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As the scale of single-cell genomics experiments grows into the millions, the computational requirements to process this data are beyond the reach of many. Herein we present Scarf, a modularly designed Python package that seamlessly interoperates with other single-cell toolkits and allows for memory-efficient single-cell analysis of millions of cells on a laptop or low-cost devices like single-board computers. We demonstrate Scarf's memory and compute-time efficiency by applying it to the largest existing single-cell RNA-Seq and ATAC-Seq datasets. Scarf wraps memory-efficient implementations of a graph-based t-stochastic neighbour embedding and hierarchical clustering algorithm. Moreover, Scarf performs accurate reference-anchored mapping of datasets while maintaining memory efficiency. By implementing a subsampling algorithm, Scarf additionally has the capacity to generate representative sampling of cells from a given dataset wherein rare cell populations and lineage differentiation trajectories are conserved. Together, Scarf provides a framework wherein any researcher can perform advanced processing, subsampling, reanalysis, and integration of atlas-scale datasets on standard laptop computers. Scarf is available on Github: https://github.com/parashardhapola/scarf. As the scale of single-cell genomics experiments grows into the millions, the computational requirements to process this data are beyond the reach of many. Here the authors present Scarf, a modularly designed Python package that makes the analysis workflow highly memory efficient such that even the largest existing datasets can be analyzed on an average modern laptop. [ABSTRACT FROM AUTHOR]

Landslides may cause severe destruction that affects both the individuals and functions vital for society. Minor landslides in an area with quick clay may trigger secondary slides, influencing a much greater area compared to slides in areas with no quick clay. Today's expanding societies demand new areas for exploitation. To effectively meet this demand, there is an increased need to identify areas where quick clay may occur. Direct or indirect methods for assessing the presence of quick clay have previously been presented as well as a strategy for site investigations in quick clay areas. In this article, a methodology for mapping quick clays for the Swedish conditions with methods commonly available in this area is presented. The methodology presented in the article is structured in steps with different levels of detail and visualized with two conceptual flowcharts. Depending on the stage of planning, different types of surveys are recommended. The methodology has been applied at four sites where integrated interpretation of airborne and ground geophysical measurements as well as geotechnical investigations have been carried out. The results from two of these sites are presented here. The study reveals that all the methods used have their advantages and limitations. However, a combined use of the information provides much more accurate interpretation that can be used for a more cost-effective future planning and decision-making. [ABSTRACT FROM AUTHOR]

Because of its serious large-scale effects on ecosystems and its transboundary nature, acid rain received for a few decades at the end of the last century wide scientific and public interest, leading to coordinated policy actions in Europe and North America. Through these actions, in particular those under the UNECE Convention on Long-range Transboundary Air Pollution, air emissions were substantially reduced, and ecosystem impacts decreased. Widespread scientific research, long-term monitoring, and integrated assessment modelling formed the basis for the policy agreements. In this paper, which is based on an international symposium organised to commemorate 50 years of successful integration of air pollution research and policy, we briefly describe the scientific findings that provided the foundation for the policy development. We also discuss important characteristics of the science–policy interactions, such as the critical loads concept and the large-scale ecosystem field studies. Finally, acid rain and air pollution are set in the context of future societal developments and needs, e.g. the UN's Sustainable Development Goals. We also highlight the need to maintain and develop supporting scientific infrastructures. [ABSTRACT FROM AUTHOR]

In the initial phase of a national project to map clay, sand and soil organic matter (SOM) content in arable topsoil in Sweden, a study area in south-west Sweden comprising about 100 000 ha of arable land was assessed. Models were created for texture, SOM and two estimated variables for lime requirement determination (target pH and buffering capacity), using a data mining method (multivariate adaptive regression splines). Two existing reference soil datasets were used: a grid dataset and a dataset created for individual farms. The predictor data were of three types: airborne gamma-ray spectrometry data, digital elevation from airborne laser scanning, and legacy data on Quaternary geology. Validations were designed to suit applicability assessments of prediction maps for precision agriculture. The predictor data proved applicable for regional mapping of topsoil texture at 50 × 50 m spatial resolution (root mean square error: clay = 6.5 %; sand = 13.2 %). A novel modelling strategy, 'Farm Interactive', in which soil analysis data for individual farms were added to the regional data, and given extra weight, improved the map locally. SOM models were less satisfactory. Variable-rate application files for liming created from derived digital soil maps and locally interpolated soil data were compared with 'ground truth' maps created by proximal sensors on one test farm. The Farm Interactive methodology generated the best predictions and was deemed suitable for adaptation of regional digital soil maps for precision agricultural purposes. [ABSTRACT FROM AUTHOR]

