Ten years of precipitation chemistry in Haifa,Israel

Rain event samples have been collected in Haifa, Israel, for nine hydrological years 1981 to 1990. Precipitation amount, pH, SO₄ ⁼, NO₃ ^?, Cl^?, NH₄ ⁺, Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺ and alkalinity of rainwater samples were recorded. The sampling and analysis program was based on WMO recommendations for background networks. The sampling was performed manually, and the analysis was based on wet chemistry for ions and atomic absorptions for metals. Data of 187 rain samples showed that the average pH was 5.3±1.1∶ 26% of the rain events were below pH of 5.6 and 23% above pH of 7.0. Some simple chemical mass-balance considerations indicate that natural sources, sea salt and soil carbonates are the main contributors to rain chemistry. However, the presence of low pH events observed over the years suggests that the impact of anthropogenic emissions may overwhelm the buffering capacity of the alkaline aerosol.     

Snow chemistry in the central Sierra Nevada,California

Precipitation and snowpack basal outflow event samples were analyzed for pH and NO and SO₄ concentrations at a site near Lake Tahoe, California. TJ seasonal minimum pH from basal outflow was synchronous with a rain-on-snow event in 1984. Outflow pH reflected the low ionic concentrations of precipitation at the site. There was no evidence for a pulse of acidified meltwater at this site either during a mid-February melt induced by high air temperatures in 1985 or during 1984 or 1985 main spring melt periods. During the mid-February 1985 melt, however, an alkalinity pulse occurred in basal outflow.     

Acid pollutants in air and precipitaion/deposition at the Sudeten Mountains,Poland

The results of several separately performed field studies on air quality in south-western Poland (Black Triangle) are presented In the period 1988–1993 atmospheric aerosol measurement and precipitation/deposition samples were collected at three locations of mountain region (810–1490 m asl). Precipitation was monitored in forest ecosystem using a 24-gauge network was carried out during June–October 1992 and 1993. The occurence of cloud at ground level over hills is difficult to categorize and quantify in mountain terrain and has constituted a basic part of our studies. Precipitation/deposition samples (seven rain and three cloud collectors) in the Karkonosze Mountains were collected over the period 1994–1995 (four field campaigns were conducted) to examine aqueous chemical interactions between constituents in samples. Meteorological data measured at the site included temperature, humidity, wind speed and direction and the amount of precipitation.     

ACID DEPOSITION DURING TWO CONTRASTING FRONTAL RAINFALL EVENTS

Analysis of the chemical composition of rain at high temporal resolution provides additional information on wet deposition processes. High resolution data was obtained using a microprocessor-based acid rain monitor at two sites in SW Scotland and SE England. Meteorological details of the transport and wet deposition processes during two frontal rain events were examined and related to rainfall composition. Rapid depletions of ion concentrations during heavy rainfall in the first event were interpreted using a rainfall scavenging model. The sub-event data for the second event showed the influence of frontal discontinuities. Increasing ionic concentrations during this second event were attributed both to the change in air mass, and to diminished upwind precipitation scavenging.     

Comparison of daily and weekly precipitation sampling efficiences using automatic collectors

Precipitation samples were collected for approximately 90 daily and 50 weekly sampling periods at Finley Farm, near Raleigh, North Carolina from August 1981 through October 1982. Ten wet-deposition samplers (AEROCHEM METRICS MODEL 301) were used; 4 samplers were operated for daily sampling, and 6 samplers were operated for weekly-sampling periods. This design was used to determine if. (1) collection efficiences of precipitation are affected by small distances between the Universal (Belfort) precipitation gage and collector; (2) measurable evaporation loss occurs and (3) pH and specific conductance of precipitation vary significantly within small distances. Average collection efficiencies were 97% for weekly sampling periods compared with the rain gage. Collection efficiencies were examined by seasons and precipitation volume. Neither factor significantly affected collection efficiency. No evaporation loss was found by comparing daily sampling to weekly sampling at the collection site, which was classified as a subtropical climate. Correlation coefficients for pH and specific conductance of daily samples and weekly samples ranged from 0.83 to 0.99.     

Precipitation chemistry at sinhagad-a hill station in India

The chemistry of precipitation in remote sites such as mountain tops is of interest in the study of atmospheric pollution and acid rain. The chemical composition measured at mountain site which is away from industrial and urban areas is useful as a reference level and it allows to determine the extent of anthropogenic contamination. Hence, rain water samples were collected at Sinhagad (18°21N, 73°45E, 1450 m asl during the monsoon season (June-September) of 1992 and were analysed for major ions. The precipitation samples collected at Sinhagad were alkaline in nature and pH values ranged between 5.9 to 6.76. The ionic composition was dominated by soil dust The concentration of Ca²⁺ was highest among all the ions. The concentrations of excess SO₃ ^2– and NO₄ ^– were small (23.8 and 15.2 eq l^–1 respectively) compared to the values of polluted regions in India. The correlation coefficient between the ions and pH values was calculated and it was found to be maximum in case of Ca²⁺. Precipitation samples collected at Sinhagad were alkaline owing to higher concentration of Ca²⁺ and lower levels of acidic pollutants (SO₄ ^2– and NO₃ ^–).     

