Concentrations Of Ions In Precipitation Research Articles

Economic and Industrial Development SignificantlyContribute to Acidity and Ionic Compositions of Rainwaterin China

To achieve a holistic understanding of the intricate interactions among human activities, atmospheric chemistry, and acid rain in China, a rigorous analysis of rainwater chemistry was made using a dataset comprising 2656 data points from 24 sites. The main cation and anion in the chemical composition of precipitation were Ca2+ and SO42− in China, with an average concentration of 169.9 μeq/L and 135.4 μeq/L, respectively. Acid rain generally occurs in southern cities such as Shenzhen, Guangzhou, Zhuhai, Xiamen, and Chongqing. There were evident regional disparities in acidity and ion concentrations in rainwater, with an increase in acidity and a decrease in ion concentrations from north to south across China. Utilizing positive matrix factorization, the study found that NH4+, SO42−, and NO3− mainly originated from anthropogenic sources such as fossil fuel combustion, vehicle exhaust emissions, agricultural fertilization, and industrial emissions (as reflected by F3 and F4). Ca2+ mainly stems from crustal factors, including industrial dust and natural crust (as represented by F1 and F4). Na+ and Cl− were traceable from marine sources (as reflected by F5), while Mg2+ originated from crust origin (as presented by F1). K+ was mainly derived from a mixed source of crust, marine, and biomass burning (as indicated by F2 and F3). The correlation analyses showed that SO42− and NO3− showed significant correlations with GDP and population. F− was associated with wastewater, which may be linked to the production of brick and tiles from clay with high fluoride contents. The pH was negatively related to industrial wastewater. Long-term analysis of precipitation chemistry in four cities suggested a clear decrease in the proportion of SO42− but a considerable increase in the proportion of NO3− in anions in metropolitans of Shanghai and Chongqing due to the environmental measures that targeted reducing sulfur dioxide (SO2) emissions and increase of vehicles. This showed that pollution control strategies had an impact on precipitation ion concentrations. These results can conclude that economic and industrial growth, which will increase energy consumption, utilization of coal combustion, and a subsequent rise in pollutant emissions, can contribute to the change in the chemical compositions of rainwater and the exacerbation of acid rain.

Significant spatial variations of the atmospheric environment at remote site of the Tibetan Plateau - a case study on major ions of precipitation around Nam Co station.

Remote region is normally considered a receptor of long-range transported pollutants. Monitoring stations are important platforms for investigating the atmospheric environment of remote regions. However, the potential contribution of very local sources around these stations may produce important influences on its atmospheric environment, which is still barely studied. In this study, major ions of precipitation were investigated simultaneously at a typical remote station (Nam Co station) and other sites nearby on the Tibetan Plateau (TP) - the so-called "The Third Pole" in the world. The results showed that despite low values compared to those of other remote regions, the concentrations of major ions in precipitation of Nam Co station (e.g., Ca2+: 32.71 μeq/L; [Formula: see text]: 1.73 μeq/L) were significantly higher than those at a site around 2.2 Km away (Ca2+: 11.47 μeq/L; [Formula: see text]: 0.64 μeq/L). This provides direct evidence that atmospheric environment at Nam Co station is significantly influenced by mineral dust and pollutants emitted from surface soil and anthropogenic pollutants of the station itself. Therefore, numbers of other related data reported on the station are influenced. For example, the aerosol concentration and some anthropogenic pollutants reported on Nam Co station should be overestimated. Meanwhile, it is suggested that it is cautious in selecting sites for monitoring the atmospheric environment at the remote station to reduce the potential influence from local sources.

Characterization of precipitation in the background of atmospheric pollutants reduction in Guilin: Temporal variation and source apportionment