Purpose: By recycling sewage sludge (SS) to productive land, its plant nutrients can be utilised. However, the use of organic fertilisers carries health risks and causes emissions of nitrous oxide (NO), methane (CH) and ammonia (NH). One measure to sanitise SS from human pathogens is addition of NH. Methods: Mesophilically digested and dewatered SS treated with urea and stored, or only stored, was applied to arable land in spring and autumn, respectively, and the effects of immediate or delayed incorporation (by 4 h) on emissions of NO, CH and, in spring, NH were investigated. Results: NO emissions in autumn from soil treated with SS were significantly higher than from soil without SS application (0.09, 1.31 and 0.68 kg NO-N ha for control, immediate and delayed incorporation, respectively). These emissions were significantly correlated with volumetric water content in soil. Corresponding NO emissions in spring were 0.15, 0.57 and 0.41 kg NO-N ha. Delayed incorporation (0.20 and 0.34 % of added N in spring and autumn, respectively) tended to reduce NO emissions compared with immediate incorporation (0.32 and 0.71 % of added N in spring and autumn, respectively). Nitrous oxide emissions from SS were apparently lower after spring than after autumn application, likely because of drier soil and crop uptake of nitrogen in spring. Methane emissions were negative or negligible. Timing of incorporation had no statistically significant effect on NH emissions. Conclusions: Nitrous oxide emissions from soil treated with SS at a rate based on the maximum permissible P level were moderate and CH emissions negligible. [ABSTRACT FROM AUTHOR]

In pediatric fluid therapy it would be preferable to describe distribution and elimination a fluid bolus based on repetitive hemoglobin (Hb) according to kinetic principles. Pulse CO-Oximetry is a recent advancement in patient monitoring that allows for the continuous noninvasive measurement of Hb (SpHb). The aim of this study was to describe the distribution and elimination of hydroxyethylstarch (HES) 130/0.4 in combination with crystalloids using a noninvasive Hb monitor in two cohorts of young children undergoing minor surgeries under general anesthesia. Two cohorts, 16 children aged 1-3 years and 12 aged 4-6 years, were investigated during anesthesia and minor surgical procedures. They were given a maintenance solution of lactated Ringer's and a fluid bolus of HES 130/0.4, 6 mL/kg over a period of 20 min. The whole procedure lasted 120 min, and SpHb values were measured every 10 min. The SpHb values were used to calculate plasma dilution, net volume, and mean residence time (MRT) of the infused fluid. A total of 377 measured SpHbs generated individual dilution plots that showed variability, particularly for the older cohort. Distribution and elimination rates of the infused fluid were calculated. Mean dilution plots were generated. There were no significant differences in dilution, net volume or MRT between groups. A non invasive Hb analyzer could be used to calculate fluid distribution. The variability in the data can probably be explained by reactions to anesthetic drugs, variability in measurement technique, variability in generating the complex capillary signals, and individual variability in baseline fluid status. The latter finding is important because this is a prerequisite for perioperative fluid planning for each individual. [ABSTRACT FROM AUTHOR]

A common practice in sensor networks is to collect sensing data and report them to the sinks or to some pre-defined data rendezvous points via multi-hop communications. Attackers may locate the sink easily by reading the destination field in the packet header or predicting the arrival of the sink at the rendezvous points, which opens up vulnerabilities to location privacy of the sinks. In this paper, we propose a random data collection scheme to protect the location privacy of mobile sinks in wireless sensor networks. Data are forwarded along random paths and stored at the intermediate nodes probabilistically in the network. The sinks will move around randomly to collect data from the local nodes occasionally, which prevents the attackers from predicting their locations and movements. We analyze different kind of attacks threatening the location privacy of the sinks in sensor networks. We also evaluate the delivery rate, data collection delay and protection strength of our scheme by both analysis and simulations. Both analytical and simulation results show that our scheme can protect location privacy of mobile sinks effectively, while providing satisfactory data collection services. [ABSTRACT FROM AUTHOR]

