Precipitation Acidity Research Articles

Ecosystem-scale compensation points of formic and acetic acid in the central Amazon

Abstract. Organic acids, central to terrestrial carbon metabolism and atmospheric photochemistry, are ubiquitous in the troposphere in the gas, particle, and aqueous phases. As the dominant organic acids in the atmosphere, formic acid (FA, HCOOH) and acetic acid (AA, CH3COOH) control precipitation acidity in remote regions and may represent a critical link between the terrestrial carbon and water cycles by acting as key intermediates in plant carbon and energy metabolism and aerosol-cloud-precipitation interactions. However, our understanding of the exchange of these acids between terrestrial ecosystems and the atmosphere is limited by a lack of field observations, the existence of biogenic and anthropogenic primary and secondary sources whose relative importance is unclear, and the fact that vegetation can act as both a source and a sink. Here, we first present data obtained from the tropical rainforest mesocosm at Biosphere 2 which isolates primary vegetation sources. Strong light and temperature dependent emissions enriched in FA relative to AA were simultaneously observed from individual branches (FA/AA = 3.0 ± 0.7) and mesocosm ambient air (FA/AA = 1.4 ± 0.3). We also present long-term observations of vertical concentration gradients of FA and AA within and above a primary rainforest canopy in the central Amazon during the 2010 dry and 2011 wet seasons. We observed a seasonal switch from net ecosystem-scale deposition during the dry season to net emissions during the wet season. This switch was associated with reduced ambient concentrations in the wet season (FA < 1.3 nmol mol−1, AA < 2.0 nmol mol−1) relative to the dry season (FA up to 3.3 nmol mol−1, AA up to 6.0 nmol mol−1), and a simultaneous increase in the FA/AA ambient concentration ratios from 0.3–0.8 in the dry season to 1.0–2.1 in the wet season. These observations are consistent with a switch between a biomass burning dominated source in the dry season (FA/AA < 1.0) to a vegetation dominated source in the wet season (FA/AA > 1.0). Our observations provide the first ecosystem-scale evidence of bidirectional FA and AA exchange between a forest canopy and the atmosphere controlled by ambient concentrations and ecosystem scale compensation points (estimated to be 1.3 ± 0.3 nmol mol−1: FA, and 2.1 ± 0.4 nmol mol−1: AA). These results suggest the need for a fundamental change in how future biosphere-atmosphere exchange models should treat FA and AA with a focus on factors that influence net exchange rates (ambient concentrations and ecosystem compensation points) rather than treating emissions and deposition separately.

Acid neutralization of precipitation in Northern China

There is an increasing concern over the impact of human-related emissions on the acid precipitation in China. However, few measurements have been conducted so far to clarify the acid-neutralization of precipitation on a regional scale. Under a network of 10 sites across Northern China operated during a 3-year period from December 2007 to November 2010, a total of 1118 rain and snow samples were collected. Of this total, 28% was acid precipitation with pH <5.6. Out of these acid samples, 53% were found heavily acidic with pH value below 5.0, indicating significantly high levels of acidification of precipitation. Most of the acidity of precipitation was caused by H2SO4 and HNO3, their relative contribution being 72% and 28%, respectively. However, the contribution of HNO3 to precipitation acidity will be enhanced due to the increasing NOx and stable SO2 emissions in future. Neutralization factors for K+, NH4 +, Ca2+, Na+, and Mg2+ were estimated as 0.06, 0.71, 0.72, 0.15, and 0.13, respectively. The application of multiple regression analysis further quantified higher NH4 + and Ca2+ contribution to the neutralization process, but the dominant neutralizing agent varied from site to site. The neutralization was less pronounced in the rural than urban areas, probably due to different levels of alkaline species, which strongly buffered the acidity. Presence of high concentrations of basic ions was mainly responsible for high pH of precipitation with annual volume-weighted mean (VWM) values larger than 5.6 at several sites. It was estimated that in the absence of buffering ions, for the given concentration of SO4 2− and NO3 −, the annual VWM pH of precipitation would have been recorded around 3.5 across Northern China. This feature suggested that emissions of particles and gaseous NH3 played very important role in controlling the spatial variations of pH of precipitation in the target areas. Implications Acid precipitation has long been recognized as a serious environmental problem in East Asia, especially in China. The present study identifies that acidity of precipitation in Northern China generated by H2SO4 and HNO3 was primarily neutralized by Ca2+ and NH4 +. However, in the future, acidity due to HNO3 may increase as a result of the increasing trends of NO x and stable trends of SO2 emissions in megacities. The reducing primary emissions of particles and gaseous ammonia may offer more clear-sky days in urban areas, but might also lead to enhanced acid precipitation in Northern China in the near future.

