Measurement and modeling of the dry deposition of peroxides

easurements of the dry deposition velocity (V_d) of hydrogen peroxide (H₂O₂) and total organic peroxides (ROOH) were made during four experiments at three forested sites. Details and uncertainties associated with the measurement of peroxide fluxes by the flux-gradient method are discussed. The results are compared to those predicted using a bulk-resistance model of the type commonly used in regional photochemical models. Good agreement between the H₂O₂ V_d measurements and a bulk resistance model is obtained when the model contains a zero surface resistance (R_c) and a common form for the laminar leaf-layer resistance (R_b) based on Schmidt and Prandtl numbers. In this case, a near-zero (<5 s m^-1) surface resistance is confirmed for H₂O₂ within experimental uncertainties. Surface resistances for ROOH were determined to be about 10–15 s m^-1 over a coniferous forest and 20–40 s m^-1 over a deciduous forest. Higher uncertainties for ROOH prevent a detailed analysis of the differences in R_c among forest types. However, the ratio of deposition velocities (ROOH/H₂O₂), computed from normalized concentration gradients, ranged from 0.28 to 0.61 (geometric mean) at the three sites. Differences in molecular diffusivities between H₂O₂ and ROOH can only account for an estimated 16% difference in V_d. Thus, the major constituent of ROOH must also be less soluble and/or less reactive than H₂O₂, which is consistent with the characteristics of methylhydroperoxide (MHP).     

Inhibitory Effects on Esterase Enzymes Buche and Ache in Rainbow Trout (Oncorhyncus mykiss) Produced by the Slow Release Insecticide Chitosan Diethyl Phosphate

The study on the toxicity of chitosan diethyl phosphate (ChDP), a controlled release insecticide, on the activities of butyrylcholinesterase (BuChE) and acetylcholinesterase (AChE) in rainbow trout exposed to this pesticide was carried out. It was found that ChDP reduced BuChE activity in O. mykiss by a factor of eight at 6 days, with high fluctuation to the end of the exposition time at 12 days. The in vitro analysis of brain AChE treated with ChDP and Phenamiphos showed that it was competitively inhibited by both organophosphates. The values obtained for K_m and V_max for the AChE-ChDP (K_m: 21.23 μ M; V_max: 43.10 μ mol/min/g) and AChE-Phenamiphos (K_m: 38.62 μ M; V_max: 38.91 μ mol/min/g) systems were relatively low compared to values of the AChE (control) system (K_m: 62.99 μ M; V_max: 63.29 μ mol/min/g). Results reported in this study confirmed that chitosan diethyl phosphate performs similarly to organophosphate pesticides, producing inhibition in cholinesterases in rainbow trout.     

Assessment of the aerosol water content in urban atmospheric particles by the hygroscopic growth measurements in Sapporo,Japan

Aerosol water content (AWC) of urban atmospheric particles was investigated based on the hygroscopic growth measurements for 100 and 200 nm particles using a hygroscopicity tandem differential mobility analyzer in Sapporo, Japan in July 2006. In most of the humidogram measurements, presence of less and more hygroscopic mode was evident from the different dependence on relative humidity (RH). The volume of liquid water normalized by that of dry particle (V_w(RH)/V_dry) was estimated from the HTDMA data for 100 and 200 nm particles. The RH dependence of V_w(RH)/V_dry was well represented by a fitted curve with a hygroscopicity parameter κ_eff. The κ_eff values for 200 nm particles were in general higher than those for 100 nm particles, indicating a higher hygroscopicity of 200 nm particles. Based on the κ_eff values, the volume mixing ratios of water-soluble inorganic compounds (ammonium sulfate equivalent) were estimated to be on average 31% and 45% for 100 and 200 nm particles, respectively. The diurnal variation of κ_eff, with relatively higher values in the noontime and nighttime and lower values in the morning and evening hours, was observed for both particle sizes. The V_w(RH)/V_dry values under ambient RH conditions were estimated from κ_eff to range from 0.05 to 2.32 and 0.06 to 2.43 for 100 nm and 200 nm particles, respectively. The degree of correlation between κ_eff and V_w(RH)/V_dry at ambient RH suggests a significant contribution of the variation of κ_eff to atmospheric AWC in Sapporo.     

