Reduction of biogenic VOC sampling losses from ozone via trans-2-butene addition

The continuous addition of trans-2-butene to air containing ozone-reactive volatile and semivolatile organic compounds prior to sampling on Tenax-TA adsorbent was found to be an effective means of removing ozone and reducing analyte losses of ozone reactive biogenic volatile organic compounds (BVOCs). To allow sufficient time for ozone scavenging to occur, the reacting mixture is passed through a heated (40 degrees C) coil of Sulfinert (Restek Corp., Bellefonte, PA) treated stainless steel tubing. The method was evaluated using a test mixture consisting of terpenes, terpenoid alcohols, and sesquiterpenes at part per trillion (pptv) levels in air in the presence of 100 parts per billion (ppbv) of ozone. The continuous addition of trans-2-butene to produce 600 ppm (ppmv) was found to be completely effective in controlling VOC losses on Tenax-TA as long as (1) sufficient time is allowed for the ozone scavenging to occur before the VOCs are adsorbed and (2) analyte enrichment on the adsorbentdoes not approach the hydroxyl radical scavenging capacity of the trans-2-butene. A manganese dioxide (MnO2) coated copper screen ozone scrubber was also tested and found to be of very limited utility.     

Measurement of atmospheric ozone by cavity ring-down spectroscopy

Ozone plays a key role in both the Earth's radiative budget and photochemistry. Accurate, robust analytical techniques for measuring its atmospheric abundance are of critical importance. Cavity ring-down spectroscopy has been successfully used for sensitive and accurate measurements of many atmospheric species. However, this technique has not been used for atmospheric measurements of ozone, because the strongest ozone absorption bands occur in the ultraviolet spectral region, where Rayleigh and Mie scattering cause significant cavity losses and dielectric mirror reflectivities are limited. Here, we describe a compact instrument that measures O3 by chemical conversion to NO2 in excess NO, with subsequent detection by cavity ring-down spectroscopy. This method provides a simple, accurate, and high-precision measurement of atmospheric ozone. The instrument consists of two channels. The sum of NO2 and converted O3 (defined as Ox) is measured in the first channel, while NO2 alone is measured in the second channel. NO2 is directly detected in each channel by cavity ring-down spectroscopy with a laser diode light source at 404 nm. The limit of detection for O3 is 26 pptv (2 sigma precision) at 1 s time resolution. The accuracy of the measurement is ±2.2%, with the largest uncertainty being the effective NO2 absorption cross-section. The linear dynamic range of the instrument has been verified from the detection limit to above 200 ppbv (r2>99.99%). The observed precision on signal (2 sigma) with 41 ppbv O3 is 130 pptv in 1 s. Comparison of this instrument to UV absorbance instruments for ambient O3 concentrations shows linear agreement (r2=99.1%) with slope of 1.012±0.002.     

Sesquiterpene emissions from pine trees--identifications, emission rates and flux estimates for the contiguous United States

Biogenic volatile organic compound (BVOC) emissions were studied using vegetation enclosure experiments. Particular emphasis was given to sesquiterpene compounds (SQT), although monoterpenes (MT) were also characterized. SQT were detected in emissions from seven (out of eight) pine species that were examined. Thirteen SQT compounds were identified; the most abundant ones were beta-caryophyllene, alpha-bergamotene, beta-farnesene, and alpha-farnesene, with emission rates increasing exponentially with temperature. Regression analysis yielded exponential dependencies of both MT and SQT emissions on temperature of the form E = E0 x exp(beta(T - T0)). This resulted in SQT basal emission rates (E0 defined at T0 = 30 degrees C) ranging between <4 and 620 ng (carbon) gdw(-1) h(-1) (gdw = gram dry weight). The average value of the exponential temperature response factor beta for SQT emissions, taken from all experiments, was 0.17 degree C(-1), whereas the value for monoterpenes was 0.11 degrees C(-1). The average, total SQT emissions from pines were estimated to be 9, 16, and 29% of the MT emissions at 20, 30, and 40 degrees C respectively. The emission factors and beta-factors determined from these measurements were used to estimate pine tree MT and SQT emission distributions for the contiguous United States using MEGAN (model of emissions of gases and aerosols from nature, Guenther et al., 2006). SQT fluxes reaching 10-40 mg m(-2) for the month of July were estimated for extensive areas of most western and southern U.S. states.     