As(III) retention kinetics, equilibrium and redox stability on biosynthesized schwertmannite and its fate and control on schwertmannite stability on acidic (pH 3.0) aqueous exposure

High As(III) enrichment in schwertmannite precipitated acid mine impacted areas is a major concern considering its acute toxicity and mobility where the current knowledge of their interaction, redox conditions and schwertmannite metastability is inadequate. In this study we have investigated such aspects through batch isotherm, microscopic and spectroscopic techniques. Schwertmannite produced by biotic process with 14.7 m 2 g −1 surface area demonstrated a rapid As(III) uptake followed by slow retention possibly into the internal absorbing sites through multilayer and heterogeneous sorption processes. Chemical, X-ray diffraction, infrared and microscopic examinations revealed that ionic exchange between schwertmannite SO 4 2 - and As(III) and surface precipitation governed the total As(III) uptake where lower dissolved SO 4 2 - and high sorbent mass enhanced As(III) retention. Redox instability of sorbed As(III) was evidenced from the near-edge spectroscopic analysis at extremely high Fe(III):As(III) ratio (5.5 × 10 5) leading to surface oxidation to As(V), while As(III) was found as the predominant redox species at high As(III):Fe(III) ratios. Only 0.83% of sorbed As(III) was released which was subsequently re-adsorbed into schwertmannite during 4 months stabilization without any evidence of mineralogical transformation.

Measurement of Organic Acids in Precipitation Collected in Suburbs of Niigata City

Measurement of Organic Acids in Precipitation Collected in Suburbs of Niigata City

Variation of low molecular weight organic acids in precipitation and cloudwater at high elevation in South China

To investigate the sources and chemical behaviors of carboxylic acids in Southern China, precipitation and corresponding cloudwater samples were collected in an acid rain-prone area of Mount Heng. The carboxylic acid levels in the samples were measured, and the concentration patterns were evaluated with respect to temporal and seasonal variations. Formic and acetic acids were predominant among the carboxylic acids identified for both precipitation and cloudwater. Most of the organic acids in the precipitation had a clear seasonal pattern, reaching higher levels during the warm season; these higher levels were attributed to the stronger source strength of biogenic emissions during this season. The cloud–fog samples did not display a similar trend. A distinctive diurnal pattern in carboxylic acids was only observed in the precipitation samples during the warm season. In cloud–fog, the ratio of formic to acetic acid differed considerably with time, with these values varying little in the precipitation samples. This result indicates that the organic acids in precipitation originate consistently from primary sources throughout the entire period, while those in cloud are mainly associated with direct emissions in the earlier stage and with secondary sources in the later period.

Characteristics of formate and acetate concentrations in precipitation at Jeju Island, Korea

HCOO − and CH 3COO − concentrations were analyzed in precipitation samples collected at two sites on Jeju Island during 1997–2003: one at Mt. Halla and the other within Jeju City. The volume-weighted mean concentrations of HCOO − and CH 3COO − were 1.28 and 0.89 μmol/L at Mt. Halla, and 2.06 and 1.15 μmol/L in Jeju City, respectively. Those ionic components showed low concentrations in summer compared to other seasons. In order to investigate major factors to affect the concentration variations of the organic acids in precipitation, the concentrations of the organic acids between growing and non-growing seasons of plants, the regression analyses and the ratios of HCOO−/CH3COO − were examined. As a result, it is considered that the concentrations of HCOO − and CH 3COO − in precipitation might be influenced mainly by photochemical conversion of precursors emitted from terrestrial vegetation during active plant growing seasons, but by direct emission from the anthropogenic sources such as vehicles during non-growing seasons. The high concentrations of HCOO − and CH 3COO − were mostly associated with northwesterly winds from the continental area, on the other hand, the low concentrations with the winds coming from the North Pacific. The contributions to precipitation acidity by HCOOH and CH 3COOH tended to increase during the plant growing seasons, remaining at a low 10% throughout most of the events, while increasing to 30–40% during occasional precipitation events.

