Oxygen and superoxide-mediated redox kinetics of iron complexed by humic substances in coastal seawater

Complexes with terrestrially derived humic substances represent one of the most reactive pools of dissolved Fe in natural waters. In this work, redox kinetics of Fe-humic substance complexes (FeL) in simulated coastal seawater were investigated using chemiluminescence techniques with particular attention given to interactions with dioxygen (O2) and superoxide (O2?-). Although rate constants of FeIIL oxidation by O2 (5.6-52 M-1 · s-1) were 4-5 orders of magnitude less than those for O2?- (6.9-23 × 105 M-1 · s-1),O2 is likely to outcompete O2?- for FeIIL oxidation in coastal seawaters where steady-state O2?- concentrations are generally subnanomolar. Rate constants for FeIIIL reduction by O2?- of 1.8-5.6 × 104 M-1 · s-1 were also determined. From the balance of FeIIL oxidation rates and O2?- -mediated FeIIIL reduction rates, steady-state FeIIL concentrations were estimated to be in the subpicomolar to picomolar range, which is generally lower than measured in situ Fe(II) concentrations under relevant conditions. This suggests that (i) processes other than O2?- -mediated reduction (such as photochemical ligand-to-metal charge transfer) may be responsible for Fe(II) formation, (ii) the in situ ligands differ significantly from the humic substances used in this work, and/ or (iii) the influence of other environmental factors such as pH and temperature on Fe redox kinetics may have to be considered.     

Hygroscopic properties of two model humic-like substances and their mixtures with inorganics of atmospheric importance

Water-soluble macromolecular polyacids can play a potentially important role in the hygroscopic properties of atmospheric aerosols. These acids have molecular structures similar to natural fulvic acids (FA) (or humic acids) and are referred to as humic-like substances (HULIS). In this study, the hygroscopicity of HULIS and the mixture of HULIS and sodium chloride (NaCl) and that of HULIS and ammonium sulfate (AS) aerosols at a mass ratio of 1:1 are studied using two natural FA: the Nordic Aquatic Fulvic Acid (NAFA) and the Suwannee River Fulvic Acid (SRFA) as model compounds in an electrodynamic balance. NAFA and SRFA both absorbed and desorbed water reversibly without crystallization and retained water at a relative humidity (RH) < 10%. NAFA and SRFA have a mass growth ratio of 1.25 and 1.45 from RH = 10% to RH = 90%, respectively. However, these results are different from those of another natural FA (the Nordic River Fulvic Acid Reference) in the literature. The differences are possibly due to the differences in the chemical composition of the natural FA, which depends on their sources and the isolation methods. These results suggest that a standardization of the isolation methods of HULIS is needed for better understanding of their atmospheric properties and environmental impacts. In general, the deliquescence and crystallization RH of FA-inorganic mixtures are comparable with those of their respective pure inorganic species. Since FA are less hygroscopic than NaCl and AS, all mixtures absorb less water compared to their respective pure inorganic species of equal particle mass. The FA-AS mixtures have a larger water uptake than the sum of those of the FA and AS individually following a simple additivity rule as noninteracting species at RH = 90%. This enhancement effect increases as the RH decreases. There is no such enhancement effect for the FA-NaCl mixtures until RH is below 90%. These results reveal that the effect of the interactions between FA and inorganic species on the water uptake of the mixtures, in general, is a function of RH.     

Kinetics and mechanisms of heterogeneous reaction of gaseous hydrogen peroxide on mineral oxide particles