Bioethanol production from lignocellulosic materials has several limitations. One aspect is the high production cost of cellulases used for saccharification of substrate and inhibition of fermenting yeast due to inhibitors released in acid hydrolysis. In the present work we have made an attempt to achieve simultaneous cellulases production, saccharification and detoxification using dilute acid hydrolysate of Saccharum spontaneum with and without addition of nutrients, supplemented with acid hydrolyzed biomass prior to inoculation in one set and after 3 days of inoculation in another set. Organisms used were T. reesei NCIM 992, and Aspergillus niger isolated in our laboratory. Cellulase yield obtained was 0.8 IU/ml on fourth day with T. reesei. Sugars were found to increase from fourth to fifth day, when hydrolysate was supplemented with nutrients and acid hydrolyzed biomass followed by inoculation with T. reesei. Phenolics were also found to decrease by 67%. [ABSTRACT FROM AUTHOR]

Cellulose is a major constituent of renewable lignocellulosic waste available in large quantities and is considered the most important reservoir of carbon for the production of glucose, for alternative fuel and as a chemical feedstock. Over the past decade, the emphasis has been on the enzymatic hydrolysis of cellulose to glucose and the efficiency of which depends on source of cellulosic substrate, its composition, structure, pretreatment process, and reactor design. In the present study, efforts were made to produce cellulase enzyme using rice straw. The produced enzyme was used for the hydrolysis of selected lignocellulosic substrate, i.e., sorghum straw. When rice straw was used as a substrate for cellulase production under solid state fermentation, the highest enzyme activity obtained was 30.7 FPU/gds, using T. reesei NCIM 992. 25 FPU/g of cellulase was added to differently treated (native, alkali treated, alkali treated followed by 3% acid treated and alkali treated followed by 3 and 5% acid treated) sorghum straw and hydrolysis was carried out at 50 °C for 60 h. 42.5% hydrolysis was obtained after 36 h of incubation. Optimization of enzyme loading, substrate concentration, temperature, time and buffer yielded a maximum of 546.00 ± 0.55 mg/g sugars (54.60 ± 0.44 g/l) with an improved hydrolysis efficiency of 70 ± 0.45%. The enzymatic hydrolyzate can be used for fermentation of ethanol by yeasts. [ABSTRACT FROM AUTHOR]

The radiative flux perturbations and subsequent temperature responses in relation to the eruption of Mount Pinatubo in 1991 are studied in the ten general circulation models incorporated in the Coupled Model Intercomparison Project, phase 3 (CMIP3), that include a parameterization of volcanic aerosol. Models and observations show decreases in global mean temperature of up to 0.5 K, in response to radiative perturbations of up to 10 W m, averaged over the tropics. The time scale representing the delay between radiative perturbation and temperature response is determined by the slow ocean response, and is estimated to be centered around 4 months in the models. Although the magniude of the temperature response to a volcanic eruption has previously been used as an indicator of equilibrium climate sensitivity in models, we find these two quantities to be only weakly correlated. This may partly be due to the fact that the size of the volcano-induced radiative perturbation varies among the models. It is found that the magnitude of the modelled radiative perturbation increases with decreasing climate sensitivity, with the exception of one outlying model. Therefore, we scale the temperature perturbation by the radiative perturbation in each model, and use the ratio between the integrated temperature perturbation and the integrated radiative perturbation as a measure of sensitivity to volcanic forcing. This ratio is found to be well correlated with the model climate sensitivity, more sensitive models having a larger ratio. Further, if this correspondence between 'volcanic sensitivity' and sensitivity to CO forcing is a feature not only among the models, but also of the real climate system, the alleged linear relation can be used to estimate the real climate sensitivity. The observational value of the ratio signifying volcanic sensitivity is hereby estimated to correspond to an equilibrium climate sensitivity, i.e. equilibrium temperature increase due to a doubling of the CO concentration, between 1.7 and 4.1 K. Several sources of uncertainty reside in the method applied, and it is pointed out that additional model output, related to ocean heat storage and radiative forcing, could refine the analysis, as could reduced uncertainty in the observational record, of temperature as well as forcing. [ABSTRACT FROM AUTHOR]

The goals for water-quality and ecosystem integrity are often defined relative to ''natural'' reference conditions in many water-management systems, including the European Union Water Framework Directive. This paper examines the difficulties created for water management by using ''natural'' as the goal. These difficulties are articulated from different perspectives in an informal (fictional) conversation that takes place after a workshop on reference conditions in water-resources management. The difficulties include defining the natural state and modeling how a system might be progressed toward the natural, as well as the feasibility and desirability of restoring a natural state. The paper also considers the appropriateness for developing countries to adopt the use of natural as the goal for water management. We conclude that failure to critically examine the complexities of having ''natural'' as the goal will compromise the ability to manage the issues that arise in real basins by not making the ambiguities associated with this ''natural'' goal explicit. This is unfortunate both for the western world that has embraced this model of ''natural as the goal'' and for the developing world in so far as they are encouraged to adopt this model. [ABSTRACT FROM AUTHOR]

