A Study on Rain Acidification Processes in Ten Cities of China

A physico-chemical sub-cloud rain acidification model is used to simulate the acidification processes of rainwater in ten cities of China, based on the observation data of the chemical components of cloud- and rainwater and the concentrations of gaseous and aerosol species. The results show that there are in-cloud process and below-cloud process in the formation of acid rain, but the relative importance of these two processes is different in various cities. The acidification of rainwater under cloud is very important in Guiyang, Shanghai, Jilin, Beijing, Changsha and Chongqing, and the in-cloud and below-cloud process contribute equally to the acidification in Guilin, however, the acidification of rainwater in cloud is more important in Nanchang and Guangzhou. Overall, the aerosol has an alkalization effect on the rain, about 11%–25% of H⁺ concentration in the rainwater is neutralized over Southern China and 60%–70% is neutralied over Northern China by aerosol species. The effect of atmospheric SO₂ on acidification of rainwater is nonlinear and is different in various regions. The effects of the variation of atmospheric NH₃, H₂O₂ and aerosol species on pH of rainwater are also discussed in detail.     

Chemical Composition of Precipitation, Throughfall and Soil Solutions at Two Forested Sites in Guangzhou, South China

Rain water at two forested sites in Guangzhou (south China) show high concentrations of SO₄ ^2?, NO₃ ^? and Ca²⁺ and display a remarkable seasonal variation, with acid rain being more important during the spring and summer than during the autumn and winter. The amount of acid rain represents about 95% of total precipitation. The sources of pollutants from which acid rain developed includes both locally derived and long-middle distance transferred atmosphere pollutants. The seasonal variation in precipitation chemistry was largely related to the increasing neutralizing capacity of base cations in rainwater in winter. Soil acidification is highlighted by high H⁺ and Al³⁺ concentrations in soil solutions. The variation in elemental concentration in soil solution was related to nitrification (H⁺, NH₄ ⁺ and NO₃ ^?) and cation exchange reaction (H⁺, Al³⁺) in soil. The negative effect of soil acidification is partly dampened by substantial deposition of base cations (Ca²⁺, Mg²⁺ and K⁺) in this area.     

Chemical Composition and Acidity of Precipitation: A Monitoring Program in Northeastern Vietnam

Rainwater has been sampled weekly from five sites (nos. 1–5) in northeastern Vietnam in the period of May 1997 to Apr. 2000 (except Hoabinh site, from Aug. 1999 to Apr. 2000). Since Aug. 1999, weekly dry deposition samples including acidic gas and aerosol have been additionally collected at Hanoi (no. 4) and Hoabinh (no. 5) using filter pack system. In general, the pH in rainwater was frequently higher than 5.0. However, the trend of lower pH was observed during the winter and the beginning of autumn (from Nov. to Apr.). Interestingly, the highest frequency of the acidifying rainwater (32 %) and the lowest pH value (min. pH = 4.0) were observed in Hoabinh site. Acidic pH of rain water was also observed in Viettri (no. 3) and Hanoi (no. 4), indicating the local effects of human and industrial activities. Ca²⁺ and SO₄ ^2? were generally found as predominant in both rainwater and aerosol. SO₂ and NH₃ in Hanoi and Hoabinh were monitored out of corresponding environmental features.     

Seasonal patterns of mineral and organic acidification in two streams in Southwestern Nova Scotia

DOC concentrations in two streams of different hydrologic order are highly variable with the higher order stream exhibiting approximately a 3 mo response lag. Seasonal variation of SO⁴ concentration and flux are similar in both streams and do not reflect the seasonal patterns in precipitation. The basins store SO₄ from May to November and lose SO₄ from December to April. Consequently, SO⁴ concentrations and flux are maximum during January to March and reach a minimum during July to September. The highly organic lower order stream exhibits relatively stable pH controlled by two competing mechanisms. The pH is dominated by organic acids during the summer and autumn and by mineral acids during the late winter and early spring. In the higher order system, the pH tends to be inversely related to changes in SO₄ concentration. These observations suggest that organic systems do respond to acidic deposition but that in some systems mineral acid influence may be restricted to the winter and spring.     