Recent studies have shown that heterogeneous reactions of hydrogen peroxide (H(2)O(2)) on aerosol surfaces may play an important role in tropospheric chemistry. The data concerning the kinetics and mechanisms of these reactions, however, are quite scarce so far. Here, we investigated, for the first time, the heterogeneous reactions of gaseous H(2)O(2) on SiO(2) and α-Al(2)O(3) particles, two major components of mineral dust aerosol, using transmission-Fourier Transform Infrared (T-FTIR) spectroscopy, and high-performance liquid chromatography (HPLC). It is found that H(2)O(2) molecularly adsorbs on SiO(2), and a small amount of molecularly adsorbed H(2)O(2) decomposes due to its thermal instability. For α-Al(2)O(3), catalytic decomposition of H(2)O(2) evidently occurs, but there is also a small amount of H(2)O(2) molecularly adsorbed on the particle surface. The BET uptake coefficients of H(2)O(2) on both particles appear to be independent of gaseous H(2)O(2) concentration (1.27-13.8 ppmv) and particle sample mass (2.8-6.5 mg for SiO(2) and 8.6-18.9 mg for α-Al(2)O(3)), but are strongly dependent on relative humidity with the values ranging from (1.55 ± 0.14) × 10(-8) and (1.21 ± 0.04) × 10(-7) at 2% RH to (0.61 ± 0.06) × 10(-8) and (0.76 ± 0.09) × 10(-7) at 76% RH for SiO(2) and α-Al(2)O(3), respectively. On the basis of the experimental results and literature data, the potential mechanisms for heterogeneous decomposition of H(2)O(2) were proposed, and the atmospheric implications of these reactions were discussed. It is found that heterogeneous reaction of H(2)O(2) on both mineral oxides plays a significant role in processing mineral aerosols, although its role as a sink for ambient H(2)O(2) is probably limited.     

Kinetic studies of heterogeneous reactions of polycyclic aromatic hydrocarbon aerosols with NO₃ radicals

Polycyclic aromatic hydrocarbons (PAHs) and their derivates are mutagenic and carcinogenic substances widely distributed in the atmospheric environment. In this study, effective rate constants for heterogeneous reactions of NO(3) radicals with five 4-ring PAHs [benzo[a]anthracene (BaA), chrysene (Ch), pyrene (Py), 1-nitropyrene (1-NP), and 1-hydroxypyrene (1-OHP)] adsorbed on suspended azelaic acid particles are investigated by a mixed-phase relative rate method with gas-phase isoprene as the reference substance. The concentrations of suspended PAH particles and gas-phase isoprene are monitored concurrently by a real-time vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and an online atmospheric gas analysis mass spectrometer, respectively. The obtained effective rate constants for the reactions of BaA, Ch, Py, 1-NP, and 1-OHP particles with NO(3) radicals are 4.3 × 10(-12), 4.0 × 10(-12), 6.4 × 10(-12), 1.3 × 10(-12), and 1.0 × 10(-11) cm(3)·molecule(-1)·s(-1), respectively, and their corresponding atmospheric lifetimes range from several minutes to half an hour at the NO(3) radical concentration of 5 × 10(8) molecules·cm(-3). In addition, the NO(3) uptake coefficients on particulate PAHs are estimated according to the consumption of PAHs under the exposure of NO(3) radicals. The experimental results of these heterogeneous reactions in the aerosol state provide supplementary knowledge for kinetic behaviors of airborne PAHs particles.     

Elemental composition of HULIS in the Pearl River Delta Region, China: results inferred from positive and negative electrospray high resolution mass spectrometric data

The HUmic-LIke Substances (HULIS) fraction isolated from aerosol samples collected at a rural location of the Pearl River Delta Region (PRD), China, during the harvest season was analyzed by both positive and negative mode electrospray ionization (ESI) coupled with an ultrahigh resolution mass spectrometer (UHRMS). With the remarkable resolving power and mass accuracy of ESI-UHRMS, thousands of elemental formulas were identified. Formulas detected in the positive (ESI+) and the negative (ESI-) mode complement each other due to differences in the ionization mechanism, and the use of both provides a more complete characterization of HULIS. Compounds composed of C, H, and O atoms were preferentially detected in ESI- by deprotonation, implying their acidic properties. Tandem MS and Kendrick Mass Defect analysis implies that carboxyl groups are abundant in the CHO compounds. This feature is similar to those of natural fulvic acids, but relatively smaller molecular weights are observed in the HULIS samples. A greater number of reduced nitrogen organic compounds were observed in the ESI+ compared to ESI-. Compounds with biomass burning origin including alkaloids, amino acids, and their derivatives are their probable constituents. Sulfur-containing species were dominantly detected in ESI-. The presence of sulfate fragments in the MS/MS spectra of these species and their high O/S ratios implies that they are mainly organosulfates. Organosulfates and nitrooxy-organosulfates were often the most intensive peaks in the ESI- spectra. They are believed to be products of reactive uptake of photooxidation products of reactive volatile organic compounds by acidic sulfate particles. The elemental compositions deduced from the UHRMS analysis confirm the conclusion from our previous study that biomass burning and SOA formation are both important sources of HULIS in the PRD region.     

