Fog Chemistry at an Urban Midwestern Site

This work investigates the oxidative aging of preformed secondary organic aerosol (SOA) derived from α-pinene ozonolysis (～100 ppb_v hydrocarbon [HC_x] with excess of O₃) within the University of California–Riverside Center for Environmental Research and Technology environmental chamber that occurs after introduction of additional hydroxyl (OH) and nitrate (NO₃) radicals. Simultaneous measurements of SOA volume concentration, hygroscopicity, particle density, and elemental chemical composition (C:O:H) reveal increased particle wall-loss-corrected SOA formation (1.5%, 7.5%, and 15.1%), increase in oxygen-to-carbon ratio (O/C; 15.6%, 8.7%, and 8.7%), and hydrophilicity (4.2%, 7.4%, and 1.4%) after addition of NO (ultraviolet [UV] on), H₂O₂ (UV on), and N₂O₅ (dark), respectively. The processing observed as an increase in O/C and hydrophilicity is attributed to OH and NO₃ reactions with first-generation vapor products and UV photolysis. The rate of increase in O/C appears to be only sufficient to achieve semivolatile oxygenated organic aerosol (SV-OOA) on a day time scale even at the raised chamber radical concentrations. The additional processing with UV irradiation without addition of NO, H₂O₂, or N₂O₅ is observed, adding 5.5% wall-loss-corrected volume. The photolysis-only processing is attributed to additional OH generated from photolysis of the nitrous acid (HONO) offgasing from chamber walls. This finding indicates that OH and NO₃ radicals can further alter the chemical composition of SOA from α-pinene ozonolysis, which is proved to consist of first-generation products.

Implications: Secondary organic aerosol (SOA) may undergo aging processes once formed in the atmosphere, thereby altering the physicochemical and toxic properties of aerosol. This study discusses SOA aging of a major biogenic volatile organic compound (VOC; α-pinene) after it initially forms SOA. Aging of the α-pinene ozonolysis system by OH (through NO or H₂O₂ injection), NO₃ (through N₂O₅ injection), and photolysis is observed. Although the reaction rate appears to be only sufficient to achieve semivolatile oxygenated organic aerosol (SV-OOA) level of oxygenation on a 1-day scale, it is important that SOA aging be considered in ambient air quality models. Aging in this study is attributed to further oxidation of gas-phase oxidation products of α-pinene ozonolysis.

Supplemental Materials: Supplemental materials are available for this paper. Go to the publisher's online edition of the Journal of the Air &; Waste Management Association for information on the referenced α-pinene ozonolysis reaction and chamber reactor temperature.     

Contributions of biogenic volatile organic compounds to the formation of secondary organic aerosols over Mt. Tai,Central East China

To better understand the contribution of biogenic volatile organic compounds to the formation of secondary organic aerosol (SOA) in high mountain regions, ambient aerosols were collected at the summit of Mt. Tai (1534 m, a.s.l.), Central East China (CEC) during the Mount Tai Experiment 2006 campaign (MTX2006) in early summer. Biogenic SOA tracers for the oxidation of isoprene, α/β-pinene, and β-caryophyllene were measured using gas chromatography/mass spectrometry. Most of the biogenic SOA tracers did not show clear diurnal variations, suggesting that they are formed during long-range atmospheric transport or over relatively long time scales. Although isoprene- and α/β-pinene-derived SOA tracers did not correlate with levoglucosan (a biomass burning tracer), β-caryophyllinic acid showed a good correlation with levoglucosan, indicating that crop residue burning may be a source for this acid. Total concentrations of isoprene oxidation products are much higher than those of α/β-pinene and β-caryophyllene oxidation products. The averaged ratio of isoprene to α/β-pinene oxidation products (R_iso/pine) was 4.9 and 6.7 for the daytime and nighttime samples, respectively. These values are among the highest in the aerosols reported in different geographical regions, which may be due to the large isoprene fluxes and relatively high levels of oxidants such as OH in CEC. Using a tracer-based method, we estimated the concentrations of secondary organic carbon (SOC) derived from isoprene, α/β-pinene, and β-caryophyllene to be 0.42–3.1 μgC m^?3 (average 1.6 μgC m^?3) during the daytime and 0.11–4.2 μgC m^?3 (1.7 μgC m^?3) during the nighttime. These values correspond to 2.9–23% (10%) and 3.2–28% (9.8%) of the total OC concentrations, in which isoprene-derived SOC accounts for 58% and 63% of total SOC during the daytime and nighttime, respectively. This study suggests that isoprene is a more significant precursor for biogenic SOA than α/β-pinene and β-caryophyllene at high altitudes in CEC.     