Prolonged simulated acid rain treatment in the subarctic: Effect on the soil respiration rate and microbial biomass

Humus chemistry and respiration rate, ATP, ergosterol, and muramic acid concentration as measures of chemical properties, microbial activity, biomass, and indicators of fungal and bacterial biomass were studied in a long-term acid rain experiment in the far north of Finnish Lapland. The treatments used in this study were dry control, irrigated control (spring water, pH 6), and two levels of simulated acid rain (pH 4 and pH 3). Originally (1985–1988), simulated acid rain was prepared by adding both H₂SO₄ and HNO₃ (1.9:1 by weight). In 1989 the treatments were modified as follows. In subarea 1 the treatments continued unchanged (H₂SO₄+HNO₃ in rain to pH 4 and pH 3), but in subarea 2 only H₂SO₄ was applied. The plots were sampled in 1992. The acid application affected humus chemistry by lowering the pH, cation exchange capacity, and base saturation (due to a decrease in Ca and Mg) in the treatment with H₂SO₄+HNO₃ to pH 4 (total proton load over 8 years 2.92 kmol ha^-1), whereas the microbial variables were not affected at this proton load, and only the respiration rate decreased by 20% in the strongest simulated acid rain treatment (total proton load 14.9 kmol ha^-1). The different ratios of H₂SO₄+HNO₃ in subareas 1 and 2 did not affect the results.     

Seasonal,annual and long-term variability in the water chemistry of a remote high mountain lake: Acid rain versus natural changes

Seasonal fluctuations as well as long-term trends in water chemistry were studied in Schwarzsee ob Sölden (Tyrol, Austria), an oligotrophic softwater lake situated at 2796 m a.s.l. The catchement is composed of granite, plagioclase and micaschists containing considerable amounts of sulphur, with little soil cover. The lake is ice covered for about nine months, during this time the deepest layers (>16m) become anoxic. During summer overturn, alkalinity (ALK) is lowest (?8 μeq l^?1) in the whole water column, whereas pH reaches its minimum (4.88) at the surface during snowmelt. A decrease of pH from 5.8 to 5.4 during winter is caused by CO₂ oversaturation, but deep water ALK increases to up to 130 μeq l^?1 due to in-lake ALK generation by reductive processes and base cation (BC) release. The seasonal pattern of ALK in SOS is driven by in-lake processes in winter, the snowmelting in spring and watershed processes and precipitation during summer. Since 1989 summer sulfate concentrations in SOS, originating mainly from the catchment, show a tendency to increase presumably caused by enhanced weathering. In contrast, SO₄ ^2? concentrations in other high mountain lakes which are dominated by atmospheric depositions show a decreasing trend. SOS is a good example for the complexity of interactions between catchment and in-lake processes which act at different time scales and depend on climate changes and atmospheric inputs.     

Studies on Atmospheric Pollution,Acid Rain and Emission Control for their Precursors in Chongqing,China

Chongqing City in China has suffered from serious air pollution and acid rain caused by low graded raw coal (sulfur=ca. 3≈5%, ash=ca. 30%) combustion. In this paper, the situation of atmospheric pollution and acid rain in Chongqing are discussed, the reduction efficiency for sulfur dioxide (SO₂) with the bio-briquetting of the raw coal that is one of countermeasures for emission control of air pollutants due to domestic consumes was determined. The research indicated that the frequency of acid rain was high, more than 50% at urban area, and its pH was low, about 4.5. Under our experimental conditions, the reducing efficiency of sulfur SO₂ emission from high sulfur coal-biomass briquette amounted to 87%. The field investigation indicated that SO₂ indoor concentrations in case of using bio-briquette dropped to 1/2≈1/3 of the raw coal.     

