Traceability of Long-Term Atmospheric Composition Observations across Global Monitoring Networks: Chemical Metrology Applied to the Measurements of Constituents in Air, Water, and Soil

High-quality and long-term comparable time series of the relevant atmospheric observations are the essential prerequisite to understand the dynamical, physical and chemical state of the atmosphere from seasonal to multi-decadal time scales. For relevant gaseous compounds such as ozone, methane (CH4) and carbon monoxide (CO), the requirements are secured by tracing back these observations to common primary standards. Periodical audits of the system in operation and the performance of measurement sites provide additional information about data quality and comparability. The results of 48 audits conducted by the World Calibration Centre for Surface Ozone, Carbon Monoxide and Methane (WCC-Empa) at global stations of the Global Atmosphere Watch programme (GAW) from 1996 to 2009 show that most of the audited sites meet the data quality objectives for ozone and methane whereas the situation is less uniform for carbon monoxide

Reductive Transformations of Anthropogenic Chemicals in Natural and Technical Systems

Reductive transformation reactions of chemical pollutants (e.g., polyhalogenated hydrocarbons, aromatic azo and nitro compounds, chromium(VI) species) in the environment are important both from an ecotoxicological and from an environmental technology point of view. Using well-defined model reactors as well as more complex 'real world' systems, several groups at EAWAG are trying to unravel compound- and system-specific factors that control the reduction of a variety of anthropogenic chemicals under different conditions in the environment. The examples presented in this article include the reduction of nitroaromatic compounds under iron- and sulfate-reducing conditions, the reductive dehalogenation of chlorinated ethenes by cob(I)alamin and by a bacterium that uses such compounds as terminal electron acceptors, and the reduction of chromium(VI) by various reduced iron species. The link between microbial and abiotic (chemical) processes involved in reductive transformations of pollutants is emphasized. The major goal of this article is to illustrate the approaches taken to elucidate the mechanisms and kinetics of environmentally relevant reduction reactions of pollutants, and to discuss how the results of such studies can be used 1) to gain insight into what is actually happening in the environment, and 2) to develop methods for the treatment of chemical wastes or contaminated sites

Oxidative Transformations of Contaminants in Natural and in Technical Systems

In this paper, we present case studies of oxidative transformations of contaminants by oxidants which are relevant in natural and in technical systems. These oxidants are reactive oxygen species (ROS), manganese(III,IV), iron(III), and molecular dioxygen (O2). Regarding ROS, we discuss i) their concentrations and their efficiencies as oxidants in natural waters and in water treatment, ii) reactions occurring in bromide-containing waters in the presence of ROS, iii) role of iron in the formation of ROS, and iv) quantitative structure-activity relationships (QSAR) of reactions of ROS with contaminants. Concerning MnIII and MnIV as oxidants, we present experimental studies on the oxidation of anilines by δ-MnO2. With respect to oxidative transformation of the hydrophilic organic contaminants ethylenediaminetetraacetate (EDTA) and nitrilotriacetate (NTA), we show that these organic complexing agents are efficiently oxidized by FeIII and O2, respectively, if catalyzed by light (for the oxidation of EDTA by FeIII and by enzymes (for the oxidation of NTA by O2)

Assessment of parameters describing representativeness of air quality in-situ measurement sites

The atmospheric layer closest to the ground is strongly influenced by variable surfacefluxes (emissions, surface deposition) and can therefore be very heterogeneous. Inorder to perform air quality measurements that are representative of a larger domainor a certain degree of pollution, observatories are placed away from population cen-5tres or within areas of specific population density. Sites are often categorised basedon subjective criteria that are not uniformly applied within different administrative do-mains. A novel approach for the assessment of parameters reflecting site represen-tativeness is presented here, taking emissions, deposition and transport towards 34sites covering Western and Central Europe into account. These parameters are di-10rectly inter-comparable among the sites and can be used to select sites that are, onaverage, more or less suitable for data assimilation and comparison with satellite andmodel data. Advection towards these sites was simulated by backward LagrangianParticle Dispersion Modelling (LPDM) to determine the sites’ annual catchment areasfor the year 2005 and advection times of 12, 24 and 48 h. Only variations caused by15emissions and transport during these periods were considered assuming that thesedominate the short-term variability of most but especially short lived trace gases. Theparameters of representativeness derived were compared between sites and a novel,uniform and observation-independent categorisation of the sites based on a clusteringapproach was established. Six groups of European background sites were identified20ranging from very remote coastal to polluted rural sites. These six categories explained50 to 80% of the inter-site variability of median mixing ratios and their standard devia-tion for NO2and O3, while differences between group means of the longer lived tracegas CO were insignificant. The derived annual catchment areas strongly dependedon the applied LPDM and input wind fields, the catchment settings and the year of25analysis. Nevertheless, the parameters of representativeness showed considerablyless variability than the catchment geometry, supporting the robustness of the derivedstation categorisation.ISSN:1680-7375ISSN:1680-736