A chamber study of secondary organic aerosol formation by linalool ozonolysis

The formation of secondary organic aerosol (SOA) produced from linalool ozonolysis was examined using a dynamic chamber system that allowed the simulation of ventilated indoor environments. Experiments were conducted under room temperature (22–23 °C) and air exchange rate of 0.67 h^?1. An effort was made to maintain the product of the concentrations of the two reagents constant. The results suggest that under the conditions when the product of the two reagent concentrations was constant, the relative concentrations play an important role in determining the total SOA formed. A combination of concentrations somewhere in ozone limiting region will produce the maximum SOA concentration. The measured reactive oxygen species (ROS) concentrations at linalool and ozone concentrations relevant to prevailing indoor concentrations ranged from 0.71 to 2.53 nmol m^?3 equivalents of H₂O₂. It was found that particle samples aged for 24 h lost a significant fraction of the ROS compared to fresh samples. The residual ROS concentrations were around 15–69%. Compared with other terpene species like α-pinene that has one endocyclic unsaturated carbon bond, linalool was less efficient in potential SOA formation yields.     

Reactive uptake of ozone at simulated leaf surfaces: Implications for ‘non-stomatal’ ozone flux

The reaction of ozone (O₃) with α-pinene has been studied as a function of temperature and relative humidity and in the presence of wax surfaces that simulate a leaf surface. The objective was to determine whether the presence of a wax surface, in which α-pinene could dissolve and form a high surface concentration, would lead to enhanced reaction with O₃. The reaction of O₃ itself with the empty stainless steel reactor and with aluminium and wax surfaces demonstrated an apparent activation energy of around 30 kJ mol^?1 for all the surfaces, similar to that observed in long-term field measurements of O₃ fluxes to vegetation. However, the absolute reaction rate was 14 times greater for aluminium foil and saturated hydrocarbon wax surfaces than for stainless steel, and a further 5 times greater for beeswax than hydrocarbon wax. There was no systematic dependence on either relative or absolute humidity for these surface reactions over the range studied (20–100% RH). Reaction of O₃ with α-pinene occurred at rates close to those predicted for the homogeneous gas-phase reaction, and was similar for both the empty reactor and in the presence of wax surfaces. The hypothesis of enhanced reaction at leaf surfaces caused by enhanced surface concentrations of α-pinene was therefore rejected. Comparison of surface decomposition reactions on different surfaces as reported in the literature with the results obtained here demonstrates that the loss of ozone at the earth's surface by decomposition to molecular oxygen (i.e. without oxidative reaction with a substrate) can account for measured ‘non-stomatal’ deposition velocities of a few mm s^?1. In order to quantify such removal, the effective molecular surface area of the vegetation/soil canopy must be known. Such knowledge, combined with the observed temperature-dependence, provides necessary input to global-scale models of O₃ removal from the troposphere at the earth's surface.     

Large outdoor chamber experiments and computer simulations: (I) Secondary organic aerosol formation from the oxidation of a mixture of d-limonene and α-pinene

