and fluxes with forest soil percolate of MeHg and THg were sampled for two years in a watershed forest of southwest China. Results showed that the depositions of THg and MeHg through litterfall and throughfall were 86 µg m−2 yr−1 and 0.8 µg m−2 yr−1 respectively, with litterfall acting as a predominant route for the input of both THg and MeHg. The estimated fluxes of THg and MeHg in the throughfall and litterfall were 3 and 4 times greater than those in the precipitation. Methylmercury in the decomposed litter migrates during its erosion by surface runoff and the concentrations of MeHg were quite consistent with that in the surface runoff. Methylmercury mainly accumulated in the lower layer of the litter and upper layer of the soil (Oi), and its transfer through the soil cross-section was delayed. THg retention was not consistent with MeHg, probably with lower soil layers (Oe and Oa) storing and enriching THg in the forest ecosystem. The forest floor of the lower soil is an effective sink for THg but not for MeHg. Methylmercury accumulated in decomposing litter and upper soil layer might transfer with soil percolate, possessing potential ecological risks for residents living around the downstream aquatic systems.

Evaluation of the Effect of the Water in the Contact Tip on Arc Stability and Weld Bead Geometry in Underwater Wet FCAW

Abstract: Underwater wet flux cored arc welding – FCAW – is an important process employed to repair marine structures with the advantages of not handling the components off the water and offers higher productivity in comparison to other conventional welding process. Under the water, wet welding activities are performed with lower stability, due to the pressure of the water surrounding the arc column and the presence of water in the gap between the contact tip and the electrode, which promotes poor electrical contact. In the present work, to compare the process stability of underwater wet FCAW with self-shielded electrode, welds were carried out using a special torch, which keeps the contact tip dry under the water. A two-level factorial design was used for experimentation and an Analysis of Variance was conducted to validate the results. Current coefficient of variation was used as the stability index. Welds performed with the torch have shown better-shaped beads and more stable arc in comparison to beads deposited with no mechanical barrier between water and the contact tip.

Atmospheric wet deposition of dissolved trace elements to Jiaozhou Bay, North China: Fluxes, sources and potential effects on aquatic environments

To analyze the fluxes, seasonal variations, sources and potential ecological effects of dissolved trace elements (TEs) in atmospheric wet deposition (AWD), one-year wet precipitation samples were collected and determined for nine TEs in Jiaozhou Bay (JZB) between June 2015 and May 2016. Both the volume-weighted mean (VWM) concentration and flux sequence for the measured TEs was Al > Mn > Zn > Fe > Pb > Se > Cr > Cd > Co. Al was the most abundant TE with a VWM concentration and wet flux of 33.8 μg L−1 and 29.2 mg m−2 yr−1, which were 2 and 3 orders of magnitude higher than those of Co, respectively. The emission intensities of pollutants, rainfall amount and wind speed were the dominating factors influencing seasonal variations of TEs in AWD. Based on enrichment factors, correlation analysis and principal component analysis, most of the TEs in AWD were primarily originated from anthropogenic activities except for Al and Fe, which are typically derived from re-suspended soil dusts. Although the TE inputs by AWD were significantly lower than those by rivers, the TE inputs via short-term heavy rains would distinctly increase surface seawater TE concentrations and then pollute the marine environment of JZB. AWD would have both profound impacts on the biogeochemical cycles of TEs and dual ecological effects (nutrient and toxicity) on aquatic organisms.

Atmospheric particulate mercury in Lhasa city, Tibetan Plateau

In an effort to understand the biogeochemical cycling and seasonal characteristics of atmospheric Hg, a total of 80 daily sampled total suspended particulates were collected at Lhasa, the largest city of Tibet, from April 2013 to August 2014 for particulate-bound Hg (HgP) analysis. Daily concentrations of atmospheric HgP ranged from 61.2 to 831 pg m−3 with an average of 224 pg m−3, which were unexpectedly comparable to those measured in most of the Chinese metropolises. Both the daily/monthly average HgP concentrations were slightly but not significantly higher during the non-monsoon season than during the monsoon season. Together with the fact that there was lack of significant relationship between HgP concentration and most meteorological parameters, no significant and distinct pattern for the seasonal characteristics of atmospheric HgP could be mainly attributed to the almost equal emission strength of two principal anthropogenic Hg sources (i.e., industrial emission sources during the non-monsoon season, and vehicular traffic and religious sources during the monsoon season). Moreover, the HgP dry deposition rate was estimated to be 35.3 μg m−2 yr−1 by using a theoretical model, which was significantly higher than those Hg wet fluxes. The elevated deposition rate implied that dry deposition may play an important role in the biogeochemical Hg cycling over the Tibetan Plateau.