Episodic acidification of a coastal plain stream in Virginia

This study investigates the episodic acidification of Reedy Creek, a wetland-influenced coastal plain stream near Richmond, Virginia. Primary objectives of the study were to quantify the episodic variability of acid-base chemistry in Reedy Creek, to examine the seasonal variability in episodic response and to explain the hydrological and geochemical factors that contribute to episodic acidification. Chemical response was similar in each of the seven storms examined, however, the ranges in concentrations observed were commonly greater in summer/fall storms than in winter/spring storms. An increase in SO _inf4 ^sup2? concentration with discharge was observed during all storms and peak concentration occurred at or near peak flow. Small increases in Mg²⁺, Ca²⁺, K⁺ concentrations and dissolved organic carbon (DOC) were observed during most storms. At the same time, ANC, Na⁺ and Cl^? concentrations usually decreased with increasing discharge. In summer/fall storms, the absolute increase in SO _inf4 ^sup2? concentration was one-third to 15 times the increase observed in winter/spring storms; the decrease in ANC during summer/fall storms was usually within the range of the decrease observed in winter/spring storms. In contrast, the decrease in Na⁺ and Cl^? concentrations during winter/spring storms was much greater than that observed during summer/fall storms. Data show that while base flow anion deficit was higher in summer/fall than in winter/spring, anion deficit decreased during most summer/fall storms. In contrast, base flow anion deficit was lower in spring and winter, but increased during winter/spring storms. Increased SO _inf4 ^sup2? concentration was the main cause of episodic acidification during storms at Reedy Creek, but increased anion deficit indicates organic acids may contribute to episodic acidification during winter/spring storms. Changes in SO _inf4 ^sup2? concentration coincident with the hydrograph rise indicate quick routing of water through the watershed. Saturation overland flow appears to be the likely mechanism by which solutes are transported to the stream during storm flow.     

Project rain: Changing acid deposition to whole catchments. The first year of treatment

Project Rain (Reversing Acidification In Norway) is a 5-yr international research project aimed at investigating the effect on water and soil chemistry of changing acid deposition to whole catchments. The project comprises 2 parallel large-scale experimental manipulations -- artificial acidification at Sogndal and exclusion of acid rain at Risdalsheia. Treatment at Sogndal commenced April 1984 with the acidification of the snowpack by addition of H₂SO₄ (SOG2) and a 1:1 mixture of H₂SO₄ and HNO₃ (SOG4). Preliminary results indicate rapid and significant response in runoff chemistry to the acid treatment; pH decreased (to as low as 4.1 during snowmelt in 1984); SO₄, NO₃, and labile Al increased. Response during snowmelt 1985 was modest relative to 1984. At Risdalsheia treatment began in June 1984 with the mounting of the transparent panels on the roofs at KIM catchment (treatment by deacidified rain) and EGIL catchment (control with ambient acid rain). Preliminary data for the first year indicate that most runoff samples from KIM contain much lower NO₃ concentrations, about 20 to 30% lower SO₄ levels and pH 0.1 to 0.3 units higher than runoff from EGIL catchment. The treatments continue in 1985–87. Project RAIN provides experimental evidence bearing on target loading, reversibility of acidification, and the processes linking acid deposition, soil acidification and freshwater acidification.     

Effect of sulphur dioxide on precipitation and on the sulphur content and acidity of soils in Alberta,Canada

Rain and snow in Alberta are seldom acid. The S content of snow is so low that the snow pack gives a deposition of less than 1 kg S ha^?1, even downwind from large SO₂ emission sources. Rainfall contributes at the most 4 kg S ha^?1 yearly near SO₂ sources, and only about 1 kg S ha^?1 in clean areas. However, rain intercepted by forest trees exposed to SO₂ emission becomes acid (pH 3.5 to 4.5) and has a S content of 3 to 4 times greater than rain. Soils absorb large amounts of S from emissions (up to 50 kg S ha ^?1 annually) but much of the S is found in non-sulphate form. Soils are slowly acidified by the SO₂ at a rate estimated at 1 pH unit in 10 to 20 yr. Water surfaces will absorb SO₂ emissions at a rate of about 4 to 15 kg S ha^?1 annually. Particulates deposit 3 to 4 times as much S as is deposited by rainfall.     

