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1.
Rainwater is a major source of dissolved iron to much of the world's oceans, including regions where iron may be a limiting nutrient for marine phytoplankton primary production. Rainwater iron is therefore potentially important in regulating global photosynthetic uptake of CO2, and hence climate. Two rainwater addition bioassay experiments (2% rain) conducted at the Bermuda Atlantic Time-series Station (BATS) during March 2000 using 50 or 100 nM FeCl2 or FeCl3 in synthetic rain (pH 4.5 H2SO4) showed an increase in chlorophyll a 50% greater than controls after three days. Addition of 20 μM hydrogen peroxide, a typical rainwater concentration at BATS, completely removed the chlorophyll a increase with both forms of iron additions, suggesting stimulation of phytoplankton growth by rainwater iron can be limited by rainwater H2O2. In laboratory experiments using Gulf Stream seawater, iron-enriched (100 nM Fe(III)) synthetic rain was mixed with seawater in a 5% rain 95% seawater ratio. Dissolved iron concentrations increased two times above concentrations predicted based on dilution alone. The increase in soluble iron probably resulted from release from seawater particles and was maintained for more than 24 hours. No increase was observed in controls that did not have iron added to the synthetic rain, or with synthetic rainwater containing both added iron and H2O2. The increase in iron concentration above that predicted by dilution indicates rain may have a larger effect on seawater iron concentrations than that calculated for rainwater iron addition alone.  相似文献   

2.
The reactivity of dissolved iron compounds towards different pollutants and photooxidants in atmospheric liquid water depends upon the oxidation state and speciation of iron. Our measurements of the oxidation state of dissolved iron eluted from aerosol particles (Dae: 0.4–1.6 m) collected in the urban atmosphere of Ljubljana showed that a large fraction of the iron content is present as Fe(II). The concentration ratio [Fe(II)]/[Fe(III)] varied between 0.9 and 3.1. The kinetics of S(IV) autoxidation catalyzed by Fe(II) under the conditions representative for acidified atmospheric liquid water and the influence of oxalate on this reaction under dark conditions was investigated. The reaction rate is the same if Fe(II) or Fe(III) is used as a catalyst under the condition that Fe(II) can be oxidized in Fe(III), which is the catalytically active species. Oxalate has a strong inhibiting effect on the S(IV) autoxidation in the presence of Fe(II). The reaction is autocatalytic with an induction period, that increases with higher concentrations of oxalate. The inhibiting effect of oxalate differs according to whether iron is initially in the Fe(II) or Fe(III) state. However, in both cases the inhibition by oxalate is a result of the formation of complexes with the catalyst.  相似文献   

3.
The reaction kinetics of S(IV) autoxidation catalyzed by single metal ions of Mn(II) and Fe(II) or Fe(III) and by a mixture of Mn(II) and Fe(II) under the conditions representative for acidified atmospheric liquid water was investigated. A simple power law kinetic model based on the stability constants for metal-sulfito complexes formed during the first step of a radical chain mechanism predicts well the kinetics for the reactions catalyzed by single metal ions. The calculated stability constants for iron (5.7×103 dm3 mol–1) and manganese (10×104 dm3 mol–1) sulfito complexes are close to those reported in the literature. The catalytic synergism between Mn(II) and Fe(II) was confirmed. For this system the following power law rate equation was suggested:rtot = SFe · rFe + SMn · rMn ,where rFe and rMn are the reaction rates in the presence of Fe(II) and Mn(II), respectively. SFe and SMn are proportional factors, which account for the synergistic effect. The proposed power law rate equation predicts the reaction kinetics very well. The values of SFe (1.35) and SMn (15) indicate that the influence of Fe(II)/Fe(III) on Mn(II)/Mn(III) cycling is larger than, vice versa, agreeing with the reaction mechanism proposed for the S(IV) autoxidation catalyzed by mixed metal ions.  相似文献   