Effects of ammonia from livestock farming on lichen photosynthesis

This study investigated if atmospheric ammonia (NH₃) pollution around a sheep farm influences the photosynthetic performance of the lichens Evernia prunastri and Pseudevernia furfuracea. Thalli of both species were transplanted for up to 30 days in a semi-arid region (Crete, Greece), at sites with concentrations of atmospheric ammonia of ca. 60 μg/m³ (at a sheep farm), ca. 15 μg/m³ (60 m from the sheep farm) and ca. 2 μg/m³ (a remote area 5 km away). Lichen photosynthesis was analysed by the chlorophyll a fluorescence emission to identify targets of ammonia pollution. The results indicated that the photosystem II of the two lichens exposed to NH₃ is susceptible to this pollutant in the gas-phase. The parameter PI_ABS, a global index of photosynthetic performance that combines in a single expression the three functional steps of the photosynthetic activity (light absorption, excitation energy trapping, and conversion of excitation energy to electron transport) was much more sensitive to NH₃ than the F_V/F_M ratio, one of the most commonly used stress indicators.     

Alleviating versus stimulating effects of bicarbonate on the growth of Vallisneria natans under ammonia stress

Bicarbonate plays a crucial role in limiting the growth of submersed aquatic macrophytes in eutrophic lakes, and high ammonia is often toxic to macrophytes. In order to evaluate the combined effect of HCO₃ ^? and total ammonia (i.e., the total of NH₃ and NH₄ ⁺) on submersed macrophytes Vallisneria natans, the growth and physiological response of V. natans in the presence of HCO₃ ^? and ammonia were studied. The results showed that with the increase of ammonia, morphological parameters of V. natans declined. In contrast, increased HCO₃ ^? concentration stimulated the growth of V. natans, especially when the NH₄ ⁺-N/NO₃ ^?-N ratio was 1:7. High ammonia concentration induced excess free amino acids (FAA) accumulation and soluble carbohydrates (SC) depletion in plant tissues. However, the elevated HCO₃ ^? promoted the synthesis of SC and rendered the decrease of FAA/SC ratio. The results also suggested that HCO₃ ^? could partially alleviate the stress of ammonia, as evidenced by the decrease of FAA/SC ratio and the growth enhancement of V. natans when the ammonia concentration was 0.58 mg?L^?1. Given the fact that HCO₃ ^? is probably the dominant available carbon source in most eutrophic lakes, the ability of V. natans to use HCO₃ ^? for SC synthesis may explain the alleviating effect of HCO₃ ^? on V. natans under ammonia stress.     

Leaching potential of phenylurea herbicides in a calcareous soil: comparison of column elution and batch studies

The transfer of eleven phenylurea herbicides through soil columns was investigated in laboratory conditions in order to determine leaching properties in a calcareous soil. Elution curves with distilled water were plotted after herbicide application on the soil column. Phenylurea retention by the soil indicating interactions with soil can be classified as follows: fenuron < fluometron ≤ isoproturon = monuron < metoxuron < monolinuron < metobromuron < chlorotoluron < linuron = diuron < chlorbromuron. The number and nature of halogen atoms on the phenyl ring had an important influence on leaching. Retention was higher for molecules with higher number of halogen, and it was also higher for bromine than chlorine. Column elution experiments were compared to batch experiments from which the distribution coefficients K _d were determined. According to Kendall correlation coefficients, parameter m/m _0max from column experiments was relatively well linked to K _d. In case of phenylurea, a linear relationship between K _d and m/m _0max was established.     