Photochemical production and consumption mechanisms of nitric oxide in seawater

Nitric oxide (NO?) is an active odd-nitrogen species that plays a critical role in determining the levels of ozone (O?) and other nitrogen species in the troposphere. Here, we provide experimental evidence for photochemical formation of NO? in seawater. Photoproduction rates and overall scavenging rate constants were measured by irradiation of surface seawater samples collected from the Seto Inland Sea, Japan. Photoproduction rates of NO? ranged from 8.7 × 10?12 M s?1 to 38.8 × 10?12 M s?1 and scavenging rate constants were 0.05-0.33 s?1. The steady state concentrations of NO? in seawater, which were calculated from the photoproduction rates and scavenging rate constants were in the range 2.4-32 × 10?11 M. Estimation from the scavenging rate constant showed that the NO? lifetime in seawater was a few seconds. Our results indicate that nitrite photolysis plays a crucial role in the formation of NO?, even though we cannot exclude minor contributions from other sources. Analysis of filtered and unfiltered seawater samples showed no significant difference in NO? photoformation rates, which suggests a negligible contribution of NO? produced by photobiological processes. Using an estimated value of the Henry's law constant (kH ≈ 0.0019 M atm?1), a supersaturation of surface seawater of 2 to 3 orders of magnitude was estimated. On the basis of the average values of the surface seawater concentration and the atmospheric NO? concentration, a sea-to-air NO? flux was estimated.     

Evaporative light scattering: a novel detection method for the quantitative analysis of humic-like substances in aerosols

The chemical composition of organic atmospheric aerosols is only poorly understood. Although a significant fraction of organic aerosols consists of humic-like substances (HULIS), only little is known about this class of compound, and accurate quantification remains difficult, partly due to the lack of appropriate standards. Here, evaporative light-scattering detection (ELSD) was applied for the first time to quantify water-soluble HULIS in aerosol particles smaller than 1 microm. This detection method was shown to be suitable for the quantification of compounds with unknown structures and lacking appropriate quantification standards. As compared to organic carbon determination of isolated HULIS, no organic carbon/organic mass (OC/OM) conversion factor needs to be applied with ELSD and therefore eliminates this significant uncertainty factor of the OC/OM method, which is frequently used to quantify HULIS. Solid-phase extraction and size-exclusion chromatography were applied to separate inorganic ions and low molecular weight compounds from HULIS before ELSD quantification. The ELSD itself provides an additional separation step where low volatility HULIS are separated from high volatility, small compounds. Electrospray ionization mass spectrometry was used to identify the molecular weight range of the compounds quantified with ELSD. The most intensive peaks were in the range of m/z 200-500, with some masses upto m/z800. We showed that UV detection using fulvic acid as surrogate quantification standard underestimates the HULIS concentration by a factor of 1.1 to 2.5, which is in agreement with earlier studies. During a 6 week winter 2005-2006 campaign at a suburban site near Zurich, Switzerland, an average of 1.1 microg/m(3) HULIS was found, which is about4-6% of the total particle mass smaller than 1 microm (PM1) and 10-35% of the organic matter in PM1.     