Seasonal variation and sources of low molecular weight organic acids in precipitation in the rural area of Anshun

Low molecular weight (LMW) organic acids are important and ubiquitous chemical constituents in the atmosphere. A comprehensive study of the chemical composition of precipitation was carried out from June 2007 to June 2008 at a rural site in Anshun, in the west of Guizhou Province, China. During this period, 118 rainwater samples were collected and the main LMW carboxylic acids were determined using ion chromatography. The average pH of rainwater was 4.89 which is a typical acidic value. The most abundant carboxylic acids were formic acid (volume weight mean concentration: 8.77 μmol L−1) and acetic acid (6.90 μmol L−1), followed by oxalic acid (2.05 μmol L−1). The seasonal variation of concentrations and wet deposition fluxes of organic acids indicated that direct vegetation emissions were the main sources of the organic acids. Highest concentrations were observed in winter and were ascribed to the low winter rainfall and the contribution of other air pollution sources northeast of the study area. The ratio of formic and acetic acids in the precipitation ([F/A] T ) was proposed as an indicator of pollution source. This suggested that the pollution resulted from direct emissions from natural or anthropogenic sources. Comparison with acid precipitation in other urban and rural areas in Guizhou showed that there was a decreasing contribution of LMW organic acids to free acidity and all anions in rainwater from urban to remote rural areas. Consequently, it is necessary to control emissions of organic acids to reduce the frequency of acid rain, especially in rural and remote areas.

Chemical composition of precipitation and its sources in Hangzhou, China

To understand the origin and chemical characteristics of precipitation in Hangzhou, rainwater samples were collected from June 2006 to May 2008. All samples were analyzed for pH, electrical conductivity, and major ions (NH⁴⁺, Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄²⁻, NO₃⁻, F⁻, and Cl⁻). Acidification of precipitation in Hangzhou was serious with volume-weighted mean pH value of 4.5, while frequency of acid rain was 95%. The calculated SO₄²⁻/NO₃⁻ ratio in Hangzhou precipitation was 2.87, which indicated that the precipitation of Hangzhou belonged to sulfate-based acid rain. The results of acid neutralization analysis showed that not all the acidity in the precipitation of Hangzhou was neutralized by alkaline constituents. The results of sea salt contribution analysis showed that nearly all SO₄²⁻, Ca²⁺, and Mg²⁺ and 33.7% of K⁺ were of non-sea origins, while all Na⁺ and Cl⁻ and 66.3% of K⁺ originated from sea sources. The principal component analysis which was used to analyze the sources of various ions indicated that chemical compositions of precipitation in Hangzhou mainly came from terrestrial sources, factory emissions, fuel wood burning, and marine sources.

Impact of the East Asian summer monsoon on long-term variations in the acidity of summer precipitation in Central China

Abstract. The acidity of precipitation has been observed at stations of the Acid Rain Monitoring Network run by the China Meteorological Administration (CMA-ARMN) since 1992. Previous studies have shown that different long-term trends exist in different regions but detailed analysis of the causes of these is lacking. In this paper, we analyze summertime precipitation acidity data from the CMA-ARMN during 1992–2006 using EOFs and show that the summertime pH in China had different trends before and after 2000. The most significant decrease of pH is found in Central China. To investigate the causes of this decrease of pH in summer, we explore the relationship between changes in the pH value, the East Asian summer monsoon index, rainfall data, and pollutants emissions. We find that the East Asian summer monsoon can significantly affect the acidity of summer precipitation in Central China. In strong monsoon years, the pH in Central China is about 0.33 lower than that in weak monsoon years. Chemical transport model simulations using fixed emissions indicate that about 65% of the pH value difference (i.e., 0.22) is related to the summer monsoon, and constitutes 18–36% of the observed pH change (0.6∼1.2) in Central China during 1992–2006. Further studies reveal a relationship between the pH in Central China and the rainfall in the middle and lower reaches of the Yangtze River (MLYR), which can explain about 24% of the variance of pH in Central China. Simulations using an annually varying emission inventory show that at least 60% of the variation in precipitation acidity in Central China can be attributed to changes in pollutant emissions. Therefore, the increase in emissions of acidic species is the most important cause for the observed decrease of pH in Central China, and changes in meteorological factors, such as rainfall and other parameters related to the East Asian summer monsoon, play a less important but still significant role.