4.
Concentrations of manganese in 56 rain events in Wilmington, NC, USA rainwater from April 1, 2005 to March 31, 2006 were 11 ± 3 nM for dissolved Mn and 1.2 ± 0.4 nM for particulate Mn. Concentrations of both forms of Mn were higher in terrestrial storms relative to marine events. This observation along with the positive correlation of Mn with pollutant indicators suggests anthropogenic inputs to rain at this location, as has been observed at other locations. The ratio of Mnpart/Mndiss was threefold larger in summer relative to winter rain, which matched the increase of particulate to dissolved Fe in rainwater suggesting influence of Saharan dust during the summer. Like Fe in rain, Mn undergoes photoreduction in rainwater, which has also been shown to be important in Mn cycling in seawater. The flux of Mn removed from the atmosphere via wet deposition is 1.5 × 10−5 moles m−2 yr−1 at this location, which is approximately twice the flux reported from two rainwater studies conducted in the early 1980s on Bermuda. Atmospheric input of Mn to the oceans is important because Mn like Fe is an essential and potentially limiting nutrient. Experiments mixing authentic rainwater and seawater demonstrate that rainwater dissolved Mn does not rapidly precipitate in seawater suggesting wet deposition is an important source of soluble, stable Mn to surface seawater.  相似文献   

5.
The Fe(II)/Fe(III)-partition in cloudwater samples collected during two field campaigns is evaluated. It turned out that the simultaneous occurrence of complexing and reducing substances in the atmosphere and the cloud processing increase the solubility of iron compounds present in aerosol particles. A correlation between the concentration of iron(II) in the liquid phase and the intensity of the solar irradiation was observed for most of the cloudwater samples. This could be due to the fact that both the photochemical reduction of the iron(III) complexes and the photochemical reductive dissolution of iron(III)(hydr)oxides are depending on the pH-value. Iron(II) seems to be oxidised back to iron(III) preferably by hydrogen peroxide during the night. Positive correlations were received e.g. between the concentration of dissolved iron and the concentration of oxalate and between the percentage of iron(III) and the concentration of hydrogen peroxide. A negative correlation was found e.g. between the concentration of dissolved iron and the pH-value. The uncertainty of the whole process of sampling and analysis was investigated and the conformity of the results was satisfying considering the sometimes difficult conditions during a field campaign.  相似文献   

6.
Precipitation samples collected at Erdemli, Turkey, during February 1996–June 1997 were analysed to determine iron content and speciation. The purpose of the measurements was to examine the atmospheric abundance of iron and to quantify its solubility in the region. Spectrophotometric analyses of Fe(II) and reducible Fe(III) in precipitation samples, along with measurements of pH, conductivity, filterable iron (Fefilt), particulate aluminium (Alpar) and particulateiron (Fepar) were performed to determine iron solubility, which principally affects its bioavailability. Backward trajectories corresponding to the sampling dates were analysed to determine the sources of atmospheric constituents arriving at the site. Among these, the mineral dust transported from the Great Sahara to the region is considered to be a rich source of iron. The concentration of Fe(II) varied from below detection limit (0.02 M) up to 0.42 M,while the maximum concentration of total reactive Fe (referred as Fe(II) + reducible Fe(III) = Fereac) was found to be 1.0 M in precipitation. A strong correlation was found between particulate Fe and Al fractions, both of crustal origin. No correlation was observed between the soluble and insoluble fractions of iron. The soluble iron fraction, Fe(II) concentration varied independently from the concentrations of reducible Fe(III), Fefilt, Fepar, and from the pH of the precipitation. The Fefilt fraction (size < 0.45 m), measuredby Atomic Absorption Spectrophotometer, and frequently interpreted to be the soluble iron fraction in the literature, was found to be significantly higher than the corresponding Fereac fraction inprecipitation samples, most likely due to the colloidal iron content of the Fefilt fraction passing through the 0.45 m pore size filter. The volume weighted mean Fefilt concentration of the precipitation samples collected during the episodic `red rain' events was found to be relatively higher. The geometric mean ratios of soluble Fe(II) and of Fereac to Total Fe (Fefilt + Fepar), werefound to be 1.6% and 2.1%, respectively, while the mean ratioof Fefilt to Total Fe was 9.6%. The flux of bioavailable iron (Fereac)fraction in most atmospheric wet deposition events was found to be sufficient for supporting the maximum primary production rates that are typical for the Eastern Mediterranean Sea.  相似文献   