Multiphase chemical kinetics of NO3 radicals reacting with organic aerosol components from biomass burning

Multiphase reactions with nitrate radicals are among the most important chemical aging processes of organic aerosol particles in the atmosphere especially at nighttime. Reactive uptake of NO(3) by organic compounds has been observed in a number of studies, but the pathways of mass transport and chemical reaction remained unclear. Here we apply kinetic flux models to experimental NO(3) exposure studies. The model accounts for gas phase diffusion within a cylindrical flow tube, reversible adsorption of NO(3), surface-bulk exchange, bulk diffusion, and chemical reactions from the gas-condensed phase interface to the bulk. We resolve the relative contributions of surface and bulk reactions to the uptake of NO(3) by levoglucosan and abietic acid, which serve as surrogates and molecular markers of biomass burning aerosol (BBA). Applying the kinetic flux model, we provide the first estimate of the diffusion coefficient of NO(3) in amorphous solid organic matrices (10(-8)-10(-7) cm(2) s(-1)) and show that molecular markers are well-conserved in the bulk of solid BBA particles but undergo rapid degradation upon deliquescence/liquefaction at high relative humidity, indicating that the observed concentrations and subsequent apportionment of the biomass burning source could be significantly underestimated.     

Patulin reduction in apple juice from concentrate by UV radiation and comparison of kinetic degradation models between apple juice and apple cider

Patulin, a mycotoxin produced by several genera of fungi, including Byssochlamys, Aspergillus, and Penicillium, has been an important concern in apple cider and apple juice due to its toxicity and health consequences. In this study, the effects of UV on the patulin level, physical and chemical properties, and sensory attributes in apple juice from concentrate were investigated. Kinetic modeling of patulin reduction by UV radiation in apple juice from concentrate was calculated and compared with the degradation rate observed previously in apple cider. From an initial patulin contamination of approximately 1,000 ppb (μg/liter), the UV exposure, ranging from 14.2 mJ/cm(2) (one pass) to 99.4 mJ/cm(2) (seven passes), was successful in reducing patulin levels by 72.57% ± 2.76% to 5.14% ± 0.70%, respectively. Patulin reduction by UV radiation followed first-order kinetic modeling in a fashion similar to first-order microbial inactivation. An exponential correlation between UV exposure and the percentage of patulin remaining was observed, giving an r(2) value of 0.9950. Apple juice was repeatedly exposed to 14.2 mJ/cm(2) for each treatment, and patulin levels were significantly decreased when compared with the level obtained with the previous UV exposure treatment. While there were no significant differences in the percentages of titratable acidity and ascorbic acid (P > 0.05), there were minor yet random sampling differences in pH and degrees Brix (1 °Brix is 1 g of sucrose in 100 g of solution; the °Brix represents the soluble solids content of the solution as percentage by weight [%, wt/wt]) (P ≤ 0.05). A significant difference (P ≤ 0.05) in sensory perception for the finished apple juice was detected between the control and the full seven-pass UV radiation treatment using an experienced consumer panel and a triangle test. Patulin reduction by UV radiation from both the current study and a previous study involving apple cider was compared, which showed that both matrices strongly fit a first-order kinetic degradation model. However, the kinetic constant for degradation in apple juice was approximately 5.5 times greater than that observed in an apple cider matrix.     

Ammonia gas permeability of meat packaging materials

Meat products are packaged in polymer films designed to protect the product from exterior contaminants such as light, humidity, and harmful chemicals. Unfortunately, there is almost no data on ammonia permeability of packaging films. We investigated ammonia permeability of common meat packaging films: low-density polyethylene (LDPE; 2.2 mil), multilayer polyolefin (MLP; 3 mil), and vacuum (V-PA/PE; 3 mil, 0.6 mil polyamide/2.4 mil polyethylene). The films were fabricated into 10 × 5 cm pouches and filled with 50 mL deionized water. Pouches were placed in a plexiglass enclosure in a freezer and exposed to 50, 100, 250, or 500 ppm ammonia gas for 6, 12, 24, and 48 h at -17 ± 3 °C and 21 ± 3 °C. At freezing temperatures, no ammonia residues were detected and no differences in pH were found in the water. At room temperature, ammonia levels and pH of the water increased significantly (P < 0.05) with increasing exposure times and ammonia concentrations. Average ammonia levels in the water were 7.77 ppm for MLP, 5.94 ppm for LDPE, and 0.89 ppm for V-PA/PE at 500 ppm exposure for 48 h at 21 ± 3 °C. Average pH values were 8.64 for MLP, 8.38 for LDPE, and 7.23 for V-PA/PE (unexposed ranged from 5.49 to 6.44) at 500 ppm exposure for 48 h. The results showed that temperature influenced ammonia permeability. Meat packaging materials have low ammonia permeability and protect meat products exposed to ammonia leaks during frozen storage.     