Assessment of parameters describing representativeness of air quality in-situ measurement sites

The atmospheric layer closest to the ground is strongly influenced by variable surfacefluxes (emissions, surface deposition) and can therefore be very heterogeneous. Inorder to perform air quality measurements that are representative of a larger domainor a certain degree of pollution, observatories are placed away from population cen-5tres or within areas of specific population density. Sites are often categorised basedon subjective criteria that are not uniformly applied within different administrative do-mains. A novel approach for the assessment of parameters reflecting site represen-tativeness is presented here, taking emissions, deposition and transport towards 34sites covering Western and Central Europe into account. These parameters are di-10rectly inter-comparable among the sites and can be used to select sites that are, onaverage, more or less suitable for data assimilation and comparison with satellite andmodel data. Advection towards these sites was simulated by backward LagrangianParticle Dispersion Modelling (LPDM) to determine the sites’ annual catchment areasfor the year 2005 and advection times of 12, 24 and 48 h. Only variations caused by15emissions and transport during these periods were considered assuming that thesedominate the short-term variability of most but especially short lived trace gases. Theparameters of representativeness derived were compared between sites and a novel,uniform and observation-independent categorisation of the sites based on a clusteringapproach was established. Six groups of European background sites were identified20ranging from very remote coastal to polluted rural sites. These six categories explained50 to 80% of the inter-site variability of median mixing ratios and their standard devia-tion for NO2and O3, while differences between group means of the longer lived tracegas CO were insignificant. The derived annual catchment areas strongly dependedon the applied LPDM and input wind fields, the catchment settings and the year of25analysis. Nevertheless, the parameters of representativeness showed considerablyless variability than the catchment geometry, supporting the robustness of the derivedstation categorisation.ISSN:1680-7375ISSN:1680-736

Inter-comparison of four different carbon monoxide measurement techniques and evaluation of the long-term carbon monoxide time series of Jungfraujoch

Despite the importance of carbon monoxide (CO) for the overall oxidative capacity of the atmosphere, there is still considerable uncertainty in ambient measurements of CO. To address this issue, an inter-comparison between four different measurement techniques was made over a period of two months at the high-alpine site Jungfraujoch (JFJ), Switzerland. The measurement techniques were Non-dispersive Infrared Absorption (NDIR), Vacuum UV Resonance Fluorescence (VURF), gas chromatographic separation with a mercuric oxide reduction detector (GC/HgO), and gas chromatographic separation followed by reduction on a nickel catalyst and analysis by a flame ionization detector (GC/FID). The agreement among all techniques was better than 2% for one-hourly averages, which confirmed the suitability of the NDIR method for CO measurements even at remote sites. The inter-comparison added to the validation of the 12-year record (1996–2007) of continuous CO measurements at JFJ. To date this is one of the longest time series of continuous CO measurements in the free troposphere over Central Europe. This data record was further investigated with a focus on trend analysis. A significant negative trend was observed at JFJ showing a decrease of 21.4±0.3% over the investigated period, or an average annual decrease of 1.78%/yr (2.65±0.04 ppb/yr). These results were compared with emission inventory data reported to the Long-range Transboundary Air Pollution (LRTAP) Convention. It could be shown that long range transport significantly influences the CO levels observed at JFJ, with air masses of non-European origin contributing at least one third of the observed mole fractions.ISSN:1680-7375ISSN:1680-736