High Reliability No-Clean Solder Paste for Designs where Flux Cannot be Dried

The miniaturization trend is driving industry to adopting low standoff components or components in cavity. The cost reduction pressure is pushing telecommunication industry to combine assembly of components and electromagnetic shield in one single reflow process. As a result, the flux outgassing/drying is getting very difficult for devices due to poor venting channel. This resulted in insufficiently dried/burnt-off flux residue. For a properly formulated flux, the remaining flux activity posed no issue in a dried flux residue for no-clean process. However, when venting channel is blocked, not only solvents remain, but also activators could not be burnt off. The presence of solvents allows mobility of active ingredients and the associated corrosion, thus poses a major threat to the reliability. In this work, a new halogen-free no-clean SnAgCu solder paste, 33-76-1, has been developed. This solder paste exhibited SIR value above the IPC spec 100 MΩ without any dendrite formation, even with a wet flux residue on the comb pattern. The wet flux residue was caused by covering the comb pattern with 10 mm × 10 mm glass slide during reflow and SIR testing in order to mimic the poorly vented low standoff components. Paste 33-76-1 also showed very good SMT assembly performance, including voiding of QFN and HIP resistance. The wetting ability of paste 33-76-1 was very good under nitrogen. For air reflow, 33-76-1 still matched paste C which is widely accepted by industry for air reflow process. The above good performance on both non-corrosion with wet flux residue and robust SMT process can only be accomplished through a breakthrough in flux technology.

Atmospheric dry and wet deposition of nitrogen species and its implication for primary productivity in coastal region of the Yellow Sea, China

The size-fractionated dry deposition fluxes of aerosol particles and nitrogen species were estimated in coastal region of the Yellow Sea from July 2005 to March 2006 using size-dependent particle dry deposition velocities and measurements for size-segregated aerosol samples. During the study period, the estimated dry deposition fluxes of aerosol particles, total dissolved nitrogen (TDN), total inorganic nitrogen (TIN), dissolved organic nitrogen (DON), ammonium and nitrate were 1067.5 ± 903.3 mg m−2 month−1, 15.9 ± 7.2 mg N m−2 month−1, 12.6 ± 6.6 mg N m−2 month−1, 3.3 ± 1.5 mg N m−2 month−1, 6.5 ± 4.2 mg N m−2 month−1 and 7.2 ± 4.5 mg N m−2 month−1, respectively. The dry deposition flux for the coarse mode of aerosol particles and nitrogen species consisted more than 66% of the total deposition flux. This result suggests that nitrogen species in coarse particles are important in the estimation of atmospheric deposition input. The estimated wet deposition fluxes of TDN, DON, TIN, ammonium and nitrate were 154.5 ± 178.9 mg N m−2 month−1, 126.9 ± 152.2 mg N m−2 month−1, 24.2 ± 34.1 mg N m−2 month−1, 85.4 ± 98.6 mg N m−2 month−1, and 40.8 ± 56.1 mg N m−2 month−1, respectively. The wet deposition contributed 65%, 72%, 55%, and 56% to the sum of the dry and wet flux of TDN, ammonium, nitrate, and DON, respectively. Inorganic nitrogen contributed much more than DON to the TDN, with a percentage of 75% and 86% in the dry and wet deposition, respectively. The dry and wet nitrogen deposition can be converted to a new primary biological productivity of 1.5–30.0 gC m−2 yr−1 in the Yellow Sea, and the nitrogen input accounts for 0.3–6.7% of the new productivity in the Yellow Sea. As an important nutrient source, the atmospheric deposition of nitrogen could have a significant influence on biogeochemical cycles.

Sensitivity model for prediction of bead geometry in underwater wet flux cored arc welding

To investigate influence of welding parameters on weld bead geometry in underwater wet flux cored arc welding (FCAW), orthogonal experiments of underwater wet FCAW were conducted in the hyperbaric chamber at water depth from 0.2 m to 60 m and mathematical models were developed by multiple curvilinear regression method from the experimental data. Sensitivity analysis was then performed to predict the bead geometry and evaluate the influence of welding parameters. The results reveal that water depth has a greater influence on bead geometry than other welding parameters when welding at a water depth less than 10 m. At a water depth deeper than 10 m, a change in travel speed affects the bead geometry more strongly than other welding parameters.

