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

Gas-liquid scattering experiments are used to measure the fraction of N2O5 molecules that are converted to HNO3 after colliding with 72 wt % H2SO4 containing 1-hexanol or 1-butanol at 216 K. These alcohols segregate to the surface of the acid, with saturation coverages estimated to be 60% of a close-packed monolayer for 1-hexanol and 44% of a close-packed monolayer for 1-butanol. We find that the alkyl films reduce the conversion of N2O5 to HNO3 from 0.15 on bare acid to 0.06 on the hexyl-coated acid and to 0.10 on the butyl-coated acid. The entry of HCl and HBr, however, is enhanced by the hexanol and butanol films. The hydrolysis of N2O5 may be inhibited because the alkyl chains restrict the transport of this large molecule and because the alcohol OH groups dilute the surface region, suppressing reaction between N2O5 and near-interfacial H3O+ or H2O. In contrast, the interfacial alcohol OH groups provide additional binding sites for HCl and HBr and help initiate ionization. These and previous scattering experiments indicate that short-chain alcohol surfactants impede or enhance sulfuric acid-mediated reactions in ways that depend on the chain length, liquid phase acidity, and nature of the gas molecule.
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PMID:The inhibition of N2O5 hydrolysis in sulfuric acid by 1-butanol and 1-hexanol surfactant coatings. 1738 2

Silica and hybrid organic-inorganic films, ca. 100-200 nm thick, can be grown on glassy carbon electrodes through reactions initiated by electrogenerated hydroxide or hydronium ions in water under reductive and oxidative conditions, respectively. A variety of different alkoxysilanes (tetramethoxysilane and organoalkoxysilanes) and supporting electrolytes were used to evaluate whether film formation takes place on glassy carbon electrodes. The results of the study indicate that the acid-base properties of the supporting electrolyte are an important factor in determining whether film formation will take place. For cathodic electrodeposition, thin films can be formed using supporting electrolytes that are close to neutral, such as KCl, KNO3, and NaClO4. For anodic electrodeposition, thin films can be formed using supporting electrolytes that are acidic, such as, KH2PO4, HNO3, H2SO4, etc. The acidity/basicity effects of the electrolytes arise in part from the strong dependence of the hydrolysis and condensation rates of the silicon alkoxide precursors on pH.
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PMID:Electrodeposited silicate films: importance of supporting electrolyte. 1930 51

An automatic direct spectrophotometric method for the simultaneous determination of nitrite and nitrate by flow-injection analysis has been developed. Nitrite reacts with 3-nitroaniline in the presence of hydrochloric acid (0.96-1.8 M HCl or pH 0.5-0.7) to form a diazonium cation, which is subsequently coupled with N-(1-naphthyl)-ethylenediamine dihydrochloride to form a stable purple azo dye, the absorbance of which is measured at 535 nm. Nitrate is reduced on-line to nitrite in a copper-coated cadmium column which is then treated with azo dye reagent and the absorbance due to the sum of nitrite and nitrate is measured; nitrate is determined from the difference in absorbance values. A copper column incorporated into the reaction manifold before the copperised cadmium column not only improves the long-term accuracy, but also extends the life time of the copperised cadmium column. Various analytical parameters, such as effect of acidity (pH), flow rate, sample size, dispersion coefficient, time, temperature, reagent concentration and interfering species, were studied. The calibration graphs were rectilinear for 0.1-3.5 mug ml(-1) of NO(3) and 10 ng ml(-1)-2.2mug ml(-1) of NO(2). The method is successfully applied to some food samples (meat, flour and cheese), environmental waters (inland and surface), beer and soil samples. Up to 30 samples can be analysed per hour with a relative precision of approximately 0.1-2%.
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PMID:Simultaneous spectrophotometric determination of nitrite and nitrate by flow-injection analysis. 1896 74