Rainfall samples were collected from three observation sites in Guilin from 2013 to 2017, and the chemical composition characteristics of precipitation and the contribution made by different ion sources were analyzed when atmospheric pollutants levels were reduced. The results showed that acid gas emissions and atmospheric pollutant concentrations continued to decline during the study period. However, the change in the volume-weighted mean pH at the three sites suggested that acid rain pollution was not alleviated and began to deteriorate after 2015. The continuing downward trend for alkaline neutralizing ions (Ca2+, NH4+) in precipitation indicated that the reduction in alkaline neutralizing substances in the atmosphere was an important factor that led to the deterioration in acid rain across Guilin. The principal component analysis and spearman correlation analysis indicated five sources of ions in precipitation. Quantitative assessment of these five sources indicated that fossil fuel combustion contributed the most ions concentration in precipitation at the three sites, followed by agriculture, terrestrial (crustal) sources, marine sources, and biomass burning. Long-distance airflow might affect the acidity, the electrical conductivity (EC), and ion concentrations in precipitation across Guilin. The airflow trajectory from the west and southeast directions corresponded to higher acidity and ion concentrations. According to the current air pollution control strategy planned by Guilin, reducing atmospheric coarse particles and NH3 at the same time may potentially lead to further deteriorations in acid rain contents. Therefore, Guilin needs to develop more reasonable pollution prevention measures that synergistically control atmospheric pollutants and acid rain pollution.

Pollution and Deposition Characteristics of Precipitation and Its Source Apportionment in Xi'an City

Chemical and deposition characteristics as well as potential sources of precipitation in Xi'an from 2000 to 2017 were analyzed based on the acid deposition monitoring network in East Asia (EANET). The pH of precipitation showed increasing trends, whereas the conductivity of precipitation showed decreasing trends between 2000 and 2017 in Xi'an. The decreasing order of ion concentration in precipitation was as follows:SO42- > Ca2+ > NH4+ > NO3- > Na+ > Cl- > Mg2+ > K+. The percentage of SO42- in the total ion concentration decreased from 38.6% in 2000 to 27.9% in 2017. The ratio of SO42- to NO3- in recent years indicated that the type of pollutant in Xi'an changed from the coal-burning type to the mixed type. The deposition of SO42- in precipitation had a declining trend, which was consistent with the results of the Mann-Kendall test. Nitrogen and sulphur depositions in precipitation were 16.89 kg·(hm2·a)-1 and 33.52 kg·(hm2·a)-1, respectively, and ammonium nitrogen (NH4+-N) was the main deposition component of atmospheric active nitrogen in the precipitation of Xi'an. Vehicle emissions were the major contributors to SO42- (15.43%) and NO3- (72.99%). NH4+ originated mainly from agriculture sources, and the percentage reached up to 75.47%.

Chemical and sulfur isotopic characteristics of precipitation in a representative urban site, South China: implication for anthropogenic influences

Nanchang, the capital of Jiangxi Province, is a major constituent of the South China Acid Rain Zone. In this study, the chemical and sulfur isotopic compositions of precipitation in this region were investigated during 2015–2016 to clarify the origin of major chemicals. The pH was < 5.6 for 72.6% of precipitation events, reflecting the predominance of acid rain. SO42−, Ca2+, NH4+, and NO3− were the four main ions, occupying 77% of the total ions in precipitation. SO42− and NO3− were the dominant acidifying species while Ca2+ and NH4+ were the dominant neutralizing species. Overall, the concentrations of ions in precipitation were lower in the rainy months than in other months. Compared with foreign cities, the concentrations of ions in precipitation, particularly SO42− and NO3−, were significantly higher in Nanchang, indicating the effect of anthropogenic pollution. Factor analyses showed that in precipitation, anthropogenic pollutants controlled SO42−, NO3−, and NH4+ whereas K+, Mg2+, and Ca2+ originated from rock weathering, and Cl− was dominantly of marine origin. Based on the sulfur isotope data, it was further found that precipitation SO42− was associated with the use of northern Chinese coal in Nanchang and homogeneous oxidation was a major mechanism affecting δ34S fluctuations in precipitation SO42− with time. This work provides deep insights into the formation of acid rain and is helpful for guiding air quality protection in South China.