Monoterpene and sesquiterpene emission estimates for the United States

Biogenic volatile organic compounds (BVOC) contribute significantly to the formation of ozone and secondary organic aerosol (SOA). The Model of Emissions of Gases and Aerosols from Nature (MEGANv2.02) is used to estimate emissions of isoprene, monoterpenes (MT), and sesquiterpenes (SQT) across the United States. Compared to the Biogenic Emission Inventory System (BEIS3.0), MEGANv2.02 estimates higher isoprene but lower MT emissions for July 2001 and January 2002. A sensitivity study of SQT and MT emission factors and algorithm parameters was conducted by assigning values to four plant functional types (PFTs) using both recent measurements and literature values. The standard deviations of the emissions factors within these PFTs were two to four times the averages because of the variation in experimental basal emissions rate data. More recently published SQT and MT basal emission rates are generally lower than those reported in the literature through 2004. With the new emissions factors, monthly average SQT emission rates for the contiguous United States are equal to 16% of the MT emissions during July and 9% of the emissions during January. The SQT emissions distribution is strongly influenced by the grass and crop PFT, for which SQT emissions data are quite limited.     

Ozone removal in the sampling of parts per billion levels of terpenoid compounds: an evaluation of different scrubber materials

Some reactive volatile organic compounds (VOCs) are prone to degradation during sampling in an ozone-rich environment. A wide variety of different chemicals have been used to remove the ozone prior to sampling, but the possibility of interference by such chemicals with the sampled VOCs has not been thoroughly examined. In the present investigation, the retention/degradation of four terpenes (alpha-pinene, beta-pinene, 3-carene, and limonene) and isoprene together with some of their oxidation products (alpha-pinene oxide, nopinone, 4-acetyl-1-methylcyclohexene (AMCH), methylglyoxal, and methacrolein) has been studied, using various ozone-removing chemicals in an attempt to evaluate their potential as ozone scrubbers in the sampling of ambient air. The chemicals included in this first screening and their ozone-removing capacity are as follows: KI, MnO2, and Na2SO3 removed ozone for more than 24 h when exposed to 73-78 ppb (150-160 microg/m3) at a sampling flow rate of 500 mL/min. Silanized poly(1,4-phenylene sulfide) (PFS) removed ozone for 5 h, unsilanized PFS removed ozone for 1 h and 50 min, and Na2S2O3 removed ozone for 20 min. The recovery of the selected compounds with the different scrubbers was >95% for all compounds for KI; >95% for the terpenes oxidation products; >90% for the terpenes and isoprene for PFS; >90% for the terpenes and isoprene for MnO2 on copper nets, Na2SO3, and Na2S2O3; and <90% for the terpenes and isoprene for carulite (a commercial mixture between MnO2, CuO, and Al2O3), CuO, and indigo carmine.     

Distribution of volatile organic compounds over a semiconductor Industrial Park in Taiwan

This study examined volatile organic compounds (VOC) concentration in ambient air collected during the years 2000--2003 at several different locations of Hsinchu Science-based Industrial Park (HSIP) in Taiwan. A canister automated GC-MS system analyzed the volatile organics in ambient air grasp samples according to T0-15 method. Oxygenated volatiles were the most abundant VOC detected in HSIP followed by aromatics that are commonly used as solvents in the semiconductor industries. The major components measured in the ambient air are 2-propanol (29-135 ppbv), acetone (12-164 ppbv), benzene (0.7-1.7 ppbv), and toluene (13-20 ppbv). At some of the sampling locations, odorous compounds such as carbon disulfide and dimethyl sulfide levels exceed threshold values. The estimated toluene/benzene ratio is very high at most of the sites. However, the total amount of VOC is reduced over the years from 2000 to 2003 due to strict implementation on use and discharge of solvents in industries. There exists no definite seasonal pattern for sporadic occurrence of high levels of some of the volatile organics. Stagnant weather conditions with low wind speeds aid accumulation of toxic species at ground level. The results entail that hi-tech semiconductor industries are still a potential source for harmful organic substances to surrounding microenvironment.     

