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Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the last years the interest about acid depositions has been shifted to heterogeneous phase reactions and, particularly, to occult precipitations (fog, mist, ecc.). It is very improbable that some kind of human health hazards could derive from acid rain exposure. Instead, the human exposure to acid fog could represent a possible respiratory vehicle for the assumption of acid pollutants as well as of many other pollutants. This last assertion can be supported by the following considerations: 1) Fog may represent an important chemical reactor that can modify the nature of pollutant material in the atmosphere (acidification and other events). 2) Fog is formed near the ground where pollution sources are located so that pollution is the heaviest. The fog water droplets coalesce around preexisting aerosol which is most highly concentrated near the ground (cities and industrial areas). Since fog water droplets contain muc less water than rain drops, they do not dilute the acidity as much as rain. 3) Finally, fog is partially inhalable. In certain areas of the world, wet deposition by fog can be important to the human health, even if the acqueous concentrations of fog droplets, the acidity per volume of air and the acid deposition rate are all important factors to consider. Particularly the pH of fog does not tell the whole story, but it represents a sufficient information about the severity of the atmospheric situation that can be correlated to seriousness of human risk.
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PMID:[Acid fog: hygiene and health observations correlated with an aspect of atmospheric pollution]. 248 49

Throughfall chemistry was studied in a mature Sitka spruce plantation in order to investigate canopy interactions, such as nitrogen absorption, cation leaching, and neutralization of rainfall passing through the canopy. The plantation had been exposed to six different simulated mist treatments including N (NH(4)NO(3)) and S (H(2)SO(4) at pH 2.5) in four replicated blocks since 1996. Throughfall and rainfall were collected from May to September 2000. The results showed that 30-35% of the applied N was retained by the canopy. There were linear relationships between the loss of H(+) and increased K(+), Mg(2+) and Ca(2+) deposition through the canopy. However these increases in K(+), Mg(2+) and Ca(2+) deposition accounted for only about 50% of total neutralization of the acidity. The relationship between the anion deficits in throughfall and the loss of H(+) implied that weak organic acid anions were involved in the neutralization of the acidity in throughfall.
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PMID:Throughfall chemistry and canopy interactions in a Sitka spruce plantation sprayed with six different simulated polluted mist treatments. 1455 95

Mature grafts of five Sitka spruce (Picea sitchensis (Bong.) Carr.) clones were exposed to simulated acid mist comprising an equimolar mixture of H(2)SO(4) and NH(4)NO(3) (1.6 and 0.01 mol m(-3)) at pH 2.5 and 5.0. Mist was applied to potted plants growing in open-top chambers on consecutive days, four times a week, at a precipitation equivalent of 1 mm per day. The total exposure to polluted mist was equivalent to three times that measured at an upland forest in SE Scotland. The aim of the experiment was to characterize the response of juvenile foliage produced by physiologically mature grafts (on seedling root stock) and compare it with the behaviour of juvenile foliage on seedlings. Development of visible foliar damage was followed through the growing season. Measurements of needle length, diameter, weight, surface area, surface was weight and wettability were made on current year needles to determine whether particular foliar characteristics increased susceptibility to injury. Significant amounts (> 10%) of visible needle damage was observed on only one of the five clones. Damage was most severe on the clone with the most horizontal branch and needle habit, but over the five clones there was no relationship between angle of branch display and damage. Likewise no combination of needle characteristics (length, width, area, amount of wax) was indicative of potential susceptibility. A comparison with previous acid misting experiments using seedlings suggests that juvenile foliage on physiologically mature trees is equally susceptible to visible injury as juvenile seedling foliage. Data of budburst differed among clones, and in this experiment exerted the over-riding influence on development of injury symptoms. Foliage exposed to a combination of strong acidity and high sulphate concentrations over the few weeks immediately following budburst suffered most visible injury. The absence of significant amounts of visible damage in UK forests probably reflects the general low susceptibility to visible injury of Sitka spruce exposed to acid mist.
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PMID:Effects of acid mist on needles from mature Sitka spruce grafts. Part II. Influence of developmental stage, age and needle morphology on visible damage. 1509 70

The concept of critical levels was developed in order to define short-term and long-term average concentrations of gaseous pollutants above which plants may be damaged. Although the usual way in which pollutants in precipitation (wet deposition) influence vegetation is by affecting soil processes, plant foliage exposed to fog and cloud, which often contain much greater concentrations of pollutant ions than rain, may be damaged directly. The idea of a critical level has been extended to define concentrations of pollutants in wet deposition above which direct damage to plants is likely. Concentrations of acidity and sulphate measured in mountain and coastal cloud are summarised. Vegetation at risk of injury is identified as montane forest growing close to the cloud base, where ion concentrations are highest. The direct effects of acidic precipitation on trees are reviewed, based on experimental exposure of plants to simulated acidic rain, fog or mist. Although most experiments have reported results in terms of pH (H(+) concentration), the accompanying anion is important, with sulphate being more damaging than nitrate. Both conifers and broadleaved tree seedlings showing subtle changes in the structural characteristics of leaf surfaces after exposure to mist or rain at or about pH 3.5, or sulphate concentration of 150 micromol litre(-1). Visible lesions on leaf surfaces occur at around pH 3 (500 micromol litre(-1) sulphate), broadleaved species tending to be more sensitive than conifers. Effects on photosynthesis and water relations, and interactions with other stresses (e.g. frost), have usually been observed only for treatments which have also caused visible injury to the leaf surface. Few experiments on the direct effects of polluted cloud have been conducted under field conditions with mature trees, which unlike seedlings in controlled conditions, may suffer a growth reduction in the absence of visible injury. Although leaching of cations (Ca(2+), Mg(2+), K(+)) is stimulated by acidic precipitation, amounts leached are small compared with root uptake, unless soils have been impoverished. This aspect of the potential effects of acidic precipitation is best considered in terms of the long-term critical-load of pollutants to the soil. Given the practical difficulties in monitoring cloud water composition, a method for defining critical levels is proposed, which uses climatological average data to identify the duration and frequency of hill cloud, and combines this information with measured or modelled concentrations of particulate sulphate in the atmosphere, to derive cloud water concentrations as a function of cloud liquid water content. For forests within 100 m of the cloud base the critical levels of particulate sulphate, corresponding to solution concentrations in the range 150-500 micromol litre(-1), are in the range 1-3.3 microg S m(-3). These concentrations are observed over much of central Europe, suggesting that many montane forests are at risk of direct effects of fossil-fuel-derived pollutants in cloud.
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PMID:Direct damage to vegetation caused by acid rain and polluted cloud: definition of critical levels for forest trees. 1509 86