7.
Iron is the most abundant transition metal in the atmosphere and can play a significant role in cloudwater chemistry where its reactivity is closely related to the partitioning between Fe(II) and Fe(III). The objective of this work is to determine the total iron content and the iron speciation in a free tropospheric site, and to understand which factors influence these parameters. We collected 147 samples of cloudwater during 34 cloud events over a period of four years at the puy de Dôme summit. Besides iron we measured other chemical compounds, solar radiation, physico-chemical and meteorological parameters potentially connected with iron reactivity. The total iron concentrations ranged from 0.1 to 9.1 μM with the major frequency occurring at low levels. The pH and presence of organic complexants seem to be the most significant factors connected with total dissolved iron; while the iron oxidation state seems to be an independent factor. Light intensity, presence of complexants or oxidants (H2O2) do not influence the Fe(II)/Fe(Total) ratio, that was quite constant at about 0.75. This could be due to the potential redox that forces the Fe(II)-Fe(III) couple to the reduced form or, more probably to the complexation by Natural Organic Matter, that can stabilize iron in its reduced form and prevent further oxidation. Our field measurements did not show the diurnal cycle observed in surface water and predicted by models of atmospheric chemistry. This result prompts a more careful review of the role of iron and, by analogy, all the transition metals in atmospheric liquid phase, often over-estimated in the literature.  相似文献   

8.
Laboratory experiments were conducted with real atmospheric aerosol particles as well as with synthetic solutions under dark conditions, to simulate some of the chemical features of aerosols. In solutions obtained by the leaching of aerosols (size range >D ae: 0.4–1.6 m) that contained sufficient amounts of transition metal ions (e.g. Fe) and organic species (e.g. oxalate), S(IV) oxidation rates were significantly lower than those expected from the Fe-catalyzed S(IV) autoxidation in Milli-Q water. The results suggest that oxalate is responsible for much of the observed inhibition. Acetate and formate also inhibit the reaction, but to a much lesser extent. Oxalate has a strong inhibiting effect on the Fe-catalyzed S(IV) autoxidation at all investigated pH values (2.8, 3.7 and 4.5). It was established that Fe(III)-oxalato complexes affect the redox cycling of Fe(II)/Fe(III) and that the observed decrease of the reaction rate is caused by the reduced amount of catalytically active Fe(III) due to the complexation with oxalate. For the system Fe-S(IV)-O2-oxalate at initial pH 3.7 the reaction rate was calculated using exponential simplification to account for oxalate influence on the amount of free Fe(III) by the following equation:–rS(IV) = k · [S(IV)] · [Fe(III))] · e -b·[Ox]  相似文献   

9.
Rainwater samples were collected at four sites, including Beijing and Mazhuang Town in the north of China, Shenzhen and Mangdang Mountain in the south of China. Character of atmospheric particles and gases were also measured at Mazhuang Town and Mangdang Mountain. Both of Beijing and Shenzhen are urban sites; Mazhuang Town and Mangdang Mountain are rural and remote sites respectively. The atmospheric pollution at rural plain site in the north of China was more serious than that at remote mountain site in the south of China. At Beijing, Mazhuang Town, Shenzhen and Mangdang Mountain the average pH values in rainwater were 6.02, 5.97, 4.72 and 4.81, respectively and the concentrations of total ions in rainwater were 1454, 1125, 187 and 191 μeq/l, respectively. While the acidity of the rain was higher in the south than that in the north, the rainwater in the north of China was more severely polluted than that in the south. The major acidic ion in the rainwater is SO42-, and NH4+ is the most important neutralizing ion in rainwater at the four sites, followed by Ca2+. The amounts of organic acid in precipitation were compared with other sites in the world. The ratios of organic acid to total free acid in rainwater at Mangdang Mountain was 13.8% and the influence of organic acid on acidity of rainwater at mountain site in the south of China is more important. The variation of atmospheric particles, gases and components in rainwater and cloud-fog water during special rain and cloud-fog events was discussed. The importance of washout process varied with atmospheric species. The impacts of rainfall, rain duration time and wind speed on wash-out process were estimated by regression analysis.  相似文献   

