Chemical composition and source apportionment of rainwater at Guiyang, SW China

This study systematically analyzed the concentrations of cations and anions and determined the pH in the rainwater at Guiyang from Oct. 2008 to Sep. 2009. The pH in the rainwater varied between 3.35 and 9.99 with a volume-weighted mean value of 4.23. The volume-weighted mean concentrations of anions followed the order SO₄ ^2->Cl^->F^->NO₃ ^-, whereas the volume-weighted mean concentrations of cations followed the order Ca²⁺>NH₄ ⁺>Na⁺>Mg²⁺>K⁺. This finding indicates that SO₄ ^2- was the main anion and that Ca²⁺ and NH₄ ⁺ were the main cations. Significant correlations between each pair of ions (SO₄ ^2-, NO₃ ^-, NH₄ ⁺, Ca²⁺, and Mg²⁺) were observed, suggesting that CaSO₄, Ca(NO₃)₂, MgSO₄, Mg(NO₃)₂, NH₄NO₃, (NH₄)₂SO₄, and/or NH₄HSO₄ exist in the atmosphere at Guiyang. The soil-derived species (such as Ca²⁺) played an important role in the neutralization of the acidity in rainwater. The SO₄ ^2- and NO₃ ^- in the rainwater were mainly from anthropogenic sources, and their contributions accounted for 98.1 % and 94.7 %, respectively. NH₄ ⁺ was also most likely derived from anthropogenic sources, such as domestic and commercial sewage, and played an important role in the neutralization of the rainwater at Guiyang.     

Rainwater Chemistry at Mt. Etna (Italy): Natural and Anthropogenic Sources of Major Ions

Major ion content of 37 wet-only rainwater samples collected on the southern flank of Mount Etna volcano was investigated. Measured pH values range from 3.80 to 7.22 and display a positive correlation with Ca²⁺ and an inverse correlation with NO₃ ^–, suggesting that anthropogenic NO_x are the most effective acidifying agents while Ca, likely as solid CaCO₃, is the prevailing proton acceptor. Na/Cl ratios indicate a dominant marine origin for both species, while K, mg and Ca contents point to additional sources (soil dust, fertilisers etc.). Nitrate and sulphate concentrations display a nearly constant ratio indicating a common anthropogenic origin, and only a few samples are characterised by sulphate excess. The analysis of time series reveals a good correlation between the excess sulphate in rainwater and SO₂ fluxes from the summit craters plume. Non sea salt chloride contents show also a significant correlation with volcanic activity indicating a magmatic sulphur and chloride contribution to rainwater. Meteoric flux estimations point to a prevailing magmatic origin for sulphur in the collected rainwaters while sea spray is the main source of chlorine.     

Studies on Intercorrelation between Ions Co-Occurring in Precipitation in the Gdańsk-Sopot-Gdynia Tricity (Poland)

The paper presents monitoring results and environmental pollution assessment for the Gdask-Sopot-Gdynia Tricity (Poland), based onanalysis of precipitation. Precipitation samples were collected over a period of 12 months (January–December 1998) at ten locations in the Tricity. The following selected ions were determined in the samples:SO₄ ^2–, F^–, Cl^–, NO₃ ^–,PO₄ ^3–, NH₄ ⁺, Na⁺,Mg²⁺, Ca²⁺, K⁺. The results were subjected to full statistical evaluation. Values of the parameters determined were correlated with each other. An attempt was made to explain co-occurrences of certain ions and the significance of their mutual effects. Pollutant concentrations and loads in precipitation were also correlated with data on wind direction and temperature in the region.Deposition of pollutants was very high in spring due to the prevailing air circulation patterns and low temperatures. Analysis of the correlations between co-occurring ions confirmed the significant impact of the location (sea coast) on the composition of rain water. Ionic ratios in rainwater were similar to those observed for sea salt samples. In addition, heavy traffic was most probably responsible for high concentrations of various forms of nitrogen and sulphates in the vicinity of major highways.     

Rapid change in nitrate and sulfate concentrations observed in early stage of precipitation and their deposition processes

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.     