Dimensionless correlations to predict VOC emissions from dry building materials

Based on the most recently published mass transfer model of volatile organic compound (VOC) emissions from dry building materials, it is found that the dimensionless emission rate and total emission quantity are functions of just four dimensionless parameters, the ratio of mass transfer Biot number to partition coefficient (Bi_m/K), the mass transfer Fourier number (Fo_m), the dimensionless air exchange rate (Nδ²/D_m) and the ratio of building material volume to chamber or room volume (Aδ/V). Through numerical analysis and data fitting, a group of dimensionless correlations for estimating the emission rate from dry building materials is obtained. The predictions of the correlations are validated against the predictions made by the mass transfer model. Using the correlations, the VOC emission rate from dry building materials can be conveniently calculated without having to solve the complicated mass transfer equations. Thus it is very simple to estimate VOC emissions for a given condition. The predictions of the correlations agree well with experimental data in the literature except in the initial few hours. Furthermore, based on the correlations, a relationship between the emission rates of a material in two different situations is deduced. With this relationship, the results for a given building material in a test chamber can be scaled to those under real conditions, if the dimensionless parameters are within the appropriate region for the correlations. The relationship also explicitly explains the impacts of air velocity, load ratio, and air exchange rate on the VOC emission rate, which determines the feasibility of assuming that the VOC emission rates in real conditions are the same as those in the test chambers.     

B-type esterases in the snail Xeropicta derbentina: an enzymological analysis to evaluate their use as biomarkers of pesticide exposure

The study was prompted to characterize the B-type esterase activities in the terrestrial snail Xeropicta derbentina and to evaluate its sensitivity to organophosphorus and carbamate pesticides. Specific cholinesterase and carboxylesterase activities were mainly obtained with acetylthiocholine (K_m = 77.2 mM; V_max = 38.2 mU/mg protein) and 1-naphthyl acetate (K_m = 222 mM, V_max = 1095 mU/mg protein) substrates, respectively. Acetylcholinesterase activity was concentration-dependently inhibited by chlorpyrifos-oxon, dichlorvos, carbaryl and carbofuran (IC50 = 1.35 × 10⁻⁵-3.80 × 10⁻⁸ M). The organophosphate-inhibited acetylcholinesterase activity was reactivated in the presence of pyridine-2-aldoxime methochloride. Carboxylesterase activity was inhibited by organophosphorus insecticides (IC50 = 1.20 × 10⁻⁵-2.98 × 10⁻⁸ M) but not by carbamates. B-esterase-specific differences in the inhibition by organophosphates and carbamates are discussed with respect to the buffering capacity of the carboxylesterase to reduce pesticide toxicity. These results suggest that B-type esterases in X. derbentina are suitable biomarkers of pesticide exposure and that this snail could be used as sentinel species in field monitoring of Mediterranean climate regions.     

Enhanced UV-B and Elevated CO<Subscript>2</Subscript> Impacts Sub-Arctic Shrub Berry Abundance,Quality and Seed Germination

This study investigated the effects of long-term-enhanced UV-B, and combined UV-B with elevated CO₂ on dwarf shrub berry characteristics in a sub-arctic heath community. Germination of Vaccinium myrtillus was enhanced in seeds produced at elevated UV-B, but seed numbers and berry size were unaffected. Elevated UV-B and CO₂ stimulated the abundance of V. myrtillus berries, whilst UV-B alone stimulated the berry abundance of V. vitis-idaea and Empetrum hermaphroditum. Enhanced UV-B reduced concentrations of several polyphenolics in V. myrtillus berries, whilst elevated CO₂ increased quercetin glycosides in V. myrtillus, and syringetin glycosides and anthocyanins in E. hermaphroditum berries. UV-B × CO₂ interactions were found for total anthocyanins, delphinidin-3-hexoside and peonidin-3-pentosidein in V. myrtillus berries but not E. hermaphroditum. Results suggest positive impacts of UV-B on the germination of V. myrtillus and species-specific impacts of UV-B × elevated CO₂ on berry abundance and quality. The findings have relevance and implications for human and animal consumers plus seed dispersal and seedling establishment.     