Acid deposition commonly occurs due to conversion of primary acidic pollutants (SO2 & NO2) into secondary pollutants (H2SO4 & HNO3 and their salts). The main natural sources of acid deposition in Alexandria include lightening and microbial processes. Anthropogenic sources include traffic, industrial, fuel burning, and incineration activities. Acid deposition has ecological and economic effects in addition to health effects. The objective of this study is to assess acidity of dry and wet depositions in the atmosphere of Alexandria. Dry samples were collected as settled dust using plastic jar. Wet samples were collected as rain water using polyethylene bottle. All samples were analyzed for pH, sulfates, and nitrates. The relatively high pH values observed in depositions of Alexandria city (6.95+/-0.22) and (7.14+/-0.49) for settled dust and rain water respectively indicating the conversion of the formed acids (H2SO4 & HNO3) into their salts. This explanation was confirmed by the relatively high concentrations of sulfates and nitrates. The average values were (14.3+/-4.21 g/km2/month and 20.5+/-9.5mg/L for sulfates), and (22.6+/-10.6 g/km2/month and 0.5+/-0.32 mg/L for nitrates) for settled dust and rainwater samples respectively. It can be concluded that Alexandria is a lucky city regarding acidity of the atmosphere due to its geographic, topographic, and meteorological features. Building up acid deposition monitoring network that covers all Egyptian cities to be a nucleus for African network, using new technologies that reduce emission of acid deposition precursors and alternative sources of energy, implementing and enforcing regulations and standards for major pollutants, and increasing public awareness are recommended.
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PMID:Study of the acidic deposition phenomenon over Alexandria city. 1899 8

Biological removal of ammonia was investigated using compost and sludge as packing materials in laboratory-scale biofilters. The aim of this study is to characterize the composition of ammonia-oxidizing bacteria (AOB) in two biofilters designed to remove ammonia. Experimental tests and measurements included analysis of removal efficiency and metabolic products. The inlet concentration of ammonia applied was 20-100 mg m(-3). Removal efficiencies of BFC and BFS were in the range of 97-99% and 95-99%, respectively. Periodic analysis of the biofilter packing materials showed ammonia was removed from air stream by nitrification and by the improved absorption of NH(3) in the resultant acidity. Nitrate was the dominant product of NH(3) transformation. Changes in the composition of AOB were examined by using nested PCR, denaturing gradient gel electrophoresis (DGGE) and sequencing of DGGE bands. DGGE analysis of biofilter samples revealed that shifts in the community structure of AOB were observed in the experiment; however, the idle phase did not cause the structural shift of AOB. Phylogenetic analysis revealed the population of AOB showed Nitrosospira sp. remains the predominant population in BFC, while Nitrosomonas sp. is the predominant population in BFS.
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PMID:Ammonia biofiltration and community analysis of ammonia-oxidizing bacteria in biofilters. 1935 65

2 mL 50% HNO3 and 1 mL 47% H2O2 were chosen for tobaccos digestion, and the acidity of final digestion solution was confined to about 2%. Standard solutions were diluted with 2% HNO3. The digestion solutions were determined by ICP-MS directly after adding internal standard elements Ge and Rh. In stead of using concentrated acid, this method not only can leave out the process of drying or dilution and extended the life of relevant components of the instrument, but also eliminate the errors of the inconsistency between digestion solutions and standard solutions could be eliminated. The contents of 30 trace elements, the results of eight representatives of which were provided, in tobaccos from seven areas were determined. The detection limits of measured elements were from 0.006 to 1.133 ng x mL(-1). The relative standard deviations were from 0.90% to 5.66%. The recovery rates of two elements (Cu, Y) were from 93% to 102%. The results showed that this method proposed could be applied to multielement simultaneous determination of tobaccos, and there is a deep relationship between the contents of the trace elements and the production place and classification of tobaccos.
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PMID:[Determination of trace elements in tobaccos by microwave digestion/ICP-MS method]. 2082 11

There are strong evidences that Mycobacterium tuberculosis survives in a non-replicating state in the absence of oxygen in closed lesions and granuloma in vivo. In addition, M. tuberculosis is acid-resistant, allowing mycobacteria to survive in acidic, inflamed lesions. The ability of M. tuberculosis to resist to acid was recently shown to contribute to the bacillus virulence although the mechanisms involved have yet to be deciphered. In this study, we report that M. tuberculosis resistance to acid is oxygen-dependent; whereas aerobic mycobacteria were resistant to a mild acid challenge (pH 5.5) as previously reported, we found microaerophilic and hypoxic mycobacteria to be more sensitive to acid. In hypoxic conditions, mild-acidity promoted the dissipation of the protonmotive force, rapid ATP depletion and cell death. Exogenous nitrate, the most effective alternate terminal electron acceptor after molecular oxygen, protected hypoxic mycobacteria from acid stress. Nitrate-mediated resistance to acidity was not observed for a respiratory nitrate reductase NarGH knock-out mutant strain. Furthermore, we found that nitrate respiration was equally important in protecting hypoxic non-replicating mycobacteria from radical nitrogen species toxicity. Overall, these data shed light on a new role for nitrate respiration in protecting M. tuberculosis from acidity and reactive nitrogen species, two environmental stresses likely encountered by the pathogen during the course of infection.
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PMID:Nitrate respiration protects hypoxic Mycobacterium tuberculosis against acid- and reactive nitrogen species stresses. 2104 46