Mechanism and elimination of a water vapor interference in the measurement of ozone by UV absorbance

A water vapor interference in ozone measurements by UV absorption was investigated using four different ozone monitors (TEI models 49 and 49C, Dasibi model 1003-AH, and a 2B Technologies model 202 prototype). In the extreme case of step changes between 0 and 90% relative humidity (RH), a large interference in the range of tens to hundreds of ppbv was found for all instruments tested, with the magnitude and sign depending on the manufacturer and model. Considering that water vapor does not absorb at the wavelength of the Hg lamp (253.7 nm) used in these instruments, another explanation is required. Based on experimental evidence and theoretical considerations, we conclude that the water vapor interference is caused by humidity effects on the transmission of uncollimated UV light through the detection cell. The ozone scrubber acts as a water reservoir, either adding or removing water from the air sample, thereby modulating the detector signal and producing a positive or negative offset. It was found for the 2B Technologies ozone monitor that use of a 1-m length of Nafion tubing just prior to the entrance to the detection cell reduces the water vapor interference to negligible levels (+/- 2 ppbv for step changes between 0 and 90% RH) while quantitatively passing ozone.     

Determination of the specific surface area of snow using ozonation of 1,1-diphenylethylene

We measured the kinetics of ozonation reaction of 1,1-diphenylethylene (DPE) in artificial snow, produced by shock freezing of DPE aqueous solutions sprayed into liquid nitrogen. It was demonstrated that most of the reactant molecules are in direct (productive) contact with gaseous ozone, thus the technique produces snow with organic molecules largely ejected to the surface of snow grains. The kinetic data were used to evaluate the snow specific surface area (～70 cm(2) g(-1)). This number is a measure of the availability of the molecules on the surface for chemical reaction with gaseous species. The experimental results were consistent with the Langmuir-Hinshelwood type reaction mechanism. DPE represents environmentally relevant compounds such as alkenes which can react with atmospheric ozone, and are relatively abundant in natural snow. For typical atmospheric ozone concentrations in polar areas (20 ppbv), we estimated that half-life of DPE on the surface of snow grains is ～5 days at submonolayer coverages and -15 °C.     

Influence of the cultivation system in the aroma of the volatile compounds and total antioxidant activity of passion fruit

The aim of this study was to investigate the influence of the cultivation system on the volatile composition of the passion fruit and to determine the odoriferous contribution of the compounds for the aroma of the organic and conventional fruit, besides to assess the total antioxidant activity. The volatile compounds were isolated from dynamic headspace, separated by high-resolution gas chromatography and the odoriferous contribution to the passion fruit aroma was evaluated using the OSME technique. Total antioxidant activity was determined using the ABTS radical reaction. The organic and conventional passion fruit showed similar volatile profile, although some differences occurred. Ethyl 2-propenoate, 2-methyl-1-propanol, diethyl carbonate and ethyl hexanoate were threefold higher in the organic fruit while butyl acetate, hexanal, cis-3-hexenyl acetate and trans-3-hexenyl butanoate were threefold higher in the conventional fruit. Hexanoate and acetate esters, and saturated alcohols described as fruity, sweet, citrus and passion-fruit aroma showed the highest odorific intensity in the organic fruit. Furthermore, trans and cis-3-hexenyl acetate and alpha-copaene, alpha-terpineol, D-limonene, trans-beta-ocimene and delta-cadinene had higher contribution to the organic passion fruit aroma. On the other hand, unsaturated alcohols, beta-myrcene and beta-linalool described as grass, sulfur-like and passion-fruit aroma were higher in the conventional fruit. The organic passion fruit showed higher levels of total phenolic compounds and total antioxidant activity than the conventional fruit, suggesting that the cultivation system influenced the production of antioxidant bioactive compounds.     