Seasonal variations of particle-associated nitrosamines by gas chromatography–mass spectrometry in the atmospheric environment of Zonguldak, Turkey

A gas chromatography–mass spectrometry method has been proposed for the determination of low-level mutagenic and carcinogenic nitrosamines in particulate matter. The method includes the collection of particulate matters (PM_2.5 and PM₁₀) using a dichotomous Partisol 2025 sampler and extraction of the compounds from aqueous solution with dichloromethane/2-propanol after sonication with a slightly basic water solution prior to their GC-MS analysis in electron impact mode. The obtained recoveries of nitrosamines ranged from 92.4 to 99.2 %, and the precision of this method, as indicated by the relative standard deviations, was within the range of 0.95–2.46?%. The detection limits obtained from calculations using the GC-MS results based on S/N?=?3 were found within the range from 4 to 22 pg/m³. The predominant nitrosamines determined in particulate matter were N-nitrosodimethylamine, N-nitrosodiethylamine, N-nitrosodibutylamine and N-nitrosomorpholine. Furthermore, N-mono- and dinitrosopiperazine and N-nitrosoethylbutylamine were also determined. N-dinitrosopiperazine was detected in PM_2.5 samples at the highest concentrations of up to 22.85 ng/m³ and in PM_2.5–10 samples at concentrations up to 7.60 ng/m³ in winter, whereas it was found in PM_2.5 samples up to 5.15 ng/m³ and in PM_2.5–10 samples up to 3.12 ng/m³ in summer. The total concentrations of nitrosamines were up to 161.4 ng/m³ in fine and 53.90 ng/m³ in coarse fractions in winter, whereas in summer were up to 35.24 and 12.60 ng/m³, respectively. The concentration levels of nitrosamines fluctuated significantly within a year, with higher means and peak concentrations in the winter compared to that in the summertime. The seasonal variations of particle-associated nitrosamine concentrations were investigated together with their relationships with meteorological parameters using Pearson’s correlation analysis in the winter and summer periods. Analysis of variance was used to determine which concentrations of nitrosamines were statistically different from one another and, together with meteorological parameters and discriminant analysis, was used to classify the particle samples by particle size according to seasons. The classification results of the particle samples in different seasons were very satisfactory, allowing 99.5 % of cases to be correctly grouped.     

Atmospheric corrosion effects of HNO3—Comparison of laboratory-exposed copper,zinc and carbon steel

The influence of nitric acid (HNO₃) on the atmospheric corrosion of copper, zinc and carbon steel was investigated in laboratory exposures at 65% relative humidity (RH), 25 °C and 0.03 cm s⁻¹ air velocity. The deposition velocity (V_d) of HNO₃ on the specimens, the corrosion rates and corrosion products were determined by gravimetry, ion chromatography, X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) microspectroscopy. Comparisons were also made with literature data on the corrosion effects of sulfur dioxide (SO₂), nitrogen dioxide (NO₂) and ozone (O₃).At 65% RH, the V_d of HNO₃ on all metals was at least 70% of that of an ideal absorbent, i.e., an impregnated filter with perfect absorption for HNO₃. The V_d of HNO₃ was much higher than that of SO₂, NO₂ or O₃, which is mainly attributed to the relatively high sticking coefficient, high solubility and high reactivity of HNO₃ compared to the other gases. During identical exposures to HNO₃, the corrosion rate of carbon steel was nearly three times higher than that of copper or zinc. However, when comparing the corrosion effects induced by HNO₃ with those induced by SO₂ alone or in combination with either NO₂ or O₃, HNO₃ turned out to be far more aggressive than SO₂. Relative to SO₂, zinc is the metal most sensitive to HNO₃, followed by copper and with carbon steel least sensitive to HNO₃.     

Hydrolysis of di-n-butyl phthalate, butylbenzyl phthalate and di(2-ethylhexyl) phthalate in human liver microsomes

