Estimates of heterogeneous formation of secondary organic aerosol during a wood smoke episode in Houston,Texas

Observational data, collected during a wood smoke episode in Houston, Texas, were used to assess the extent to which acid-catalyzed reactions of carbonyls might contribute to secondary organic aerosol (SOA) formation. The wood smoke episode was chosen for this analysis because of relatively high concentrations of acidic aerosol, coupled with high concentrations of SOA precursors during the episode. Photochemical modeling, coupled with ambient measurements, indicated that acid aerosol-mediated organic aerosol formation reactions, not accounted for in most current photochemical models, may have led to SOA formation of up to a few μg m⁻³. In photochemical simulations, acid-mediated organic aerosol formation was modeled by calculating the rate of impingement of aldehyde molecules on acidic particles, and then assuming that a fraction of the impingements resulted in reaction. For reaction probabilities on the order of 0.005–0.0005, the model predicted SOA concentrations were consistent with estimates of SOA based on observations. In addition, observed concentrations of particulate phase ammonium during the episode were consistent with high concentrations of the types of organic acids that would be formed through acid-catalyzed reactions of carbonyls. Although there are substantial uncertainties in the estimates of heterogeneous SOA formation, collectively, these data and modeling analyses provide evidence for the importance of acid-catalyzed SOA formation reactions.     

Impact of clouds and aerosols on ozone production in Southeast Texas

A radiative transfer model and photochemical box model are used to examine the effects of clouds and aerosols on actinic flux and photolysis rates, and the impacts of changes in photolysis rates on ozone production and destruction rates in a polluted urban environment like Houston, Texas. During the TexAQS-II Radical and Aerosol Measurement Project the combined cloud and aerosol effects reduced j(NO₂) photolysis frequencies by nominally 17%, while aerosols reduced j(NO₂) by 3% on six clear sky days. Reductions in actinic flux due to attenuation by clouds and aerosols correspond to reduced net ozone formation rates with a nearly one-to-one relationship. The overall reduction in the net ozone production rate due to reductions in photolysis rates by clouds and aerosols was approximately 8 ppbv h^?1.     

The role of copper(II) chloride in the formation of organic chlorine in fly ash

In the de-novo synthesis and formation of PCDD/PCDF, the transfer of inorganic chlorine to the carbonaceous material of fly ash plays an important role. Here, copper acts as a catalyst in the chlorination reaction. In experiments in the range of 250-350 degrees C under helium, we determined the stoichiometry of the chlorination reaction with model systems. Therefore, it was necessary to develop a method to quantify the copper(II) and copper(I) ions. In a combination of solid electron paramagnetic (spin) resonance spectroscopy (EPR) for Cu(I), and X-ray fluorescence spectroscopy (XRFA) analysis for Cu (total), we found a way for the quantification of copper(I) and (II). With these experiments, we can show that the chlorination reaction is relatively fast and comes to a stop under helium, after the copper(II) is reduced. The ratio between the organic chlorine formed and copper(II) reduced is, at the end of the reaction, 0.5, which is in agreement with the following reaction: 2CuCl2 + R-H-->2CuCl + R-Cl + HCl.     

Spatial patterns of organic chlorine and chloride in Swedish forest soil

The concentration of organic carbon, organic chlorine and chloride was determined in Swedish forest soil in the southern part of Sweden and the spatial distribution of the variables were studied. The concentration of organically bound chlorine was positively correlated to the organic carbon content, which is in line with previous studies. However, the spatial distribution patterns strongly indicate that some other variable adds structure to the spatial distribution of organic chlorine. The distribution patterns for chloride strongly resembled the distribution of organic chlorine. The spatial distribution of chloride in soil depends on the deposition pattern which in turn depends on prevailing wind-direction, amount of precipitation and the distance from the sea. This suggests that the occurrence of organic chlorine in soil is influenced by the deposition of chloride or some variable that co-varies with chloride. Two clearly confined strata were found in the area: the concentrations of organic chlorine and chloride in the western area were significantly higher than in the eastern area. No such difference among the two areas was seen regarding the carbon content.     