Chemical characteristics of precipitation and the indicative significance for sand dust events in the northern and southern slopes of Wushaoling Mountain, northwestern China

Precipitation chemistry analysis is essential to evaluate the atmospheric environmental quality and identify the sources of atmospheric pollutants. In this study, we collected a total of 480 precipitation samples at 6 sampling sites in the northern and southern slopes of Wushaoling Mountain from May 2013 to July 2014 to analyze the chemical characteristics of precipitation and to identify the main sources of ions in precipitation. Furthermore, we also explored the indicative significance for sand dust events in the northern and southern slopes of Wushaoling Mountain based on the precipitation chemistry analysis. During the sampling period (from May 2013 to July 2014), the pH values, EC (electrical conductivity) values and concentrations of cations (Ca2+, Mg2+, Na+, K+ and NH4+) and anions (SO42–, NO3–, Cl–, NO2– and F–) in precipitation were different in the northern and southern slopes at daily and seasonal time scales, with most of the values being higher in the northern slope than in the southern slope. The chemical type of precipitation in the southern and northern slopes was the same, i.e., SO42–-Ca2+-NO3–-Na+. The concentrations of ions in precipitation were mainly controlled by terrigenous material and anthropogenic activities (with an exception of Cl–). The concentration of Cl– in precipitation was mainly controlled by the sea salt fraction. The concentrations of Na+ and Cl– showed an increasing trend after the occurrence of sand dust events both in the northern and southern slopes. In addition, after the occurrence of sand dust events, the concentrations of K+, Mg2+, SO42–, NO3– and Ca2+ showed an increasing trend in the southern slope and a decreasing trend in the northern slope. It is our hope that the results may be helpful to further understand the atmospheric pollution caused by sand dust events in the Wushaoling Mountain and can also provide a scientific basis for the effective prevention of atmospheric pollution.

Deposition of sulphur and nitrogen in Europe 1900–2050. Model calculations and comparison to historical observations

As a contribution to an EU project which dealt with the effects of climate change, air pollution impacts and ecosystems, two different atmospheric chemical transport models were used to simulate the depositions of acidifying and eutrophying pollutants over Europe for the period 1900–2050. Given the unavoidable uncertainties in the historical inputs to these simulations (emissions, meteorology), we generated a new and unique data-set for the purposes of model evaluation; comprising data from the European Air Chemistry Network (EACN) in operation from 1955 to early 1980s and more recent data from the EMEP monitoring network. The two models showed similar and reasonable skills in reproducing both the EACN and EMEP observational data although the MATCH model consistently simulates higher concentrations and depositions than the EMEP model. To further assess the models’ ability to reproduce the long-term trend in sulphur and nitrogen deposition we compared modelled concentrations of major ions in precipitation with data extracted from a glacier in the European Alps. While, the shape and timing of the nss-sulphate data agrees reasonably, the ice core data indicate persistently high nitrogen concentrations of oxidised and reduced nitrogen after the 1980s which does not correspond to the model simulations or data from Western Europe in the EMEP monitoring network. This study concludes that nss-sulphate deposition to Europe was already clearly elevated in the year 1900, but has now (mid-2010s) decreased to about 70% of what it was at the beginning of the last century. The deposition of oxidised nitrogen to Europe peaked during the 1980s but has since decreased to half of its maximum value; still it is 3–4 times higher than in the year 1900. The annual deposition of reduced nitrogen to Europe is currently more than two times as high as the conditions in the year 1900.

Hydrochemical Characteristics and Sources of Ions in Precipitation at the East Qilian Mountains