合肥市降水化学组成成分分析

为研究合肥市降水的化学组成成分,于2010年4—9月在合肥市国家基本气象站设立了采样点,进行降水的采集,对降水化学组成成分进行了测定,并系统分析了化学组成成分的特点。结果表明:合肥降水中阴离子主要为SO24-,阳离子主要为NH4+和Ca2+,[SO24-]/[NO3-]当量浓度比值范围为1.23～6.33,大部分样本的比值<3,说明酸雨类型以硝硫混合型为主。降水的酸度与单一离子当量浓度的相关性并不明显,应该是受多种离子综合影响的结果,SO24-与NO3-,Ca2+与Mg2+,NH4+与SO24-,NH4+与NO3-均表现出较好的相关性。     

Some observations on the acidity and composition of rainwater in Sydney,Australia, during the summer of 1980–81

During the summer of 1980–81, a rudimentary form of wet-only event sampling was employed to collect a total of 294 rainwater samples at 12 sites spread across the metropolitan region of Sydney, Australia's largest city. From the samples were determined conductivity, pH, ammonium, chloride and nitrate ion concentrations as well as deposited water volume. Supplementary data consisting of city-wide averaged SO₂, NO₂, NO, and O₃ concentrations and 950 mb wind speed and direction were obtained for times coinciding with the period during which each event occurred.The pH of rainwater upwind of the city and unaffected by urban/industrial emissions was found to be usually 5, whereas the volume-weighted mean pH of all the metropolitan samples was 4.4, indicating that local emissions significantly increased rainwater acidity in the near field. Time available for conversion of precursors to acids averaged 1–2 h only.Considerable day-to-day variability in rainwater composition was observed. Factors identified as contributing to this variability included precursor gas concentration, wind speed, wind direction, amount of water deposited per event and possibly time of day. These results show that physical/meteorological factors cannot be excluded from consideration if variance in rainwater composition data is to be explained.     

Episodes of extreme rainwater pollution and its relationship with synoptic situation (Wielkopolski National Park,Poland)

Synoptic conditions of extreme rainwater pollution episodes, evidenced by maximum values of parameters measured in the protected area of Wielkopolski National Park (western-central Poland), were analysed in this study. Precipitation samples were tested for the following parameters: pH, electrical conductivity and the concentration of the following elements: F^-, Cl^-, NO₂^-, NO₃^-, PO₄^3-, SO₄^2- and Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺. It was assumed, that in winter, western advection of Atlantic air masses was the most frequent aerosol and pollution transport scenario for the investigated area. In summer the most heavily pollution occur at the intensified meridional flow over the central Europe, indicating advection of cooler air from northern Europe and the North Sea. In most of cases, the weather conditions causing extreme concentration of examined pollutants, were determined by the movement of weather fronts over considerable parts of Poland and by precipitation caused by those fronts.     

A Long Term Study on Chemical Composition of Rainwater at Dayalbagh, a Suburban Site of Semiarid Region

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.     

Rainwater acidity and ion concentration correlations in a midwest storm system

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.     

Chemical compositions of wet precipitation and anthropogenic influences at a developing urban site in southeastern China

A comprehensive study on the chemical compositions of wet precipitation was carried out from January 2004 to December 2004 in Jinhua, southeastern China's Zhejiang Province. All samples were analyzed for pH, electrical conductivity and major ions (F⁻, Cl⁻, NO₃⁻, SO₄²⁻, K⁺, Na⁺, Ca²⁺, Mg²⁺ and NH₄⁺). The rainwater was typically acidic with a volume-weighted mean pH of 4.54, which ranged from 3.64 to 6.76. SO₄²⁻ and NO₃⁻ were the main anions, while NH₄⁺ and Ca²⁺ were the main cations. The concentrations of these major ions were generally higher compared to those reported in other parts of the world, but much lower than those in northern China.Wet deposition fluxes of major ions showed pronounced seasonal variations with maximum in spring and minimum in autumn. Significant correlations were found in soil-derived species among Ca²⁺, Mg²⁺ and K⁺ and sea-salt species between Na⁺ and Cl⁻. Other relatively good correlations were also observed between Ca²⁺ and SO₄^2-, Mg²⁺ and SO₄^2-, Mg²⁺ and NO₃⁻, Mg²⁺ and Cl⁻. Principal component analysis was also performed on individual precipitation to find possible sources of the major ionic species. Varimax rotated four components accounting for 85.9% of the total variance, and were interpreted as acid and alkaline pollutants, sea spray and mixed source, soil and acid/neutralization. Calculation of enrichment factors for rainwater components relative to soil and seawater indicated that Ca²⁺ and K⁺ mainly originated from the terrestrial source, and SO₄^2- and NO₃⁻ were mostly attributed for the anthropogenic activities in the study area. In general, the results suggested that precipitation chemistry is strongly influenced by anthropogenic sources rather than natural and marine sources. The pollutants in rainwater were mainly derived from long distance transport, local industry and traffic sources.     