Anomalous Early Triassic sediment fluxes due to elevated weathering rates and their biological consequences

Analysis of 16 marine Permian-Triassic boundary sections with a near-global distribution demonstrates systematic changes in sediment fluxes and lithologies in the aftermath of the end-Permian crisis. Sections from continent-margin and platform settings exhibit higher bulk accumulation rates (BARs) and more clay-rich compositions in the Griesbachian (earliest Triassic) relative to the Changhsingian (latest Permian). These patterns, which largely transcend regional variations in tectonic setting, sequence stratigraphic factors, and facies, are hypothesized to have resulted from a substantial (average ∼7×) increase in the flux of eroded material from adjacent land areas owing to accelerated rates of chemical and physical weathering as a function of higher surface temperatures, increased acidity of precipitation, and changes in landscape stability tied to destruction of terrestrial ecosystems. This sediment surge may have been a contributory factor to the latest Permian marine biotic crisis as well as to the delayed recovery of Early Triassic marine ecosystems owing to the harmful effects of siltation and eutrophication. Contemporaneous deep-sea sections show no increases in sediment flux across the Permian-Triassic boundary owing to their remoteness from continental siliciclastic sources and location below the paleo–carbonate compensation depth.

Chemical characteristics and sources of organic acids in precipitation at a semi-urban site in Southwest China

In order to investigate the chemical characteristics and sources of organic acids in precipitation in Southwest China, 105 rainwater samples were collected at a semi-urban site in Anshun from June 2007 to June 2008. Organic acids and major anions were analyzed along with pH and electrical conductivity. The pH values varied from 3.57 to 7.09 for all the rainfall events sampled, with an average of 4.67 which was typical acidic value. Formic, acetic and oxalic acids were found to be the predominant carboxylic acids and their volume weighted average (VWA) concentrations were 8.77, 6.93 and 2.84 μmol l−1, respectively. These organic acids were estimated to account for 8.1% to the total free acidity (TFA) in precipitation. The concentrations of the majority organic acids at studied site had a clear seasonal pattern, reaching higher levels during the non-growing season than those in growing season, which was attributed to dilution effect of heavy rainfall during the growing season. The seasonal variation of wet deposition flux of these organic acids confirmed higher source strength of biogenic emissions from vegetation during the growing season. Formic-to-acetic acids ratio (F/A), an indicator of primary versus secondary sources of these organic acids, suggested that primary sources from vehicular emission, biomass burning, soil and vegetation emissions were dominant sources. In addition, the lowest concentrations of organic acids were found under type S, when air masses originated from the marine (South China Sea) during Southern Asian Monsoon period. And the highest concentrations were observed in precipitation events from Northeast China (type NE), prevailing mostly during winter with the lowest rainfall.

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 SO42-, and NH4+ is the most important neutralizing ion in rainwater at the four sites, followed by Ca2+. The amounts of organic acid in precipitation were compared with other sites in the world. The ratios of organic acid to total free acid in rainwater at Mangdang Mountain was 13.8% and the influence of organic acid on acidity of rainwater at mountain site in the south of China is more important. The variation of atmospheric particles, gases and components in rainwater and cloud-fog water during special rain and cloud-fog events was discussed. The importance of washout process varied with atmospheric species. The impacts of rainfall, rain duration time and wind speed on wash-out process were estimated by regression analysis.

Trends of the precipitation acidity over China during 1992–2006

The trends of the precipitation acidity from 1992 to 2006 were studied, based on the long-term acid rain observations at 74 sites in China. The results show that there was no remarkable change or extension of acid rain area (i.e., with annual mean of precipitation pH<5.6) during the 15 years. The largest and continuous acid rain area exists in the south of the Yangtze River, while the acid rain areas north of the Yangtze River remain separate. The severe acid rain area (i.e., with annual mean of precipitation pH<4.5) exists mainly in the south of the Yangtze River. The overall precipitation acidity for the 74 stations showed different trends before 1999 and after 2000. In the period 1992–1999, the precipitation acidity at most of the sites remained steady or showed a decreasing trend. After 2000, however, an increasing trend of the precipitation acidity was observed at many sites in North China, Central China, East China, and South China. As a result, the pattern of acid rain area changed during 1992–2006. The precipitation over North China, Central China, and South China became more acidified in the 15 years, with more pronounced trends in North China and the north of Central China. A slight decrease in the precipitation acidity was found in Southwest China, an area characterized as severest acid rain area for about two decades after the early 1980s. Consequently, the center of severe acid rain area in the south of the Yangtze River moved eastwards. The non-hydrogen conductivity (NHC), which is defined as the difference between the measured precipitation conductivity and the H + conductivity calculated from measured pH, was estimated and treated as a proxy of soluble ions in precipitation. The result shows that the overall trend of the NHC before 1999 was pronounced and positive, while the trend after 2000 was inconspicuous or slightly negative. During 2000–2006, the change rate of pH was positively correlated to that of the NHC at 21 sites, implying that the increasing acidities found at these sites may partly be attributed to the decrease in the concentration of airborne particulate matter in recent years. China, acid rain, precipitation acidity, trend

