Simulation of the dissolution of weathered versus unweathered limestone in carbonic acid solutions of varying strength

A simulation was undertaken within a climatic chamber to investigate limestone dissolution under varied carbonic acid (H₂CO₃) strengths as a possible analogue for future increases in atmospheric CO₂ arising from global warming. Twenty‐eight samples cut from a block of Bath (Box Hill) limestone from Somerville College, Oxford, which had been removed during restoration after 150 years in an urban environment, were weighed and placed in closed bottles of thin plastic containing varying concentrations of H₂CO₃. Half of the stone samples were derived from exposed surfaces of the stone block (weathered) while the others were obtained from the centre of the block on unexposed surfaces (unweathered). The purpose of this was to compare dissolution of previously weathered versus unweathered surfaces in strong (pH 4·73) versus weak (pH 6·43) solutions of H₂CO₃. A temperature of c. 19 °C was maintained within the chamber representing a plausible future temperature in Oxford for the year 2200 given current warming scenarios. The simulation lasted 25 days with a few stone samples being removed midway. Stone samples show reduced weight in all cases but one. There was greater dissolution of stone samples in a strong H₂CO₃ solution as conveyed by higher concentrations of total hardness and Ca²⁺ in the water samples as well as enhanced microscopic dissolution features identified using SEM. The simulation confirms that enhanced atmospheric CO₂ under global warming, given adequate moisture, will accelerate dissolution rates particularly of newly replaced limestone building stones. However, previously weathered surfaces, such as those on historical stone exposed for a century or more, appear to be less susceptible to the effects of such increased rainfall acidity. Conservation techniques which remove weathered surfaces, such as stone cleaning, may accelerate future decay of historical limestone structures by increasing their susceptibility to dissolution. Copyright © 2006 John Wiley & Sons, Ltd.     

The Henry's Law Constants of the Haloacetic Acids

Henry's law constants K_H (mol kg^-1 atm^-1) have been measured between 278.15 K and 308.15 K for the following organic acids: CH₂FCOOH (ln(K_H[298.15 K]) = 11.3 ± 0.2), CH₂ClCOOH (11.59 ± 0.14), CH₂BrCOOH (11.94 ± 0.21), CHF₂COOH (10.32 ± 0.10), CHCl₂COOH (11.69 ± 0.11), CHBr₂COOH (12.33 ± 0.29), CBr₃COOH (12.61 ± 0.21), and CClF₂COOH (10.11 ± 0.12). The variation of K_H with temperature was determined for all acids except CH₂FCOOH and CBr₃COOH, with _r H° for the dissolution reaction ranging from –85.2 ± 2.6 to –57.1 ± 2.5 kJ mol^-1, meaning that their solubility is generally more sensitive to temperature than is the case for the simple carboxylic acids. The Henry's law constants show consistent trends with halogen substitution and, together with their high solubility compared to the parent (acetic) acid (ln(K_H[298.15 K]) = 8.61), present a severe test of current predictive models based upon molecular structure. The solubility of haloacetic acids and strong dissociation at normal pH mean that they will partition almost entirely into cloud and fog in the atmosphere (0.05–1.0 g H₂O m^-3), but can reside in both phases for the liquid water contents typical of aerosols (10^-5-10^-4 g H₂O m^-3).     

Formic and acetic acids in atmospheric condensate in Wilmington,North Carolina

Formic and acetic acids occurred in atmospheric condensate with concentrations similar to rainwater collected in Wilmington, North Carolina, during the sampling period from June to October of 1990. Atmospheric concentrations of these acids (calculated from the condensate concentrations) were higher in continental versus maritime air masses. Concentrations of formic and acetic acids were correlated with each other in both condensate and air. Traffic was a source of acetic acid and of bisulfite to atmospheric condensate in this study.     

郑州市酸雨变化特征及影响因素分析

通过对1992-2006年郑州酸雨观测站数据以及2001年4月-2006年12月郑州空气质量逐日数据进行统计分析,发现郑州市降水酸性呈现增强趋势,主要发生在秋、冬两个季节,频率在40%以上,冬季酸雨发生天数要多于秋季,降水酸度在秋末至12月较强。影响酸雨的主要因子为PM10、SO2与NO2浓度和降水量,PM10主要通过与酸性气体的化学反应来影响降水电导率K值,降水对大气中PM10的净化有较强的作用。连续性降水过程中降水pH值有减小趋势的占57.14%,主要在于降水对地面的湿润作用有效地阻止了来自地面的可溶性微粒进入大气中,不能足够吸收大气中酸性物质,致使酸性物质直接进入降水中造成降水持续酸化。     

On the scavenging of SO2 by cloud and rain drops: IV. A wind tunnel and theoretical study of the absorption of SO2 in the ppb(v) range by water drops in the presence of H2O2

An experimental study involving the Mainz vertical wind tunnel is described where the rate of SO₂ removed from the air by freely suspended water drops was measured for SO₂ concentrations in the gas phase ranging between 50 and 500 ppb, and for various H₂O₂ concentrations in the liquid phase. In a first set of experiments, the pH inside the SO₂ absorbing drops was monitored by means of colour pH indicators added to the drops. In a second set of experiments, the amount of SO₂ scavenged by the drops was determined as sulfate by an ionchromatograph after the drops had been removed from the vertical air stream of the wind tunnel after various times of exposure to SO₂. The results of our experimental study were compared with the theoretical gas diffusion model of Walcek and Pruppacher which was reformulated for the case of SO₂ concentrations in the ppbv(v) range for which the main resistance to diffusion lies in the gas phase surrounding the drop. Excellent agreement between experiment and theory was obtained. Encouraged by this agreement, the theory was used to investigate the rate of sulfate production inside a drop as a function of pH. The sulfate production rate, which includes transport and oxidation, was compared with the production rate based on bulk equilibrium, as cited in the literature.     