Simulations of subtropical marine low clouds and their radiative properties by nine coupled ocean-atmosphere climate models participating in the fourth assesment report (AR4) of the intergovernmental panel on climate change (IPCC) are analyzed. Satellite observations of cloudiness and radiative fluxes at the top of the atmosphere (TOA) are utilized for comparison. The analysis is confined to the marine subtropics in an attempt to isolate low cloudiness from tropical convective systems. All analyzed models have a negative bias in the low cloud fraction (model mean bias of −15%). On the other hand, the models show an excess of cloud radiative cooling in the region (model mean excess of 13 W m−2). The latter bias is shown to mainly originate from too much shortwave reflection by the models clouds rather than biases in the clear-sky fluxes. These results confirm earlier studies, thus no major progress in simulating the marine subtropical clouds is noted. As a consequence of the combination of these two biases, this study suggests that all investigated models are likely to overestimate the radiative response to changes in low level subtropical cloudiness. [ABSTRACT FROM AUTHOR]

Exceedance of steady-state critical loads for soil acidification is consistently found in southern China and parts of SE Asia, but there is no evidence of impacts outside of China. This study describes a methodology for calculating the time to effects for soils sensitive to acidic deposition in Asia under potential future sulfur (S), nitrogen (N), and calcium (Ca) emission scenarios. The calculations are matched to data availability in Asia to produce regional-scale maps that provide estimates of the time (y) it will take for soil base saturation to reach a critical limit of 20% in response to acidic inputs. The results show that sensitive soil types in areas of South, Southeast, and East Asia, including parts of southern China, Burma, Hainan, Laos, Thailand, Vietnam, and the Western Ghats of India, may acidify to a significant degree on a 0-50 y timescale, depending on individual site management and abiotic and biotic characteristics. To make a clearer assessment of risk, site-specific data are required for soil chemistry and deposition (especially base cation deposition); S and N retention in soils and ecosystems; and biomass harvesting and weathering rates from sites across Asia representative of different soil and vegetation types and management regimes. National and regional assessments of soils using the simple methods described in this paper can provide an appreciation of the time dimension of soil acidification--related impacts and should be useful in planning further studies and, possibly, implementing measures to reduce risks of acidification. [ABSTRACT FROM AUTHOR]

The Swedish Regional Climate Modelling Programme, SWECLIM, was a 6.5-year national research network for regional climate modeling, regional climate change projections and hydrological impact assessment and information to a wide range of stakeholders. Most of the program activities focussed on the regional climate system of Northern Europe. This led to the establishment of an advanced, coupled atmosphere-ocean-hydrology regional climate model system, a suite of regional climate change projections and progress on relevant data and process studies. These were, in turn, used for information and educational purposes, as a starting point for impact analyses on different societal sectors and provided contributions also to international climate research. [ABSTRACT FROM AUTHOR]

The concentrations of chlorofluorocarbons (CFC-11, CFC-12, and CFC-113) and tritium were determined in groundwater in fractured crystalline bedrock at Finnsjön, Sweden. The specific goal was to investigate the accuracy of CFC dating in such an environment, taking potential degradation and mixing of water into consideration. The water was sampled to a depth of 42 m in three boreholes along an 800-m transect, from a recharge area to a local discharge area. The CFC-113 concentration was at the detection limit in most samples. The apparent recharge date obtained from CFC-11 was earlier than from CFC-12 for all samples, with a difference of over 20 years for some samples. The difference was probably caused by degradation of CFC-11. The CFC-12 dating of the samples ranged from before 1945 to 1975, with the exception of a sample from the water table, which had a present-day concentration. Conclusions about flow paths or groundwater velocity could not be drawn from the CFCs. The comparison between CFC-12 and tritium concentrations showed that most samples could be unmixed or mixtures of waters with different ages, and the binary mixtures that matched the measured concentrations were determined. The mixing model approach can be extended with additional tracers. [ABSTRACT FROM AUTHOR]