10.
The concentrations of H+, nitrate (NO3 -), and sulfate (SO4 2-) in rainwater and their temporal changes were analyzed on the basis of continuous observation from 1 July 1991 to 30 June 1992 at a suburb of Nagoya, Japan. The yearly average for pH was 4.4. In general, an increasing pH with increase in precipitation amount was observed for rain events. Relatively high pH rainwater was sometimes observed at the beginning of rainfall, even though high concentrations of NO3 - and SO4 2- were involved. The high pH values were considered to be caused by the neutralization process with particulate matter containing cations. The yearly averaged ratio of equivalent concentration of nitrate to sulfate (N/S) in rainwater was 0.58. In the early stage of rain, the N/S value was usually more than 1.0 due to the difference of scavenging process between NO3 - and SO4 2-. High values of N/S ranging from 5 to 10 were found under the atmospheric conditions of calm winds and low humidity, during which it is possible that atmospheric particles float for a long time in the air before a rain event. The adsorption of NO3 - in the early stage of rainfall by particulate matter was suggested from the difference in scavenging processes of NO3 - and SO4 2-. A possible scavenging process, called limb cloud scavenging, is presented to explain the interaction of particles and nitrate ions at the early stage of rain. In limb cloud scavenging, the repeated migration of cloud particles or raindrops between the inside and outside of clouds increases the absorption of ions to a highly condensed level, thus increasing the N/S value of rainwater. The influence of global scale seasonal phenomena with large amounts of particulates, such as typhoons or Asian dust storms, was also studied.  相似文献   

11.
This study demonstrates that oxalate has a strong inhibiting effect onFe-catalyzed S(IV) oxidation by oxygen in aqueous solution. While thepseudo-first order rate constant of S(IV) oxidation was determined to be1.6 × 103 M-1 s-1 in experimentswithout oxalate, the oxidation of S(IV) was totally inhibited at a molarconcentration ratio of iron:oxalate = 1:5 at an oxalate concentration of 4M. Under these conditions, the Fe(II)/Fe(III) ratio remained nearlyconstant during the observed reaction time. The determined rate constants wereindependent of the initial oxidation state of iron. However, with increasingconcentrations of oxalate, a longer induction period is observed forexperiments with iron initially in the Fe(II) oxidation state.  相似文献   

12.
Simultaneous measurements of rain acidity and dimethyl sulfide (DMS) at the ocean surface and in the atmosphere were performed at Amsterdam Island over a 4 year period. During the last 2 years, measurements of sulfur dioxide (SO2) in the atmosphere and of methane sulfonic acid (MSA) and non-sea-salt-sulfate (nss-SO4 2-) in rainwater were also performed. Covariations are observed between the oceanic and atmospheric DMS concentrations, atmospheric SO2 concentrations, wet deposition of MSA, nss-SO4 2-, and rain acidity. A comparable summer to winter ratio of DMS and SO2 in the atmosphere and MSA in precipitation were also observed. From the chemical composition of precipitation we estimate that DMS oxidation products contribute approximately 40% of the rain acidity. If we consider the acidity in excess, then DMS oxidation products contribute about 55%.  相似文献   

13.
The effect of UV-visible light and natural sunlight on the Fe(III)-catalyzed oxidation of dissolved sulfur dioxide has been studied under the conditions representative for those of acidified atmospheric liquids. The experimental results have shown that both sunlight and UV-visible light enhance the rate of Fe(III)-catalyzed oxidation of aqueous sulfite with wavelength ranging from 300 to 575 nm. The light enhanced oxidation is mainly due to photochemical formation of OH radicals from Fe(OH)2+ complexes in the wavelength region below 420 nm and SO3•− free radicals from Fe(III) sulfite complexes above 420 nm in the absence of organic ligands. Like the Fe(III)-catalyzed thermal chemical oxidation, the Fe(III)-catalyzed photochemical oxidation is also first order with respect to sulfite ion concentration. The sunlight irradiation can increase the Fe(III)-catalyzed oxidation of S(IV) over 45%. The presence of organic complex ligands, such as oxalate, can completely inhibit the Fe-catalyzed oxidation of S(IV) in the dark. However, the photolysis of Fe(III)-oxalato complexes generates oxalate free radicals, leading to the formation of H2O2 and OH radicals and the oxidation of S(IV). The rate of Fe(III)-catalyzed oxidation of S(IV) species is found to increase with increasing light intensity. The effects of sunlight on the Fe(III)-catalyzed oxidation of S(IV) should be taken into account when predicting the daytime rates of sulfuric acid formation in atmospheric water droplets.  相似文献   