Precipitation of the northwest China is different from that in other regions of China. The vapor reaches this region after long distance transportation with little precipitation, and the ratio of precipitation variation is large. Wushaoling at the east Qilian Mountains is an important divided line of climate in China. The east region of it is affected by South Asia and East Asia monsoon, while the west region of it is influenced by Westerly circulation. So ion combinations in precipitation are complex for the trajectories of water vapor transportation, the natural environments and the development levels of social and economy in different regions. Precipitation samples were collected at Heisongyi located at the east Qilian Mountains. Hydrochemical characteristics and sources of ions were analyzed by factor analysis, Enrichment factor analysis and back trajectory analysis. EC values in precipitation ranged from 29.20 to 892.00 μS·cm-1, which were controlled by alkaline element. The precipitation was weak alkaline with pH values ranging from 7.02 to 8.89. EC values in precipitation were higher in autumn and winter than in spring and summer, opposite to pH values. The type of precipitation was SO42--Ca2+ for the cation concentrations following the order of Ca2+ >Mg2+ >Na+ >NH4+ >K+ and the anion concentrations following the order of SO42- >Cl- >NO3-. The concentrations of K+, Mg2+, Ca2+, NH4+, Cl-, NO3- and SO42- were the highest in autumn, but the peak value of Na+ concentration appeared in winter. As a whole, ion concentrations were higher in autumn and winter than in spring and summer. Enrichment factor indicated that Na+and Cl- mainly came from marine source but Na+ partly originated from crust source in winter and Cl- partly originated from anthropogenic source in winter, and that K+, Mg2+ and Ca2+ mainly came from crust source except that Mg2+ partly originated from anthropogenic source in winter, and that NO3- and SO42- mainly came from anthropogenic source. The trajectories of water vapor transportation from directions of northwest, north, north with southeast, northwest with southeast, northwest with southwest, northwest with north and southeast were ion original sources in precipitation, and the major trajectory came from northwest direction. Among these trajectories of water vapor transportation, that from northwest, north and north with southeast appeared in each season, but that from northwest with southeast appeared in spring and summer, that from northwest with southwest and northwest and north with southeast appeared in summer. Though ions originated from marine transport by Westerly and monsoon, from crust provided by desert and Gobi in central Asia, Xingjiang and Mongolian plateau, and from humanity activity related to cities pollution and industrial and agriculture production of oasis at all trajectories, the concentrations of ions in precipitation were effected by the strong and weak variations of different weather systems.

Wet deposition at the base of Mt Everest: Seasonal evolution of the chemistry and isotopic composition

The chemistry of wet deposition was investigated during 2012–2014 at the Pyramid International Laboratory in the Upper Khumbu Valley, Nepal, at 5050 m a.s.l., within the Global Atmosphere Watch (GAW) programme. The main hydro-chemical species and stable isotopes of the water molecule were determined for monsoon rain (July–September) and snow samples (October–June). To evaluate the synoptic-scale variability of air masses reaching the measurement site, 5 day back-trajectories were computed for the sampling period. Ion concentrations in precipitation during the monsoon were low suggesting that they represent global regional background concentrations. The associations between ions suggested that the principal sources of chemical species were marine aerosols, rock and soil dust, and fossil fuel combustion. Most chemical species exhibited a pattern during the monsoon, with maxima at the beginning and at the end of the season, partially correlated with the precipitation amount. Snow samples exhibited significantly higher concentrations of chemical species, compared to the monsoon rainfall observations. Particularly during 2013, elevated concentrations of NO3−, SO42− and NH4+ were measured in the first winter snow event, and in May at the end of the pre-monsoon season. The analysis of large-scale circulation and wind regimes as well as atmospheric composition observations in the region indicates the transport of polluted air masses from the Himalayan foothills and Indian sub-continent up to the Himalaya region. During the summer monsoon onset period, the greater values of pollutants can be attributed to air-mass transport from the planetary boundary layer (PBL) of the Indo-Gangetic plains. Isotopic data confirm that during the monsoon period, precipitation occurred from water vapor that originated from the Indian Ocean and the Bay of Bengal; by contrast during the non-monsoon period, an isotopic signature of more continental origin appeared, indicating that the higher recorded NO3− and SO42− concentrations could be ascribed to a change in air circulation patterns. A comparison of recent monsoon deposition chemistry with data from the 1990's shows similar levels of contaminants in the rainfall. However, non-monsoon deposition can be significant, as it largely contributed to the ion wet deposition fluxes for all analyzed species in 2013.

The hydrochemistry properties of precipitation in karst tourism city (Guilin), Southwest China

A comprehensive study on the chemical compositions of rainwater was carried out from January 2008 to November 2011 in Guilin, China. The 396 samples were analyzed for pH and electrical conductivity, and 44 among of 396 samples were analyzed for major ions. The result shows that pH value ranges from 3.44 to 7.16, and the occurrences of acid rain may increase with natural factors and human activities. The order of the main ion concentration in precipitation is SO4 2− > Ca2+ > NH4 + > NO3 − > Cl− > Na+ > F− > Mg2+ > K+ (weighted average). The correlation of the main cations, neutralization factors (NF), enrichment factor, and ionic ratio shows that acid rain can be mitigated slightly by the neutralization effect of a large amount of alkali ions. The SO4 2−, NO3 −, NH4 +, and a fraction of Ca2+ may originate from emissions of human activities, and the K+, Mg2+, and a majority of Ca2+ may originate from weathering of soil and rock. Mg2+ may transport long distance from large cities in the surrounding area. Among them, hyper-accumulation of NO3 − is produced by lots of vehicle and festival emissions. The hydrochloride may increase rainfall acidity, which refers to the temporary acidity. In addition to the input of pH value and acid ions, the input of alkali ions should be considered in the future evaluation of acid deposition in cites.