Colloid transport in a heterogeneous partially saturated sand column

Colloid transport was studied in heterogeneous sand columns under unsaturated steady-state conditions, using two sizes of acid-cleaned sand to pack the column. Heterogeneity was created by placing three continuous tubes of fine sand (3.6% of the total volume) within a column of coarse sand (mean grain diameters 0.36 and 1.2 mm, respectively). Experiments were performed under three flow rates (0.1, 0.2, and 0.4 cm/ min) applied by a rain simulator atthe top of the column. Constant water-content profile in the coarse sand was achieved by applying corresponding suction at the column bottom. Three sizes of latex microspheres (1, 0.2, and 0.02 microm) and soluble tracers (LiBr), diluted in a weak base (pH 7.3, ionic strength 0.0023 M) solution, were used simultaneously. Introduction of preferential pathways reduced front-arrival time about 2-fold and increased colloid recovery which, at the 0.2 cm/min flow rate, was higher than at 0.4 and 0.1 cm/min. Maximum solution flux from coarse to fine sand (due to differences in matric pressure) at 0.2 cm/min, verified by hydrodynamic modeling, could explain this phenomenon. Results suggest that in heterogeneous soil, maximum colloid recovery does not necessarily occur at maximum water content. This has clear implications for colloid transport in natural soils, many of which are heterogeneous.     

Generation of reactive oxygen species mediated by humic-like substances in atmospheric aerosols

Particulate matter (PM)-mediated reactive oxygen species (ROS) generation has been implicated in health effects posed by PM. Humic-like substances (HULIS) are an unresolved mixture of water-extracted organic compounds from atmospheric aerosol particles or isolated from fog/cloudwater samples. In this study, we use a cell-free dithiothreitol (DTT) assay to measure ROS production mediated by HULIS. The HULIS samples are isolated from aerosols collected at a rural location and a suburban location in the Pearl River Delta, China. In our experiments, ROS activities by residue metal ions in the HULIS fraction are suppressed by including a strong chelating agent in the DTT assay. Under conditions of DTT consumption not exceeding 90%, the HULIS-catalyzed oxidation of DTT follows the zero-order kinetics with respect to DTT concentration, and the rate of DTT oxidation is proportional to the dose of HULIS. The ROS activity of the aerosol HULIS, on a per unit mass basis is 2% of the ROS activity by a reference quinone compound, 1,4-naphthoquinone and exceeds that of two aquatic fulvic acids. The HULIS fraction in the ambient samples tested exhibits comparable ROS activities to the organic solvent extractable fraction, which would contain compounds such as quinones, a known organic compound class capable of catalyzing generation of ROS in cells. HULIS was found to be the major redox active constituent of the water-extractable organic fraction in PM. It is plausible that HULIS contains reversible redox sites, thereby serving as electron carriers to catalyze the formation of ROS. Our work suggests that HULIS could be an active PM component in generating ROS and further work is warranted to characterize its redox properties.     

3 种工况下PBAT/PLA材料中抗氧剂168及其降解产物的迁移

采用气相色谱-质谱法研究抗氧剂168及其降解产物从不同工况（紫外、高湿、盐雾）处理下的聚己二酸-对苯二甲酸丁二醇酯/聚乳酸（poly(butyleneadipate-co-terephthalate)/polylactic acid,PBAT/PLA）复合膜中向脂肪类食品模拟物异辛烷的迁移规律,并对每个工况下复合膜的老化程度进行力学性能以及红外光谱表征。结果表明：紫外、高湿工况对PBAT/PLA复合膜降解影响较大。紫外2 d、高湿60 d、盐雾40 d后复合膜的拉伸强度在10、15、17 MPa左右,分别下降了61.1%、41.6%、35.9%,断裂伸长率分别下降了93.5%、34.1%、21.5%。抗氧剂质量分数对复合膜性能影响不显著（P＞0.05）。物质迁移量与其在迁移实验前复合膜中的含量呈正相关。未处理的复合膜中抗氧剂168迁移量最高,为85.39 mg/kg。随着复合膜老化抗氧剂降解产物的含量增加,主要产物为三(2,4-二叔丁基苯基)磷酸酯,紫外工况下产生最多,迁移量为3.04～99.50 mg/kg。物质的迁出率受温度、含量以及复合膜老化程度三者同时影响。     

