The field campaigns of the European Tracer Experiment (ETEX): overview and results

As part of the European Tracer Experiment (ETEX) two successful atmospheric experiments were carried out in October and November, 1994. Perfluorocarbon (PFC) tracers were released into the atmosphere in Monterfil, Brittany, and air samples were taken at 168 stations in 17 European countries for 72 h after the release. Upper air tracer measurements were made from three aircraft. During the first experiment a westerly air flow transported the tracer plume north-eastwards across Europe. During the second release the flow was eastwards. The results from the ground sampling network allowed the determination of the cloud evolution as far as Sweden, Poland and Bulgaria. This demonstrated that the PFT technique can be successfully applied in long-range tracer experiments up to 2000 km. Typical background concentrations of the tracer used are around 5–7 fl ?^-1 in ambient air. Concentrations in the plume ranged from 10 to above 200 fl/?^-1. The tracer release characteristics, the tracer concentrations at the ground and in upper air, the routine and additional meteorological observations at the ground level and in upper air, trajectories derived from constant-level balloons and the meteorological input fields for long-range transport models are assembled in the ETEX database. The ETEX database is accessible via the Internet. Here, an overview is given of the design of the experiment, the methods used and the data obtained.     

Perfluorinated compounds in Haihe River and Dagu Drainage Canal in Tianjin, China

In this study, nine perfluorinated compounds (PFCs) were investigated in water and sediment of Haihe River (HR) and Dagu Drainage Canal (DDC), Tianjin, China. The total PFCs in water samples from DDC (40-174 ng L⁻¹) was much greater than those from HR (12-74 ng L⁻¹). PFC contamination was severe at lower reaches of HR due to industry activities, while high PFCs were found in the middle of DDC due to the effluents from wastewater treatment plants. Perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) were the predominant PFCs in aqueous phase. The total PFCs in sediments from DDC (1.6-7.7 ng g⁻¹ dry weight) were lower as compared to HR (7.1-16 ng g⁻¹), maybe due to the dredging of sediment in DDC conducted recently. PFOS was the major PFC in HR sediments followed by PFOA; while PFHxA was the major PFC in DDC sediments. Organic carbon calibrated sediment-water distribution coefficients (K_OC) were calculated for HR. The Log K_OC ranged from 3.3 to 4.4 for C7-C11 perfluorinated carboxylic acids, increasing by 0.1-0.6 log units with each additional CF₂ moiety. The log K_OC for 8:2 fluorotelomer unsaturated acid was reported for the first time with a mean value of 4.0. The log Koc of PFOS was higher than perfluoronanoic acid by 0.8 log units.     

Partitioning behaviour of perfluorinated alkyl contaminants between water, sediment and fish in the Orge River (nearby Paris, France)

This paper reports on the partitioning behaviour of 15 perfluorinated compounds (PFCs), including C₄-C₁₀ sulfonates and C₅-C₁₄ carboxylic acids, between water, sediment and fish (European chub, Leuciscus cephalus) in the Orge River (nearby Paris). Total PFC levels were 73.0 ± 3.0 ng L⁻¹ in water and 8.4 ± 0.5 ng g⁻¹ in sediment. They were in the range 43.1-4997.2 ng g⁻¹ in fish, in which PFC tissue distribution followed the order plasma > liver > gills > gonads > muscle. Sediment-water distribution coefficients (log K_d) and bioaccumulation factors (log BAF) were in the range 0.8-4.3 and 0.9-6.7, respectively. Both distribution coefficients positively correlated with perfluoroalkyl chain length. Field-based biota-sediment accumulation factors (BSAFs) are also reported, for the first time for PFCs other than perfluorooctane sulfonate. log BSAF ranged between −1.3 and 1.5 and was negatively correlated with the perfluoroalkyl chain length in the case of carboxylic acids.     

