Volume-weighted Mean pH Research Articles

Comparison of the Chemical Composition of Precipitation on the Western and Eastern Coasts of Korea

Precipitation samples were collected at two coastal sites on the Korean Peninsula, Kangwha on the western coast and Yangyang on the eastern coast, from September 1991 to February 1997. The samples were analyzed for concentrations of major ions, in addition to pH and electrical conductivity. The annual volume-weighted mean pH values were 4.89 and 5.05 at Kangwha and Yangyang, respectively. The pH was generally lower at Kangwha than that at Yangyang, especially during the winter, because of reduced neutralizing inputs and greater acid inputs in winter. Dominant ions were different with NH4 + and SO4 2- most important at Kangwha and Na+ and Cl- at Yangyang. Neglecting sea salt components, nss-SO4 2- and NO3 - were important anions and nss-Ca2+ and NH4 + were important cations at both sites. Concentrations of these ions were 1.2–1.6 times higher at Kangwha than at Yangyang. Annual mean concentrations of these ions varied little during the study, while larger seasonal variations were observed. Annual mean nss-SO4 2-/NO3 - ratios at Kangwha and Yangyang were 2.8 and 2.6. The 5 yr annual mean values of nss-SO4 2-/NO3 - showed no trend at Kangwha but a decreasing tendency at Yangyang. The decreasing trend is similar to the decreasing trend in emissions of SO2/NOx in South Korea. Regional differences in chemical composition between Kangwha and Yangyang appear to be associated with long-range transport of acidic gases and alkaline dust originated from other regions.

Rainwater chemistry at the summit and southern flank of the Itatiaia massif, Southeastern Brazil

Wet deposition and related rainwater chemistry were studied at the Itatiaia massif, on which is settled the Itatiaia National Park (INP). Samples were simultaneously collected on a weekly basis over 12 months, using automated wet and dry samplers, at the INP-Headquarters (INP-Hq; altitude=820 m) and the Itatiaia Plateau (It-Pt; altitude=2460 m). Conductivity, pH, Na+, K+, Mg2+, Ca2+, NH4+, Cl−, NO3− and SO42− were determined in 36 rainwater samples. Volume-weighted mean (VWM) pH was lower at the INP-Hq (4.9) than at the It-Pt (5.3). Very strong correlation between Cl− and Na+ was found for the INP-Hq (r=0.99). At the Itatiaia massif, SO42−, NO3−, and NH4+ comprised together about 60% of the total inorganic ions and appear to exert the major control on rainwater pH.

Precipitation chemistry in the coast of the Metropolitan Region of Rio de Janeiro, Brazil

Precipitation chemistry was studied in the Metropolitan Region of Rio de Janeiro (MRRJ). This study reveals that rainwater in the MRRJ is affected by emissions of air pollutants and provides essential data for future estimates of regional biogeochemical cycles and the impacts of acid deposition on tropical ecosystems. The volume-weighted mean (VWM) pH was 4.77, varying from 3.50 to 6.85. Sea-salt aerosols were the dominant sources of the Na +, Cl − and Mg 2+. Excess SO 4 2-, Ca 2+ and K + comprised 82, 91, and 87% of their total VWM concentrations, respectively. There were very strong correlations ( r>0.75, P<0.01) for NO 3 − and H +, NO 3 − and excess(exc-)SO 4 2−, NH 4 + and exc-K +, and exc-SO 4 2− and exc-Ca 2+, suggesting causal relationships between these ion pairs. The VWM concentrations of all major ions, except H +, were higher in the dry season, with dry to wet VWM concentration ratios varying from 1.1 (NH 4 +) to 4.7 (for total K +).

Monitoring of Acid Rain over Korean Peninsula

In order to investigate the temporal and spacial deposition characteristics of acid rain, five monitoring sites were set up in the central part of Korean Peninsula. Rainwater samples were collected by wet-only sampler from 1992 to 1997. The pH and conductivity values were measured and the major water soluble ionic components were also analyzed. Ion balance between anion and cation sum was calculated to check out the data quality of samples. The acidity of rainwater was influenced by the local sources and meteorological factors such as surface wind, moving path of storm, precipitation process, and so on. Backward trajectories were depicted to investigate the effect due to moving path of weather system. The rainwater shows strong acidity in winter and weak in summer. The pH and ion concentrations were highly dependent on synoptic weather system. In addition, we sampled fog/cloud at Mt. Sobaek (BAPMoN Station) from June to August 1995 and characterized the fog/cloud chemistry according to surface wind system of sampling site. The volume-weighted mean pH of fog/cloud samples is 4.39 at Mt. Sobaek during the sampling period.

