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In the present study, photocatalytic reactions of nitrogen oxides (NOx = NO + NO2) were studied on commercial TiO2 doped facade paints in a flow tube photoreactor under simulated atmospheric conditions. Fast photocatalytic conversion of NO and NO2 was observed only for the photocatalytic paints and not for non-catalytic reference paints. Nitrous acid (HONO) was formed in the dark on all paints studied, however, it efficiently decomposes under irradiation only on the photocatalytic samples. Thus, it is concluded that photocatalytic paint surfaces do not represent a daytime source of HONO, in contrast to other recent studies on pure TiO2 surfaces. As main final product, the formation of adsorbed nitric acid/nitrate anion (HNO3/NO3?) was observed with near to unity yield. In addition, traces of H2O2 were observed in the gas phase only in the presence of O2. Formation of the greenhouse gas nitrous oxide (N2O) could be excluded. The uptake kinetics of NO, NO2 and HONO was very fast under atmospheric conditions (e.g. γ(NO + TiO2) > 10?5). Thus, the uptake on urban surfaces (painted houses, etc.) will be limited by transport. For a hypothetically painted street canyon, an average reduction of nitrogen oxide levels of ca. 5% is estimated. Since the harmful HNO3/NO3? is formed on the surface of the photoactive paints, whereas it is formed in the gas phase in the atmosphere, the use of photocatalytic paints may also help to reduce acid deposition, e.g. on plants, or nitric acid related health issues.  相似文献   
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The city of Santiago, Chile experiences frequent high pollution episodes and as a consequence very high ozone concentrations, which are associated with health problems including increasing daily mortality and hospital admissions for respiratory illnesses. The development of ozone abatement strategies requires the determination of the potential of each pollutant to produce ozone, taking into account known mechanisms and chemical kinetics in addition to ambient atmospheric conditions. In this study, the photochemical formation of ozone during a summer campaign carried out from March 8–20, 2005 has been investigated using an urban photochemical box model based on the Master Chemical Mechanism (MCMv3.1). The MCM box model has been constrained with 10 min averages of simultaneous measurements of HONO, HCHO, CO, NO, j(O1D), j(NO2), 31 volatile organic compounds (VOCs) and meteorological parameters. The O3–NOx–VOC sensitivities have been determined by simulating ozone formation at different VOC and NOx concentrations. Ozone sensitivity analyses showed that photochemical ozone formation is VOC-limited under average summertime conditions in Santiago. The results of the model simulations have been compared with a set of potential empirical indicator relationships including H2O2/HNO3, HCHO/NOy and O3/NOz. The ozone forming potential of each measured VOC has been determined using the MCM box model. The impacts of the above study on possible summertime ozone control strategies in Santiago are discussed.  相似文献   
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The amounts of formaldehyde and nitrous acid (HONO) in gas phase and dews of Santiago de Chile were simultaneously measured. Formaldehyde concentrations values in the liquid phase (dews) correlate fairly well with those in the gaseous phase and are even higher than those expected from gas–dew equilibrium. On the other hand, nitrite concentrations in dews were considerably smaller (ca. 15 times) than those expected from the gas-phase concentrations. This under-saturation is attributed to diffusion limitations due to the relatively large HONO solubility. In agreement with this, under-saturation increases with the rate of dew formation and the pH of the collected waters, factors that should increase the rate of gas to liquid HONO transfer required to reach equilibrium.  相似文献   
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Background

The decreasing NOX concentrations at urban measurement stations in Germany are in agreement with the reduction of NOX emissions from vehicular traffic. However, the measured NO2 concentrations are stagnating nationwide. In 2010, at more than the half of the urban measurement stations in Germany, annual mean values for NO2 exceeded the new Europe-wide limit value of 40 μg/m3 (20 ppbv) NO2. Similar findings are reported from many other member states of the European Union.

Results

The observed trend of the airborne NO2 concentrations has different reasons. Firstly, the NO2/NOx emission ratio has increased significantly during the last two decades. Furthermore, secondary NO2, caused by the titration reactions of NO with ozone (O3) and peroxy radicals (RO2), is responsible for the major fraction (approximately 70%) of the measured NO2. However, secondary NO2 shows a highly nonlinear dependency on NOx and thus, is decreasing much more slowly than expected from the decreasing NOx levels. Based on the results from the present study, the increased NO2/NOX emission ratio can only explain a minor fraction of the observed high airborne NO2 concentration in the city center.