Simulation of aerosol radiative properties with the ORISAM-RAD model during a pollution event (ESCOMPTE 2001)

The aim of this study is to present the organic and inorganic spectral aerosol module-radiative (ORISAM-RAD) module, allowing the 3D distribution of aerosol radiative properties (aerosol optical depth, single scattering albedo and asymmetry parameter) from the ORISAM module. In this work, we test ORISAM-RAD for one selected day (24th June) during the ESCOMPTE (expérience sur site pour contraindre les modèles de pollution atmosphérique et de transport d’emissions) experiment for an urban/industrial aerosol type. The particle radiative properties obtained from in situ and AERONET observations are used to validate our simulations. In a first time, simulations obtained from ORISAM-RAD indicate high aerosol optical depth (AOD)0.50–0.70±0.02 (at 440 nm) in the aerosol pollution plume, slightly lower (10–20%) than AERONET retrievals. In a second time, simulations of the single scattering albedo (ω_o) have been found to well reproduce the high spatial heterogeneities observed over this domain. Concerning the asymmetry parameter (g), ORISAM-RAD simulations reveal quite uniform values over the whole ESCOMPTE domain, comprised between 0.61±0.01 and 0.65±0.01 (at 440 nm), in excellent agreement with ground based in situ measurements and AERONET retrievals. Finally, the outputs of ORISAM-RAD have been used in a radiative transfer model in order to simulate the diurnal direct radiative forcing at different locations (urban, industrial and rural). We show that anthropogenic aerosols strongly decrease surface solar radiation, with diurnal mean surface forcings comprised between −29.0±2.9 and −38.6±3.9 W m⁻², depending on the sites. This decrease is due to the reflection of solar radiations back to space (−7.3±0.8<ΔF_TOA<−12.3±1.2 W m⁻²) and to its absorption into the aerosol layer (21.1±2.1<ΔF_ATM<26.3±2.6 W m⁻²). These values are found to be consistent with those measured at local scale.     

Biogeochemical dynamics of perfluorinated alkyl acids and sulfonates in the River Seine (Paris, France) under contrasting hydrological conditions

The biogeochemical dynamics of 15 perfluorinated compounds (PFCs) were investigated in a heavily urbanised river (River Seine, Paris, France). The target compounds included C4-C10 sulfonates and C5-C14 acids; eleven PFCs were detected and ∑PFCs ranged between 31 and 91 ng L⁻¹ (median: 47 ng L⁻¹). The molecular pattern was dominated by the perfluoroalkyl sulfonates PFHxS and PFOS (>54% of ∑PFCs), which were the only PFCs quantified in both the dissolved and particulate phases. For these PFCs, the sorbed fraction positively correlated with suspended sediment levels. Total PFC levels negatively correlated with river flow rate, which varied between 150 and 640 m³ s⁻¹. This suggests the predominance of point sources (likely WWTP effluent discharge), but a contribution of non-point sources such as combined sewer overflow could not be excluded. The annual PFC mass flow was estimated at 500 kg, which is less than observed for other large European rivers.     

The change of gaseous carbon fluxes following the switch of dominant producers from macrophytes to algae in a shallow subtropical lake of China

Successions of lake ecosystems from clear-water, macrophyte-rich conditions into turbid states with abundant phytoplankton have taken place in many shallow lakes in China. However, little is know about the change of carbon fluxes in lakes during such processes. We conducted a case study in Lake Biandantang to investigate the change of carbon fluxes during such a regime shift. Dissolved aquatic carbon and gaseous carbon (methane (CH₄) and carbon dioxide (CO₂)) across air–water interface in three sites with different vegetation covers and compositions were studied and compared. CH₄ emissions from three sites were 0.62±0.36, 0.70±0.36, and 1.31±0.57 mg m⁻² h⁻¹, respectively. Correlation analysis showed that macrophytes, rather than phytoplankton, directly positively affected CH₄ emission. CO₂ fluxes of three sites in Lake Biandantang were significantly different, and the average values were 77.8±20.4, 52.2±14.1 and 3.6±26.8 mg m⁻² h⁻¹, respectively. There were an evident trend that the larger macrophyte biomass, the lower CO₂ emissions. Correlation analysis showed that in different sites, dominant plant controlled CO₂ flux across air–water interface. In a year cycle, the percents of gaseous carbon release from lake accounting for net primary production were significantly different (from 39.3% to 2.8%), indicating that with the decline of macrophytes and regime shift, the lake will be a larger carbon source to the atmosphere.     