Chemical composition of precipitation in a forest area of Chongqing,Southwest China

Experiments were carried.out in Chongging-a city seriously damaged by acid precipitation in southwest China — to explore chemical compositions of open bulk precipitation, throughfall and stemflow in a Masson pine (Pinus massoniana) forest. The results showed that annual mean pH values of and annual ion depositions in the three types of rain water were 4.47 and 50.6 g m^?2, 3.82 and 69.7 g m^?2, and 2.92 and 0.215 g m^?2 respectively. pH values demonstrated an obvious seasonal variation; they were lower in winter than in the rest of the year. Ca²⁺ and NH _inf4 ^sup+ together made up more than 80% of the total cation, while SO _in4 ^sup2? alone contributed over 90% to the total anion. This high level of SO _in4 ^sup2? in rain water in Chongqing, which outran those found in other cities in China, was closely related to the combustion of locally produced coal that contains 3 to 5% sulphur. Thus, acid precipitation in Chongqing is of a typical sulphuric-acid type.     

Plotting of Acid Rain and Sulfur Dioxide Pollution Control Zones and Integrated Control Planning in China

The distribution and characteristics of acid rain and SO₂ pollution were presented, indicating that the areas with sulfur deposition over critical loads reached 21.9% of the territory in 1995. In order to control the acid rain and SO₂ pollution effectively, the Acid Rain Control Zone and SO₂ Pollution Control Zone (Two Control Zones for short) were designated based on the analysis of sulfur deposition. The corresponding integrated pollution control planning was formulated based on the life cycle approach of sulfur in coal and the technical options for SO₂ mitigation were also recommended for different sources such as coal industry, power industry, industrial boilers and kilns, and household stoves. Based on the countermeasures suggested, the SO₂ would be reduced by about 4.92Mt/yr during 2001–2005 and by 4.16Mt/yr during 2006–2010.     

Lysimeter study of effects of acid deposition on properties and leaching of gleyed dystric brunisolic soil in Norway

The effects of artificial rain of various acidities were studied in a lysimeter experiment. Lysimeters, 29 cm in diameter, and 40 cm deep contained a Gleyed Dystric Brunisol. Natural structure, stratification and original vegetation were maintained. Artificial rain was produced from groundwater with “high” concentrations of neutral salts and from rainwater with lower concentrations. pH levels of 6, 4, 3 and 2 were established by adding H₂SO₄. Effects of dilution with given amounts of acid were examined by comparing the effects of 50 mm “rain” month^?1 of pH 3 and pH 2 with 500 mm “rain” month^?1 of pH 4 and pH 3, respectively. The study continued for 5 yr. Totals of 1250 or 12500 mm “rain” were applied in addition to a natural input of 2773 mm. Increased input of SO₄ ^2? increased the output of SO₄ ^2? but, as concentration increased, sorption of SO₄ ^2? in the soil also increased. Concentrations of base cations in the leachate increased parallel to the output of SO₄ ^2?. However, significant effects on leaching of base cations and on the content of exchangeable cations in the soil, was only found in the pH 2 treatment with 1250 mm of “rain” and in the pH 4 and pH 3 treatment with 12500 mm of “rain”.     