Carboxylic monoacids in the air of mayombe forest (Congo): Role of the forest as a source or sink

In the tropical rain forests of the Congo during the dry season, from June to September 1987, carboxylic acid partial pressures (P _gas) in the air above the canopy, at ground level, and at the boundary layer, were estimated from water samples such as fog and rainwater. The concentrations of these acids were also measured in the sap of tree leaves. Tree leaves act as a sink or as a source if the acid P _gas is greater of lower than the acid concentrations in molecular form in sap. For each of these soluble gases, there is a value of P _gas where the exchange is nul. This is called the compensation point. Values of the compensation point for some tree leaves were evaluated according to Henry's law. Henry's law coefficients at ppm levels were redetermined for formic (HCOOH), acetic (CH₃COOH), propionic (CH₃CH₂COOH), and isobutyric (CH₃CH(CH₃)COOH) acids.By comparison of P _gas and compensation points, it is concluded that the forest was a potential source for these acids. The soil-or the litter-acts as a significant source of a carboxylic acid of C₃ or C₄ atoms in the aliphatic chain. This carboxylic acid, not yet fully characterized, could play an important role in the rain acidity in forested zones of the equatorial areas.The direct emission of these carboxylic acids by vegetation was the main source in the boundary layer above the forest. The average emissions were 3.1×10⁹, 7.8×10⁹, and 8.4×10⁹ molecules cm^-2 s^-1 for HCOOH, CH₃COOH, and CH₃CH₂COOH, respectively. The savanna is an exogenous source of HCOOH and CH₃CH₂COOH during moderately rainy days for 30% of the time. The ozonolysis of isoprene seems to be a small source of HCOOH.     

Factors Influencing Nitrogen Speciation in Coastal Rainwater

Rainwater was collected from 129 rain events between February 2002 and August 2003 and analyzed for ammonium (NH₄⁺), nitrate (NO₃⁻), organic nitrogen (ON) and free amino acids (AA). Inorganic nitrogen (NO₃⁻ + NH₄⁺) was the dominant form of N representing 85% of total nitrogen based on volume-weighted averages. The remainder of the N occurred as organic nitrogen species of which free amino acids contribute approximately 17%. A significant, and in some cases the majority (> 75%), of the remaining ON could be accounted for by macromolecular uncharacterized humic like substances. This has important ramifications with respect to the long range transport of atmospheric ON because humic materials are recalcitrant and therefore may travel long distances from their source. There was a distinct seasonality to the N speciation data with maximum concentrations of NH₄⁺, ON and AA occurring in the spring. Air-mass back trajectory analysis indicates there is a strong anthropogenic component to the NO₃⁻, NH₄⁺ and AA signal but not ON. There was a strong positive correlation between amino acid concentrations and ammonium which suggests they have similar sources and sinks in rainwater. Finally, large episodic additions of NH₄⁺ and AA during tropical events could significantly impact short term bioavailable N budgets in estuaries impacted by these storms. Approximately three times as much NH₄⁺ and AA were deposited during Hurricane Isabel (317 μ moles ⋅ m⁻² and 84 μ moles ⋅ m⁻² respectively) compared to the mean impact of average summertime rain events at this location.     

Chemical character of precipitation and related particles and trace gases in the North and South of China

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 SO₄^2-, 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.     

STUDY ON THE CHEMICAL CHARACTERISTICS OF POLLUTING FOG IN GUANGZHOU AREA IN SPRING

Samples of fog water collected in the area of Guangzhou during February, March and April of 2005 are used in this work to study the chemical composition of fog water in polluting fog there. Three typical episodes of polluting fog are analyzed in terms of ionic concentration and their possible sources. It is found that the concentration of various ions in fog water is much higher than those in rainwater. Fog not only blocks visual range but contains liquid particles that result in high degree of pollution and are very harmful to human health. SO₄⁼ is the anion with the highest concentration in fog water, followed by NO₃^-.For the cation, Ca⁺⁺ and NH₄⁺ are the highest in concentration. It is then known that rainwater is more acidic than fog water, indicating that ionic concentration of fog water is much higher than that of rainwater, but there are much more buffering materials in fog water, like NH₄⁺ and Ca⁺⁺. There is significant enrichment of Ca⁺⁺, SO₄⁼, and Mg⁺⁺ in fog water. In the Guangzhou area, fog water from polluting fog is mainly influenced continental environment and human activity. The episodes of serious fog pollution during the time have immediate relationships with the presence of abundant water vapor and large amount of polluting aerosol particles.     