Do aerosols act as catalysts in the OH radical initiated atmospheric oxidation of volatile organic compounds?

Smog chamber/FTIR techniques were used to study the relative reactivity of OH radicals with methanol, ethanol, phenol, C₂H₄, C₂H₂, and p-xylene in 750 Torr of air diluent at 296±2 K. Experiments were performed with, and without, 500–8000 μg m⁻³ (4000–50 000 μm² cm⁻³ surface area per volume) of NaCl, (NH₄)₂SO₄ or NH₄NO₃ aerosol. In contrast to the recent findings of Oh and Andino (Atmospheric Environment 34 (2000) 2901, 36 (2002) 149; International Journal of Chemical Kinetics 33 (2001) 422) there was no discernable effect of aerosol on the rate of loss of the organic compounds via reaction with OH radicals. Gas kinetic theory arguments cast doubt upon the findings of Oh and Andino. The available data suggest that the answer to the title question is “No”. As part of this work the rate constants for reactions of OH radicals with methanol, ethanol, and phenol in 750 Torr of air at 296 K were determined to be: k_OH+CH3OH=(8.12±0.54)×10⁻¹³, k_OH+C2H5OH=(3.47±0.32)×10⁻¹² and k_OH+phenol=(3.27±0.31)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹.     

Occurrence and source characterization of perfluorochemicals in an urban watershed

Perfluorochemicals (PFCs) are used in numerous applications, mainly as surfactants, and occur ubiquitously in the environment as complex mixtures. This study was undertaken to characterize the occurrence and sources of commonly detected PFC compounds in surface waters of the Marina catchment, a watershed that drains an urbanized section of Singapore. Of the 19 target PFCs, 13 were detected with perfluorooctanoic acid (PFOA) (5-31 ng L⁻¹) and perfluorooctane sulfonate (PFOS) (1-156 ng L⁻¹) being the dominant components. Other compounds detected included perfluoroalkyl carboxylates (C7-C12) and perfluoroalkyl sulfonates (C6 and C8). Sulfonamide compounds detected 2-(N-ethylperfluorooctanesulfonamido) acetic acid (N-EtFOSAA), 2-(N-methylperfluorooctanesulfonamido) acetic acid (N-MeFOSAA), perfluorooctanesulfonamido acetic acid (FOSAA) and perfluorooctanesulfonamide (FOSA) were putative transformation products of N-EtFOSE and N-MeFOSE, the N-ethylated and N-methylated ethyl alcohol derivatives, respectively. Surface water concentrations were generally higher during dry weather than during storm water flow: the median concentrations of total PFCs in dry and wet weather were 57 and 138 ng L⁻¹ compared to 42 and 79 ng L⁻¹, respectively, at Stamford and Alexandra canal, suggesting the presence of a continuous source(s) which is subject to dilution during storm events. In rain water, median concentrations were 6.4 ng L⁻¹, suggesting rain contributed from 12-25% to the total PFC load for non-point source sites. The longitudinal concentration profile along one of the canals revealed a point source of sulfonated PFCs (PFOS), believed to originate from aqueous film-forming foam (AFFF). Sources were characterized using principal component analysis (PCA) and by plotting PFHxS/PFOA against PFOS/PFOA. Typical surface waters exhibit PFOS/PFOA and PFHxS/PFOA ratios below 0.9 and 0.5, respectively. PCA plots reveal waters impacted by “non-typical” PFC sources in Alexandra canal.     