A regional atmospheric climate model, including an interactive module of the tropospheric sulfur cycle, has been used to conduct yearlong equilibrium simulations of the temperature response due to anthropogenic sulfate aerosol forcing on cloud albedo. A main purpose is to examine differences in the magnitudes as well as patterns of forcing and response between simulations conducted with high (0.4° × 0.4°, HR) and low (2.0° × 2.0°, LR) spatial resolutions. Averaged over the model domain, the annual mean indirect forcing differs by only 7% between HR and LR and there is no difference in the annual mean temperature response. The results thus indicate that it is not important to represent small-scale variability (≤2.8°) when the average indirect climate effect over Europe is considered. However, a notable difference in the geographical distributions of forcing and response is obtained when different resolutions are employed. In addition, a clear correspondence between the patterns of radiative forcing and temperature response is obtained when HR is used. The correspondence is less obvious in the LR simulation. It is interesting to compare the present results with those of Roeckner et al. 1999, who found a poor correspondence between the patterns of forcing and response in their simulations using a coarse resolution GCM. [ABSTRACT FROM AUTHOR]

During glacial periods, dust deposition rates and inferred atmospheric concentrations were globally much higher than present. According to recent model results, the large enhancement of atmospheric dust content at the last glacial maximum (LGM) can be explained only if increases in the potential dust source areas are taken into account. Such increases are to be expected, due to effects of low precipitation and low atmospheric (CO2) on plant growth. Here the modelled three-dimensional dust fields from Mahowald et al. and modelled seasonally varying surface-albedo fields derived in a parallel manner, are used to quantify the mean radiative forcing due to modern (non-anthropogenic) and LGM dust. The effect of mineralogical provenance on the radiative properties of the dust is taken into account, as is the range of optical properties associated with uncertainties about the mixing state of the dust particles. The high-latitude (poleward of 45°) mean change in forcing (LGM minus modern) is estimated to be small (-0.9 to +0.2 W m-2), especially when compared to nearly -20 W m-2 due to reflection from the extended ice sheets. Although the net effect of dust over ice sheets is a positive forcing (warming), much of the simulated high-latitude dust was not over the ice sheets, but over unglaciated regions close to the expanded dust source region in central Asia. In the tropics the change in forcing is estimated to be overall negative, and of similarly large magnitude (-2.2 to -3.2 W m-2) to the radiative cooling effect of low atmospheric (CO2). Thus, the largest long-term climatic effect of the LGM dust is likely to have been a cooling of the tropics. Low tropical sea-surface temperatures, low atmospheric (CO2) and high atmospheric dust loading may be mutually reinforcing due to multiple positive feedbacks, including the negative radiative forcing effect of dust. [ABSTRACT FROM AUTHOR]

We use the global mercury model published by Bergan et al. (1999) to evaluate the potential role of ozone and the hydroxyl radical as gas phase oxidants for the oxidation of elemental mercury in the atmosphere. The magnitude of natural and man-made mercury emissions are taken from recent literature estimates. We consider only two mercury reservoirs, elemental mercury, Hg0, and the more soluble divalent form, HgII. Wet and dry deposition of HgII is explicitly treated. Applying monthly mean fields of ozone for the oxidation of gas phase Hg0 and using the reaction rate by Hall (1995) yields a global transformation of Hg0 to HgII which is too slow to keep the simulated concentration of Hg0 near observed values. This shows that there must be additional important removal processes for Hg0 or that the reaction rate proposed by Hall (1995) is too slow. A simulation in which the oxidation rate was artificially increased, so that the global turn-over time of Hg0 is one year and the simulated average concentration of Hg0 realistic, produces latitudinal and seasonal variations in Hg0 that do not support the hypothesis that gas phase reaction with O3 is the major oxidation process for Hg0. Recent studies indicate that OH may be an important gas phase oxidant for Hg0 (Sommar et al., 2001). Using OH as the sole oxidant and applying the oxidation rate by Sommar et al., we calculate a concentration of Hg0 well below (about a factor of three) the observations. By prescribing a slower rate, corresponding to a turn-over time of Hg0 of one year, we calculate concentrations of both Hg0 in surface air and HgII in precipitation which correspond reasonably well, both in magnitude and temporal variation, with seasonal observations in Europe and North America. This result supports the suggestion that the oxidation by OH is an important pathway for the removal of Hg0. In view of the uncertainties associated with our calculations, this conclusion should still be regarded as tentative. [ABSTRACT FROM AUTHOR]