酱油种类及添加量对牛肱二头肌的嫩化作用

研究酱油种类及添加量对牛肱二头肌的嫩化作用。将3 种质量浓度15 g/100 mL的酱油溶液与3 g /100 mL的食盐溶液按不同的比例混合,配制9 组腌制液,并以3 g/100 mL的食盐溶液作为对照组（记为C0）,按肉液比为1∶4（m/V）将牛肱二头肌肉块（2.5 cm×2.5 cm×2.5 cm）腌制72 h（4 ℃）,分析酱油种类及添加量对肉样pH值、剪切力、胶原蛋白含量、肌节长度及肌原纤维碎裂指数（myofibrillar fragmentation index,MFI）等指标的影响。结果表明：酱油腌制会降低肉样的pH值（P＜0.05）,但对肉样的持水力和总胶原蛋白含量无显著影响（P＞0.05）;酱油含量高的腌制液具有更低的pH值,使肉样的可溶性胶原蛋白含量及MFI变大、肌节长度变短,进而提高肉的嫩度;当腌制液中的酱油比例较高时,肉样的嫩度与多汁性感官评分更高,总体可接受度更好。在3 种酱油中,低pH值酱油对牛肱二头肌的嫩化效果更好。     

Weathering of silane treated wood

Outdoor and artificial weathering tests were performed on specimens of Scots pine sapwood treated with silanes to achieve water repellent properties. During outdoor weathering, the treatment caused a reduction in (liquid) water uptake but the sorption of moisture (air humidity) was not affected by silane treatment. The water repellent effect of vacuum-pressure treated specimens remained stable over the tested exposure period of one year, as was shown in dipping tests. Evaluation of silane treated specimens did not reveal any reduction of crack formation during exposure to weathering. The application of silanes in combination with UV light stabilizers enhanced the effectiveness of these protectants and led to higher colour stability during artificial weathering in a QUV device.     

Modeling of Escherichia coli inactivation by UV irradiation at different pH values in apple cider

This study examined the effects and interactions of UV light dose (1,800 to 20,331 microJ/cm2) and apple cider pH (2.99 to 4.41) on the inactivation of Escherichia coli ATCC 25922, a surrogate for E. coli O157:H7. A predictive model was developed to relate the log reduction factor of E. coli ATCC 25922 to the UV dose. Bacterial populations for treated and untreated samples were enumerated with the use of nonselective media. The results revealed that UV dose was highly significant in the inactivation of E. coli, whereas pH showed no significant effect at higher UV doses. Doses of 6,500 microJ/cm2 or more were sufficient to achieve a greater than 5-log reduction of E. coli. Experimental inactivation data were fitted adequately by a logistic regression model. UV irradiation is an attractive alternative to conventional methods for reducing bacteria in unpasteurized apple cider.     

低聚异麦芽糖产品中主要组分的毛细管电泳分析方法

在未涂渍的石英毛细管中 ,以 75mmol/L硼砂 (pH 1 0 5 )为运行电解质 ,在检测波长 2 1 4nm、分离电压 1 5kV下对低聚异麦芽糖的主要组分的α 萘胺衍生物进行了快速分离测定。结果表明 ,该方法重现性好 ,迁移时间和峰面积的相对标准偏差分别在 0 5 %和 2 0 %以内。异麦芽糖、异麦芽三糖、潘糖浓度在 0 0 0 5～ 1 0 0 0mg/mL范围内 ,含量均与其峰面积之间呈现良好的线性关系。该法灵敏度高 ,成本低 ,为测定低聚异麦芽糖产品中主要组分提供了一种高效快速的方法     

Full-scale chamber investigation and simulation of air freshener emissions in the presence of ozone