Atmospheric deposition and net retention of ions by the canopy in a tropical montane forest, Monteverde, Costa Rica

Meteorological variables, bulk cloud water and precipitation (BCWP), and bulk precipitation (BP) were measured above the canopy, and throughfall (TF; n = 20) was collected beneath an epiphyte-laden canopy of a tropical montane forest (TMF) for 1 y at Monteverde, Costa Rica. Total deposition (cloud + wet + dry) of inorganic ions to the canopy was estimated using a sodium (Na+) mass balance technique. Annual BCWP and BP depths were 2678 mm and 1792 for events where mean windspeeds (u) ≥ 2 m s&amp;supminus1;, and 4077 mm and 3191 mm for all events, respectively. Volume-weighted mean pH and concentrations of nitrate-N (NO3−-N) and ammonium-N (NH4+-N) were 4.88, 0.09 and 0.09 mg l&amp;supminus1; in BCWP, and 5.00, 0.05 and 0.05 mg l&amp;supminus1; in BP, respectively. Cloud water and mist deposition to the canopy was estimated to be 356 mm. Estimated deposition of free acidity (H+), NO3−-N, and NH4+-N to the canopy was 0.49, 3.4 and 3.4 kg ha&amp;supminus1; y&amp;supminus1;, respectively. Mean TF depth was 1054 ± 83 mm (mean ± S.E.) for events where u ≥ 2 m s&amp;supminus1;, and 2068 ± 132 mm for all events. Volume-weighted mean pH and concentrations of NO3−-N and NH4+-N in TF were 5.72, 0.04 mg l&amp;supminus1;, and 0.07 mg l&amp;supminus1;, respectively. Mean fluxes of H+, NO3−-N, and NH4+-N in TF were 0.04 ± 0.01, 0.6 ± 0.2 and 1.3 ± 0.2 kg ha&amp;supminus1; y&amp;supminus1;, and percent net retention of these ions by the canopy was 92 ± 2, 80 ±6, and 61 ± 6%, respectively. Phosphate, potassium, calcium and magnesium were leached from the canopy. Seasonal data suggest that biomass burning increased concentrations of NO3− and NH4+ in cloud water and precipitation at the end of the dry season. Regardless, a large majority of the inorganic N in atmospheric deposition was retained by the canopy at this site.

Chemical composition and deposition of rain in the central Amazon, Brazil

Major solute concentrations in wet deposition were measured for 115 individual events from October 1988 to June 1990 at Lake Calado, Amazonas, Brazil. A continuous record from July 1989 through June 1990 included 210 events that ranged in size from 0.2 to 85 mm (annual total, 2754 mm). The 95 events chemically analyzed during this period (45% of the total) were evenly distributed over all storm sizes. The volume-weighted mean (VWM) of the measured ionic sum was low (36 μeq l −1), and H+ was the most abundant ion (VWM pH = 4.8). Organic acids made substantial contributions to both measured dissolved organic carbon and H+. Small interannual differences are apparent in a comparison with rain data collected from the same study site in 1984. The composition of rain appeared to be derived from a constant source of oceanic and rain-forest aerosols, and was not significantly influenced by local or regional biomass burning.

Effects of prescribed burning and drought on the solute chemistry of mixed-conifer forest streams of the Sierra Nevada, California

Solute concentrations in atmospheric depositionand stream water were measured in two mixed-conifercatchments (Tharp‘s and Log creeks) in the SierraNevada of California from 1984 through 1995, a periodincluding a 6-year drought and a prescribed burn inone catchment. The effects of prescribed burning inthe Tharp‘s Creek catchment significantly increasedthe concentrations of most solutes in stream water. In the first year after prescribed burning, the VWM(volume-weighted mean) concentrations of acid anionsin stream water increased proportionally more thanthose of the base cations, and ANC (acid neutralizingcapacity) more than doubled. Sulfate and NO 3 - increased proportionally more in streamwater than any other ions after the fire, but pre- andpost-burn VWM pH were not significantlydifferent. VWM SO 4 2- and NO 3 - concentrations the first year after burning occurredwere about 16- and 2,000-fold above pre-burnbaselines, respectively, while that of Cl-increased 4-fold. Net retention (precipitationinputs minus streamwater outputs) of H+,NO 3 - , NH 3 + , SO 4 2- and Cl- occurred in both catchments, except afterprescribed burning of the Tharp’s Creek catchment inthe fall of 1990, which caused a net export ofSO 4 2- , Cl- and K+ thefirst year after the burn. Most solutes remained abovepre-disturbance concentrations by the end of the thirdyear after burning, whereas H+ and SiO2remained below. Periodic increases in theconcentrations of Na+, Ca2+ and SO 4 2- , and decreases in ANC and SiO2occurred during a 6-year drought monitored in theadjacent undisturbed catchment of Log Creek.