A global assessment of precipitation chemistry and deposition of sulfur, nitrogen, sea salt, base cations, organic acids, acidity and pH, and phosphorus

A global assessment of precipitation chemistry and deposition has been carried out under the direction of the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) Scientific Advisory Group for Precipitation Chemistry (SAG-PC). The assessment addressed three questions: (1) what do measurements and model estimates of precipitation chemistry and wet, dry and total deposition of sulfur, nitrogen, sea salt, base cations, organic acids, acidity, and phosphorus show globally and regionally? (2) has the wet deposition of major ions changed since 2000 (and, where information and data are available, since 1990) and (3) what are the major gaps and uncertainties in our knowledge? To that end, regionally-representative measurements for two 3-year-averaging periods, 2000–2002 and 2005–2007, were compiled worldwide. Data from the 2000–2002 averaging period were combined with 2001 ensemble-mean modeling results from 21 global chemical transport models produced in Phase 1 of the Coordinated Model Studies Activities of the Task Force on Hemispheric Transport of Air Pollution (TF HTAP). The measurement data and modeling results were used to generate global and regional maps of major ion concentrations in precipitation and deposition. A major product of the assessment is a database of quality assured ion concentration and wet deposition data gathered from regional and national monitoring networks. The database is available for download from the World Data Centre for Precipitation Chemistry (http://wdcpc.org/). The assessment concludes that global concentrations and deposition of sulfur and nitrogen are reasonably well characterized with levels generally highest near emission sources and more than an order of magnitude lower in areas largely free of anthropogenic influences. In many parts of the world, wet deposition of reduced nitrogen exceeds that of oxidized nitrogen and is increasing. Sulfur and nitrogen concentrations and deposition in North America and Europe have declined significantly in line with emission reduction policies. Major regions of the world, including South America, the more remote areas of North America, much of Asia, Africa, Oceania, polar regions, and all of the oceans, are inadequately sampled for all of the major ions in wet and dry deposition, and particularly so for phosphorus, organic forms of nitrogen, and weak acids including carbonates and organic acids. Measurement-based inferential estimates of dry deposition are limited to sulfur and some nitrogen in only a few regions of the world and methods are highly uncertain. The assessment concludes with recommendations to address major gaps and uncertainties in global ion concentration and deposition measurements.

Trends in cation, nitrogen, sulfate and hydrogen ion concentrations in precipitation in the United States and Europe from 1978 to 2010: a new look at an old problem