The effect of variability in industrial emissions on ozone formation in Houston, Texas

Ambient observations have indicated that high concentrations of ozone observed in the Houston/Galveston area are associated with plumes of highly reactive hydrocarbons, mixed with NO_x, from industrial facilities. Ambient observations and industrial process data, such as mass flow rates for industrial flares, indicate that the VOCs associated with these industrial emissions can have significant temporal variability. To characterize the effect of this variability in emissions on ozone formation in Houston, data were collected on the temporal variability of industrial emissions or emission surrogates (e.g., mass flow rates to flares). The observed emissions variability was then used to construct regionwide emission inventories with variable industrial emissions, and the impacts of the variability on ozone formation were examined for two types of meteorological conditions, both of which lead to high ozone concentrations in Houston. The air quality simulations indicate that variability in industrial emissions has the potential to cause increases and decreases of 10–52 ppb (13–316%), or more, in ozone concentration. The largest of these differences are restricted to regions of 10–20 km², but the variability also has the potential to increase regionwide maxima in ozone concentrations by up to 12 ppb.     

Effect of matrix on heterogeneous phase chlorine substitution reactions for dibenzo-p-dioxin and HCl in air

Five materials were used in gas-solid phase reactions between dibenzo-p- dioxin(DD) and HCl in order to determine the role of organic and inorganic components in fly ash on chlorine substitution reactions of chlorinated dioxins. The five solids were: granular activated carbon, silica gel, diatomaceous earth, Tenax-GC, and fly ash. Conditions for reactions were 10 min at 150°C with 5% HCl in air. Extent of chlorination was measured using GC/MS analyses of extracts of fly ash after treatment processes and was expressed as the ratio monochloroDD/original unreacted DD. These ratios were: fly ash, 1.082; silica gel, 0.059; activated carbon, 0.024; and Tenax-GC, 0.001. Measurement of similar behavior on diatomaceous earth was impossible since starting material and possible products were irreversibly adsorbed completely. The major chlorinated dioxin produced under these conditions was 2-chlorodibenzo-p- dioxin which is the isomer favored through an electrophilic substitution mechanism.     

Second-order chlorine decay and trihalomethanes formation in a pilot-scale water distribution systems

It is well known that model-building of chlorine decay in real water distribution systems is difficult because chlorine decay is influenced by many factors (e.g., bulk water demand, pipe-wall demand, piping material, flow velocity, and residence time). In this paper, experiments were run to investigate the kinetic model of chlorine decay and the formation model of trihalomethanes (THMs) in pilot-scale water distribution systems. Experimental results show that the rate constants of chlorine decay, including wall decay and bulk decay, increasing with temperature. Moreover, the kinetic model of chlorine decay and the formation model of THMs describe experiment data of pilot-scale water distribution systems. The effect of different piping material on chlorine decay and THMs formation were also investigated. The rate constants of chlorine decay are ranked in order: stainless steel pipe, ductile iron pipe, and last, polyethelene pipe because wall decay is the largest in stainless steel pipe than that in other piping material. Correspondingly, the rate of THMs formation follows the order of stainless steel pipe, ductile iron pipe, and last, polyethelene pipe because of less chlorine in bulk water reacting with the trihalomethane formation potential (THMFP).     

The effect of chlorine on the formation of photochemical oxidants in Southern Telemark,Norway

Hourly average concentrations of up to 15 ppbv of PAN were measured during the summer 1982 a few km downwind of the chemical industries in southern Telemark, Norway, in sea breeze situations. The O₃/PAN ratio was as low as 6 by volume for the highest PAN concentrations. The chemical industries are emitters of, among other gases, C1₂, NO_x, SO₂, and hydrocarbons. A model for the chemistry and dilution of the plume from the main industrial complex is described. The emission of C1₂ seems to be the cause of the photochemical activity. The release of atomic chlorine through the rapid photodissociation of C1₂ is calculated to give maximum hydroxyl concentration close downwind of the main industrial complex where also the peak concentrations of SO₂ and NO_x are found, giving rise to rapid nitric acid and sulphate formation. A reduction in the NO_x emissions would increase the photochemical activity, while it is calculated that reducing the C1₂ emissions would reduce the formation of photochemical oxidants. It is shown that PAN is a much better indicator of the photochemical activity than O₃.     

Hg reactions in the presence of chlorine species: homogeneous gas phase and heterogeneous gas-solid phase

The kinetics of Hg chlorination (with HCl) was studied using a flow reactor system with an online Hg analyzer, and speciation sampling using a set of impingers. Kinetic parameters, such as reaction order (alpha), overall rate constant (k'), and activation energy (Ea), were estimated based on the simple overall reaction pathway. The reaction order with respect to C(Hg), k', and Ea were found to be 1.55, 5.07 x 10(-2) exp(-1939.68/T) [(microg/m3)(-055)(s)(-1)]. and 16.13 [kJ/ mol], respectively. The effect of chlorine species (HCl, CH2Cl2) on the in situ Hg capture method previously developed (28) was also investigated. The efficiency of capture of Hg by this in situ method was higher than 98% in the presence of chlorine species. Furthermore, under certain conditions, the presence of chlorine enhanced the removal of elemental Hg by additional gas-phase oxidation.     