Precipitation chemistry in Japan 1989?1993

Precipitation chemistry in Japan was discussed on a wet-only sample database obtained in a nationwide survey from April 1989 to March 1993. Wet-only samples were collected at 29 stations over Japan on a biweekly basis. Commonly determined chemical parameters were measured in laboratories. The volume-weighted annual mean pH at each site ranged from 4.50 to 5.83 with a mean of 4.76. Concentration ranges and means (parenthesized) on an equivalent basis for major ions were as follows: nss-SO4 2−; 5.2–58.9 (38.6), NO3 −; 1.8–25.0 (14.1), NH4 +; 0.55–29.8 (18.3), nss-Ca2+; 2.0–34.5(14.2), Na+; 6.4–275.3 (49.1), Cl−; 13.7–322.4 (63.5) β eq L−1. Acid-base relationships for Phase-II records were quantitatively discussed in terms of three measures: pH, fractional acidity, and our proposed pAi.

Effect of acid deposition on forested catchment in the western Tokyo, Japan

Acid deposition and its effect on Andisols were investigated in the forest experimental station, the Rolling Land Laboratory (RLL), located in the Tama Hill region of Central Japan. The annual volume-weighted mean pH value of open bulk precipitation was 4.8 in the period 1990 to 1992. Nitrate deposition at RLL was larger than for sulfate, which was obviously different from results in Japan Environment Agency (JEA) stations or in study areas of Europe and North America. Abundant nitrate deposition was ascribed to the high emissions from a non-point source, mainly cars. Although sulfate concentration in throughfall fluctuated, its concentration in soil solution was kept at a low level. This was attributed to the high sulfate adsorption capacity of the Andisols.

Effect of acidic deposition on forested andisols in the Tama Hill region of Japan

Acid deposition and its effect on Andisols was investigated in the forest experimental station, the Rolling Land Laboratory, the Tama Hill region, central Japan. The annual volume-weighted mean pH value of open bulk precipitation was 4·8. The acidity of stemflow from coniferous trees was attributed to dry deposition of air pollutants. The acidic stemflow affected the chemical composition of the soil solution and the pH of soils around the coniferous trees. The concentration of aluminum in the soil solution was accompanied by nitrate which was provided by nitrification in the low soil pH range. The concentration of aluminum in the soil solution, which ranged from 0·02 to 0·12 mmol c liter −1 is similar to the critical levels for the roots of the trees. Andisols in the surface horizon are acidified due to the atmospheric acid deposition, even though seepage from the catchment is still neutral.

Influence of sea salt aerosols and long range transport on precipitation chemistry at El Verde, Puerto Rico

The chemistry of bulk precipitation was measured from November 1983 to September 1987 at El Verde in the Luquillo Experimental Forest, Puerto Rico. Wet-only precipitation was also analyzed as part of the National Atmospheric Deposition Program from 1984 to 1987. Volume-weighted mean pH was 5.14 in bulk precipitation and 5.12 in wet precipitation. Concentrations of most species were correlated negatively with weekly rainfall. Sea salt aerosols contributed most of the Na+, Cl−, Mg2+ and K+ found in wet and bulk precipitation; sulfate and calcium, however, were derived primarily from non-sea salt sources. Due to the high rainfall (3.4 m annually during the study period) and close proximity of the study site to the ocean, deposition rates of the major cations and anions were high relative to many other tropical sites. Precipitation chemistry at El Verde appears to be affected by several factors. During summer, Saharan dusts contribute a significant portion of the excess Ca2+, K+ and Mg2+. During winter months, cold fronts may transport SO42− and NO3− from North America and the western part of Puerto Rico to the sampling site.