Effective diffusivity of the uranyl ion in a granite from Inada, Ibaraki, Japan

The effective diffusivity of uranium(VI) in Inada granite has been determined by through-diffusion. Experiments were performed at room temperature (20–25°C) in a 0.1 mol 1⁻¹ KCl solution where uranium is present predominantly as the poorly sorbing UO₂²⁺. An effective diffusivity (D_e) of (3.6 ± 1.6) × 10⁻¹⁴ m² s⁻¹ was obtained, close to that for uranine (nonsorbing organic tracer), but one order of magnitude lower than those obtained for Sr²⁺ and NpO₂⁺, and two orders of magnitude lower than that obtained for I⁻. According to well established theory, a proportional relationship exists between D_e and the diffusivity in the bulk of the solution (D_v). The effective diffusivity obtained in granite was not proportional to D_v. This agrees with results obtained for effective diffusivity in a Swedish granite. The ratio D_e/D_v was found to be not constant but increased with D_e or D_v. This result suggests a limit to the application of the theory.     

Kinetics of OH-initiated oxidation of oxygenated organic compounds in the aqueous phase: new rate constants, structure–activity relationships and atmospheric implications

The kinetics of OH oxidation of several organic compounds of atmospheric relevance were measured in the aqueous phase. Relative kinetics were performed using various organic references and OH sources. After validation of the protocol, temperature-dependent rate constants for the reactions of OH radical with ethyl ter-butyl ether (, E_a/R=580 (±560) K), n-butyl acetate ( (±0.4)×10⁹ M⁻¹ s⁻¹, E_a/R=1000 (±200) K), acetone ( (±0.05)×10⁹ M⁻¹ s⁻¹, E_a/R=1400 (±500) K), methyl ethyl ketone (, E_a/R=1200 (±200) K), methyl iso-butyl ketone (, E_a/R=1200 (±300) K) and methylglyoxal (, E_a/R=1100 (±300) K) were determined. A non-Arrhenius behavior was found for phenol, in good agreement with the contribution of an OH addition to the mechanism, which also includes H-abstraction by OH radicals. Global rate constants of acetaldehyde, propionaldehyde, butyraldehyde and valeraldehyde were studied at 298 K only, as these compounds partly hydrate in the aqueous phase. All the obtained data (except those of phenol) complemented by literature data were used to investigate three methods to estimate rate constants for H-abstraction reactions of OH radicals in aqueous solutions when measured data were not available: Evans-Polanyi-type correlations, comparisons with gas-phase data, structure activity relationships (SAR). The results show that the SAR method is promising; however, the data set is currently too small to extend this method to temperatures other than 298 K. The atmospheric impact of aqueous phase OH oxidation of water-soluble organic compounds is discussed with the determination of their global atmospheric lifetimes, taking into account both gas- and aqueous-phase reactivities. The results show that atmospheric droplets can act as powerful photoreactors to eliminate soluble organic compounds from the atmosphere.     

A study of the atmospheric reaction of CH3S with O3 as a function of temperature

The atmospheric reaction of the methylthiyl radical (CH₃S) with O₃ was investigated as a function of temperature (259–381 K), in the pressure range of 25–300 Torr, using the technique of laser photolysis/laser-induced fluorescence. The resulting Arrhenius expression, with an uncertainty of ±2σ, was k₁(T=259–381 K)=(1.02±0.30)×10⁻¹² exp[(432±77) K/T] cm³ molecule⁻¹ s⁻¹. The obtained rate constant k₁ was independent of pressure over the limited range employed. Our results are compared with the previous studies carried out, at single temperature and as a function of temperature, by different techniques.     

Bulgarian emergency response models–validation against ETEX first release

In the paper, the performance of two Bulgarian dispersion models is tested against European Tracer Experiment (ETEX) first release data base. The first one is the LED puff model which was the core of the Bulgarian Emergency Response System during all releases of ETEX. The second one is the newly created Eulerian dispersion model EMAP. These models have two important features: they are PC-oriented and they use quite a limited amount of input meteorological information. First, a number of runs with various source configurations are made on meteorological data produced by ECMWF. The aim of these runs is to verify the models’ ability to simulate reliably ETEX first release. To this end, a set of statistical criteria selected in ATMES (Atmospheric Transport Models Evaluation Study, see Klug et al., 1992 are used. The best runs for both models are obtained when the source is presented as a column towering from the ground to heights of 400–700 m. These runs took part in the second phase of ETEX (ETEX-II), the so called ATMES-type exercise where EMAP ranked ninth and LED - fourteenth among 34 models. Here, additional sets of EMAP are presented where in the first run the value of the horizontal diffusion coefficient is varied and in the other runs different meteorological data sets are tested. The results obtained from the first run show that the values of K_h=4–6×10⁴ m² s^-1 produce fields which fit experimental data best. The other sets of runs show that the higher the frequency of the meteorological data, the better the simulation. The results can be improved by linear interpolation of the meteorological parameters with time, the best fitting obtained with interpolation at each time step.     