This work merges kinetic models for α-pinene and d-limonene which were individually developed to predict secondary organic aerosol (SOA) formation from these compounds. Three major changes in the d-limonene and α-pinene combined mechanism were made. First, radical–radical reactions were integrated so that radicals formed from both individual mechanisms all reacted with each other. Second, all SOA model species from both compounds were used to calculate semi-volatile partitioning for new semi-volatiles formed in the gas phase. Third particle phase reactions for particle phase α-pinene and d-limonene aldehydes, carboxylic acids, etc. were integrated. Experiments with mixtures of α-pinene and d-limonene, nitric oxide (NO), nitrogen dioxide (NO₂), and diurnal natural sunlight were carried out in a dual 270 m³ outdoor Teflon film chamber located in Pittsboro, NC. The model closely simulated the behavior and timing for α-pinene, d-limonene, NO, NO₂, O₃ and SOA. Model sensitivities were tested with respect to effects of d-limonene/α-pinene ratios, initial hydrocarbon to NO_x (HC₀/NO_x) ratios, temperature, and light intensity. The results showed that SOA yield (Y_SOA) was very sensitive to initial d-limonene/α-pinene ratio and temperature. The model was also used to simulate remote atmospheric SOA conditions that hypothetically could result from diurnal emissions of α-pinene, d-limonene and NO_x. We observed that the volatility of the simulated SOA material on the aging aerosol decreased with time, and this was consistent with chamber observations. Of additional importance was that our simulation did not show a loss of SOA during the daytime and this was consistent with observed measurements.     

The effects of increasing atmospheric ozone on biogenic monoterpene profiles and the formation of secondary aerosols

Monoterpenes are biogenic volatile organic compounds (BVOCs) which play an important role in plant adaptation to stresses, atmospheric chemistry, plant–plant and plant–insect interactions. In this study, we determined whether ozonolysis can influence the monoterpenes in the headspace of cabbage. The monoterpenes were mixed with an air-flow enriched with 100, 200 or 400 ppbv of ozone (O₃) in a Teflon chamber. The changes in the monoterpene and O₃ concentrations, and the formation of secondary organic aerosols (SOA) were determined during ozonolysis. Furthermore, the monoterpene reactions with O₃ and OH were modelled using reaction kinetics equations. The results showed that all of the monoterpenes were unequally affected: α-thujene, sabinene and d-limonene were affected to the greatest extend, whereas the 1,8-cineole concentration did not change. In addition, plant monoterpene emissions reduced the O₃ concentration by 12–24%. The SOA formation was dependent on O₃ concentration. At 100 ppbv of O₃, virtually no new particles were formed but clear SOA formation was observed at the higher ozone concentrations. The modelled results showed rather good agreements for α-pinene and 1,8-cineole, whereas the measured concentrations were clearly lower compared to modelled values for sabinene and limonene. In summary, O₃-quenching by monoterpenes occurs beyond the boundary layer of leaves and results in a decreased O₃ concentration, altered monoterpene profiles and SOA formation.     

Radical-driven carbonyl-to-acid conversion and acid degradation in tropospheric aqueous systems studied by CAPRAM

Model studies on the aqueous phase radical-driven processing of carbonyl compounds and acids in clouds and deliquescent particles were performed. The model exposed that aqueous radical conversions of carbonyl compounds and its oxidation products can contribute potentially to the formation of functionalised organic acids. The main identified C₂–C₄ organic gas phase precursors are ethylene glycol, glycolaldehyde, glyoxal, methylglyoxal and 1,4-butenedial. The aqueous phase is shown to contribute significantly with about 93%/63%, 47%/8%, 31%/4%, 7%/4%, 36%/8% to the multiphase oxidative fate of these compounds under remote/urban conditions. Interestingly, the studies revealed that aqueous chemical processing is not only limited to in-cloud conditions but also proceeds in deliquescent particle phase with significant fluxes. Oxalic acid is shown to be formed preferably in deliquescent particles subsequent to the in-cloud oxidations. Mean aqueous phase oxalate formation fluxes of about 12, 42 and 0.4 ng m^?3 h^?1 in the remote, urban and maritime scenario, respectively. Additionally, the turnovers of the oxidation of organics such as methylglyoxal by NO₃ radical reactions are identified to be competitive to their OH pendants. At the current state of CAPRAM, mean C₂–C₄ in-cloud oxidation fluxes of about 0.12 and 0.5 μg m^?3 h^?1 are modelled under the idealised remote and urban cloud conditions.Finally, turnovers from radical oxidations were compared with those of thermal reactions. It is demonstrated that, based on the sparse kinetic data available organic accretion reaction might be of interest in just a few cases for cloud droplets and aqueous particles but generally do not reach the oxidative conversion rates of the main radical oxidants OH and NO₃. Interestingly, oxidation reactions of H₂O₂ are shown to be competitive to the OH radical conversions in cases when H₂O₂ is not readily used up by the S(IV) oxidation.     