14.
Rainwater samples were collected for the monsoon period of 1988 and 1991–1996 at Dayalbagh (Agra), a suburban site situated in semiaridregion. The mean pH was 7.01 ±1.03 well above 5.6, which is the reference pH. Concentration of Ca2+ was observed to be highest followed by Mg2+, NH4 +,SO4 2–, Cl–,NO3 –, Na+, F– and K+. The ratios of SO4 2– + NO3 – andCa2+ + Mg2+ (TA/TC) have been considered as indicatorfor acidity. In the Agra region ratio of TA/TC is quite below 1.0 indicating alkaline nature of rainwater. The lowest value of 0.24 was observed in 1991 likely due to the lowest rain depth of the decade. The highest value of 0.54 was observed in 1996, a year with a large rain depth and increase in line (vehicular traffic) and area sources (population growth). Good correlation between Ca2+ and NO3 –,Ca2+ and SO4 2– andSO4 2– and NO3 –,indicates that wind carried dust and soil play a significant role in neutralization of precipitation acidity.  相似文献   

15.
To explore the freezing effect on iron (Fe) solubility in natural environments, especially in Polar regions, event based freshly fallen snow samples were collected at Newark, New Jersey on the US East Coast for two consecutive winter seasons (2014–2015 and 2015–2016). These samples were analyzed for the concentrations of soluble iron (Fesol) using UV-Vis Spectroscopy and filterable iron (Fefil) and total iron (Fetot) using Atomic Absorption Spectroscopy. The average fractional solubility of the Fesol (the portion that passes through a 0.22 μm pore-size filter) with respect to the total Fe in the samples was 23.3?±?12.2%, with the majority of the soluble Fe being present as Fe(III). Approximately 48.5% of the total Fe existed as Fefil (the portion that passes through 0.45 μm pore size filter media). No significant correlation was found between the soluble ionic species and soluble Fe. Six snow events were kept frozen for 10 days, and analyzed in periodic intervals to study the post-freezing modification in Fe solubility. Events 1 and 2 showed increasing trend in the soluble Fe concentrations; however, the events 5, 6, 7, and 8 showed no noticeable increments. The pattern shown in Events 1 and 2 is associated with high fraction of Fefil and one unit pH drop, suggesting that the freeze-induced modification in Fe solubility could be linked with the amount of Fefil and the acidity change in the samples. To further investigate the freeze-induced compaction of particles, samples from three events 6, 7, and 10 were analyzed by SEM-STEM-EDS microscopy, and the results showed that due to freezing, in general, the particles in the ice-melt counterparts tend to compact and cluster and form larger aggregates compared to the particles in snow-melt. These results show, despite the freeze-induced compaction in snow was observed from STEM images, the snow freezing might not have significant effect in increasing Fe solubility from materials in the snow. These results further suggest that freezing process with fresh snow in high-latitude regions may not impose significant modification on Fe solubility in snow.  相似文献   

16.
The influence of sunlight and dissolved organic carbon (DOC) on the photochemically mediated cycling of hydrogen peroxide (H2O2) was investigated in rainwater samples collected in Wilmington, North Carolina USA. Upon exposure to simulated sunlight 14 of 19 authentic rainwater samples exhibited significant decreases in H2O2. The concentration of hydrogen peroxide did not change significantly in organic-free synthetic rainwater spiked with H2O2 in the light or in dark controls suggesting that the loss was not due to direct photolysis or dark mediated reactions. There was a significant correlation between pseudo-first order rate constants of H2O2 decay and initial H2O2 concentrations. There was also a significant correlation between the rate constant and the abundance of DOC suggesting that rainwater organic carbon plays an important role during photolytic decay either via direct reaction or indirectly through production of peroxide reactive species or scavenging of peroxide generating radicals. Several rain samples exhibited an initial increase in H2O2 during the first 2 h of irradiation. These increases were generally small and most likely do not represent a significant input of peroxide in precipitation. The photo-induced destruction of H2O2 is important because it may partly explain the late afternoon decrease of peroxide concentrations observed in earlier field studies and the substantial under saturation (<10%) of this oxidant in rainwater compared with gas phase concentrations.  相似文献   