Ammonia (NH(3)) is one important precursor of inorganic fine particles; however, knowledge of the impacts of NH(3) emissions on aerosol formation in China is very limited. In this study, we have developed China's NH(3) emission inventory for 2005 and applied the Response Surface Modeling (RSM) technique upon a widely used regional air quality model, the Community Multi-Scale Air Quality Model (CMAQ). The purpose was to analyze the impacts of NH(3) emissions on fine particles for January, April, July, and October over east China, especially those most developed regions including the North China Plain (NCP), Yangtze River delta (YRD), and the Pearl River delta (PRD). The results indicate that NH(3) emissions contribute to 8-11% of PM(2.5) concentrations in these three regions, comparable with the contributions of SO(2) (9-11%) and NO(x) (5-11%) emissions. However, NH(3), SO(2), and NO(x) emissions present significant nonlinear impacts; the PM(2.5) responses to their emissions increase when more control efforts are taken mainly because of the transition between NH(3)-rich and NH(3)-poor conditions. Nitrate aerosol (NO(3)(-)) concentration is more sensitive to NO(x) emissions in NCP and YRD because of the abundant NH(3) emissions in the two regions, but it is equally or even more sensitive to NH(3) emissions in the PRD. In high NO(3)(-) pollution areas such as NCP and YRD, NH(3) is sufficiently abundant to neutralize extra nitric acid produced by an additional 25% of NO(x) emissions. The 90% increase of NH(3) emissions during 1990-2005 resulted in about 50-60% increases of NO(3)(-) and SO(4)(2-) aerosol concentrations. If no control measures are taken for NH(3) emissions, NO(3)(-) will be further enhanced in the future. Control of NH(3) emissions in winter, spring, and fall will benefit PM(2.5) reduction for most regions. However, to improve regional air quality and avoid exacerbating the acidity of aerosols, a more effective pathway is to adopt a multipollutant strategy to control NH(3) emissions in parallel with current SO(2) and NO(x) controls in China.
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PMID:Impact assessment of ammonia emissions on inorganic aerosols in East China using response surface modeling technique. 2193 16

This study compares two sets of measurements of the composition of bulk precipitation and throughfall at a site in southern England with a 20-year gap between them. During this time, SO(2) emissions from the UK fell by 82%, NO(x) emissions by 35% and NH(3) emissions by 7%. These reductions were partly reflected in bulk precipitation, with deposition reductions of 56% in SO(4)(2-), 38% in NO(3)(-), 32% in NH(4)(+), and 73% in H(+). In throughfall under Scots pine, the effects were more dramatic, with an 89% reduction in SO(4)(2-) deposition and a 98% reduction in H(+) deposition. The mean pH under these trees increased from 2.85 to 4.30. Nitrate and ammonium deposition in throughfall increased slightly, however. In the earlier period, the Scots pines were unable to neutralise the high flux of acidity associated with sulphur deposition, even though this was not a highly polluted part of the UK, and deciduous trees (oak and birch) were only able to neutralise it in summer when the leaves were present. In the later period, the sulphur flux had reduced to the point where the acidity could be neutralised by all species - the neutralisation mechanism is thus likely to be largely leaching of base cations and buffering substances from the foliage. The high fluxes are partly due to the fact that these are 60-80 year old trees growing in an open forest structure. The increase in NO(3)(-) and NH(4)(+) in throughfall in spite of decreased deposition seems likely due to a decrease in foliar uptake, perhaps due to the increasing nitrogen saturation of the catchment soils. These changes may increase the rate of soil microbial activity as nitrogen increases and acidity declines, with consequent effects on water quality of the catchment drainage stream.
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PMID:The effects of a changing pollution climate on throughfall deposition and cycling in a forested area in southern England. 2228 83

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 NO(x) 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.
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PMID:Acid neutralization of precipitation in Northern China. 2244 36


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