Modeling secondary organic aerosol formation from oxidation of α-pinene, β-pinene, and d-limonene

The biogenic species α-pinene, β-pinene, and d-limonene are among the most abundant monoterpenes emitted globally. They are also important precursors to secondary organic aerosol (SOA) formation in the atmosphere. This study involves the development of proposed oxidation mechanisms for these three species. Semi- and non-volatile oxidation products with the potential to lead to SOA formation are predicted explicitly. Simulation code that describes the gas-phase oxidation mechanisms including reactions that lead to ozone (O₃) formation is coupled to an equilibrium absorptive partitioning code. The coupled model is used to simulate both gas-phase chemistry and SOA formation associated with oxidation of these three species in chamber experiments involving single as well as multiple oxidants. For the partitioning model, required molecular properties of the oxidation products are taken from the literature or estimated based on structural characteristics. The predicted O₃ and SOA concentrations are typically within ±50% of measured values for most of the experiments except for the experiments with low initial hydrocarbon concentrations and the nitrate radical experiments with α-pinene. The developed model will be used to update a gas-phase chemical mechanism and a SOA formation module used in a three-dimensional air quality model.     

An examination of oxidant amounts on secondary organic aerosol formation and aging

The effect of HO_x radicals (OH and HO₂) and ozone (O₃) on aerosol formation and aging has been studied. Experiments were performed in presence as well as in absence of oxygen in a flow-through chamber at 299 K for three organic precursor gases, isoprene, α-pinene and m-xylene. The HO_x source was the UV photolysis of humidified air or nitrogen and was measured with a GTHOS (Ground-based Tropospheric Hydrogen Oxides Sensor). The precursor gases concentration was monitored with an online GC-FID. The aerosol mass was then quantified by a Tapered Element Oscillating Microbalance (TEOM). Typical oxidant mixing ratios were (0–4.5) ppm for O₃, 200 pptv for OH and 3 ppbv for HO₂. A simple kinetics model is used to infer the aerosol production mechanism. In the present of O₃ (or O₂), the SOA yields were 0.46, 0.036 and 0.12 for α-pinene with an initial concentration of 100 ppbv (RH = 37%), isoprene with an initial concentration of 177 ppbv (RH = 50%) and m-xylene with an initial concentration of 100 ppbv (RH = 37%), respectively. When the chosen precursor gases reacted with HO_x in the absence of O₃, the maximum SOA yields were significantly increased by factors of 1.6 for isoprene 1.1 for α-pinene, and 3 for m-xylene respectively. The comparison of the calculated and measured potential aerosol mass concentrations as function of time shows that presence of ozone or oxygen can influence the aerosol yield and the absence of ozone or oxygen in the system resulted in high concentrations of its organic aerosol products.     

Stable carbon kinetic isotope effects for the production of methacrolein and methyl vinyl ketone from the gas-phase reactions of isoprene with ozone and hydroxyl radicals

The stable-carbon kinetic isotope effects (KIEs) associated with the production of methacrolein (MACR) and methyl vinyl ketone (MVK) from the reactions of isoprene with ozone and OH radicals were studied in a 25 L reaction chamber at (298±2) K and ambient pressure. The time dependence of both the stable-carbon isotope ratios and the concentrations was determined using a gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS) system. The average yields of ¹³C-containing MACR and MVK generated from the ozone reaction of ¹³C-containing isoprene differed by ?3.6‰ and ?4.5‰, respectively, from the yields for MACR and MVK containing only ¹²C. For MACR and MVK generated from the OH-radical oxidation of isoprene the corresponding values were ?3.8‰ and ?2.2‰, respectively. These values indicate a significant depletion in the ¹³C abundance of MACR and MVK upon their formation relative to isoprene’s pre-reaction ¹³C/¹²C ratio, which is supported by theoretical interpretations of the oxidation mechanism of isoprene and its ¹³C-substituted isotopomers. Numerical model calculations of the isoprene + O₃ reaction predicted a similar depletion in ¹³C for both reaction products upon production. Furthermore, the model predicts mixing ratios and stable carbon delta values for isoprene, MACR, and MVK that were in agreement with the experimental results. The combined knowledge of isotope enrichment values with KIEs will reduce uncertainties in determinations of the photochemical histories of isoprene, MACR, and MVK in the troposphere. The studies presented here were conducted with using isoprene without any artificial isotope enrichment or depletion and it is therefore very likely that these results are directly applicable to the interpretation of studies of isoprene oxidation using stable carbon isotope ratio measurements.     