Ozone levels in passenger cabins of commercial aircraft on North American and transoceanic routes

Ozone levels in airplane cabins, and factors that influence them, were studied on northern hemisphere commercial passenger flights on domestic U.S., transatlantic, and transpacific routes. Real-time data from 76 flights were collected in 2006--2007 with a battery-powered UV photometric monitor. Sample mean ozone level, peak-hour ozone level, and flight-integrated ozone exposures were highly variable across domestic segments (N = 68), with ranges of < 1.5 to 146 parts per billion by volume (ppbv), 3--275 ppbv, and < 1.5 to 488 ppbv-hour, respectively. On planes equipped with ozone catalysts, the mean peak-hour ozone level (4.7 ppbv, N = 22)was substantially lower than on planes not equipped with catalysts (47 ppbv, N = 46). Peak-hour ozone levels on eight transoceanic flight segments, all on planes equipped with ozone catalysts, were in the range < 1.5 to 58 ppbv. Seasonal variation on domestic routes without converters is reasonably modeled by a sinusoidal curve that predicts peak-hour levels to be approximately 70 ppbv higher in Feb--March than in Aug--Sept The temporal trend is broadly consistent with expectations, given the seasonal cycle in tropopause height. Episodically elevated (>100 ppbv) ozone levels on domestic flights were associated with winter-spring storms that are linked to enhanced exchange between the lower stratosphere and the upper troposphere.     

Verifying three types of methane fluxes from soils by testing the performance of a novel mobile photoacoustic method versus a well-established gas chromatographic one

The performance of a novel portable, tunable diode laser, resonant photoacoustic (TDL-PA) analyzer developed for field measurements of CH4 was compared to a commonly applied offline gas chromatographic (GC) method. This comparative studywas realized under normal field conditions parallel to long-term weekly GC monitoring of four different soil types with very different methane budgets. The method used for gas-exchange measurements was the well-known closed-chamber technique. The TDL-PA analyzer detects methane at 1650.957 nm [R (5) line of the 2v3 band], guaranteeing high precision without the need for correction procedures. The two techniques correlated well (R2 = 0.988) over the entire concentration range (0.15-33 ppmv CH4) tested at highly varying flux rates between -30 and -12 ppbv CH4 min(-1) for uptakes and between 2.5 and 362 ppbv CH4 min(-1) for emissions. The two analyzers proved to be interchangeable, leaving the online advantages to the TDL-PA. A suitable CH4 online GC solution for chamber measurement is not available as a portable system. Additionally, the data sampling rate of 2 Hz enables a direct coupling to other infrared gas analyzers with the high time resolution commonly required to determine plant CO2 assimilation rates or soil respiration rates.     

Oxidation of antibacterial molecules by aqueous ozone: moiety-specific reaction kinetics and application to ozone-based wastewater treatment

Ozone and hydroxyl radical (*OH) reaction kinetics were measured for 14 antibacterial compounds from nine structural families, to determine whether municipal wastewater ozonation is likely to result in selective oxidation of these compounds' biochemically essential moieties. Each substrate is oxidized by ozone with an apparent second-order rate constant, k'(O3,app) > 1 x 10(3) M(-1) s(-1), at pH 7, with the exception of N(4)-acetylsulfamethoxazole (K'(O3,app) is 2.5 x 102 M(-1) s(-1)). k'(O3,app) values (pH 7) for macrolides, sulfamethoxazole, trimethoprim, tetracycline, vancomycin, and amikacin appear to correspond directly to oxidation of biochemically essential moieties. Initial reactions of ozone with N(4)-acetylsulfamethoxazole, fluoroquinolones, lincomycin, and beta-lactams do not lead to appreciable oxidation of biochemically essential moieties. However, ozone oxidizes these moieties within fluoroquinolones and lincomycin via slower reactions. Measured k'(O3,app) values and second-order *OH rate constants, k'(*OH,app) were utilized to characterize pollutant losses during ozonation of secondary municipal wastewater effluent. These losses were dependent on k'(O3,app), but independent of k'(*OH,app). Ozone doses > or =3 mg/L yielded > or =99% depletion of fast-reacting substrates (K'(O3,app) > 5 x 10(4) M(-1) s(-1)) at pH 7.7. Ten substrates reacted predominantly with ozone; only four were oxidized predominantly by .OH. These results indicate that many antibacterial compounds will be oxidized in wastewater via moiety-specific reactions with ozone.     