Industrial emissions of SO2 and NOx, resulting in the formation and deposition of sulfuric and nitric acids, affect the health of both terrestrial and aquatic ecosystems. Since the mid-late 20th century, legislation to control acid rain precursors in both Europe and the US has led to significant declines in both SO4–S and H+ in precipitation and streams. However, several authors noted that declines in streamwater SO4–S did not result in stoichiometric reductions in stream H+, and suggested that observed reductions in base cation inputs in precipitation could lessen the effect of air pollution control on improving stream pH. We examined long-term precipitation chemistry (1978–2010) from nearly 30 sites in the US and Europe that are variably affected by acid deposition and that have a variety of industrial and land-use histories to (1) quantify trends in SO4–S, H+, NH4–N, Ca, and NO3–N, (2) assess stoichiometry between H+ and SO4–S before and after 1990, and (3) examine regional synchrony of trends. We expected that although the overall efforts of developed countries to reduce air pollution and acid rain by the mid-late 20th century would tend to synchronize precipitation chemistry among regions, geographically varied patterns of fossil fuel use and pollution control measures would produce important asynchronies among European countries and the United States. We also expected that control of particulate versus gaseous emission, along with trends in NH3 emissions, would be the two most significant factors affecting the stoichiometry between SO4–S and H+. Relationships among H+, SO4–S, NH4–N, and cations differed markedly between the US and Europe. Controlling for SO4–S levels, H+ in precipitation was significantly lower in Europe than in the US, because (1) alkaline dust loading from the Sahara/Sahel was greater in Europe than the US, and (2) emission of NH3, which neutralizes acidity upon conversion to NH4 +, is generally significantly higher in Europe than in the US. Trends in SO4–S and H+ in precipitation were close to stoichometric in the US throughout the period of record, but not in Europe, especially eastern Europe. Ca in precipitation declined significantly before, but not after 1990 in most of the US, but Ca declined in eastern Europe even after 1990. SO4–S in precipitation was only weakly related to fossil fuel consumption. The stoichiometry of SO4–S and H+ may be explained in part by emission controls, which varied over time and among regions. Control of particulate emissions reduces alkaline particles that neutralize acid precursors as well as S-containing particulates, reducing SO4–S and Ca more steeply than H+, consistent with trends in the northeastern US and Europe before 1990. In contrast, control of gaseous SO2 emissions results in a stoichiometric relationship between SO4–S and H+, consistent with trends in the US and many western European countries, especially after 1991. However, in many European countries, declining NH3 emissions contributed to the lack of stoichiometry between SO4–S and H+.Recent reductions in NOx emissions have also contributed to declines in H+ in precipitation. Future changes in precipitation acidity are likely to depend on multiple factors including trends in NOx and NH3 emission controls, naturally occurring dust, and fossil fuel use, with significant implications for the health of both terrestrial and aquatic ecosystems.

Characteristics of inorganic ions in precipitation at different altitudes in the Yulong Snow Mountain, China

The present study investigated the chemical composition of summer precipitation at different altitudes in Yulong Snow Mountain, hoping to obtain some basic information about the chemical characteristics of precipitation. A couple of precipitation samples at different altitudes in the Yulong Snow Mountain area in southeastern China were collected from July 26 to July 31, 2005 for chemical analyses. Sea-salt tracer analysis showed that Cl- and Na+ had high proportion from marine sources, while the other ions mainly were from non-marine sources. Statistics showed that the cation concentrations ranged from 0.51 to 5.26 mg L-1 and anion concentrations ranged from 0.99 to 4.90 mg L-1. Further analysis showed that terrestrial ions, especially from the proximal terrestrial sources, largely affected the ion concentrations in precipitation. Ion concentrations of precipitation were correlated significantly with local atmospheric circulation at altitude 2,950-4,800 m, and also correlated closely with human activities at altitude 2,400-2,950 m. Limestone, the majority of local rocks, caused high cation concentrations in precipitation, such as Ca2+ and Mg2+. The majority of vapors in the region came from the Indian Ocean whereas parts came from the eastern Pacific. The inorganic ions in precipitation increased significantly in the Yulong Snow Mountain area during this century. Compared with most of the high altitude Mountains in China, the precipitations in the Yulong Snow Mountain area had higher concentrations of inorganic ions and low acidic ion concentrations. The conclusions can provide a basis for study of regional climate characteristics, environment and ecological characteristics of Yulong Snow Mountain area.

Modeling nitrate aerosol distributions and its direct radiative forcing in East Asia with RAMS-CMAQ

The geographical and seasonal characteristics in nitrate aerosol and its direct radiative forcing over East Asia are analyzed by using the air quality modeling system RAMS-CMAQ coupled with an aerosol optical properties/radiative transfer module. For evaluating the model performance, nitrate ion concentration in precipitation, and mixing ratios of PM10, and some gas precursors of aerosol during the whole year of 2007 are compared against surface observations at 17 stations located in Japan, Korea, and China, and the satellite retrieved NO2 columns. The comparison shows that the simulated values are generally in good agreement with the observed ones. Simulated monthly averaged values are mostly within a factor of 2 of the measurements at the observation stations. The distribution patterns of NO2 from simulation and satellite measurement are also similar with each other. Analysis of the distribution features of monthly and yearly averaged mass concentration and direct radiative forcing (DRF) of nitrate indicates that the nitrate aerosol could reach about 25–30% of the total aerosol mass concentration and DRF in Sichuan Basin, Southeast China, and East China where the high mass burden of all major aerosols concentrated. The highest mass concentration and strongest DRF of nitrate could exceed 40μg/m3 and −5W/m2, respectively. It also indicates that other aerosol species, such as carbonaceous and mineral particles, could obviously influence the nitrate DRF for they are often internally mixed with each other.