Conclusions

A further reduction of primary NO2 emissions, due to improved exhaust gas treatment, will not have a strong influence on urban NO2 levels, and a further significant reduction of the NOX emissions, in particular from vehicular traffic, is necessary in order to meet the annual mean limit value for NO2 of about 20 ppb in the future.  相似文献   
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In response to the recent focus by the U.S. EnvironmentalProtection Agency on bioassessment of lakes, a multimetric index was developed for New Jersey lakes and reservoirs using benthicmacroinvertebrates. Benthic samples were collected fromreference and impaired lakes with muck and intermediate sedimentsin central and northern New Jersey during summer 1997. We used astepwise process to evaluate properties of candidate metrics andselected five for the Lake Macroinvertebrate Integrity Index(LMII): Hilsenhoff Biotic Index (HBI), percent chironomidindividuals, percent collector-gatherer taxa, percentoligochaetes/leeches, and number of Diptera taxa. We scoredmetrics as the fraction of the best expected value (based on allsites) achieved at a site and summed them into the LMII. Evaluation of the LMII showed that it discriminated well betweenreference and impaired lakes and was strongly related to severalpotential stressors. Chemical and physical gradients distinguished between reference and impaired lakes, and the LMIIsummarized these gradients well. The LMII corresponded stronglywith land use, but some lakes with more urban land use stillachieved high scores. Based on a power analysis, the ability ofthe LMII to detect differences in condition was sensitive to thenumber of samples from each lake.  相似文献   
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CO/CO2 ratios have been measured in different locations of Santiago de Chile city. Measurements were carried out in a tunnel (prevailing emissions from cars with catalytic converter) and close to heavy traffic streets. Concentrations measured along the city traffic tunnel or temporal profiles of concentrations measured near heavy traffic streets allow an estimation of CO/CO2 ratios emitted from mobile sources. Values obtained range from 0.0045 ± 0.0006 to 0.0100 ± 0.0004 and depend on the prevailing type of mobile sources. In particular, lowest values were found close to a street with heavy traffic dominated by diesel-powered public transportation, while the highest values were found at the city tunnel. Places located near streets of mixed mobile sources (public buses and cars) showed intermediate values. Average CO/CO2 ratios are compatible with emission factors proposed for Santiago’s main mobile sources.  相似文献   
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The oxidation capacity of the highly polluted urban area of Santiago de Chile has been evaluated during a winter measurement campaign from May 25 to June 07, 2005, with the results compared and contrasted with those previously evaluated during a summer campaign from March 8 to 20, 2005. The OH radical budget was evaluated in both campaigns employing a simple quasi-photostationary state model (PSS) constrained with simultaneous measurements of HONO, HCHO, O3, NO, NO2, j(O1D), j(NO2), 13 alkenes and meteorological parameters. In addition, a zero dimensional photochemical box model based on the Master Chemical Mechanism (MCMv3.1) has been used for the analysis of the radical budgets and concentrations of OH, HO2 and RO2. Besides the above parameters, the MCM model has been constrained by the measured CO and other volatile organic compounds (VOCs) including alkanes and aromatics. Total production and destruction rates of OH and HO2 in winter are about two times lower than that during summer. Simulated OH levels by both PSS and MCM models are similar during the daytime for both winter and summer indicating that the primary OH sources and sinks included in the simple PSS model are predominant. On a 24 h basis, HONO photolysis was shown to be the most important primary OH radical source comprising 81% and 52% of the OH initiation rate during winter and summer, respectively followed by alkene ozonolysis (12.5% and 29%), photolysis of HCHO (6.1% and 15%), and photolysis of O3 (<1% and 4%), respectively. During both winter and summer, there was a balance between the OH secondary production (HO2 + NO) and destruction (OH + VOCs) showing that initiation sources of RO2 and HO2 are no net OH initiation sources. This result was found to be fulfilled also for all other studies investigated. Seasonal impacts on the radical budgets are also discussed.  相似文献   
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Fluvial cohesive sediment is of fundamental environmental and multidisciplinary concern owing to its significant impact on energy, nutrient and trace element fluxes, river sediment budgets as well as habitat quality. Consequently, numerous studies in geomorphology, hydraulics, hydrology and river ecology accentuate the importance of fluvial fine grained sediment. Increased deposition of fine grained particles for instance can negatively effect benthic habitats. Settling velocity and deposition rates of fines are key terms in sediment transport models. Thus, the knowledge of transport and quantitative deposition dynamics are necessary prerequisites for a sustainable sediment and habitat management as well as a reliable, physically based modelling of fine sediment conveyance and contaminant transfer in streams. However, it is generally a challenging task to characterise and trace fine-grained particle transport, deposition and resuspension dynamics in a fluvial environment. One inherent complexity of fluvial cohesive sediment dynamics is for instance the relevance of interparticle forces and flocculation/aggregation processes. Owing to this complexity and the lack of standardized methods cohesive particle transport mechanisms are hardly predictable in a specific field situation. Consequently, interdisciplinary research approaches are needed. This article discusses specific findings and research gaps in the field of cohesive sediment research.  相似文献   
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