Volatile organic compound (VOC) emissions from one electrical plug-in type of pine-scented air freshener and their reactions with O3 were investigated in the U.S. Environmental Protection Agency indoor air research large chamber facility. Ozone was generated from a device marketed as an ozone generator air cleaner. Ozone and oxides of nitrogen concentrations and chamber conditions such as temperature, relative humidity, pressure, and air exchange rate were controlled and/or monitored. VOC emissions and some of the reaction products were identified and quantified. Source emission models were developed to predict the time/concentration profiles of the major VOCs (limonene, alpha-pinene, beta-pinene, 3-carene, camphene, benzyl propionate, benzyl alcohol, bornyl acetate, isobornyl acetate, and benzaldehyde) emitted bythe air freshener. Gas-phase reactions of VOCs from the air freshener with O3 were simulated by a photochemical kinetics simulation system using VOC reaction mechanisms and rate constants adopted from the literature. The concentration-time predictions were in good agreement with the data for O3 and VOCs emitted from the air freshener and with some of the primary reaction products. Systematic differences between the predictions and the experimental results were found for some species. Poor understanding of secondary reactions and heterogeneous chemistry in the chamber is the likely cause of these differences. The method has the potential to provide data to predict the impact of O3/VOC interactions on indoor air quality.     

Observation of ClNO₂ in a mid-continental urban environment

In the troposphere, nitryl chloride (ClNO?), produced from uptake of dinitrogen pentoxide (N?O?) on chloride containing aerosol, can be an important nocturnal reservoir of NO(x) (= NO + NO?) and a source of atomic Cl, particularly in polluted coastal environments. Here, we present measurements of ClNO? mixing ratios by chemical ionization mass spectrometry (CIMS) in Calgary, Alberta, Canada over a 3-day period. The observed ClNO? mixing ratios exhibited a strong diurnal profile, with nocturnal maxima in the range of 80 to 250 parts-per-trillion by volume (pptv) and minima below the detection limit of 5 pptv in the early afternoon. At night, ClNO? constituted up to 2% of odd nitrogen, or NO(y). The peak mixing ratios of ClNO? observed were considerably below the modeled integrated heterogeneous losses of N?O?, indicating that ClNO? production was a minor pathway compared to heterogeneous hydrolysis of N?O?. Back trajectory analysis using HYSPLIT showed that the study region was not influenced by fresh injections of marine aerosol, implying that aerosol chloride was derived from anthropogenic sources. Molecular chlorine (Cl?), derived from local anthropogenic sources, was observed at mixing ratios of up to 65 pptv and possibly contributed to formation of aerosol chloride and hence the formation of ClNO?.     

Photochemical formation of hydroxyl radical from effluent organic matter

The photochemical formation of hydroxyl radical (HO?) from effluent organic matter (EfOM) was evaluated using three bulk wastewater samples collected at different treatment facilities under simulated sunlight. For the samples studied, the formation rates of HO?(R(HO?)) were obtained from the formation rate of phenol following the hydroxylation of benzene. The values of R(HO?) ranged from 2.3 to 3.8 × 10(-10) M s(-1) for the samples studied. The formation rate of HO? from nitrate photolysis (R(NO3)(HO?)) was determined to be 3.0 × 10(-7) M(HO)? M(NO3)(-1) s(-1). The HO? production rate from EfOM (R(EfOM)(HO?)) ranged from 0.76 to 1.3 × 10(-10) M s(-1). For the wastewater samples studied, R(EfOM)(HO?) varied from 1.5 to 2.4 × 10(-7) M(HO)? M(C)(-1) (s-1) on molarcarbon basis, which was close to HO? production from nitrate photolysis. The apparent quantum yield for the formation of HO? from nitrate (Φ(NO3-HO?)(a)) was determined as 0.010 ± 0.001 for the wavelength range 290-400 nm in ultrapure water. The apparent quantum yield for HO? formation in EfOM (Φ(EfOM-HO?)(a)) ranged from 6.1 to 9.8 × 10(-5), compared to 2.99 to 4.56 × 10(-5) for organic matter (OM) isolates. The results indicate that wastewater effluents could produce significant concentrations of HO?, as shown by potential higher nitrate levels and relatively higher quantum yields of HO? formation from EfOM.