On the effect of large-scale atmospheric transport on chemistry and amount of atmospheric precipitation in the center of European Russia

The dependence of precipitation amount, acidity, and ionic composition on the atmospheric circulation is studied based on the computation of the back trajectories over the period of 1982–1993. Quantitative estimates of basic parameters of trajectories are derived, and their significant difference in the summer and wintertime is considered. The trajectory frequency for the cases with precipitation in the center of European Russia is computed at the regular grid points depending on the diurnal precipitation amount, acidity, and sulfate/chloride ratio. It is shown that in case of abundant precipitation both in summer and winter the highest frequency of trajectories is observed in the same regions. In the case of low precipitation, seasonal differences are observed. It is revealed that precipitation with pH > 5 is mostly connected with the air inflow from Scandinavia and the north of European Russia, while during the trajectory passage over Central and Southern Europe pH < 5 prevails in precipitation. The chlorine ions prevail most often when trajectories pass over central regions of the Mediterranean and of Middle Asia and (although somewhat less) over Scandinavia and northern Russian seas.

The trans-boundary factor in chemical composition variability of atmospheric precipitation in the southern Far East

Presented are the results from investigating the chemical composition dynamics of atmospheric precipitation in the Far-Eastern region of Russia for the last 25 years. It is shown that the increase in acidity of atmospheric precipitation is due to the trans-boundary transfer of acid-forming pollutants from industrial centers of East Asia, which is borne out by the results derived from analyzing synoptic data.

Effects of precipitation variation on severe acid rain in southern China

Acid rain has been recognized as a serious environmental problem in China since the 1980s, but little is known about the effects of the climatic change in regional precipitation on the temporal and spatial variability of severe acid rain. We present the effects of the regional precipitation trend change on the area and intensity of severe acid rain in southern China, and the spatio-temporal distribution characteristics of SO2 and NO2 concentrations are analyzed on the basis of SO2 and NO2 column concentration data. The results are as follows. (1) The emission levels of SO2 and NO2 have reached or passed the precipitation scavenging capacity in parts of southern China owing to the emission totals of SO2 and NO2 increasing from 1993 to 2004. (2) Notable changes in the proportion of cities subject to severe acid rain occurred mainly in the south of the middle-lower reaches of the Yangtze River during 1993–2004. With an abrupt change in 1999, the severe acid rain regions were mainly located in central and western China during 1993–1999 and moved obviously eastward to the south of the lower-middle reaches of the Yangtze River with the proportion of cities subject to severe acid rain increasing significantly from 2000 to 2004. (3) The spatial distribution and variation in the seasonal precipitation change rate of more than 10 mm/10a are similar to those of severe acid rain in southern China. An abrupt change in 1999 is seen for winter and summer precipitation, the same as for the proportion of cities subject to severe acid rain in southern China. The significant increase in summer storm precipitation from 1991 to 1999 mitigated the annual precipitation acidity in the south of the Yangtze River and reduced the area of severe acid rainfall. On the other hand, the decrease in storm rainfall in summer expanded the area of severe acid rainfall in the south of the Yangtze River in 2000–2006. Therefore, the change in seasonal precipitation is an important factor in the severe acid rain regions moving eastward and expanding in southern China.