Diester phthalates are industrial chemicals used primarily as plasticizers to import flexibility to polyvinylchloride plastics. In this study, we examined the hydrolysis of di-n-butyl phthalate (DBP), butylbenzyl phthalate (BBzP) and di(2-ethylhexyl) phthalate (DEHP) in human liver microsomes. These diester phthalates were hydrolyzed to monoester phthalates (mono-n-butyl phthalate (MBP) from DBP, mono-n-butyl phthalate (MBP) and monobenzyl phthalate (MBzP) from BBzP, and mono(2-ethylhexyl) phthalate (MEHP)) by human liver microsomes. DBP, BBzP and DEHP hydrolysis showed sigmoidal kinetics in V-[S] plots, and the Hill coefficient (n) ranged 1.37-1.96. The S₅₀, V_max and CL_max values for DBP hydrolysis to MBP were 99.7 μM, 17.2 nmol min⁻¹ mg⁻¹ protein and 85.6 μL min⁻¹ mg⁻¹ protein, respectively. In BBzP hydrolysis, the values of S₅₀ (71.7 μM), V_max (13.0 nmol min⁻¹ mg⁻¹ protein) and CL_max (91.3 μL min⁻¹ mg⁻¹ protein) for MBzP formation were comparable to those of DBP hydrolysis. Although the S₅₀ value for MBP formation was comparable to that of MBzP formation, the V_max and CL_max values were markedly lower (<3%) than those for MBzP formation. The S₅₀, V_max and CL_max values for DEHP hydrolysis were 8.40 μM, 0.43 nmol min⁻¹ mg⁻¹ protein and 27.5 μL min⁻¹ mg⁻¹ protein, respectively. The S₅₀ value was about 10% of DBP and BBzP hydrolysis, and the V_max value was also markedly lower (<3%) than those for DBP hydrolysis and MBzP formation for BBzP hydrolysis. The ranking order of CL_max values for monoester phthalate formation in DBP, BBzP and DEHP hydrolysis was BBzP to MBzP ? DBP to MBP > DEHP to MEHP > BBzP to MBP. These findings suggest that the hydrolysis activities of diester phthalates by human liver microsomes depend on the chemical structure, and that the metabolism profile may relate to diester phthalate toxicities, such as hormone disruption and reproductive effects.     

Precision of atmospheric dry deposition data from the Clean Air Status and Trends Network

A collocated, dry deposition sampling program was begun in January 1987 by the US Environmental Protection Agency to provide ongoing estimates of the overall precision of dry deposition and supporting data entering the Clean Air Status and Trends Network (CASTNet) archive. Duplicate sets of dry deposition sampling instruments were installed adjacent to existing instruments and have been operated for various periods at 11 collocated field sites. All sampling and operations were performed using standard CASTNet procedures. The current study documents the bias-corrected precision of CASTNet data based on collocated measurements made at paired sampling sites representative of sites across the network. These precision estimates include the variability for all operations from sampling to data storage in the archive. Precision estimates are provided for hourly, instrumental ozone (O₃) concentration and meteorological measurements, hourly model estimates of deposition velocity (V_d) from collocated measurements of model inputs, hourly O₃ deposition estimates, weekly filter pack determinations of selected atmospheric chemical species, and weekly estimates of V_d and deposition for each monitored filter pack chemical species and O₃.Estimates of variability of weekly pollutant concentrations, expressed as coefficients of variation, depend on chemical species: NO₃⁻∼8.1%; HNO₃∼6.4%; SO₂∼4.3%; NH₄⁺∼3.7%; SO₄²⁻∼2.3%; and O₃∼1.3%. Precision of estimates of weekly V_d from collocated measurements of model inputs also depends on the chemical species: aerosols ∼2.8%; HNO₃∼2.6%; SO₂∼3.0%; and O₃∼2.0%. Corresponding precision of weekly deposition estimates are: NO₃⁻∼8.6%; HNO₃⁻∼5.2%; SO₂∼5.6%; NH₄⁺∼3.9%; SO₄²⁻∼3.5%; and O₃∼3.3%. Precision of weekly concentration, V_d estimates, and deposition estimates are comparable in magnitude and slightly smaller than the corresponding hourly values. Annual precision estimates, although uncertain due to their small sample size in the current study, are consistent with the corresponding weekly values.     

