Soil-Atmosphere exchange of radiatively and chemically active gases

Exchanges between the soils and the atmosphere may control or significantly affect the global budgets of many environmentally important trace gases, both natural and man-made. Flux measurements, taken in several ecosystems, show that soils are a substantial source of chloroform (8 ± 4 μg/m²/d) and a sink for methyl chloride (-10 _-3 ⁺⁶ μg/m²/d). The known sources and sinks of these gases are insufficient to explain the observed concentrations. Our findings will help to balance the global budget of chloroform but may put the budget of methyl chloride further out of balance. We also found, consistent with previous research, that soils are a substantial source of nitrous oxide and carbon monoxide and take up hydrogen and methane. The uptake of man-made chlorocarbons was observed, but the rates are small. Observed fluxes of non-methane hydrocarbons showed few patterns except that soils may be a source of ethane and butane.     

Latitudinal distributions of trace gases in and above the boundary layer

Statistical analyses of global atmospheric concentrations provide evidence that C₂Cl₄, CHCl₃ and CH₃CCl₃ (methylchloroform) are more abundant in the tropical boundary layer than above it (α ? 0.09) by 27% (±27%), 21% (?21%, +12%) and 6.4% (±6%) respectively. The air samples on which these results are based were collected by cryogenic techniques during the June 1978 project GAMETAG flights and analyzed soon afterwards by gas chromatography (EC/GC and GC/FID), thus providing latitudinal concentrations of CO, CH₄, CCl₃F, CCl₂F₂, CH₃CCl₃ and light C₂-hydrocarbons, both in and above the boundary layer. In August 1980, after further development of analytical techniques, the stored air samples were re-analyzed to establish the latitudinal distributions of CH₃I, CHCl₃, C₂Cl₄, C₂F₃Cl₃ (F-113) and CHClF₂ (F-22) in and above the boundary layer. Stability studies, spanning a year, show that the concentrations of these gases do not change in the flasks.     

Mesoscale influence on long-range transport — evidence from ETEX modelling and observations

During the first European Tracer Experiment (ETEX) tracer gas was released from a site in Brittany, France, and subsequently observed over a range of 2000 km. Hourly measurements were taken at the National Environmental Research Institute (NERI) located at Risø, Denmark, using two measurement techniques. At this location, the observed concentration time series shows a double-peak structure occurring between two and three days after the release. By using the Danish Emergency Response Model of the Atmosphere (DERMA), which is developed at the Danish Meteorological Institute (DMI), simulations of the dispersion of the tracer gas have been performed. Using numerical weather-prediction data from the European Centre for Medium-Range Weather Forecast (ECMWF) by DERMA, the arrival time of the tracer is quite well predicted, so also is the duration of the passage of the plume, but the double-peak structure is not reproduced. However, using higher-resolution data from the DMI version of the HIgh Resolution Limited Area Model (DMI-HIRLAM), DERMA reproduces the observed structure very well. The double-peak structure is caused by the influence of a mesoscale anti-cyclonic eddy on the tracer gas plume about one day earlier.     

Occupational risk of exposure to methicillin-resistant Staphylococcus aureus (MRSA) and the quality of infection hygiene in nursing homes

• Staff members were not colonised with MRSA. • But staff were exposed to MRSA from air, sedimented dust and surfaces. • MRSA was found in the rooms of MRSA-colonised residents but not in common areas. • Staff worry about MRSA and spreading it to other residents, family, and acquaintances. • The use of protective eyewear and facemasks could be improved. Methicillin-resistant Staphylococcus aureus (MRSA) is an increasing health concern across the globe and is often prevalent at long-term care facilities, such as nursing homes. However, we know little of whether nursing home staff is exposed to MRSA via air and surfaces. We investigated whether staff members at nursing homes are colonised with and exposed to culturable MRSA, and assessed staff members’ self-reported knowledge of MRSA and compliance with infection hygiene guidelines. Five nursing homes with MRSA positive residents were visited in Copenhagen, Denmark. Personal bioaerosol exposure samples and environmental samples from surfaces, sedimented dust and bioaerosols were examined for MRSA and methicillin-susceptible S. aureus (MSSA) to determine occupational exposure. Swabs were taken from staffs’ nose, throat, and hands to determine whether they were colonised with MRSA. An online questionnaire about MRSA and infection control was distributed. No staff members were colonised with MRSA, but MRSA was detected in the rooms of the colonised residents in two out of the five nursing homes. MRSA was observed in air (n = 4 out of 42, ranging from 2.9–7.9 CFU/m³), sedimented dust (n = 1 out of 58, 1.1 × 10³ CFU/m²/d), and on surfaces (n = 9 out of 113, 0.04–70.8 CFU/m²). The questionnaire revealed that half of the staff members worry about spreading MRSA to others. Identified aspects for improvement were improved availability and use of protective equipment, not transferring cleaning supplies (e.g., vacuum cleaners) between residents’ rooms and to reduce worry of MRSA, e.g., through education.     