Spatial, Temporal and Interannual Variability of Methanesulfonate and Non-Sea-Salt Sulfate in Rainwater in the Southern Indian Ocean (Amsterdam, Crozet and Kerguelen Islands)

Methanesulfonate (MS^–) and non-sea-salt sulfate (nss-SO ₄ ^2– ), two of the major oxidation products of atmospheric dimethylsulfide (DMS), have been continuously measured in rainwater at three remote islands in the Southern Indian Ocean: Amsterdam since 1991, Crozet since 1992, and Kerguelen since 1993. The annual volume weighted mean (VWM) concentrations of nss-SO ₄ ^2– in rainwater were 3.19, 3.04 and 4.57 eq l^–1 at Amsterdam, Crozet, and Kerguelen, respectively while the VWM of MS^– were 0.24, 0.15 and 0.30 eq l^–1, respectively. At all three islands, MS^– presented a well-distinguished seasonal variation with a maximum during summer whereas the seasonal variation of nss-SO ₄ ^2– was less pronounced, possibly due to the increased anthropogenic influence during the winter period. Furthermore, MS^– presented significant interannual variations, in particular at Amsterdam and Crozet, which is closely related to the sea-surface temperature (SST) anomalies). Finally, the nss-SO ₄ ^2– deposition at Crozet Island presented a decreasing interannual trend, reflecting probably reductions in sulfur emissions from Southern Africa. On the contrary no interannual tendency was observed in the nss-SO ₄ ^2– concentrations at Amsterdam Island, indicating that the biogeochemical sulfur cycle at this area is mainly influenced by biogenic emissions.     

Continuous measurement of methane flux over a larch forest using a relaxed eddy accumulation method

We measured the methane flux of a forest canopy throughout a year using a relaxed eddy accumulation (REA) method. This sampling system was carefully validated against heat and CO₂ fluxes measured by the eddy covariance method. Although the sampling system was robust, there were large uncertainties in the measured methane fluxes because of the limited precision of the methane gas analyzer. Based on the spectral characteristics of signals from the methane analyzer and the diurnal variations in the standard deviation of the vertical wind velocity, we found the daytime and nighttime precision of half-hourly methane flux measurements to be approximately 1.2 and 0.7?μg?CH₄?m^?2?s^?1, respectively. Additional uncertainties caused by the dilution effect were estimated to affect the accuracy by as much as 0.21?μg?CH₄?m^?2?s^?1 on a half-hourly basis. Diurnal and seasonal variations were observed in the measured fluxes. The biological emission from plant leaves was not observed in our studies, and thus could be negligible at the canopy-scale exchange. The annual methane sink was 835?±?175?mg?CH₄?m^?2?year^?1 (8.35?kg?CH₄?ha^?1?year^?1), which was comparable to the flux range of 379–2,478?mg?CH₄?m^?2?year^?1 previously measured in other Japanese forest soils. This study indicated that the REA method could be a promising technique to measure canopy scale methane fluxes over forests, but further improvement of precision of the analyzer will be required.     

Rainwater chemistry and bulk atmospheric deposition in a tropical semiarid ecosystem: the Brazilian Caatinga