A laser-photolysis fragment-fluorescence (LPFF) method for the detection of gaseous nitric acid in ambient air

The development and first tests of a novel method for the direct, sensitive, selective, and fast detection of gaseous nitric acid in air are described. The detection method is based on the laser-photolysis fragment-fluorescence (LPFF) method using 193 nm (ArF) laser light. The photolysis process yielding OH fluorescence has been thoroughly investigated. Up to now, the method has been found to be practically free of interferences. The mixing ratio for nitric acid is measured on-line with a detection limit of about 0.1 ppbv for an accumulation time of the signal of 10–15 min. A number of tests and field measurements were performed to demonstrate the feasibility and limits of the described detection method.     

Two-dimensional modelling of some CFC replacement compounds

The Cambridge 2-D Eulerian model has been used to study the potential atmospheric distributions and lifetimes of a number of CFC replacement compounds and their degradation products. The study has focused on HFC 134a and HCFCs 123, 141b and 142b and the major products formed by their atmospheric degradation. The loss of these compounds and their products by hydroxyl radical attack, photolysis and in-cloud hydrolysis have been investigated. The study has shown that HCFCs 141b and 142b have sufficiently long lifetimes to enter the stratosphere in significant quantities, where degradation leads to an increase in the total stratospheric chlorine concentration. The study has also highlighted areas where further experimental work would be valuable, in particular characterisation of the product channels for the degradation reactions and determination of the removal rates of the products in the aqueous phase.     

A Laboratory and Theoretical Study on the Uptake of SO2 Gas by Large and Small Water Drops Containing Heavy Metal Ions

Laboratory experiments have been carried out to investigate the uptake of sulfur dioxide by water drops containing heavy metal ions where the metal ions serve as catalysts to oxidise the taken up S(IV) into S(VI). During the gas uptake the drops were freely suspended at their terminal velocity in the airstream of the Mainz vertical wind tunnel. Two series of experiments were carried out, one with large millimeter size water drops containing manganese or iron ions, and the other with small water drops containing manganese ions and having radii in hundreds of micron size range. The experimental results were compared against model computations using the Kronig–Brink model and the fully mixed model, modified for the case that heavy metal ions present in the liquid phase act as catalysts for the oxidising process. The results of the model calculations show that there are only small differences between the predicted gas uptake according to the two models. In addition it was found that the experimental obtained results from the uptake of SO₂ by water drops containing heavy metal ions for both, large and small water drops did agree with the model results.     

Products and Mechanism of the Gas Phase Reaction of Ozone with β-Pinene

Gas phase ozonolysis of -pinene was performedin a 570 l static reactor at 730 Torr and 296 K insynthetic air and the products were analysed by acombination of gas phase FTIR spectroscopy, HPLC andIC analyses of gas phase and aerosol samples,respectively. The reaction mechanism was investigatedby adding HCHO, HCOOH and H₂O as Criegeeintermediate scavenger and cyclohexane as OH radicalscavenger. Main identified products (yields inparentheses) in the presence of cyclohexane as OHradical scavenger were HCHO (0.65 ± 0.04),nopinone (0.16 ± 0.04), 3-hydroxy-nopinone (0.15± 0.05), CO₂ (0.20 ± 0.04), CO (0.030± 0.002), HCOOH (0.020 ± 0.002), the secondaryozonide of -pinene (0.16 ± 0.05), andcis-pinic acid (0.02 ± 0.01). The decompositionof the primary ozonide was found to yieldpredominantly the excited C₉-Criegee intermediateand HCHO (0.84 ± 0.04) and to a minor extent theexcited CH₂OO intermediate and nopinone (0.16± 0.04). Roughly 40% of the excitedC₉-Criegee intermediate becomes stabilised andcould be shown to react with HCHO, HCOOH and H₂O. The atmospherically important reaction of thestabilised C₉-Criegee intermediate with H₂Owas found to result in a nopinone increase of (0.35± 0.05) and in the formation of H₂O₂(0.24 ± 0.03). Based on the observed products,the unimolecular decomposition/isomerisationchannels of the C₉-Criegee intermediate arediscussed in terms of the hydroperoxide and esterchannels. Subsequent reactions of the nopinonylradical, formed in the hydroperoxide channel, lead tomajor products like 3-hydroxy-nopinone but also tominor products like cis-pinic acid. A mechanismfor the formation of this dicarboxylic acid isproposed and its possible role in aerosol formationprocesses discussed.     

High urine hippuric acid level among police working close to traffic in an urban area,Thailand: a preliminary study

Toluene is of particular concern because recent research indicating that toluene exposure can result in several toxicities. Hence, toluene exposure is of particular concern because of ongoing exposure to thousands of workers in the industrial plants. Determination of the urine hippuric acid level is accepted as a helpful for monitoring risk groups of workers. Apart from the industrial workers, there are other occupations with high risk for toluene exposure. In this study, we study another at-risk occupation, the police. In this study, 45 urine samples were obtained from 45 Thai police working close to traffic in an urban area for determination for urine hippuric acid level. The average urine hippuric acid level was 0.70 ± 0.70 mg/gCr, respectively. This average is significant higher than that of the control non-exposed Thais (P < 0.05). Working in the air pollution in the urban area can be health hazard for the police. Exposure to the toluene from automobile exhaust can be an important occupational problem for these police.