Temporal variation in the surface-water chemistry of a blanket bog on Dartmoor, southwest England: analysis of 5 years' data

Blanket‐bog peats, mapped as the Winter Hill and Crowdy associations by the Soil Survey of England and Wales, are an oceanic manifestation of the ombrotrophic ‘raised‐bog’ (Hochmoor) peats that cover large tracts in the boreal zone of the northern hemisphere. This paper examines monthly analyses from 1992 to 1997 of major ions and other variables from an upland blanket bog in southwest England in relation to seasonality, rainfall, and the chemical composition of rainwater. Average ionic composition of surface water (and peat) integrates variable atmospheric solute inputs over the years. The dominant ions in the surface water, Na⁺ and Cl^–, showed only weak seasonality, but divalent cations a stronger seasonal pattern with a summer maximum. Mean pH ranged from c. 4.4 in February to c. 4.2 in August. Changes in concentration of different cations were closely interlinked by cation exchange. The anion deficit, accounted for by anionic groups on the dissolved organic matter, was strongly seasonal with a summer maximum, as was optical absorbance at 320 nm. Nitrate and NH₄⁺ were both at much smaller concentrations than in rain. Nitrate exceeded 1 μmol l^?1 only during cold periods in winter, mainly following drought in the summer of 1995; NH₄⁺ reached a few μmol l^?1 only in summer. There was evidence of net retention of S by the peat in wet sites and during wet periods, and of net release of SO₄^2– (and acidity) under dry conditions. The 1995 summer drought and ensuing dry year in 1996 had marked and persistent effects on pH, apparent ion deficit (DEF), SO₄^2–, the divalent cations and Fe.     

Atmospheric aerosols and gases in rural Nova Scotia and their dependence on air flow

Various species including nitrate, HN0₃ and Pb were sampled in Antigonish, Nova Scotia and their fluctuations were compared to those of simultaneously sampled acid and sulphate (reported previously). The 24 hr average aerosol nitrate, ～0.3 μg m^?3, was similar in the summer and winter. Nitric acid made up ～42 % of the total (aerosol and gaseous) nitrate in the summer and winter, but nitrate and HN0₃ were correlated only in the summer. Windroses are used to show the dependence of sulphate, nitrate and aerosol acid on wind direction. Lead had a 24 hr average concentration of 71 ng m^?3, was of mainly local origin and was not able to be correlated with other parameters.     

A comparison of summer and winter measurements of atmospheric nitrogen and sulphur compounds

Summer and winter concentrations of acidic atmospheric species and their precursors were measured in central Ontario. Large seasonal differences in concentrations were observed for some species. The concentrations of primary emission species, S0₂ and NO_x, were much larger in winter, whereas 0₃ and aerosol S0₄ were much reduced. HN0₃, PAN and aerosol N0₃ showed little seasonal change; PAN represented about 30% of the total oxidized nitrate. During pollution episodes and in summer, the molar ratio of nitrate (aerosol N0₃ plus HN0₃) to aerosol S0₄ was about 0.1 to 0.2; however, during winter, this molar ratio was about 1 to 2.     

Effects of low-level SO2 fumigation on decomposition of western wheatgrass litter in a mixed-grass prairie

Litter bags were used to determine the effects of SO₂ and substrate-S content on decomposition rates of western wheatgrass tillers in the field. Atmospheric SO₂ decreased monthly decomposition rates 32 to 44% in spring and early summer and 12% in dry late summer. Increased S content of the substrate (980 μg g^?1 vs 590 μg g^?1 in control) had no measurable effect on decomposition. The observed inhibition was probably caused by reduced pH and/or accumulation of toxic derivatives of SO₂ in the microenvironment of organisms on the decaying leaf surfaces.     