Atmospheric size distribution of PAHs: evidence of a high-volume sampling artifact

The purpose of this study was to characterize atmospheric levels of four- to six-ring polycyclic aromatic hydrocarbons (PAHs) in the vicinity of a horizontal stud S?derberg aluminum smelter in terms of the size distribution of particulate matter (September to December 2002). It was found that the vast majority of the PAHs was associated with particle diameters less than 1 and 3 microm. A profile comparison of the PAH mixture--using benzo[a]pyrene (B[a]P) relative abundance ratios (PAH/B[a]P)--for the cascade impactor filters indicated the formation of a sampling artifact. Overall, the PAH stability scale generated in this study agrees with those produced experimentally for ozone and nitrogen dioxides or developed using other in situ measurement techniques. Correlations of the four- to six-ring PAHs with other atmospheric variables suggested that smelter plume conditions and particle characteristics may play a potentially important role in the overall PAH reactivity. To our knowledge, this is the first study to report a sampling artifact for the four- to six-ring PAHs during in situ high volume sampling under real world conditions.     

Measurements of atmospheric carboxylic acids and carbonyl compounds in São Paulo City, Brazil

Winter atmospheric measurements of gaseous lower carbonyl and carboxylic acids were carried out simultaneously (in 1999) at two distinct urban sites located in the city of S?o Paulo, Brazil. The greater metropolitan area of S?o Paulo is the largest industrialized region of Latin America and has a highly polluted atmosphere. It has an unconventional mix of vehicle types in that a variety of gasoline blends, including oxygenated ones, are used. Mixing ratios of formic and acetic acids ranged, respectively, from 0.6 to 19.4 and from 0.1 to 10.6 ppbv in one of the sites studied and from 1.4 to 18.4 and from 0.4 to 6.7 ppbv in the other site. High values of formic to acetic ratios were found, especially in the latter site (average = 4.3), suggesting that photochemical production was the predominant source of the formic and acetic acid during the afternoon. Differing from the acids, levels of carbonyls were similar at both sites. Higher average mixing ratios of acetaldehyde and formaldehyde were found in the morning (18.9 and 17.2 ppbv) and gradually decreased from midday (9.5 and 11.8 ppbv) to evening (7.2 and 10.2 ppbv). In the morning, vehicular direct emission seemed to be the main primary source of formaldehyde and acetaldehyde, whereas at midday and evening these compounds appeared to be mainly formed by photochemistry. Secondary photochemical production of organic acids and aldehydes (rather than primary emissions from vehicles) was shown to be more important in S?o Paulo's atmosphere from midday to evening, particularly on days with strong solar radiation.     

Development and validation of a canister method for measuring ethylene oxide in ambient air

A sampling and analytical method for measuring ethylene oxide (EO) in ambient air was developed and evaluated. The method is based on the use of evacuated canisters and gas chromatography-mass spectrometry (GC-MS). The objectives of this work were to characterize the performance of the method with respect to the following: (1) stability/recovery of ethylene oxide in a canister over a 15-day holding time; (2) detection capability; and (3) measurement of EO in an ambient air matrix. Both electropolished and silica-lined stainless steel canisters were evaluated in this study. The method evaluation involved both laboratory and field tests. The recovery of the EO was evaluated both on an absolute basis and relative to a spiked internal standard of toluene. EO spiked at levels of 2 ppbv and 20 ppbv was found to be stable for holding times of up to 15 days at 25 degrees C in both a humidified nitrogen matrix and in ambient air. The detection limit of the method was found to be 0.25 ppbv using EPA's traditional approach of seven replicate analyses of a low-level standard and 0.20 ppbv using a probability-based approach. EO recoveries in the laboratory stability study generally were 100 +/- 25%, and did not vary by canister type, nor did the EO recoveries decrease with holding time. Field studies demonstrated that the method is capable of detecting EO (as well as benzene and toluene) in an ambient air matrix.     