Calibration of collection procedures for the determination of precipitation chemistry

Precipitation is currently collected by several methods, including several different designs of collection apparatus. We are investigating these differing methods and designs to determine which gives the most representative sample of precipitation for the analysis of some 25 chemical parameters. The experimental site, located in Ithaca, New York, has 22 collectors of 10 different designs. The designs include bulk (wet and dry deposition collected together), wet only (only rain and snow) and wet/dry (collects wet and dry deposition separately). In every sampling period, which varies from 1 day to 1 mo, depending on the time variable being tested, the following chemical parameters are determined: conductivity, pH, Ca, Mg, Na, K, NH₄, N0₃, N_total Si0₄, PO₄, P_total, Cl, SO₄, DOC, Zn, Cu, Mn, Fe, Al, Ni, Cd, Pb, Ag, DDT, DDE, Dieldrin and PCB's. The results of the investigation lead us to conclude that:

1. Precipitation samples must exclude dry deposition if accurate information on the chemical content of precipitation is required.
2. Substantial contamination results when glass and plastic collectors are used to sample precipitation for inorganic and organic components, respectively.
3. The inorganic components of precipitation samples of low pH (3.5 to 4.5), with the exception of P0₄ and Cl, exhibited no significant change in concentration when stored at 4\dgC for a period of 8 mo. We believe this is due to the stabilizing influence of a large concentration of H ions.
4. If quantitative information on the chemical composition is required, precipitation samples should be collected at no longer than weekly intervals if immediate collection is not possible.

     

Measurement of acid precipitation in Norway

Since January 1972, chemical analysis of daily precipitation samples from about 20 background stations in Norway has been carried out on a routine basis. Air monitoring is carried out at six stations. The chemical analysis program is: sulphate, pH and acidity in precipitation, sulphates and SO₂ in air. In addition, more detailed chemical analysis of aerosol and precipitation has been carried out at selected stations. Some results for the measurement period 1972 to 1974 are presented. Comparison of air and precipitation concentrations of S compounds show that the precipitation scavenging efficiency is very high under the conditions in southern Norway.     

Stability of Ionic Components in Precipitation Samples — A Case Study in Taipei

The changes in ionic contents were studied in acidic precipitation samples collected for precipitation events in Taipei, which is near the sea. The storage cases under investigation include filtration, refrigeration, and light. Thus the experimental design leads all precipitation samples collected in the same rain event stored under different conditions. They were then analyzed six times successively within two months to provide the information containing potential ionic composition change. The measured constituents are H⁺, K⁺, Na⁺, Ca²⁺, Mg²⁺, NH₄ ⁺, NO₃ ^?, SO₄ ^2?, and Cl^?. The comparison of measured ionic concentrations corresponding to different storage methods yield no significant difference. The increases of NO₃ ^? and decreases of NH₄ ⁺ with time were observed to be of similar magnitude, while the variation of pH values is significant. The presented study indicated the important role played by sample storage in determining the ionic composition of precipitation samples.     

Characterizinig Precipitation Chemistry in Changhua, Central Taiwan Using Weather Conditions And Multivariate Analysis

Few studies of atmospheric deposition come from the fast growing region of Southeast Asia. Precipitation in Changhua City in central Taiwan was collected to examine its chemical composition and relationship with meteorological patterns. Fifty percent of the precipitation measurements had pH<5.0. Deposition fluxes of most ions were comparable to that reported for heavily industrialized temperate regions. Storms associated with air masses which originated in China had higher ion concentrations than other storms, suggesting substantial contribution of long-range transport. Two factors, a sea salt factor and an anthropogenic factor, explained more than 70% of the variation in precipitation chemistry. A third factor had a high loading only on H⁺, suggesting that pH of precipitation in Changhua City was not dominated only by acidic or basic ions alone. Instead it is determined by all components. The influences of soil and dust, as indicated by high loading on Ca²⁺ and K⁺, cannot be recognized without sea salt correction.     

