Application and test of a simple tool for operational footprint evaluations

We present a user-friendly tool for footprint calculations of flux measurements in the surface layer. The calculations are based on the analytical footprint model by Kormann, R. and Meixner, F.X. [2001. An analytical footprint model for Non-neutral Stratification. Boundary-Layer Meteorology 99, 207-224]. The footprint density function of a flux sensor is determined using readily available data from standard eddy covariance measurements. This footprint density function is integrated over defined surface areas given as quadrangular polygons representing e.g. agricultural fields. We illustrate the use and performance of the tool by applying it to CO2 flux measurements with three eddy covariance system at the Swiss CarboEurope grassland site. Two flux towers were positioned in the centre of two neighbouring fields, respectively, that showed a very different CO2 flux during the study period. The third tower was located near the border of the two fields and was frequently influenced by both fields to a similar degree. The calculated footprint fractions were used to simulate the latter flux from the other two systems. The measured and simulated fluxes showed a good agreement and thus support the reliability of the footprint calculation. The presented simple footprint tool can be used as a routine quality check for flux monitoring stations influenced by surface areas with varying vegetation covers and/or land-use.     

Symptoms prevalence among office workers of a sealed versus a non-sealed building: Associations to indoor air quality

ObjectivesAn increasing number of complaints related to time spent in artificially ventilated buildings have been progressively reported and attributed, at least in part, to physical and chemical exposures in the office environment. The objective of this research was to investigate the association between the prevalence of work-related symptoms and the indoor air quality, comparing a sealed office building with a naturally ventilated one, considering, specially, the indoor concentration of TPM, TVOCs and the main individual VOCs.MethodsA cross-sectional study was performed to compare the prevalence of sick building syndrome (SBS) symptoms among 1736 office workers of a sealed office building and 950 of a non-sealed one, both in Rio de Janeiro's downtown. The prevalence of symptoms was obtained by a SBS standardized questionnaire. The IAQ of the buildings was evaluated through specific methods, to determine the temperature, humidity, particulate matter and volatile organic compound (VOC) concentrations.ResultsUpper airways and ophthalmic symptoms, tiredness and headache were highly prevalent in both buildings. Some symptoms were more prevalent in the sealed building: “eye dryness” 33.3% and 27.1% (p: 0.01); “runny nose” 37.3% and 31.3% (p: 0.03); “dry throat” 42% and 36% (p: 0.02); and “lethargy” 58.5% and 50.5% (p: 0.03) respectively. However, relative humidity and indoor total particulate matter (TPM) concentration as well as total volatile organic compounds (TVOCs) were paradoxically greater in the non-sealed building, in which aromatic compounds had higher concentration, especially benzene. The analysis between measured exposure levels and resulting symptoms showed no association among its prevalence and TPM, TVOCs, benzene or toluene concentration in none of the buildings.ConclusionsOther disregarded factors, like undetected VOCs, mites, molds and endotoxin concentrations, may be associated to the greater prevalence of symptoms in the sealed building.     

High-resolution modelling of AOT40 and stomatal ozone uptake in wheat and grassland: a comparison between 2000 and the hot summer of 2003 in Switzerland

The aim was to compare the ozone risk for agricultural crops in Switzerland during the hot and dry year 2003 with the more 'normal' situation in 2000. An improved version of the Ozone DEposition Model ODEM was used at a 2 x 2 km resolution. The distribution of the index AOT40 was compared with the accumulated stomatal ozone flux, AF(st). Averaged AOT40 at 2 m and at canopy height was much higher in 2003 than in 2000, but inter-annual differences in AF(st) for wheat and grasslands were small due to the limiting effect of low soil water contents in 2003. AOT40 suggested larger potential yield losses in wheat in 2003, while using AF(st) with a threshold of 6 nmol m(-2) s(-1) (AF(st)6) yielded similar estimates for both years. The data show that modelling of AF(st) can be used to differentiate ozone risks between regions and years at a national scale.     

Uncertainty assessment of contaminant plume length estimates in heterogeneous aquifers

The Virtual Aquifer approach is used in this study to assess the uncertainty involved in the estimation of contaminant plume lengths in heterogeneous aquifers. Contaminant plumes in heterogeneous two-dimensional conductivity fields and subject to first order and Michaelis-Menten (MM) degradation kinetics are investigated by the center line method. First order degradation rates and plume lengths are estimated from point information obtained along the plume center line. Results from a Monte-Carlo investigation show that the estimated rate constant is highly uncertain and biased towards overly high values. Uncertainty and bias amplify with increasing heterogeneity up to maximum values of one order of magnitude. Calculated plume lengths reflect this uncertainty and bias. On average, plume lengths are estimated to about 50% of the true plume length. When plumes subject to MM degradation kinetics are investigated by using a first order rate law, an additional error is introduced and uncertainty as well as bias increase, causing plume length estimates to be less than 40% of the true length. For plumes with MM degradation kinetics, therefore, a regression approach is used which allows the determination of the MM parameters from center line data. Rate parameters are overestimated by a factor of two on average, while plume length estimates are about 80% of the true length. Plume lengths calculated using the MM parameters are thus closer to the correct length, as compared to the first order approximation. This approach is therefore recommended if field data collected along the center line of a plume give evidence of MM kinetics.     