Automated system for monitoring trace C2H2 in ambient air by cavity ring-down spectroscopy combined with sample preconcentration

A fully automated instrument combining a continuous wave cavity ring-down spectrometer and dual-trap sample preconcentration has been implemented for monitoring C2H2 mixing ratios in ambient air. A distributed feedback diode laser operating in the near-infrared region (lambda approximately 1534.973 nm in air) detects C2H2 in absorption via the P(17) rotational line of the (v1 + v3) vibrational combination band. The instrument is shown to be capable of fast, quantitative, and precise monitoring of C2H2 mixing ratios, with a detection limit of approximately 8 pptv (parts per trillion by volume). It thus has potential to be deployed for analysis of air samples in many rural and urban environments. In situ measurements were carried out at 30 min intervals over periods of up to 15 h on several days for indoor and outdoor air samples. For indoor air monitored on a Sunday, the C2H2 mixing ratio was stable at 1.45 +/- 0.04 ppbv (parts per billion by volume). On weekdays, both indoor and outside air analyses showed peaks in the range 2-4 ppbv in the early morning and late afternoon that coincided with periods of busy road traffic.     

An investigation of the adsorption of C5-C12 hydrocarbons in the ppmv and ppbv ranges on Carbotrap B

The effects of concentration and temperature on the breakthrough volumes (Vb) of 23 volatile organic compounds on Carbotrap B have been determined using the frontal chromatography method. From the measured Vb, original isotherms have been produced and adsorption parameters based on the Langmuir, Freundlich, and Dubinin-Polyani adsorption models have been calculated. The calculated adsorption parameters describe the behavior of these VOC on Carbotrap B under the experimental conditions and are useful data for VOC sampling applications including adsorption modeling of pumped and diffusive sampling. Each of the adsorption models give similar results and are in good agreement with the experimental data in the ppmv concentration range. It will be shown that contrary to previous assumptions the Langmuir adsorption parameters obtained at ppmv concentrations cannot be used to predict Vb at ppbv concentrations and the calculated parameter mmax does not represent the maximum adsorbent capacity. The Freundlich and Dubinin-Polyani models are shown to be more successful in describing the adsorption behavior of the VOC at ppbv levels where Vb is independent of concentration. The isosteric heats of adsorption (-delta Hst) for some of the compounds have been determined using the Van't Hoff equation which can be used to predict the effect of temperature on Vb.     

Remediation of fungicide residues on fresh produce by use of gaseous ozone

Ozone fumigation was explored as a means for degrading organic fungicide residues on fresh produce. Fungicides sorbed onto model abiotic glass surfaces or onto grape berries were fumigated separately in a flow-through chamber. Gaseous ozone at a constant concentration of 150 ± 10 ppmv (μL·L(-1)) selectively oxidized fungicides sorbed to model surfaces. Over 140 min, boscalid and iprodione levels did not change significantly based on a single-factor analysis of variance (ANOVA) at the 95% level of confidence (p = 0.05); however, pseudo-first-order losses resulted in observable rate constants of ozonolysis, k(ozonolysis) (min(-1)), of 0.0233 ± 0.0029 (t(1/2) ≈ 29.7 min), 0.0168 ± 0.0028 (t(1/2) ≈ 41.3 min), and 0.0127 ± 0.0010 (t(1/2) ≈ 54.6 min) for fenhexamid, cyprodinil, and pyrimethanil, respectively. The relative degradation of fungicides on berries at gaseous ozone concentrations of 900 ± 12 ppmv (μL·L(-1)) over 2 h was similar to that on glass; decreases in residue concentration were observed for only fenhexamid (～ 64%), cyprodinil (～ 38%), and pyrimethanil (～ 35%) with corresponding k(ozonolysis) (min(-1)) of 0.0085 ± 0.0021 (t(1/2) ≈ 81.5 min), 0.0039 ± 0.0008 (t(1/2) ≈ 177.7 min), and 0.0036 ± 0.0007 (t(1/2) ≈ 192.5 min). Heterogeneous rate constants of gaseous ozone reacting with a sorbed fungicide, k(O(3)) (M(-1)·min(-1)), were calculated for both surfaces and indicate losses proceed ～ 15-fold slower on grapes. The kinetics and mechanism of fungicide removal, supported by gas chromatography- and liquid chromatography-mass spectrometry product analyses, is discussed in the context of facilitating compliance with maximum residue level (MRL) tolerances for fresh produce.     