Numerical study of droplet size dependent chemistry in oceanic, wintertime stratus cloud at southern mid-latitudes

Cloud droplet chemistry is modelled for the first 150 m of rise in a wintertime, mid-latitude, marine stratus cloud using observations made at and near the Cape Grim Baseline Station as a source of input parameters. The emphasis in this work was to study the variation in droplet chemistry as a function of both droplet size and nucleus composition, with a particular focus on the way in which oxidation of dissolved sulfur dioxide varied. At 150 m above the condensation level, solute concentration as a function of droplet size was found to increase by as much as 2 to 3 orders of magnitude for only a factor of 2 increase in droplet radius, primarily as a consequence of the 1/r dependence in the droplet growth equation. This type of size dependence exists at all levels in the model cloud, and has a significant influence on oxidation rate of sulfur dioxide in droplets growing on ‘sulfate’ nuclei, oxidation by ozone being favoured in the smallest droplets, but oxidation by hydrogen peroxide being favoured in the larger droplets. Oxidation by ozone is favoured at all sizes in droplets formed on sea-salt nuclei as a result of the initially high alkalinity of these droplets, and in the cloud overall is calculated to be the more important oxidation pathway. Although based on a simplified chemical scheme, these results suggest that both size-dependent and nucleus-dependent chemistry of cloud droplets may need to be considered explicitly in cloud modelling work. Volume-weighted mean pH values in the range 5 to 6 were predicted from sensitivity studies in which input variables were varied over reasonable ranges, in agreement with two sets of bulk cloud-water pH data obtained by aircraft near Cape Grim.

Historical trends in tree-ring growth and chemistry across an air-quality gradient in Wisconsin

Basal-area increment and chemical composition of xylem wood were measured in three old-growth (ca. 75–100 years) white pine (Pinusstrobus L.) and three sugar maple (Acersaccharum) Marsh.) stands across a pH and SO4 gradient in precipitation in Wisconsin. In 1986 the volume-weighted mean pH and SO4 content of precipitation ranged from 4.5 to 5.0 and from 21 to 11 kg • ha−1, respectively, from southeastern to northwestern Wisconsin. With one exception (a white pine site at Point Beach in eastern Wisconsin), basal-area increment increased from the 1890s until the 1950s (sugar maple) or 1970s (white pine), then levelled off. Growth efficiency, estimated as the ratio of basal area to exposed crown area or crown volume for the 1980–1985 period, was similar for sugar maple across the gradient; however, growth efficiency of white pine was lower at Point Beach than at the two northern Wisconsin sites. Lead concentrations in xylem wood of both species have increased with time, except at Crotte Creek in northwestern Wisconsin, and Pb concentrations in xylem wood of both species were significantly greater in southeastern than in northwestern Wisconsin. Sulfur concentrations in xylem wood of white pine have increased since the 1960s at Point Beach and at one site in north central Wisconsin; S concentrations are significantly greater for both species in southeastern than in northern Wisconsin. Concentrations of Ca, Mg, and K in xylem wood of sugar maple have decreased over the past century. Whereas xylem wood concentrations of Mn and Zn generally show no age-related trends, Fe and P concentrations have increased markedly at all sites, particularly during the past decade. Although additional research is needed to determine the potential of dendrochemistry in evaluating the consequences of environmental pollution, the age- and site-related trends in chemical composition of xylem wood of white pine and sugar maple appear to be related to vehicular emissions (Pb), air pollution (S), migration along ray paths during conversion of sapwood into heartwood (P, Fe, Ca, K, Mg), and possibly reallocation of nutrients from the labile soil pool to perennial tree tissues during stand development (Ca, K, Mg).

PH and hydrogen ion deposition patterns in precipitation for the continental United States and Canada

Maps of both volume-weighted mean pH and mean H+ deposition in precipitation were developed for the continental United States and Canada using data from 12 precipitation chemistry monitoring networks. The maps were constructed using 1981–1982 laboratory pH data from approximately 130 monitoring sites. The area of greatest acidity (lowest pH/highest H+ deposition) is located in the northern Ohio Valley and southeastern Ontario, an area corresponding to high SOx and NOx emissions.

PH of bulk precipitation during 3 consecutive annual courses in the Trachypogon savannas of the Orinoco Llanos, Venezuela

Bulk precipitation was daily collected and individual pH measured at the Trachypogon savannas, Venezuela, over a consecutive 3-year period. The volume-weighted mean pH as calculated, were 5.8, 5.6 and 5.8 for 1981, 1982 and 1983, respectively. The annual variation of pH ranged from 4.9 to 6.9: 4.8 to 6.3 and 5.4 to 6.8 units in 1981, 1982 and 1983, respectively. However, in this savanna area, which is relatively remote from heavy sources of industrial pollution, the annual proportion of daily rains with pH < 5.0, occurring mainly at the onset and end of the wet season, were 2.0,3.0 and 0.0% for 1981, 1982 and 1983, respectively. DOI: 10.1111/j.1600-0889.1985.tb00078.x