Acid Deposition in Bandung, Indonesia

LAPAN has measured rain acidity in Bandung, the location is Cipedes since 1985, with average pH in 1985 was 6.25. The pH condition 1985–1999 as follow: The monthly average of pH in period 1985–1992 was >5.6: in the middle of 1996–1997 it had big variation and than decrease until now. The monthly average of pH in 1997 until now was <5.6. The pH has decreasing trend, the reason was increasing fuel combustion for transportation and household because the area around the observation was change from rural to be transportation and settlement area. The rain acidity comparison in Cipedes (rural site), Cicahuem (busy site), and Tanjungsari (remote site) hold in 1986–1987, the result was Tanjungsari the remote site had the lowest pH. It's suggested the reason was sulphur compound from Kamojang crater and air pollution from industrial area in south-east of Bandung were blown by the wind through this place. The influence of air pollution to acid rain was studied by measurement NO₃ ^? and SO₄ ^2? in 5 places around Bandung, the results were: North of Bandung had the lowest NO₃ ^? concentration because the traffics were low: but had the highest SO₄ ^2? concentration; it's caused by emission of sulphur compounds from Tangkuban Perahu Montain. South of Bandung had the highest NO₃ ^? concentration because the traffics were crowded and a lot of industries around it. In general Bandung had SO₄ ^2? concentration higher than NO₃ ^? concentration, it's suggested due to the influence of sulphur compound from Tangkuban Perahu Montain. The observation rain acidity in Ciater at Tangkuban Perahu Montain started in 1996, the result in period 1996–1998 as follow: The pH had decreasing trend, it's due to the traffic near this observation increase, so the air pollution around this area increase, it will influence the rain acidity. The maximum monthly average of ph was 6.78 and minimum was 4.63, the pH monthly average generally < 6. In El NINO year 1997, the monthly average of pH in April and December were > 6.5.     

Temporal variation in aluminum speciation and concentration during snowmelt

Precipitation samples in Alberta were collected and analyzed monthly from six Alberta Environment stations. Samples were collected with Sangamo samplers and analyzed for the major ions, pH and acidity. The data were tabulated and analyzed for spatial distribution, seasonal variation, temporal trends, ionic character and wet sulphate deposition. The major ionic species in Alberta precipitation are Ca²⁺, SO _inf4 ^sup2? , NH _inf4 ^sup+ and N0 _inf3 ^sup? . The spatial distribution shows a slight decrease in pH from southern Alberta (pH 6.0) to northern Alberta (pH 5.4). The seasonal variation shows higher hydrogen ion content in the summer months (pH 5.4 in summer and pH 5.8 in winter). Temporal trends are not apparent over the five year period investigated. The five year average wet sulphate deposition rate in Alberta is 9.1 kg ha^?1 yr^?1.     

Effect of simulated sulfuric acid rain on the chemistry of a sulfate-adsorbing forest soil

Simulated H₂SO₄ rain (pH 3.0, 3.5, 4.0) or control rain (pH 5.6) was applied for 3.5 yr to large lysimeter boxes containing a sulfate-adsorbing forest soil and either red alder (Alnus rubra Bong) or sugar maple (Acer saccharum Marsh.) seedlings. After removal of the plants and the litter layer, soil samples were obtained at 15-cm intervals to a total depth of 90 cm. Elevated SO₄ concentrations caused by the simulated H₂SO₄ rain were most pronounced for the top 15 cm, but extended down to 45 cm (maple) or 75 cm (alder). There were no effects on SO₄ concentrations at a depth of 75 to 90 em. This confirmed the existence of a sulfate front between 20 cm and 100 cm, as postulated earlier on the basis of extracted soil solutions. Decreases in Mg and Ca concentrations, base saturation, and soil pH were limited to the uppermost 15 cm and, in most cases, to the pH 3.0 treatment. Concentrations of Mg and Ca for the pH 3.0 treatments were greater than control at a depth of 15 to 30 cm, indicating transport of these cations from the soil surface. Concentrations of Na and K, and cation exchange capacity, were not affected by simulated H₂SO₄ rain. Elevated concentrations of NO₃ and extractable Zn throughout the alder systems indicated (1) either increased rates of symbiotic N-fixation or decreased rates of N immobilization; and (2) mobilization of Zn by all acid rain treatments.