Precipitation chemistry within Kvarner Bay area,Northern Adriatic (Croatia), 1984–1991

The results of rainwater analyses collected at five sampling sites within Kvarner Bay area are presented for the period 1984–1991. The samples were collected on a daily basis in open buckets thus representing bulk samples. Although measurements are referred to as wet deposition samples, they are actually an upper limit for the wet deposition. The rainwater was initially analysed for pH, sulphate and nitrate content, while during the period March 1990 — May 1991 the analyses were extended to major ion concentrations: hydrogen, sulphate, nitrate, chloride, ammonium, sodium, potassium, calcium and magnesium. The pH frequency distribution, pH medians and precipitation weighted average (PWA) concentrations of hydrogen, sulphate and nitrate are presented, as well as wet deposition rates of sulphur (as sulphate) and nitrogen (as nitrate). The dependence of hydrogen, sulphate and nitrate mean concentrations on wind directions and seasons for Site 1 is also given. The highest precipitation acidity is obtained at urban and industrial Site 1 (city of Rijeka) because of the local washout of the atmosphere and influence of dry deposition, and at remote Site 4 (Lake Vrana) due to long-range transport. The neutralizing potential of sea salt and soil dust is responsible for partial neutralization of rainwater at other sites. The influence of sea salt on chemical composition of rainwater is observed at all sites. The estimated wet deposition rates of sulphate and nitrate are close to the values reported for Southeast Europe. The wet deposition rate for ammonium ion at Site 1 is almost double comparative regional values.     

Precipitation chemistry and atmospheric processes in the forested part of Croatia

The influence of mesoscale weather patterns on the chemical composition of daily precipitation samples is analysed. The data of pH, sulphur from sulphates and total nitrogen are analysed for two rural sites: Plitvice station in forested part of Central Croatia (1981 to 1990) and Puntijarka suburban station on the mountain near Zagreb, the capital of Croatia (1982–1991). The two prevailing weather types in precipitation days are selected and the comparison of chemical composition of precipitation is made for each of them. The frequency distributions of pH, sulphur and nitrogen show that concentration of major ions in precipitation apparently depends on the regional scale weather type. It is shown that the seasonal variation of deposition is related to the seasonal variation in precipitation amount. In both weather types Plitvice receives more pollution than Puntijarka that is closer to urban and industrial pollution sources. Both locations are under the prevailing influence of regional pollution sources.     

模拟降水变化下黄土丘陵区草地群落特征及其物候期响应

在全球气候变化背景下,黄土高原降水格局呈现出季节波动增强和极端降水事件增加趋势,降水格局变化势必会引起草地群落特征和物候期发生重要改变。为研究黄土丘陵区草地生态系统对降水改变的响应,选取黄土丘陵区退耕草地为研究对象,连续定位观测自然恢复小区不同降雨梯度下(0,±20%,±40%,±60%)物候动态变化,探究了物候期和群落结构对降水变化的响应状况。结果表明:(1)不同降水条件下群落物种组成及丰度存在明显差异,与对照组相比,增雨与减雨均提高了物种的种类。增雨60%群落种类最多,为18种。(2)降水梯度递增处理下,群落盖度呈先增加后降低趋势,地上生物量随呈单峰趋势。增雨20%处理和减雨20%处理均能够显著提高群落植被盖度和地上生物量,地上生物量在增雨处理下明显高于减雨处理。(3)丰富度和Shannon-Wiener指数总体上都呈增加趋势,减雨20%,40%,60%均使Pielou均匀度指数降低。(4)不同降水条件对物种物候期的影响显著(p<0.05),群落返青期、繁殖期和和枯黄期在减雨处理下显著提前,而增雨处理则使其繁殖期和枯黄期发生推迟。综上,群落物种组成、植被盖度和地上生物量在不同降水处理下表现出显著差异,而物种多样性对降水变化响应不敏感。     

An automatic sequential rain sampler

A sequential rain sampler is described. It was designed to automatically operate unattended in remote areas. Precipitation water is sampled sequentially in order to study the evolution of contaminant concentrations as a function of rain intensities and duration. A few preliminary results are presented; they are related to rain samples collected in a semi-rural area.     

Effects of varying air trajectories on spatial and temporal precipitation chemistry patterns

This study was designed to determine if judicious use of synoptic data and an operational trajectory model could identify probable source regions of anthropogenic pollutants in northeastern United States precipitation and thus relate receptor measurements to emissions data without consideration of the complex intervening meteorological and chemical processes. The storm event of April 8 to 10, 1979, was selected for intensive study. Precipitation chemistry data were obtained from event samples at six MAP3S sampling sites and from hourly samples at Brookhaven National Laboratory. Concentrations of hydrogen, sulfate, nitrate and ammonium ions were used as receptor data. Some emissions data for SO_x and NO_x were obtained from the MAP3S emissions inventory. Surface and upper air meteorological data were analyzed. Backward trajectories ending at each of the sampling sites during the precipitation period were computed with the Heffter Interactive-Terminal Transport Model using selected transport layers. Results show that concentrations of pollutant species in event precipitation samples were much higher at stations at end points of trajectories passing through the Ohio River valley than at stations with other trajectories. Likewise, concentrations at Brookhaven were much higher during the end period of a trajectory through the same region than with more northerly and more southerly tracks. The model produced back trajectories consistent with synoptic flows. Concentrations of air pollutants in precipitation were roughly proportional to the number of major pollutant sources along the trajectory. These results suggest that a larger number of studies might identify more restricted source areas or even establish a quantitative relationship between source emissions along a trajectory and concentrations in precipitation at receptor sites.     