Factorial analysis of the trihalomethane formation in the reaction of colloidal,hydrophobic, and transphilic fractions of DOM with free chlorine

Background, aim, and scope  

This study focuses on the factors that affect trihalomethane (THMs) formation when dissolved organic matter (DOM) fractions (colloidal, hydrophobic, and transphilic fractions) in aqueous solutions were disinfected with chlorine.     

自由氯、一氯胺和二氧化氯对饮用水中粪肠球菌的消毒动力学研究

以粪肠球菌为研究对象,研究了自由氯、一氯胺和二氧化氯在不同pH值和温度下的消毒效果,并将灭活速率常数表示为pH和温度的函数,对Chick—Watson模型进行了修正。结果表明,随着pH的上升,自由氯和一氯胺的灭活率减小,二氧化氯的灭活率则增大。温度对一氯胺的影响较小,对自由氯和二氧化氯的影响较显著。修正后含有pH和温度两参数的消毒动力学模型可以很好地模拟消毒过程,增强了模型的通用性。     

Photochemical ozone and nitric oxide formation in air-nitrogen dioxide mixtures containing sulfur dioxide or chlorine

Experiments were performed to investigate the effects of sulfur dioxide (0–10 ppm) and chlorine (0–15 ppm) on ozone and nitric oxide concentrations in irradiated mixtures of nitrogen dioxide (1–5 ppm) and air. The mixtures were irradiated by ultraviolet fluorescent lamps while flowing at a steady speed through a 9m long, 15.2cm i.d. Pyrex tube. The presence of sulfur dioxide produced no measurable change in the ozone and nitric oxide concentrations. The addition of small quantities of chlorine increased the ozone concentration in much the same manner as the addition of a hydrocarbon. A reaction model was developed for the chlorine-nitrogen dioxide-air mixtures. The observed increase in ozone concentration could only be predicted if the following two reactions were included : ClOO + NO → NO₂ + ClO and ClOO + NO → ClNO + O₂. Significant quantities of unexpected condensation nuclei were also observed in the chlorine-nitrogen dioxide-air mixtures.     

Dioxins and furans formation in pilot incineration tests of sewage sludge spiked with organic chlorine

The factors affecting polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) formation were studied in sewage sludge incineration tests carried out on a demonstrative plant. The plant includes a circulating fluidised bed furnace (FBF) and a rotary kiln furnace (RKF), operating alternatively. During the tests sewage sludge was spiked with chlorinated hydrocarbons and the operating parameters of the afterburning chamber were varied. PCDD/F were sampled in each test before the bag filter, thus collecting the above contaminants before abatement systems. From the tests it appeared that PCDD/F were always produced in more abundance in the tests carried out by FBF than by RKF. The higher PCDD/F concentrations in the tests by FBF were reached when sewage sludge was spiked with a high dosage of a surrogate organic mixture of chlorinated hydrocarbons and when the afterburning chamber was used only as transit equipment with the burner off. The distribution of the different PCDD/F homologues was compared. P5CDFs were generally the prevalent fraction, with very few exceptions for the tests by RKF at high temperature of the afterburning chamber. As for FBF tests, it was found that the PCDD/F homologue profile depends on the afterburning chamber temperature.     

Removal and formation of chlorinated triclosan derivatives in wastewater treatment plants using chlorine and UV disinfection

Triclosan, a common antimicrobial agent, may react during the disinfection of wastewater with free chlorine to form three chlorinated triclosan derivatives (CTDs). This is of concern because the CTDs may be photochemically transformed to tri- and tetra-chlorinated dibenzo-p-dioxins when discharged into natural waters. In this study, wastewater influent, secondary (pre-disinfection) effluent, and final (post-disinfection) effluent samples were collected on two occasions each from two activated sludge wastewater treatment plants, one using chlorine disinfection and one using UV disinfection. Concentrations of triclosan and three CTDs were determined using ultra performance liquid chromatography-triple quadrupole mass spectrometry with isotope dilution methodology. Triclosan and the CTDs were detected in every influent sample at levels ranging from 453 to 4530 and 2 to 98 ng L⁻¹, respectively, though both were efficiently removed from the liquid phase during activated sludge treatment. Triclosan concentrations in the pre-disinfection effluent ranged from 36 to 212 ng L⁻¹, while CTD concentrations were below the limit of quantification (1 ng L⁻¹) for most samples. In the treatment plant that used chlorine disinfection, triclosan concentrations decreased while CTDs were formed during chlorination, as evidenced by CTD levels as high as 22 ng L⁻¹ in the final effluent. No CTDs were detected in the final effluent of the treatment plant that used UV disinfection. The total CTD concentration in the final effluent of the chlorinating treatment plant reached nearly one third of the triclosan concentration, demonstrating that the chlorine disinfection step played a substantial role in the fate of triclosan in this system.     