A flux-based assessment of the effects of ozone on foliar injury, photosynthesis, and yield of bean (Phaseolus vulgaris L. cv. Borlotto Nano Lingua di Fuoco) in open-top chambers

Stomatal ozone uptake, determined with the Jarvis' approach, was related to photosynthetic efficiency assessed by chlorophyll fluorescence and reflectance measurements in open-top chamber experiments on Phaseolus vulgaris. The effects of O₃ exposure were also evaluated in terms of visible and microscopical leaf injury and plant productivity. Results showed that microscopical leaf symptoms, assessed as cell death and H₂O₂ accumulation, preceded by 3-4 days the appearance of visible symptoms. An effective dose of ozone stomatal flux for visible leaf damages was found around 1.33 mmol O₃ m⁻². Significant linear dose-response relationships were obtained between accumulated fluxes and optical indices (PRI, NDI, ΔF/F_m^′). The negative effects on photosynthesis reduced plant productivity, affecting the number of pods and seeds, but not seed weight. These results, besides contributing to the development of a flux-based ozone risk assessment for crops in Europe, highlight the potentiality of reflectance measurements for the early detection of ozone stress.     

多层生物滤塔净化硫化氢废气研究

以木屑为填料,采用多层生物滤塔净化H2S气体,研究其适宜的工艺条件及生物降解宏观动力学.结果表明,填料分层可提高H2S去除率,当进气容积负荷＜153.2 g H2S/(m3·d)时,H2S的去除率保持在90%以上;进气浓度低于70 mg/m3,下层200mm填料对H2S总去除率的贡献在50%以上;填料含水率为50%～6...     

Washout ratios of nitrate,non-sea-salt sulfate and sea-salt on Virginia key,Florida and on American Samoa

On Virginia Key, Miami, Florida, 257 rainwater samples were collected on a event basis from May 1982 to April 1985. At the same site, 171 aerosol samples were collected throughout 1984. All of these samples were analyzed for nitrate, non-sea-salt (NSS) sulfate and sodium to assess the temporal variations in the concentrations and to determine the washout ratios of each of the constituents. The annual volume-weighted mean concentrations in rainwater are: nitrate—0.51 μg ml⁻¹; NSS sulfate—0.74 μg ml⁻¹; Na—1.93 μg ml⁻¹. Only sodium exhibited a significant seasonal cycle; its concentrations were markedly higher during the winter. In aerosols, the mean concentrations are: nitrate—1.9 μg m⁻³; NSS sulfate—2.8 μg m³; Na—3.7 μg m⁻³. Nitrate and NSS sulfate exhibit consistent seasonal cycles with concentrations being significantly higher during the winter and spring. We estimate that wet deposition accounts for the majority of the total fluxes of each constituent: 80% for nitrate, 95 % for NSS sulfate, and 67% for Na. Annual washout ratios at Virginia Key arc similar for nitrate and NSS sulfate, 330 and 290, respectively. That for Na is about a factor of two higher, 550. Comparable long-term ratios were calculated for American Samoa based on aerosol data from the SEAREX program and rainwater data from the National Atmospheric Deposition Program: 270 for nitrate, 420 for NSS sulfate, and 520 for Na. The comparability of the Virginia Key and Samoa results suggest that these ratios may be applicable over a wide area of the world ocean. Estimates from nonconcurrent data for the washout ratios at Bermuda were factors of two to four higher. Regression equations for washout ratio vs event rainfall (logW = loga + blogR) at Virginia Key were essentially the same for all three constituents with ‘a’ ranging from 1100 to 1300 and ‘b’ ranging from −0.26 to −0.29. The coefficients for American Samoa were markedly different: ‘a’ ranged from 2900 to 3600 and ‘b’ ranged from −0.51 to −0.56.     

Kinetics of phenol biodegradation at high concentration by a metabolically versatile isolated yeast Candida tropicalis PHB5