Acid and alkaline deposition in precipitation on the Western coast of Sardinia,Central Mediterranean (40° N, 8° E)

The ionic composition of 53 precipitation samples collected at a coastal site in western Sardinia (Torregrande) was measured in order to determine concentrations and fluxes of the major ions. Precipitation events were sampled over a two year period, Oct'92/Oct'93 and Oct'93/Oct'94. Despite the proximity to the African continent and the detection of Saharan inputs reflected in high pH values and high_nssCa fluxes, there is evidence for acidic rain with over 54% of the events having pH values <5.6. This would suggest long-range transport of anthropogenic inputs, as there is no obvious local source. Within the study period, a marked decrease in median pH is recorded at Torregrande in '93/'94, decreasing from 5.94 to 5.18. This is coupled with an increase in total annual flux of NO₃ from 27 to 63 μg/cm², making the average flux of NO₃ in the two years comparable with that at Capo Carbonara (48 μg/cm²). Particulate fluxes at Torregrande show a marked inter- as well as intra-annual variability, from 70 to 200 μg/cm². Variations of pH seems to be partially due to the total particulate as well as_nssCa fluxes. A statistic of Saharan enriched rain episodes of the two sites showed a peak transport season in April–May and October which is two times greater at Capo Carbonara. Rainfall on the west coast, therefore, appears to be less affected by Saharan dust than rainfall on the southern coast and therefore shows greater signs of acidification due to anthropogenic inputs.     

Evaluation of Precipitation Composition at an Urban and a Rural Area for the Central Korean Peninsula

Precipitation samples were collected using wet-only samplers on a daily basis at Chunchon (rural area) and Seoul (urban area) from January to December in 1998. The pH, electrical conductivity, and the concentrations of major ions were analyzed. The volume-weighted annual average values of pH for both sites were identical. However, for volume weighted average pH of precipitations below 20 mm in Chunchon was significantly (p<0.05) lower than that in Seoul. The value of [NO₃ ^?]/[nss-SO₄ ^2?], calculated from average composition of rainfalls below 20mm, were 0.42 and 0.61 in Seoul and Chunchon, respectively. This supports that acidification of precipitation by nitrogen oxides, a part of which might be transported from the Seoul metropolitan area, caused the difference in pH between Chunchon and Seoul.     

The effect of a local source on the composition of precipitation in south-central Maine

Bulk precipitation samples were collected from ten sites in south-central Maine during the period 18 June to 30 September, 1974. Data from the chemical analyses of the precipitation were used to determine regional deposition patterns of the ionic constituents. Acidic pH values ranging from 3.8 to 5.0 are characteristic of the region, but relatively alkaline pH values of 5.5 to 7.0 were observed in the precipitation from one collection site. Systematic increases in sulphate and Na deposition in the samples from this site suggest a local source. The observations of the bulk precipitation analysis lead to a study of the chemical composition of precipitation near a kraft paper mill. Samples were collected during single precipitation events. The results indicate that this source can affect background levels of composition up to a distance of at least 20 km and that considerable care must be taken in the selection of sites for sampling background precipitation.     

The variability of pH in convective storms

The rainwater pH was measured in a total of 22 storms which occurred in 1972 and 1974 in the METROMEX (METROpolitan Meteorological EXperiment) rainwater sampling network. The network consists of 81 collectors in an area of 1800 kM² over and east of St. Louis, Missouri. The data set is composed of dry fallout samples as well as precipitation samples which have been analyzed independently. An analysis of the frequency distribution of these data shows the rainfall samples form a bimodal distribution of pH with relative frequency maxima at pH 7.0 and 4.0 while the dry samples are unimodal with the maximum frequency at pH 7.0. The areal distribution of precipitation weighted mean pH indicates a variability unrelated to total precipitation. However, the derived deposition of H+ is more similar to the areal rainfall pattern than to the pH. The dH is defined which incorporates both the rainfall and pH which is useful for climatological trend studies of acid rainfall. Examples of two individual storm events illustrate an inexplicable area-wide variation from nearly an all acid rain (pH ? 4.5) to an all alkaline rain (pH ? 5.5). These case studies indicate some of the meteorological as well as chemical problems which must be considered when attempting to characterize convective storm rainfall pH.