Heterogeneous Fenton degradation of bisphenol A catalyzed by efficient adsorptive Fe3O4/GO nanocomposites

A new method for the degradation of bisphenol A (BPA) in aqueous solution was developed. The oxidative degradation characteristics of BPA in a heterogeneous Fenton reaction catalyzed by Fe₃O₄/graphite oxide (GO) were studied. Transmission electron microscopic images showed that the Fe₃O₄ nanoparticles were evenly distributed and were ～6 nm in diameter. Experimental results suggested that BPA conversion was affected by several factors, such as the loading amount of Fe₃O₄/GO, pH, and initial H₂O₂ concentration. In the system with 1.0 g L^?1 of Fe₃O₄/GO and 20 mmol L^?1 of H₂O₂, almost 90 % of BPA (20 mg L^?1) was degraded within 6 h at pH 6.0. Based on the degradation products identified by GC–MS, the degradation pathways of BPA were proposed. In addition, the reused catalyst Fe₃O₄/GO still retained its catalytic activity after three cycles, indicating that Fe₃O₄/GO had good stability and reusability. These results demonstrated that the heterogeneous Fenton reaction catalyzed by Fe₃O₄/GO is a promising advanced oxidation technology for the treatment of wastewater containing BPA.     

Degradation of Acid Orange 7 in aqueous solution by dioxygen activation in a pyrite/H2O/O2 system

Increasing attention has been paid to pyrite due to its ability to generate hydroxyl radicals in air-saturated solutions. In this study, the mineral pyrite was studied as a catalyst to activate molecular oxygen to degrade Acid Orange 7 (AO7) in aqueous solution. A complete set of control experiments were conducted to optimize the reaction conditions, including the dosage of pyrite, the AO7 concentration, as well as the initial pH value. The role of reactive oxygen species (ROS) generated by pyrite in the process was elucidated by free radical quenching reactions. Furthermore, the concentrations of Fe(II) and total Fe formed were also measured. The mechanism for the production of ROS in the pyrite/H₂O/O₂ system was that H₂O₂ was formed by hydrogen ion and superoxide anion (O₂ ^·?) which was produced by the reaction of pyrite activating O₂ and then reacted with Fe(II) dissolved from pyrite to produce ^·OH through Fenton reaction. The findings suggest that pyrite/H₂O/O₂ system is potentially practical in pollution treatment. Moreover, the results provide a new insight into the understanding of the mechanism for degradation of organic pollutants by pyrite.     

Degradation kinetics of anthracene by ozone on mineral oxides

To further understand the role of substrates on the heterogeneous reactions of polycyclic aromatic hydrocarbons, the reactions of ozone with anthracene adsorbed on different mineral oxides (SiO₂, α-Al₂O₃ and α-Fe₂O₃) and on Teflon disc were investigated in dark at 20 °C. No reaction between ozone and anthracene on Teflon disc was observed when the ozone concentration was ～1.18 × 10¹⁴ molecules cm^?3. The reactions on mineral oxides exhibited pseudo-first-order kinetics for anthracene loss, and the pseudo-first-order rate constant (k_1,obs) displayed a Langmuir–Hinshelwood dependence on the gas-phase ozone concentration. The adsorption equilibrium constants for ozone (K_O3) on SiO₂-1, SiO₂-2, α-Al₂O₃ and α-Fe₂O₃ were (0.81 ± 0.26) × 10^?15 cm³, (2.83 ± 1.17) × 10^?15 cm³, (2.48 ± 0.77) × 10^?15 cm³ and (1.66 ± 0.45) × 10^?15 cm³, respectively; and the maximum pseudo-first-order rate constant (k_1,max) on these oxides were (0.385 ± 0.058) s^?1, (0.101 ± 0.0138) s^?1, (0.0676 ± 0.0086) s^?1 and (0.0457 ± 0.004) s^?1, respectively. Anthraquinone was identified as the main surface product of anthracene reacted with ozone. Comparison with previous research and the results obtained in this study suggest that the reactivity of anthracene with ozone and the lifetimes of anthracene adsorbed on mineral dust in the atmosphere are determined by the nature of the substrate.     