Precipitation chemistry in Croatia during the period 1981–2006

The spatial, temporal changes and trends changes in precipitation chemistry in Croatia during the period 1981-2006 were analysed using data from 27 sampling sites. The origins of air masses that arrived over Croatia were evaluated by the sector analysis of two-dimensional back trajectories. The distribution per sector of the volume-weighted concentrations of the main ions (sulfate, nitrate, chloride, ammonium, calcium, magnesium, sodium, and potassium) and the pH were also inspected. The trend in the annual volume-weighted concentrations of the major ions in precipitation and pH was tested using the nonparametric Mann-Kendall test and Sen's slope estimator. The sulfate and nitrate ion concentrations significantly decreased for the majority of sites. The main decline of the sulfate ion concentration occurred after 1990. Changes in the anthropogenic sulfur emission patterns over Europe in the last two decades resulted in different acidity and sulfate ion concentrations related to a particular sector compared to earlier times. In addition, precipitation chemistry in Croatia was also influenced by geographical and climatological diversity. Finally, the war and post-war activities were identified as possible anthropogenic sources of some base cations, i.e., potassium and calcium.

Major ionic composition of precipitation in the Nam Co region, Central Tibetan Plateau

A total of 48 precipitation samples have been collected from individual precipitation events at the Nam Co Monitoring and Research Station for Multisphere Interactions (Nam Co Station, 30°47′N, 90°58′E; 4730 m a.s.l) located in the central Tibetan Plateau from August 2005 to August 2006. All samples were analyzed for major cations (NH 4 +, Na +, K +, Ca 2+ and Mg 2+) and anions (Cl −, NO 3 − and SO 4 2−), conductivity and pH. Precipitation pH values ranged from 6.03 to 7.38 with an average value of 6.59. The high pH is due to large inputs of crustal aerosols in the atmosphere, which contain a large fraction of carbonate. Ca 2+ is the dominant cation in precipitation with an average value of 65.58 μeq L − 1 (4.91–301.41 μeq L − 1 ), accounting for 54% of the total cations in precipitation. HCO 3 − is the predominant anion, accounting for 62% of the total anions. When compared with data from a snow pit in the Zhadang Glacier 50 km away (5800 m a.s.l), major ion concentration in precipitation at the Nam Co Station is much higher due to local aerosol inputs. Correlation and empirical orthogonal function (EOF) analysis indicate that regional crustal aerosols and species from combustion emissions of residents are the major sources for these ions, lake salt aerosols from the Nam Co nearby and regional mineral aerosols from dry lake sediments are secondary sources, and sea salt contribution is the least due to the long distance transport.

Canopy uptake of atmospheric N deposition at a conifer forest: Part II- response of chlorophyll fluorescence and gas exchange parameters

Spruce foliage was sprayed with NH4+ NO3- and control solutions to investigate the effect of canopy nitrogen (N) uptake on chlorophyll fluorescence and gas exchange at a RockyMountain subalpine forest (Niwot Forest) at the Niwot Ridge Long-Term Ecological Research site. N-treated branches received NH4+NO3- in an ion-matrix solution that was representative of mean precipitation ion concentrations. Branches were sprayed with NH4+NO3- to increase the wet N deposition to experimental branches 60% above ambient. Control branches received only the ion-matrix solution (no N), while background branches received only natural precipitation. N content of N-treated new growth and old growth shoots was 2 and 8% greater, respectively, than the background and control shoots N content. N-treatment enhanced photosynthetic efficiency (Fv ‘/Fm’) of old growth spruce shoots (≥1 yr old); N-treated shoots (Fv’/Fm’) was 11.12% greater than control and background shoots Fv’/Fm’ (p ≥ 0.05). Greater maximum carboxylation rates accompanied this increased photosynthetic efficiency with the N-treated old growth shoots Vcmax 14.15% greater than background and control shoots Vcmax (p ≥ 0.05). New growth gas exchange and fluorescence results were similar (although p > 0.05). Both inorganic N assimilation and the incorporation of applied N into the photosynthetic apparatus likely account for the above results of this conifer study.