Net fluxes of pesticides from the Scheldt Estuary into the North Sea: a model approach

A hydrological model was constructed with the commercially available modelling environment ECoS for the calculation of mixing plots of dissolved pesticide concentrations in the Scheldt Estuary. The model was based on a one-dimensional advection-dispersion equation and dispersion coefficients were calculated from measured salinity profiles. The model could correctly predict the movement of water masses within the estuary. Nominal flushing times of the estuary were calculated with the fraction-of-freshwater method and ranged between 25 and 95 days, depending on the freshwater discharge. Model calculations demonstrated that the application-related time profiles of pesticide input may well induce curvature in the calculated estuarine mixing plot even if the pesticide behaves conservatively. Calculated mixing plots were compared with experimental data and good agreement was obtained between the measurements and the conservative mixing plot of atrazine. For metolachlor an additional direct emission had to be modelled to explain the differences between the experimental data and the conservative mixing plot. For dichlorvos and simazine. on the other hand, an estuarine loss constant had to be included in the model. Using a least-squares procedure the estuarine loss constants for dichlorvos and simazine were estimated at half-lives of five and 26 days, respectively. Because mixing plots were strongly influenced by the time profiles of pesticide input, standard procedures in which net fluxes are calculated from mixing plots, were not applicable. Therefore, net fluxes were calculated with a newly developed procedure in which the estuarine loss constants and the estuarine flushing time were combined. For the non-conservative compounds dichlorvos and simazine, the net fluxes to the North Sea were found to be 96 and 64%, respectively, lower than the gross fluxes transported by the River Scheldt.     

Simulating the impacts of fire: A computer program

Recurrent fire has played a dominant role in the ecology of southwestern ponderosa pine forests. To assess the benefits or losses of fire in these forests, a computer simulation model, called BURN, considers vegetation (mortality, regeneration, and production of herbaceous vegetation), wildlife (populations and habitats), and hydrology (streamflow and water quality). In the formulation of the model, graphical representations (time-trend response curves) of increases or losses (compared to an unburned control) after the occurrence of fire are converted to fixedterm annual ratios, and then annuities for the simulation components. Annuity values higher than 1.0 indicate benefits, while annuity values lower than 1.0 indicate losses. Studies in southwestern ponderosa pine forests utilized in the development of BURN are described briefly.     

Observed trends for CF3-containing compounds in background air at Cape Meares, Oregon, Point Barrow, Alaska, and Palmer Station, Antarctica

The concentrations of CF(3)-containing compounds in archived air samples collected at Cape Meares, Oregon, from 1978 to 1997, at Point Barrow, Alaska, from 1995 to 1998, and at Palmer Station, Antarctica, from 1991 to 1997, were determined by high resolution gas chromatography and high resolution mass spectrometry. The CF(3)-containing compounds measured by this method and discussed here are: the perfluorinated compound, C(3)F(8) (FC 218); four perhalogenated compounds, CF(3)Cl (CFC 13), CF(3)CF(2)Cl (CFC 115), CF(3)CFCl(2) (CFC 114a), and CF(3)Br (Halon 1301); and three hydrofluorocompounds, CF(3)H (HFC 23), CF(3)CH(3) (HFC 143a), and CF(3)CH(2)F (HFC 134a). For four of these compounds, very few measurements have been previously reported. The atmospheric concentrations of all of the CF(3)-containing compounds continuously increased in time over the sample collection periods. From these data, the annual rates of emission into the atmosphere have been estimated. The emission rates fall into one of three distinct categories. The annual emission rates of C(3)F(8), CF(3)H, CF(3)CH(3), and CF(3)CH(2)F have continuously increased over the last two decades. That of CF(3)CFCl(2) has decreased continuously. Emission rates for CF(3)Cl, CF(3)CF(2)Cl, and CF(3)Br reached maximum levels in the late 1980s, and have been decreasing in the 1990s. The emission rates of C(3)F(8), CF(3)CH(3) and CF(3)CH(2)F were nearly zero 20 years ago but have increased rapidly during the last decade.     

Local physical habitat quality cloud the effect of predicted pesticide runoff from agricultural land in Danish streams

The combination of intensive agricultural activities and the close connectivity between land and stream emphasise the potential risk of pesticide exposure in Danish streams. Benthic macroinvertebrates are applied in the assessment of stream ecological status, and some sensitive species have been shown to respond strongly to brief pulses of pesticide contamination. In this study we investigate the impact of agriculturally derived pesticides on stream macroinvertebrate communities in Denmark. As a measure of toxic pressure we apply the Runoff Potential. We investigated a total of 212 streams. These were grouped into distinct classes according to the magnitude of pesticide contamination in the period from 2003-2006. A total of 24 different macroinvertebrate indices were applied to detect effects of pesticide runoff (e.g. the SPEAR-index and the number of EPT taxa). We found high predicted pesticide runoff in 39% of the streams, but we found no significant effect of predicted pesticide exposure on stream macroinvertebrate indices. We, additionally, examined the influence of a series of environmental parameters ranging from site scale to catchment scale on the macroinvertebrate community. Relative proportions of gravel, sand and silt in bed sediments explained most of the variation in macroinvertebrate indices as well as the upstream riparian habitat quality. We suggest that the Runoff Potential model overestimate pesticide runoff contamination in Danish streams due the presence of buffer strips enforced by Danish legislation. When pesticide runoff contamination is low to moderate, poor physical properties (indirectly related to agricultural activity) are the main impediment for the ecological quality of Danish streams.