Aerosols formed from the chemical reaction of monoterpenes and ozone

Chamber experiments were conducted to study the aerosol products from the ozonolysis of the major atmospheric monoterpenes; α-pinene, β-pinene and limonene. It was found that the α-pinend–O₃ reaction produced mainly 2′. 2′-dimethyl-3′-acetyl cyclobutyl ethanal (pinonaldehyde), the β-pinene–O₃ reaction, mainly 6,6-dimethyl-bicyclo [3.1.1] heptan-2-one and the limonene–O₃ reaction, several unidentified products. These products were sought in forest aerosols and pinonaldehyde was detected in the atmosphere.     

Effect of high concentrations of inorganic seed aerosols on secondary organic aerosol formation in the m-xylene/NOx photooxidation system

High concentrations (>15 μm³ cm^?3) of CaSO₄, Ca(NO₃)₂ and (NH₄)₂SO₄ were selected as surrogates of dry neutral, aqueous neutral and dry acidic inorganic seed aerosols, respectively, to study the effects of inorganic seeds on secondary organic aerosol (SOA) formation in irradiated m-xylene/NO_x photooxidation systems. The results indicate that neither ozone formation nor SOA formation is significantly affected by the presence of neutral aerosols (both dry CaSO₄ and aqueous Ca(NO₃)₂), even at elevated concentrations. The presence of high concentrations of (NH₄)₂SO₄ aerosols (dry acidic) has no obvious effect on ozone formation, but it does enhance SOA generation and increase SOA yields. In addition, the effect of dry (NH₄)₂SO₄ on SOA yield is found to be positively correlated with the (NH₄)₂SO₄ surface concentration, and the effect is pronounced only when the surface concentration reaches a threshold value. Further, it is proposed that the SOA generation enhancement is achieved by particle-phase heterogeneous reactions induced and catalyzed by the acidity of dry (NH₄)₂SO₄ seed aerosols.     

Effect of ethylenediamine-N,N′-disuccinic acid on Fenton and photo-Fenton processes using goethite as an iron source: optimization of parameters for bisphenol A degradation

The main disadvantage of using iron mineral in Fenton-like reactions is that the decomposition rate of organic contaminants is slower than in classic Fenton reaction using ferrous ions at acidic pH. In order to overcome these drawbacks of the Fenton process, chelating agents have been used in the investigation of Fenton heterogeneous reaction with some Fe-bearing minerals. In this work, the effect of new iron complexing agent, ethylenediamine-N,N'-disuccinic acid (EDDS), on heterogeneous Fenton and photo-Fenton system using goethite as an iron source was tested at circumneutral pH. Batch experiments including adsorption of EDDS and bisphenol A (BPA) on goethite, H₂O₂ decomposition, dissolved iron measurement, and BPA degradation were conducted. The effects of pH, H₂O₂ concentration, EDDS concentration, and goethite dose were studied, and the production of hydroxyl radical (^?OH) was detected. The addition of EDDS inhibited the heterogeneous Fenton degradation of BPA but also the formation of ^?OH. The presence of EDDS decreases the reactivity of goethite toward H₂O₂ because EDDS adsorbs strongly onto the goethite surface and alters catalytic sites. However, the addition of EDDS can improve the heterogeneous photo-Fenton degradation of BPA through the propagation into homogeneous reaction and formation of photochemically efficient Fe-EDDS complex. The overall effect of EDDS is dependent on the H₂O₂ and EDDS concentrations and pH value. The high performance observed at pH 6.2 could be explained by the ability of O ₂ ^?? to generate Fe(II) species from Fe(III) reduction. Low concentrations of H₂O₂ (0.1 mM) and EDDS (0.1 mM) were required as optimal conditions for complete BPA removal. These findings regarding the capability of EDDS/goethite system to promote heterogeneous photo-Fenton oxidation have important practical implications for water treatment technologies.     