We assessed the rainwater chemistry, the potential sources of its main inorganic components and bulk atmospheric deposition in a rural tropical semiarid region in the Brazilian Caatinga. Rainfall samples were collected during two wet seasons, one during an extremely dry year (2012) and one during a year with normal rainfall (2013). According to measurements of the main inorganic ions in the rainwater (H⁺, Na⁺, NH₄ ⁺, K⁺, Ca²⁺, Mg²⁺, Cl^?, NO₃ ^?, and SO₄ ^2?), no differences were observed in the total ionic charge between the two investigated wet seasons. However, Ca²⁺, K⁺, NH₄ ⁺ and NO₃ ^? were significant higher in the wetter year (p < 0.05) which was attributed to anthropogenic activities, such as organic fertilizer applications. The total ionic contents of the rainwater suggested a dominant marine contribution, accounting for 76 % and 58 % of the rainwater in 2012 and 2013, respectively. The sum of the non-sea-salt fractions of Cl^?, SO₄ ^2?, Mg²⁺, Ca²⁺ and K⁺ were 19 % and 33 % in 2012 and 2013, and the nitrogenous compounds accounted for 2.8 % and 6.0 % of the total ionic contents in 2012 and 2013, respectively. The ionic ratios suggested that Mg²⁺ was probably the main neutralizing constituent of rainwater acidity, followed by Ca²⁺. We observed a low bulk atmospheric deposition of all major rainwater ions during both wet seasons. Regarding nitrogen deposition, we estimated slightly lower annual inputs than previous global estimates. Our findings contribute to the understanding of rainfall chemistry in northeastern Brazil by providing baseline information for a previously unstudied tropical semiarid ecosystem.     

Chemistry of rainwater and aerosols over Bay of Bengal during CTCZ program

For the first time, simultaneous study on physical and chemical characteristics of PM₁₀, PM_2.5, and rainwater chemistry was attempted over the Bay of Bengal in monsoon season of 2009. The aerosols and rainwater samples were collected onboard ship ‘SK-261, ORV Sagar Kanya’ during Oceanographic Observations in the Northern Bay of Bengal under the Continental Tropical Convergence Zone (CTCZ) program conducted during 16 July to 19 Aug 2009. Aerosol samples collected by PM₁₀ and PM_2.5 were analyzed for various water soluble (Na⁺, K⁺, Ca²⁺, Mg²⁺, NH ₄ ⁺ , Cl^?, SO ₄ ^2? and NO ₃ ^? and acid soluble (Fe²⁺, Al³⁺, Zn²⁺, Mn³⁺ and Ni²⁺) ionic constituents. The pH of rainwater varied from 5.10 to 7.04. Chloride ions contributed most to the total ion concentration in aerosol and rainwater, followed by Na⁺. Significant contributions of SO ₄ ^2? , NO ₃ ^? and NH ₄ ⁺ found in PM_2.5, PM₁₀ and high concentrations of TSP and non sea-salt SO ₄ ^2? over the mid-ocean is attributed to the long range transport of anthropogenic pollution from the Indian continent. The scavenging ratio was maximum for coarse particles such as Ca²⁺ and minimum for fine particles like NH ₄ ⁺ _.     

Synergistic Effects of Nitrogen Amendments and Ethylene on Atmospheric Methane Uptake under a Temperate Old-growth Forest

An increase in atmospheric nitrogen (N) deposition can promote soil acidification, which may increase the release of ethylene (C2H4) under forest floors. Unfortunately, knowledge of whether increasing N deposition and C2H4 releases have synergistic effects on soil methane (CH4) uptake is limited and certainly deserves to be examined. We conducted some field measurements and laboratory experiments to examine this issue. The addition of (NH4)2SO4 or NH4Cl at a rate of 45 kg N ha-1 yr-1 reduced the soil CH4 uptake under a temperate old-growth forest in northeast China, and there were synergistic effects of N amendments in the presence of C2H4 concentrations equal to atmospheric CH4 concentration on the soil CH4 uptake, particularly in the NH4Cl-treated plots. Effective concentrations of added C2H4 on the soil CH4 uptake were smaller in NH+4 -treated plots than in KNO3-treated plots. The concentration of ca 0.3 μl C2H4 L-1 in the headspace gases reduced by 20% soil atmospheric CH4 uptake in the NH4Cl-treated plots, and this concentration was easily produced in temperate forest topsoils under short-term anoxic conditions. Together with short-term stimulating effects of N amendments and soil acidification on C2H4 production from forest soils, our observations suggest that knowledge of synergistic effects of NH+4 , rather than NO3- , amendments and C2H4 on the in situ soil CH4 uptake is critical for understanding the role of atmospheric N deposition and cycling of C2H4 under forest floors in reducing global atmospheric CH4 uptake by forests. Synergistic functions of NH4+ -N deposition and C2H4 release due to soil acidification in reducing atmospheric CH4 uptake by forests are discussed.     

Covariations in oceanic dimethyl sulfide,its oxidation products and rain acidity at Amsterdam Island in the Southern Indian Ocean

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%.