Changing Chemical Composition of Precipitation in Wilmington, North Carolina, U.S.A.: Implications for the Continental U.S.A.

The H+(aq) concentration in Wilmington, NC, precipitation has decreased by approximately 50% during the preceding two decades, similar to trends seen nationwide. The decrease in acidity is important because solution pH plays a key role in atmospheric reactions, and because the change is so large. This study presents the first long-range study of dissolved organic carbon (DOC) levels in precipitation which demonstrates that DOC concentrations have decreased by approximately half in Wilmington, NC, precipitation. The concentrations of H+(aq) and DOC are highly correlated primarily because small organic acids contribute to both DOC and H+(aq) in precipitation. Ammonium ion concentrations in precipitation have increased due to increased agricultural activities, and this also affects precipitation pH. The reduction of SO2 emissions in 1995 imposed by the Clean Air Act Amendment, better control of emissions of volatile organic compounds, and the increase in ammonia emissions all contribute to the decreasing H+(aq) in precipitation nationwide. These compositional changes in precipitation have many environmental implications, such as decreased acid deposition to lakes, changing speciation for trace metals in precipitation, increased ammonium deposition to coastal waters, and decreased DOC transport to the open ocean.

Changes in precipitation chemistry in Lithuania for 1981–2004

This paper considers the spatial and temporal variability in concentrations of the potentially acidifying ions in precipitation in Lithuania during the 1981-2004 period. Chemical analysis of precipitation included measurements of pH, conductivity, sulfate (SO4(2-)), nitrate (NO3-), chloride (Cl-), ammonium (NH4+), sodium (Na+), potassium (K+), and calcium (Ca2+). Temporal trends in the potentially acidifying ion concentrations in precipitation and wet deposition were evaluated using the non-parametric Mann-Kendall test and Sen's slope estimator. A statistically significant decline was observed in non-sea salt sulfate (nssSO4(2-)) and hydrogen (H+) ions concentrations (82% and 79%, respectively) and wet depositions (88% and 74%, respectively). Temporal trends both in concentration and wet deposition of nitrate and ammonium were not as pronounced as trends in sulfate concentration. Analysis of air mass backward trajectories was applied to reveal the influence of air mass originating in different regions on wet deposition of acidifying species in Lithuania. Sector analysis clearly showed that wet deposition of sulfur and nitrogen in Lithuania is to a large extent anthropogenic and the main source regions of acidifying species contributing to wet deposition in Lithuania are in South and Central Europe.

Effects of season and low-level air pollution on physiology and element content of lichens from the U.S. Pacific Northwest

Lichens were collected from three low-elevation sites in the western Cascade Range: HJ Andrews, OR (clean) and Bull Run, OR, and Pack Forest, WA (moderately enhanced nitrogen and sulfur deposition). The latter sites were within 50 km of Portland and Seattle/Centralia urban-industrial areas, respectively. Tissue concentrations of sulfur, nitrogen, and other macronutrients; rates of net carbon uptake; concentrations of photosynthetic pigments; and thallus density were correlated with season and seasonal changes in Platismatia glauca. Ion concentrations in precipitation and total wet deposition were measured from natural settings. Concentrations of depositional ions in precipitation, including NO 3 − and NH 4 +, were generally highest at Bull Run and Pack Forest; SO 4 2− concentrations and acidity were highest at Pack Forest. Total wet deposition was higher in the winter rainy season than the dry summer season at all three sites. Lichens adapted physiologically and morphologically to the higher light intensity and the warm, dry climate of summer through decreased optimal water content for CO 2 uptake, increased concentrations of carotenoids and increased thallus density. Compared to the clean site, the sites with enhanced deposition were associated in P. glauca with year-round higher tissue concentrations of N, S, K, and Na; higher concentrations of total chlorophyll and carotenoids; higher OD 435/415 ratios; higher CO 2 uptake and lower thallus density in summer; and a general absence of other sensitive lichens. These results indicate that moderate levels of fertilizing air pollutants can stimulate carbon uptake and provide protection against chlorophyll degradation in air pollution-tolerant lichens of the Pacific Northwest, especially during the dry summer season.