An aerosol flow tube study of the interaction of N2O5 with calcite, Arizona dust and quartz

The interaction of N₂O₅ with dispersed samples of Arizona Test Dust (ATD), Calcite (CaCO₃) and quartz (SiO₂) was investigated at varying relative humidity using an aerosol flow reactor. Reactive uptake coefficients, γ, obtained at close to zero relative humidity were (4.8 ± 0.7) × 10⁻³ for CaCO₃, (8.6 ± 0.6) × 10⁻³ for Quartz and (9.8 ± 1.0) × 10⁻³ for ATD. In the case of calcite, evidence was obtained for an enhanced rate of uptake at relative humidities above ≈ 50%. The results are compared to literature values obtained using bulk substrates and to previous aerosol uptake data on Saharan dust.     

Microbial characterization of nitrification in a shallow, nitrogen-contaminated aquifer, Cape Cod, Massachusetts and detection of a novel cluster associated with nitrifying Betaproteobacteria

Groundwater nitrification is a poorly characterized process affecting the speciation and transport of nitrogen. Cores from two sites in a plume of contamination were examined using culture-based and molecular techniques targeting nitrification processes. The first site, located beneath a sewage effluent infiltration bed, received treated effluent containing O₂ (> 300 µM) and NH₄⁺ (51–800 µM). The second site was 2.5 km down-gradient near the leading edge of the ammonium zone within the contaminant plume and featured vertical gradients of O₂, NH₄⁺, and NO₃⁻ (0–300, 0–500, and 100–200 µM with depth, respectively). Ammonia- and nitrite-oxidizers enumerated by the culture-based MPN method were low in abundance at both sites (1.8 to 350 g^− 1 and 33 to 35,000 g^− 1, respectively). Potential nitrifying activity measured in core material in the laboratory was also very low, requiring several weeks for products to accumulate. Molecular analysis of aquifer DNA (nested PCR followed by cloning and 16S rDNA sequencing) detected primarily sequences associated with the Nitrosospira genus throughout the cores at the down-gradient site and a smaller proportion from the Nitrosomonas genus in the deeper anoxic, NH₄⁺ zone at the down-gradient site. Only a single Nitrosospira sequence was detected beneath the infiltration bed. Furthermore, the majority of Nitrosospira-associated sequences represent an unrecognized cluster. We conclude that an uncharacterized group associated with Nitrosospira dominate at the geochemically stable, down-gradient site, but found little evidence for Betaproteobacteria nitrifiers beneath the infiltration beds where geochemical conditions were more variable.     

Risk assessment for human consumption of perfluorinated compound-contaminated freshwater and marine fish from Hong Kong and Xiamen

Perfluorinated compounds (PFCs) are man-made fluoro-surfactants that are identified as global pollutants and can pose health risks to humans and wildlife. Two aspects of risk assessment were conducted in this study, including exposure and response. Exposure was estimated by using the concentrations of PFCs in fish and applying standard exposure factors. Among different PFCs, PFOS, PFOA, PFNA, PFDA, PFUdA and PFTrDA were detected. Total concentrations of PFC in fish ranged from 0.27-8.4 ng g⁻¹ to 0.37-8.7 ng g⁻¹ respectively in Hong Kong and Xiamen. The calculated hazard ratio (HR) of PFOS for all fish was less than 1.0. However, the HR for mandarin fish in Hong Kong and bighead carp, grass carp and tilapia in Xiamen, had HR values of approximately 0.5, indicating that frequent consumption of these 4 more contaminated fish species might pose an unacceptable risk to human health. Our data support the notion that the released/disposed chemical pollutants into water systems make fish a source of environmental toxicants to humans. The risks and potential effects of PFCs to health of coastal population in the Pearl River Delta are of concern.     