Decomposition of phenylarsonic acid by AOP processes: degradation rate constants and by-products

The paper presents results of the studies photodegradation, photooxidation, and oxidation of phenylarsonic acid (PAA) in aquatic solution. The water solutions, which consist of 2.7 g dm^?3 phenylarsonic acid, were subjected to advance oxidation process (AOP) in UV, UV/H₂O₂, UV/O₃, H₂O₂, and O₃ systems under two pH conditions. Kinetic rate constants and half-life of phenylarsonic acid decomposition reaction are presented. The results from the study indicate that at pH 2 and 7, PAA degradation processes takes place in accordance with the pseudo first order kinetic reaction. The highest rate constants (10.45?×?10^?3 and 20.12?×?10^?3) and degradation efficiencies at pH 2 and 7 were obtained at UV/O₃ processes. In solution, after processes, benzene, phenol, acetophenone, o-hydroxybiphenyl, p-hydroxybiphenyl, benzoic acid, benzaldehyde, and biphenyl were identified.     

Degradation of ethylenethiourea pesticide metabolite from water by photocatalytic processes

In this study, photocatalytic (photo-Fenton and H₂O₂/UV) and dark Fenton processes were used to remove ethylenethiourea (ETU) from water. The experiments were conducted in a photo-reactor with an 80 W mercury vapor lamp. The mineralization of ETU was determined by total organic carbon analysis, and ETU degradation was qualitatively monitored by the reduction of UV absorbance at 232 nm. A higher mineralization efficiency was obtained by using the photo-peroxidation process (UV/H₂O₂). Approximately 77% of ETU was mineralized within 120 min of the reaction using [H₂O₂]₀ = 400 mg L^?1. The photo-Fenton process mineralized 70% of the ETU with [H₂O₂]₀ = 800 mg L^?1 and [Fe²⁺] = 400 mg L^?1, and there is evidence that hydrogen peroxide was the limiting reagent in the reaction because it was rapidly consumed. Moreover, increasing the concentration of H₂O₂ from 800 mg L^?1 to 1200 mg L^?1 did not enhance the degradation of ETU. Kinetics studies revealed that the pseudo-second-order model best fit the experimental conditions. The k values for the UV/H₂O₂ and photo-Fenton processes were determined to be 6.2 × 10^?4 mg L^?1 min^?1 and 7.7 × 10^?4 mg L^?1 min^?1, respectively. The mineralization of ETU in the absence of hydrogen peroxide has led to the conclusion that ETU transformation products are susceptible to photolysis by UV light. These are promising results for further research. The processes that were investigated can be used to remove pesticide metabolites from drinking water sources and wastewater in developing countries.     

Microwave treatment of dairy manure for resource recovery: Reaction kinetics and energy analysis

A newly designed continuous-flow 915 MHz microwave wastewater treatment system was used to demonstrate the effectiveness of the microwave enhanced advanced oxidation process (MW/H₂O₂-AOP) for treating dairy manure. After the treatment, about 84% of total phosphorus and 45% of total chemical oxygen demand were solubilized with the highest H₂O₂ dosage (0.4% H₂O₂ per %TS). The reaction kinetics of soluble chemical oxygen demand revealed activation energy to be in the range of 5–22 kJ mole^?1. The energy required by the processes was approximately 0.16 kWh per liter of dairy manure heated. A higher H₂O₂ dosage used in the system had a better process performance in terms of solids solubilization, reaction kinetics, and energy consumption. Cost-benefit analysis for a farm-scale MW/H₂O₂-AOP treatment system was also presented. The results obtained from this study would provide the basic knowledge for designing an effective farm-scale dairy manure treatment system.