Wet deposition of mercury at Lhasa, the capital city of Tibet

Quantifying the contribution of mercury (Hg) in wet deposition is important for understanding Hg biogeochemical cycling and anthropogenic sources, and verifying atmospheric models. Mercury in wet deposition was measured over the year 2010, in Lhasa the capital and largest city in Tibet. Precipitation samples were analyzed for total Hg (HgT), particulate-bound Hg (HgP), and reactive Hg (HgR). The volume-weighted mean (VWM) concentrations and wet deposition fluxes of HgT, HgP and HgR in precipitation were 24.8ngL−1 and 8.2μgm−2yr−1, 19.9ngL−1 and 7.1μgm−2yr−1, and 0.5ngL−1 and 0.19μgm−2yr−1, respectively. Concentrations of HgT and HgP were statistically higher during the non-monsoon season than during the monsoon season, while HgR concentrations were statistically higher during the monsoon season than during the non-monsoon season. Most HgT, HgP and HgR wet deposition occurred during the monsoon season. Concentrations of HgP and HgR were 77% and 5% of the HgT on average (VWM), respectively. Concentrations of HgT and HgP were weakly negatively correlated with precipitation amount (r2=0.09 and 0.10; p<0.05), indicating that below-cloud scavenging of Hg from the local atmosphere was an important mechanism contributing Hg to precipitation. High HgP%, as well as a significant positive correlation between HgT and HgP, confirms that Hg wet deposition at Lhasa was primarily occurring in the form of atmospheric HgP below-cloud scavenging. Moreover, the HgT concentration, rather than the precipitation amount, was found to be the governing factor affecting HgT wet deposition flux. A comparison among modeled wet and dry deposition fluxes, and measurements suggested that estimates of both wet and dry Hg deposition fluxes by the GEOS-Chem model were 2 to 3 times higher than the measured annual wet flux.

Atmospheric wet and dry deposition of polycyclic aromatic hydrocarbons (PAHs) determined using a modified sampler

Wet and dry deposition samples were collected along with the ambient air samples between September 2008 and June 2009 in an urban site, BUTAL, Turkey. A modified deposition sampler was used for dry and wet periods. Average dissolved and particle phase wet deposition flux values were determined to be 7.4 ± 7.3 μg/m 2 day and 21 ± 30 μg/m 2 day, respectively. The highest PAH wet fluxes were observed in the winter and fall seasons. Dissolved and particle phase rainwater concentrations of PAHs were 290 ng/L and 665 ng/L. The average of total (particle + gas) atmospheric concentration of ∑ 12PAH was 130 ± 160 ng/m 3. In general, percentages of PAHs with five or more aromatic rings were bigger in particle phase in air. Average washout ratios of PAH compounds were determined 8.97 × 10 5 and 8.52 × 10 5 for gas and particle phase, respectively. Gas phase washout ratios of high molecular weight PAHs were greater than the lower molecular weight PAHs.

Estimation of net nitrogen flux between the atmosphere and a semi‐natural grassland ecosystem in Hungary

The aim of this work is to estimate the net N balance (deposition – emission) between the atmosphere and a semi‐arid, semi‐natural grassland (Bugac station, Central Hungary, CarboEurope IP, NitroEurope IP level 3 site). Dry deposition of N compounds has been determined by the inferential method, based on continuous monitoring of NO2 gas and daily 24‐hour concentration measurements of HNO3 vapour, NH3 gas, and NH4+ and NO3− particles, using dry deposition velocities from the literature, measured above surfaces with the same characteristics as Bugac station. The bi‐directional flux of NH3 within the atmosphere and the canopy (excluding soil emission) has also been estimated by the inferential method. Wet deposition of nitrate and ammonium ions was calculated on the basis of daily precipitation sampling and concentration measurements of nitrate and ammonium ions. To estimate the soil‐atmosphere exchange of different gaseous N forms (N2, NO, N2O, NH3), the DNDC model was used as validated by the chamber measurements of NO and N2O soil emission fluxes. Soil emissions of NO and N2O have been determined by dynamic and static soil chamber methods, respectively. The measurement and modelling activity covers a complete year. Using the measured and modelled data, the calculated N balance at Bugac station between August 2006 and July 2007 is estimated at −8.8 kg N ha−1 year−1 (deposition) as a sum of the deposition and emission terms (−10.4 and 1.6 kg N ha−1 year−1, respectively). Due to the warm and dry weather during the examined period, wet fluxes were substantially lower than usual, which may also have altered the regular yearly course of dry deposition and emission.