Long-term variation of PM2.5 levels and composition at rural, urban, and roadside sites in Hong Kong: Increasing impact of regional air pollution

Long-term study of air pollution plays a decisive role in formulating and refining pollution control strategies. In this study, two 12-month measurements of PM_2.5 mass and speciation were conducted in 00/01 and 04/05 to determine long-term trend and spatial variations of PM_2.5 mass and chemical composition in Hong Kong. This study covered three sites with different land-use characteristics, namely roadside, urban, and rural environments. The highest annual average PM_2.5 concentration was observed at the roadside site (58.0±2.0 μg m⁻³ (average±2σ) in 00/01 and 53.0±2.7 μg m⁻³ in 04/05), followed by the urban site (33.9±2.5 μg m⁻³ in 00/01 and 39.0±2.0 μg m⁻³ in 04/05), and the rural site (23.7±1.9 μg m⁻³ in 00/01 and 28.4±2.4 μg m⁻³ in 04/05). The lowest PM_2.5 level measured at the rural site was still higher than the United States’ annual average National Ambient Air Quality Standard of 15 μg m⁻³. As expected, seasonal variations of PM_2.5 mass concentration at the three sites were similar: higher in autumn/winter and lower in summer. Comparing PM_2.5 data in 04/05 with those collected in 00/01, a reduction in PM_2.5 mass concentration at the roadside (8.7%) but an increase at the urban (15%) and rural (20%) sites were observed. The reduction of PM_2.5 at the roadside was attributed to the decrease of carbonaceous aerosols (organic carbon and elemental carbon) (>30%), indicating the effective control of motor vehicle emissions over the period. On the other hand, the sulfate concentration at the three sites was consistent regardless of different land-use characteristics in both studies. The lack of spatial variation of sulfate concentrations in PM_2.5 implied its origin of regional contribution. Moreover, over 36% growth in sulfate concentration was found from 00/01 to 04/05, suggesting a significant increase in regional sulfate pollution over the years. More quantitative techniques such as receptor models and chemical transport models are required to assess the temporal variations of source contributions to ambient PM_2.5 mass and chemical speciation in Hong Kong.     

Per- and polyfluorinated compounds in house dust and indoor air from northern Norway - a pilot study

Polyfluorinated compounds (PFCs) are an extremely versatile class of compounds and are used in a variety of consumer applications and products. Recent studies have suggested that PFCs in indoor air and dust could act as sources of human exposure and outdoor air contamination. This study presents method development and analysis of a wide range of PFCs in dust and air using active sampling techniques with commercially available sampling equipment (forensic nozzles with filter housings for dust collection and polyurethane foam (PUF)-XAD₂-PUF sandwich-tubes for air sampling) using both liquid and gas chromatography mass spectrometry. The developed method was validated and tested for applicability to analyze dust and air samples at both low and high concentrations (0.5 ng and 25 ng per analyte per air sample, respectively). Samples from private households and an office building were analyzed to explore differences in distribution patterns and concentrations. Perfluorooctane sulfonate, perfluorodecane sulfonate, perfluoroheptanoate, perfluorooctanoate and perfluorononanoate were observed in all samples of dust from private households, in the range from 1 to 80.1 ng g⁻¹. Fluorotelomer alcohols (FTOHs) were the predominant PFCs in indoor air samples with ∑FTOHs ranging between 4.7 and 17.9 ng m⁻³. The concentrations found in the present study are generally lower than those previously reported. This variation may be due to differences associated with geographical locations and lifestyles. However, use of different sampling techniques and strategies among studies can introduce large variations in PFC concentration found, making direct comparisons challenging.     