Reductive dechlorination of chlorofluorocarbons and hydrochlorofluorocarbons in sewage sludge and aquifer sediment microcosms

The reductive transformation of the 10 most-widely distributed fluorinated volatile compounds and of tetrachloroethene was investigated for up to 177 days under anaerobic conditions in sewage sludge and aquifer sediment slurries. Concentrations of parent compounds and of degradation products were identified by GC-MS. We observed transformation of CFC-11 to HCFC-21 and HCFC-31, of CFC-113 to HCFC-123a, chlorotrifluoroethene and trifluoroethene, of CFC-12 to HCFC-22, of HCFC-141b to HCFC-151b, and of tetrachloroethene to vinyl chloride and ethene. CFC-114, CFC-115, HCFC-142b, HFC-134a and HCFC-22 were not transformed. The results suggest that with both inocula studied here, hydrogenolysis is the primary reductive dechlorination reaction. CFC-113 was the only compound where a dichloro-elimination was observed, leading to the formation of chlorotrifluoroethene as temporal intermediate and to trifluoroethene as end product. The relative reduction rates of chlorofluoromethanes compared reasonably well with theoretical rates calculated based on thermochemical data according to the Marcus theory. Some of the accumulating HCFCs and haloethenes observed in this study are toxic and may be of practical relevance in anaerobic environments.     

Application of a three-dimensional model for assessing effects of small clear-cuttings on radiation and soil temperature

A three-dimensional model Mixfor-3D of soil–vegetation–atmosphere transfer (SVAT) was developed and applied to estimate possible effects of tree clear-cutting on radiation and soil temperature regimes of a forest ecosystem. The Mixfor-3D model consists of several closely coupled 3D sub-models describing: forest stand structure; radiative transfer in a forest canopy; turbulent transfer of sensible heat, H₂O and CO₂ between ground surface and the atmospheric surface layer; evapotranspiration of ground surface vegetation and soil; heat and moisture transfer in soil. The model operates with the horizontal grid resolution, 2 m × 2 m; vertical resolution, 1 m and primary time step, 1 h.     

Assessment of the nitrogen and carbon budget of two managed temperate grassland fields

Greenhouse gas budgets as well as the productivity of grassland systems are closely related to the carbon (C) and nitrogen (N) cycles. Within the framework of the CarboEurope and NitroEurope projects we have measured C and N exchange on the field scale at the grassland site Oensingen previously converted from arable rotation. The site is located on the Swiss Central Plateau and consists of two parallel fields of equal size. One field was subjected to intensive management with average nitrogen input of 230 kg-N ha⁻¹ year⁻¹ and 4–5 cuts per year, and the other to an extensive management with no fertilisation and less frequent cutting. The total C budget of the fields was assessed by measuring the CO₂ exchange by eddy covariance and analysing the carbon import by manure application and export by harvest. The N budget of the managed grassland is more complex. Besides the management related import and export, it includes gaseous exchange in many different forms (NO, NO₂, HNO₃, N₂O, NH₃, N₂) needing different analytical techniques, as well as input by rain and leaching of N-compounds with the soil water. The main (“level-3”) field sites in the NitroEurope project are supposed to measure 95% of the N fluxes at the field scale. For several of the N fluxes specific measurements have been performed for 1 year or longer at the site. Some of the remaining N budget components (dry and wet deposition) could be estimated from results of a national deposition network, while other components (NH₃ and N₂ emission) were estimated based on literature parameterisations. However, we found indications that the (systematic) uncertainties of these estimated N-fluxes are large and that it is important to make site-specific measurement for all relevant budget components. The suitability of corresponding experimental methods is discussed.Analysis of the C budget over a 6-year period (2002–2007) showed a significant mean difference between the two newly established grassland fields with a likely net carbon loss for the extensive management and a net sequestration for the intensive management. Since the C/N ratio of the soil organic matter of the grassland is constrained in a rather narrow range around 9.3, the change in the soil carbon pool is supposed to be accompanied by a corresponding change in the N storage. This approach provided an alternative method to check the N budget of the two grassland fields derived from the individual N fluxes.