Degradation of ozone-refractory organic phosphates in wastewater by ozone and ozone/hydrogen peroxide (peroxone): the role of ozone consumption by dissolved organic matter

Ozonation is very effective in eliminating micropollutants that react fast with ozone (k > 10(3) M(-1) s(-1)), but there are also ozone-refractory (k < 10 M(-1) s(-1)) micropollutants such as X-ray contrast media, organic phosphates, and others. Yet, they are degraded upon ozonation to some extent, and this is due to (?)OH radicals generated in the reaction of ozone with organic matter in wastewater (DOM, determined as DOC). The elimination of tri-n-butyl phosphate (TnBP) and tris-2-chloroisopropyl phosphate (TCPP), added to wastewater in trace amounts, was studied as a function of the ozone dose and found to follow first-order kinetics. TnBP and TCPP concentrations are halved at ozone to DOC ratios of ～0.25 and ～1.0, respectively. The (?)OH rate constant of TCPP was estimated at (7 ± 2) × 10(8) M(-1) s(-1) by pulse radiolysis. Addition of 1 mg H(2)O(2)/L for increasing the (?)OH yield had very little effect. This is due to the low rate of reaction of H(2)O(2) with ozone at wastewater conditions (pH 8) that competes unfavorably with the reaction of ozone with wastewater DOC. Simulations based on the reported (No?the et al., ES&T 2009, 43, 5990-5995) (?)OH yield (13%) and (?)OH scavenger capacity of wastewater (3.2 × 10(4) (mgC/L)(-1) s(-1)) confirm the experimental data. Based on a typically applied molar ratio of ozone and H(2)O(2) of 2, the contribution of H(2)O(2) addition on the (?)OH yield is shown to become important only at high ozone doses.     

固相微萃取-气相色谱-质谱分析青钱柳叶挥发性成分

采用固相微萃取（SPME）和气相色谱-三重串联四极杆质谱联用仪（GC-QQQ-MS）相结合的方法对两个产地（江西修水野生和浙江文成人工栽培）的青钱柳叶挥发性成分进行研究,并比较了它们在挥发性化学成分及含量上的差异。结果表明:在两个产地的青钱柳叶中共鉴定出91种挥发性成分,其中两者共有挥发性成分45种,且主要是碳氢化合物类、醇类、醛类、酯类、酮类、醚类和萘类化合物,但两个样品在挥发性成分的具体组成和含量上存在一定的差异。野生青钱柳叶的挥发性成分主要是β-瑟林烯（18.52%）、石竹烯（8.11%）、β-甜没药烯（6.01%）、β-榄香烯（5.36%）、顺-香叶基丙酮（4.02%）等,人工栽培青钱柳叶的挥发性成分主要是β-波旁烯（11.05%）、β-瑟林烯（10.91%）、石竹烯（7.03%）、苯甲醇（7.01%）、2,6-二甲基-6-（4-甲基-3-戊烯基）-双环[3.1.1]庚-2-烯（5.36%）、2,6,11-三甲基十二烷（5.16%）等。