Validation of the operational emergency response model at the Swedish Meteorological and Hydrological Institute using data from etex and the chernobyl accident

The Eulerian atmospheric tracer transport model MATCH (Multiscale Atmospheric Transport and Chemistry model) has been extended with a Lagrangian particle model treating the initial dispersion of pollutants from point sources. The model has been implemented at the Swedish Meteorological and Hydrological Institute in an emergency response system for nuclear accidents and can be activated on short notice to provide forecast concentration and deposition fields.The model has been used to simulate the transport of the inert tracer released during the ETEX experiment and the transport and deposition of ¹³⁷Cs from the Chernobyl accident. Visual inspection of the results as well as statistical analysis shows that the extent, time of arrival and duration of the tracer cloud, is in good agreement with the observations for both cases, with a tendency towards over-prediction for the first ETEX release. For the Chernobyl case the simulated deposition pattern over Scandinavia and over Europe as a whole agrees with observations when observed precipitation is used in the simulation. When model calculated precipitation is used, the quality of the simulation is reduced significantly and the model fails to predict major features of the observed deposition field.     

Levels and composition of volatile organic compounds on commuting routes in Detroit, Michigan

Vehicle emissions can constitute a major share of ambient concentrations of many volatile organic compounds (VOCs) and other air pollutants in urban areas. Especially high concentrations may occur at curbsides, vehicle cabins, and other microenvironments. Such levels are not reflected by monitoring at fixed sites. This study reports on measurements of VOCs made from buses and cars in Detroit, MI. A total of 74 adsorbent tube samples were collected on 40 trips and analyzed by GC-MS for 77 target compounds. Three bus routes, selected to include residential, commercial and heavily industrialized areas, were sampled simultaneously on four sequential weeks during morning and afternoon rush hour periods. Nineteen compounds were regularly detected and quantified, the most prevalent of which included hexane/2-methyl pentane (15.6±5.8 μg m⁻³), toluene (10.2±7.9 μg m⁻³), m,p-xylene (6.8±4.7 μg m⁻³), benzene (4.5±3.0 μg m⁻³), 1,2,4-trimethylbenzene (4.0±2.6 μg m⁻³), o-xylene (2.2±1.6 μg m⁻³), and ethylbenzene (2.1±1.5 μg m⁻³). VOC levels in bus interiors and outdoor levels along the roadway were similar. Despite the presence of large industrial sources, route-to-route variation was small, but temporal variation was large and statistically significant. VOC compositions and trends indicate the dominance of vehicle sources over the many industrial sources in Detroit with the possible exceptions of styrene and several chlorinated VOCs. In-bus levels exceeded concentrations at fixed site monitors by a factor of 2–4. VOC concentrations in Detroit traffic are generally comparable to levels measured elsewhere in the US and Canada, but considerably lower than measured in Asia and Europe.     

Comportement photochimique du nitro-4 phenol en solution aqueuse

The quantum yield of the phototransformation of 4-nitrophenol has been evaluated as 4.5×10⁻⁵±0.6×10⁻⁵ at pH=2; at 3.0×10⁻⁵±0.6×10⁻⁵ at pH=5.5; 1.8×10⁻⁵±0.5×10⁻⁵ at pH=8.3. However the half-life is relatively low and no accumulation of aromatic or quinonic products was observed. Hydroquinone (QH₂) is the main organic primary product formed when an air-saturated or degassed solution was irradiated in 365 nm monochromatic light (about 80% of the 4-nitrophenol initially converted at pH=5.5 in the absence of oxygen). In air-saturated neutral or acidic solution, the formation of NO⁻₃ ions accounted for about 80% of the 4-nitrophenol converted, but in degassed medium a mixture NO : NO⁻₂ : NO⁻₃ is formed. An heterolytical mechanism of photohydrolysis with primary formation of QH₂ and HNO₂ is suggested. Several by-products as benzoquinone, 4-nitrosophenol, 4-nitrocatechol and nitrohydroquinone are formed according to the conditions. Many secondary reactions are involved as the disproportionation or the oxidation of HNO₂, the oxidation of QH₂ by HNO₂ and oxidations induced by excitation of NO⁻₂ and NO⁻₃.