Ammonium absorption rates by intact nodulated and unnodulated soybean plants (Glycine max [L.] Merr., Amsoy 71) were determined from the liquid phase of a mist assay chamber. From the gas phase, simultaneous measurements of acetylene reduction rates were made from nodulated plants. Ammonium absorption capacity was consistently greater in unnodulated plants.At the beginning of flowering, plant roots were sprayed with an uptake solution ranging from 0.05 to 1.0 millimolar NH(4)Cl, and root nodules concurrently were exposed to 0.12 atmosphere acetylene. The NH(4) (+) absorption system of both nodulated and unnodulated plants were nearly saturated at 0.3 to 0.5 millimolar NH(4) (+).Increasing the pH from 4.0 to 6.8 stimulated NH(4) (+) absorption rate in both flowering and preflowering nodulated and unnodulated plants. Acetylene reduction rate was not altered by short-term exposure to increased acidity. Short-term exposure to lower absorption solution temperatures from 32 degrees C to 18 degrees C did not significantly affect NH(4) (+) absorption rate in flowering nodulated or unnodulated plants. However, acetylene reduction rate increased as the absorption solution temperature increased. The Q(10) value was 1.5 for the reaction rate. Increasing external NO(3) (-) concentration from 0.1 to 5.0 millimolar NO(3) (-) did not significantly influence the kinetics of NH(4) (+) absorption or acetylene reduction rate.
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PMID:Simultaneous Measurement of NH(4) Absorption and N(2) Fixation by Glycine max L. : RESPONSE TO TEMPERATURE, pH, AND EXTERNAL NITROGEN CONCENTRATION. 1666 29

To characterize the primary PM2.5 emission from coal-fired power plants in China, and to quantitatively evaluate the effects of flue gas denitrification and desulfurization on PM2.5 emission, a pulverized coal fired (PC) power plant and a circulating fluidized bed (CFB) plant were selected for measuring the mass concentration and water-soluble ion composition of PM2.5 in flue gas. The results showed that the mass concentration of PM2.5 generated from the CFB was much higher than that from the PC, while the mass concentrations of PM2.5 emitted from these two plants were very similar, because the CFB was equipped with an electrostatic-bag precipitator (EBP) with higher PM2.5 removal efficiency than the common electrostatic precipitator (ESP). Although the total concentration of water-soluble ions in PM2.5 generated from the PC was lower than that from the CFB, the total concentration of water-soluble ions in PM2.5 emitted from the PC was much higher than that from the CFB, which implied that PM2.5 emission from the PC was greatly affected by the flue gas treatment installations. For example, the flue gas denitrification system produced H2SO4 mist, part of which reacted with the excessive NH3 in the flue gas to form NH4HSO4 in PM2.5 and to increase the acidity of PM2.5. In addition, the escaping of desulfurization solution during the flue gas desulfurization process could also introduce NH4+ and SO2- into PM2.5. Therefore, although the main water-soluble ions in PM2.5 generated from both of the plants were Ca2+ and SO(4)2-, the major cation was changed to NH4+ when emitted from PC.
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PMID:[Characteristics of Water-Soluble Inorganic Ions in PM2.5 Emitted from Coal-Fired Power Plants]. 2648 99

This study assessed the effect of the recently-introduced Life+ (ILIP, Valsamoggia, Italy) active packaging system on the postharvest quality of sweet cherries and strawberries. This system uses Equilibrium Modified Atmosphere Packaging (EMAP) to achieve specific intra-package conditions with three synergistic elements: an unvented and anti-mist heat sealable container, an active (naturally-antimicrobial) pad, and a heat-sealed, laser micro-perforated film of a specified gas permeability. Post-packaging quality parameters were monitored for 10 (strawberries) and 15 days (cherries): headspace gas concentration, weight loss, titratable acidity, total soluble solids, pH, disease incidence, and sensory quality. Results showed that use of the Life+ system delayed postharvest senescence by maintaining fruit color, acidity, and vitamin C content, and decreasing fruit weight loss and decay. The use of EMAP in sweet cherry resulted in enhanced sensory qualities compared to traditional perforated containers. The results suggest that the Life+ system leads to better sensory properties and improved shelf-life for strawberries and sweet cherries.
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PMID:The Postharvest Quality of Fresh Sweet Cherries and Strawberries with an Active Packaging System. 3140 43