Investigations of emissions and heterogeneous formation of HONO in a road traffic tunnel

Simultaneous measurements of nitrous acid (HONO) and nitrogen dioxide (NO₂) using a differential optical absorption spectroscopy system, nitrogen oxide (NO) by an in situ chemiluminescence analyser and carbon dioxide (CO₂) by a gas chromatographic technique were carried out in the Wuppertal Kiesbergtunnel. At high traffic density HONO concentrations of up to 45 ppbV were observed. However, at low traffic density unexpectedly high HONO concentrations of up to 10 ppbV were measured caused by heterogeneous HONO formation on the tunnel walls. In addition to the tunnel campaigns, emission measurements of HONO, NO₂, NO and CO₂ from different single vehicles (a truck, a diesel and a gasoline passenger car) were also performed. For the correction of the HONO emission data, the heterogeneous HONO formation on the tunnel walls was quantified by two different approaches (a) in different NO₂ emission experiments in the tunnel without traffic and (b) on tunnel wall residue in the laboratory. The HONO concentration corrected for heterogeneous formation on the tunnel walls, in relation to the CO₂ concentration can be used to estimate the amount of HONO, which is directly emitted from the vehicle fleet. From the measured data, emission ratios (e.g. HONO/NO_x) and emission indices (e.g. mg HONO kg⁻¹ fuel) were calculated. The calculated emission index of 88±18 mg HONO kg⁻¹ fuel allows an estimation of the HONO emission rates from traffic into the atmosphere. Furthermore, the heterogeneous formation of HONO from NO₂ on freshly emitted exhaust particles is discussed.     

Fe3+和Cu2+对饮用水氯消毒副产物三卤甲烷形成的影响

为了研究水中存在Br-的情况下,Fe3+和Cu2+对三卤甲烷(THMs)的生成及CHCl3、CHBrCl2、CHBr2Cl、CHBr3 4种消毒副产物相对分布的影响,以腐殖酸模拟氯消毒过程中的前体物进行实验。结果表明,在pH为6、7和9 3种条件下,Fe3+抑制了THMs的生成,pH=6时只有CHCl3生成量随着Fe3+浓度的增加逐渐减少,其余3种消毒副产物均在增加,pH=7时4种消毒副产物浓度均减小并在Fe3+浓度为2 mg/L时生成量最低,pH=9时的生成趋势与pH=6时类似。Cu2+能促进THMs的生成,在pH为6、7和9时,当加入0.5 mg/L Cu2+时,THMs总量分别增加了16.7%、22.6%和2.5%,随着pH增加,THMs总量增加。在3种pH环境中,Cu2+对THMs生成的影响大于Fe3+,在偏酸性环境中,Fe3+影响THMs生成,产生的致癌风险高,当金属离子浓度为2.5 mg/L时,致癌风险相差最高为15%,在中性和偏碱性环境中,Cu2+影响THMs生成,产生的致癌风险高。     

Influence of iron and copper oxides on polychlorinated diphenyl ether formation in heterogeneous reactions

Polychlorinated diphenyl ether (PCDE) has attracted great attention recently as an important type of environmental pollutant. The influence of iron and copper oxides on formation of PCDEs was investigated using laboratory-scale flow reactors under air and under nitrogen at 350 °C, a temperature corresponding to the post-combustion zone of a municipal solid waste incinerator. The results show that the 2,2′,3,4,4′,5,5′,6-otachlorodiphenyl ether (OCDE) formed from the condensation of pentachlorophenol (PCP) and 1,2,4,5-tetrachlorobenzene (Cl₄Bz) is the predominant congener formed on the SiO₂/Fe₂O₃ surface with and without oxygen. This indicated that HCl elimination between PCP and 1,2,4,5-Cl₄Bz molecules formed 2,2′,3,4,4′,5,5′,6-OCDE in the presence of Fe₂O_3. On the other hand, decachlorodiphenyl ether, nonachlorodiphenyl ether, and OCDE were the dominant products on the SiO₂/CuO surface without oxygen, although the 2,2′,3,4,4′,5,5′,6-OCDE was the dominant product on the SiO₂/CuO surface with oxygen. Therefore, the presence of Fe₂O₃ and CuO influences the formation and homologue distribution of PCDEs, which shifted towards the lower chlorinated species. Fe₂O₃ can promote both the condensation and dechlorination reaction without oxygen_. On the contrary, with oxygen, Fe₂O₃ suppresses the condensation of chlorobenzene and chlorophenol to form PCDEs and polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). CuO can increase the formation of lower chlorinated PCDEs and PCDDs without oxygen. In conclusion, the different fly ash components have a major influence on PCDE emissions.     