A highly tolerant phenol-degrading yeast strain PHB5 was isolated from wastewater effluent of a coke oven plant and identified as Candida tropicalis based on phylogenetic analysis. Biodegradation experiments with C. tropicalis PHB5 showed that the strain was able to utilize 99.4 % of 2,400 mg l^?1 phenol as sole source of carbon and energy within 48 h. Strain PHB5 was also observed to grow on 18 various aromatic hydrocarbons. Haldane model was used to fit the exponential growth data and the following kinetic parameters were obtained: μ _max?=?0.3407 h^?1, K _S?=?15.81 mg l^?1, K _i?=?169.0 mg l^?1 (R ²?=?0.9886). The true specific growth rate, calculated from μ _max, was 0.2113. A volumetric phenol degradation rate (V _max) was calculated by fitting the phenol consumption data with Gompertz model and specific degradation rate (q) was calculated from V _max. The q values were fitted with Haldane model, yielding following parameters: q _max?=?0.2766 g g^?1 h^?1, K _S ′?=?2.819 mg l^?1, K _i ′?=?2,093 (R ²?=?0.8176). The yield factor (Y _X/S ) varied between 0.185 to 0.96 g g^?1 for different initial phenol concentrations. Phenol degradation by the strain proceeded through a pathway involving production of intermediates such as catechol and cis,cis-muconic acid which were identified by enzymatic assays and HPLC analysis.     

Characterization of PM2.5-bound polycyclic aromatic hydrocarbons in Atlanta

Twenty-four hour PM_2.5 samples from a rural site, an urban site, and a suburban site (next to a major highway) in the metropolitan Atlanta area in December 2003 and June 2004 were analyzed for 19 polycyclic aromatic hydrocarbons (PAH). Extraction of the air samples was conducted using an accelerated solvent extraction method followed by isotope dilution gas chromatography/mass spectrometry determination. Distinct seasonal variations were observed in total PAH concentration (i.e. significantly higher concentrations in December than in June). Mean concentrations for total particulate PAHs in December were 3.16, 4.13, and 3.40 ng m^?3 for the urban, suburban and rural sites, respectively, compared with 0.60, 0.74, and 0.24 ng m^?3 in June. Overall, the suburban site, which is impacted by a nearby major highway, had higher PAH concentration than did the urban site. Total PAH concentrations were found to be well correlated with PM_2.5, organic carbon (OC), and elemental carbon (EC) in both months (r² = 0.36–0.78, p < 0.05), although the slopes from the two months were different. PAHs represented on average 0.006% of total PM_2.5 mass and 0.017% of OC in June, compared with 0.033% of total PM_2.5 and 0.14% of OC in December. Total PAH concentrations were also correlated with potassium ion (r² = 0.39, p = 0.014) in December, but not in June, suggesting that in winter biomass burning can potentially be an important source for particulate PAH. Retene was found at a higher median air concentration at the rural site than at the urban and suburban sites—unlike the rest of the PAHs, which were found at lower levels at the rural site. Retene also had a larger seasonal difference and had the weakest correlation with the rest of the PAHs measured, suggesting that retene, in particular, might be associated with biomass burning.     

Solubility of organic acids in various methanol and salt concentrations: the implication on organic acid sorption in a cosolvent system

The well-known cosolvency-induced sorption model is not applicable to predict the sorption of carboxylic acids in cosolvent system. To investigate the phenomenon, sorption and solubility of chlorinated phenols (2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP)) and carboxylic acids (benzoic acid and 2,4-dichlorophenoxyacetic acid (2,4-D)) were measured in soil-methanol mixture with various ionic strengths. The sorption (K_m) of chlorinated phenols was explained by a cosolvency-induced sorption model; the inverse log-linear relationship between the K_m and methanol volume fraction (f_c). However, the K_m of carboxylic acids increased with increasing f_c. This discrepancy was attributed to the effect of the carboxylic moiety. To explain the effect, solubility was measured for benzoic acid and 2,4,6-TCP from various liquid conditions. For both solutes, the cosolvency power (σ) increased with CaCl₂ concentrations and the salting constant (K^s) became smaller as f_c increased. However, the σ value at a given salt concentration and the K^s value at a given f_c were greater for 2,4,6-TCP than for benzoic acid, both of which were due to the greater hydrophobicity of the former. Overall, the solubility profiles of the both solutes on combination of f_c and CaCl₂ concentration evidenced no specific role of the carboxylic moiety. Therefore, it can be reasonably concluded that the positive relationship between K_m and f_c for carboxylic organic acid can be attributed to the modification of the activity coefficient occurred in the solid phase, which cannot be traceable by cosolvency-based model.