17.
The chemical composition, as well as the sources contributing to rainwater chemistry have been determined at Skukuza, in the Kruger National Park, South Africa. Major inorganic and organic ions were determined in 93 rainwater samples collected using an automated wet-only sampler from July 1999 to June 2002. The results indicate that the rain is acidic and the averaged precipitation pH was 4.72. This acidity results from a mixture of mineral acids (82%, of which 50% is H2SO4) and organic acids (18%). Most of the H2SO4 component can be attributed to the emissions of sulphur dioxide from the industrial region on the Highveld. The wet deposition of S and N is 5.9 kgS⋅ha−1⋅yr−1 and 2.8 kgN⋅ha−1⋅yr−1, respectively. The N deposition was mainly in the form of NH4 +. Terrigenous, sea salt component, nitrogenous and anthropogenic pollutants have been identified as potential sources of chemical components in rainwater. The results are compared to observations from other African regions.  相似文献   

18.
The pH and the concentrations of sulfate, nitrate, ammonia, and calcium in rainwater were measured for two periods of a single midwest rainstorm which occurred over a mesometeorological network in central Illinois on 24–25 July 1979. Regression analysis was used to compare ion concentrations with rainfall amount, and ion balance was used to compare cation and anion concentrations at individual sites. Only the ions SO4 2- and NO3 - show any significant relationship to rainfall amount, decreasing as rainwater amounts increase (r=–0.57 and –0.60, respectively). During the first period of the rainstorm, a sequential sampler measurements allowed the calculation of detailed temporal variations in SO4 2-, pH, and rain rate. SO4 2- decreased, and pH increased as the rate increased and the opposite temporal pattern occurred as the rain decreased at the end of the period. Reasons for these variations are discussed.Research done while a visiting scientist at the Illinois State Water Survey, Champaign, Illinois, U.S.A.  相似文献   

19.
Precipitation samples collected during 2005–2009 from a rural forest station of Bhubaneswar were analyzed for their chemical composition. The samples were collected through a wet-only (WO) collector and two bulk (B1 and B2) collectors. The ions were evenly balanced indicating good data quality. The overall pH of rainwater was slightly acidic and ~47% of all rain events during the period were acidic (pH?<?5.6). Multilinear regression analysis showed relation between the free acidity (H+) and other components in rainwater. Enrichment factors (EF) of the major components with respect to their sources such as marine and crustal were calculated. Maximum EF was observed for NO 3 ? for both marine and crustal sources for all the three collectors. Source apportionments were also carried for the ions. Trend analysis showed continuous increase in most of the ions over years during the study period driven by anthropogenic emissions. Statistical/factorial analysis established correlation among different ions.  相似文献   

20.
北京地区酸雨特征及影响因素   总被引：17，自引：1，他引：16       下载免费PDF全文
利用2003—2008年北京地区3个酸雨观测站(北京市观象台、昌平站、上甸子站)的酸雨观测资料并结合探空及大气成分资料,分析了近年来北京地区的酸雨变化特征,研究了不同气象条件和大气污染物对酸雨的影响。结果表明:2003—2008年降水平均pH值均小于5.6,且近6年来,降水pH值呈波动下降的趋势。北京地区夏、秋两季降水平均pH值及K值较春、冬季节低;pH值及K值随降水量的增大呈下降趋势,而强酸雨频率则随降水量的增大呈上升趋势;在偏南气流影响下,降水酸度增强且酸沉降量大,酸雨污染严重;当连续发生逆温状况时,酸雨出现频率增大;大气污染物SO_2,NO_2,PM_(2.5)的浓度与降水pH值成负相关关系,说明近地层污染物浓度对降水酸度有重要影响。  相似文献   

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