Modeling solute transport in one-dimensional homogeneous and heterogeneous soil columns with continuous time random walk

In this paper, we used the continuous time random walk (CTRW) framework to characterize the transport process in 1250-cm long one-dimensional homogenous and heterogeneous soil columns at the experiments conducted by Huang et al. [Huang, K., Toride, N., van Genuchten, M.Th., 1995. Experimental investigation of solute transport in large, homogeneous and heterogeneous, saturated soil columns. Trans. Porous Media. 18, 283-302]. The transport process was also simulated by using the advection-dispersion equation (ADE) and the spatial fractional advection-dispersion equation (FADE) for comparison. In the homogeneous soil column, the non-Fickian behavior is found at the distances less than 1000cm with beta values larger than 1.60, but less than 2, and Fickian form transport is obtained at distances larger than 1000cm with beta values larger than 2. In the heterogeneous soil column, we found the most anomalous behavior at distances from 200cm to 700cm with beta values ranging from 0.894 to 0.958, and non-Fickian transport process is observed at distances larger than 800cm with beta values in the range between 1 and 1.3. More significant non-Fickian behavior is found for transport in the heterogeneous soil column than that in the homogeneous soil column. The CTRW fits to the breakthrough curves (BTCs) have lower values of root mean square error (RMSE) and higher values of determination coefficient (r(2)), with respect to the fits of ADE and FADE. The CTRW model also is better captures the full evolution of BTCs, and especially their tails.     

Concentrations of chlorine, bromine and iodine in Japanese rivers

Concentrations of halogens (Cl, Br and I) in 30 Japanese rivers were measured by ion chromatography and inductively coupled plasma mass spectrometry to understand their behavior in the terrestrial environment. Concentrations of Cl, Br and I in each river, obtained at 10 sampling points from the upper stream to the river mouth, tended to increase near the river mouth. The ranges of geometric means of Cl, Br and I in each river were 1.0–19.4 mg l⁻¹, 2.5–67.9 μg l⁻¹, and 0.18–8.34 μg l⁻¹, respectively. To compare halogen behavior, the concentration ratios, Br/Cl and I/Cl, were calculated. The Br/Cl range was (2.3–7.8) × 10⁻³ (geometric mean: 3.74 × 10⁻³), and it was nearly constant except for the Yoneshiro river. It was estimated that 60–80% of total Br in the middle to lower parts of this river was the excess Br. The Br chemical form in all the rivers is generally considered to be Br⁻. The I/Cl ratios had different trends in rivers flowing into the Japan Sea and Pacific Ocean, possibly due to the different geological features in the river catchments.     

Spatial, temporal, and interspecies patterns in fine particulate matter in Texas

The Big Bend Regional Aerosol and Visibility Observational (BRAVO) field study was conducted from July to October 1999 and was followed by several years of modeling and data analyses to examine the causes of haze at Big Bend National Park TX (BBNP). During BRAVO, daily speciated fine (diameter <2.5 microm) particulate concentrations were measured at 37 sites throughout Texas. At the primary receptor site, K-Bar Ranch, there were many additional measurements including a "high-sensitivity" version of the 24-hr fine particulate elemental data. The spatial, temporal, and interspecies patterns in these data are examined here to qualitatively investigate source regions and source types influencing the fine particulate concentrations in Texas with an emphasis on sources of sulfates, the largest contributor to fine mass and light extinction. Peak values of particulate sulfur (S) varied spatially and seasonally. Maximum S was in Northeast Texas during the summer, whereas peak S at BBNP was in the fall. Sulfate acidity at BBNP also varied by month. Sources of Se were evident in Northeast Texas and from the Carbón I and II plants. High S episodes at BBNP during BRAVO had several different trace element characteristics. Carbon concentrations at BBNP during BRAVO were probably mostly urban-related, with arrival from the Houston area likely. The Houston artificial tracer released during the second half of BRAVO was highly correlated with some carbon fractions. There was evidence of the influence of African dust at sites throughout Texas during the summer. Patterns in several trace elements were also examined. Vanadium was associated with air masses from Mexico. Lead concentrations in southern Texas have dropped dramatically over the past several years.