Occurrence of perfluoroalkyl acids in precipitation from Shenyang, China

Perfluorosulfonates (PFSAs) and perfluorocarboxylates (PFCAs) in precipitation collected from Shenyang, China were determined. Snow samples were collected in the snow event on March 4, 2007 from 34 sites involving both the urban and suburban areas in Shenyang. The snowmelt was preconcentrated by solid phase extraction and analyzed using LC-MS method. Measurable amounts of perfluoroalkyl acids (PFAS) were found in precipitation samples from Shenyang, demonstrating that wet deposition is one possible pathway for the removing of the selected PFAS chemicals from atmosphere. Major PFAS detected were PFOS (<0.38–51 ng/L), PFOA (0.82–13 ng/L) and PFHpA (0.76–11 ng/L), with their mean concentration of 5.4, 3.3 and 2.9 ng/L, respectively. Other PFSAs and PFCAs were detected at much lower frequency or below the limit of detection in all the samples. The work presented here offers some basis for the investigation on the environmental behavior and the evaluation of human exposure to PFAS.

Analysis of cloud and precipitation chemistry at Whiteface Mountain, NY

Federal and state programs over the past two decades have resulted in the reduction of emissions of precursors of acid rain. Concomitant with these changes, measured concentrations of acidity in precipitation and in watersheds have shown a downward trend or improvement. However, another pathway for these precursors is through cloud and fog events that often tend to occur at high-elevation regions affecting the fauna and flora as well. In this study we report on long-term measurements of cloud water and precipitation chemistry made from 1994 onwards at a high-elevation location, Whiteface Mountain NY, in the northeastern United States. Trends and inter-relationship between the ions were examined along with ambient SO 2 measurements and Adirondack lakes chemistry data.

Relationship between acidity and ionic composition of wet precipitation: A two years study at an urban site, Thessaloniki, Greece

Wet precipitation samples were collected in the city center of Thessaloniki, northern Greece, for two years with different rainfall amount (April 2002–March 2004). All samples were analyzed for major anions and cations (Cl −, NO 3 −, SO 4 2−, NH 4 +, Na +, K +, Ca 2+ and Mg 2+). HCO 3 − concentrations were calculated through pH measurements. Arithmetic mean pH values of 6.06 and 6.57 were found for the two periods. 10.5% of the first year rain events (April 2002–March 2003) and 2.5% of the second (April 2003–March 2004) exhibited pH ≤ 4.5. The quite typical, for Mediterranean areas, trend Ca 2+ > SO 4 2− > NH 4 + > Cl − > NO 3 − was observed in the majority of the samples. The study of the relationship between the ionic concentrations and the precipitation amount gave information about the scavenging mechanism of ions (below or in-cloud). 67% of the rain acidity was found to be due to sulfuric acid and the rest 33% to nitric acid. The calculation of Neutralization Factors (NF) and the application of Multiple Linear Regression Analysis (MLR), showed the higher Ca 2+ contribution to the neutralization process. The impact of maritime sources was extracted from the SSF of Cl − and Mg 2+, while the anthropogenic origin of SO 4 2− was supported by the high NSSF (~ 98%). The local calcareous soil dust and possible long-range transport are the main sources of Ca 2+ in the area. A case study by using trajectory analysis to predict a long-range transport of pollutants from Etnean volcano, Italy, to the study area, is described.

Relating Tree Ring Chemistry of Pinus densiflora to Precipitation Acidity in an Industrial Area of South Korea

To test the possible use of tree ring chemical properties as proxies for precipitation acidity ([H+]), we investigated the relationships between tree ring chemistry (δ13C, δ15N, Ca-to-Al ratio, and N concentration) of Pinus densiflora and precipitation [H+] between 1992 and 2005 in an industrial area in the southwest region of South Korea. Statistical analyses showed that all tree ring chemistry parameters were significantly correlated with precipitation [H+]. Tree ring δ13C was negatively correlated with precipitation acidity (r = −0.67, P < 0.01), reflecting the photosynthetic fixation of 13C-depleted CO2 from fossil fuel combustion that would be the primary source of precipitation acidity. A positive correlation of N concentration (r = 0.89, P < 0.001) and a negative correlation of δ15N (r = −0.63, P < 0.05) in tree rings with precipitation acidity most likely reflected the influence of 15N-depleted N compounds deposited via precipitation. The Ca-to-Al ratio was negatively (r = −0.58, P < 0.05) correlated with precipitation acidity, indicating that soil acidification caused the loss of Ca from the soil and solubilization of Al resulting from acid precipitation. Such relationships suggest that δ13C, δ15N, N concentration, and Ca-to-Al ratio in tree rings can be reliably used to evaluate the impact of acid precipitation on the studied P. densiflora stands.