Rain water and dustfall deposition samples were collected at Pune, an urban site (1992–98) and at Sinhagad, a rural site (1992–94). The samples were collected with wet-only and bulk collectors at Pune and with bulk collector at Sinhagad. The samples were analyzed for major ions, pH and conductivity. The study showed that the rain water at both places is alkaline (pH > 5.6). The average pH at Pune was 6.1. Neutralising components, indicated by Ca and non sea salt (nss) Mg have higher concentrations than the acidifying components SO4 and NO3. The wet deposition fluxes of all the ionic components were higher than the dustfall fluxes. Relative contribution from dustfall was largest for K, Ca, Mg and NO3. Dustfall was greater at Pune, compared to Sinhagad for all components and up to double for Ca. [ABSTRACT FROM AUTHOR]

Atmospheric deposition in India is generally described as alkaline and well buffered against an increase of acidifying components. Such conclusion has been based on measurements usually performed in urban or suburban areas. Our data on deposition in NE India (in the countryside N of Bhubaneswar) obtained with wet-only and bulk collectors show that: 1) the weighted mean concentrations (and wet deposition) of H+ and HCO3- are almost equal, with dustfall contributing a negligible amount of HCO3-, 2) the deposition of potential acidity, defined as the acidity that would give the same acidity contribution to the receiving surface as the actual deposition provided that all ammonium was converted to nitrate in the soil, could be as high as 40 mmol H+ m-2 a-1 corresponding to a pH of 4.3 in precipitation. The low buffer capacity against acidification and high potential acidity were discovered from long- term measurements in a vegetation covered rural area. Similar measurements in a nearby suburban area gave a much higher input of HCO3- both in wet deposition and dustfall. Further increase of the emission of acidifying components in the region will increase the acid deposition. [ABSTRACT FROM AUTHOR]

Points out the danger of circular logic if climate model inputs are determined from the same temperature record against which climate model outputs are tested. Guidelines for avoiding this danger; Conditions that must be fulfilled for a successful attempt to quantify climate forcings; Notion of a missing forcing.

A new model of psychiatric care, implying a complete integration of out-patient and in-patient activities, has been recently implemented in the Umea psychiatric sector in Northern Sweden. The model implies that all personnel linked with a sector work in the wards, at the out-patient clinic, and in the community irrespective of professional category. Such a model has many advantages. It allows for quick intervention when a patient is in need of care, permits 'continuity of care' in the sense that the patient is seen by the same people both when an outpatient and when in hospital, assigns every patient to the most appropriate level of care, and contributes to a sizeable reduction in the number of admissions. [ABSTRACT FROM AUTHOR]

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A derivation in terms of a statistical theory of power coupling is performed in order to estimate the effects of the radiation modes of an optical waveguide. Earlier, the loss term introduced in this theory was always of heuristic origin. In this paper, we derive an identical term from first principles. Accordingly, we find that coupling from radiation to guided modes along the waveguide can be neglected. [ABSTRACT FROM AUTHOR]

Focuses on atmospheric chemistry. Effect of man-made changes in the cloud condensation nuclei (CNN) on the physical characteristics and amount of clouds; Reference to a study by Facchini et al in the September 1999 issue of 'Nature'; Indirect effect of aerosol on climate; Application of empirical approach to estimate the magnitude of surface tension; Importance of surfactant effect on cloud brightness and climate.

This paper is an introduction to the special issue of Ambio (Ambio Vol. 26 No 1, February 1997) commemorating the 100-year anniversary ofthe publication of Svante Arrhenius' landmark paper on the greenhouse effect. Arrhenius' most significant achievements in this particularfield of science are briefly summarized and an attempt is made to provide a realistic explanation of the fundamental physical processes contributing to the greenhouse effect. [ABSTRACT FROM AUTHOR]

Ozone measurements, performed since 1987, at the Swedish TOR/EUROTRAC station Areskutan (lat. 63.4 deg. N, long. 13.1 deg. E, 1250 m above sea level) are analyzed. The annual average ozone concentration at the site has increased by about 0.4 ppbv (?1%) per year during the period 1987-1994. The corresponding trends for individual months showa decrease during April-September and an increase during the rest ofthe year. The ozone budget at Areskutan has been investigated using back trajectories of the air parcels, and the cosmogenic radionuclide7 Be as a tracer of stratospheric air. From a simple diagnostic model, it is estimated that the contribution of stratospheric ozone to the concentrations measured at Areskutan is 5 ppbv (or 14% ofthe measured values) on average, reaching a maximum of 23 ppbv (50%), during the episodes of direct stratospheric influence. In spring, the stratospheric contribution to ozone budget at Areskutan is at its maximum, and approximately equal to the net photochemical ozone production in the air mass affecting the site, whereas in winter, it is compensated by ozone chemical sink during the transport of air masses from polluted European regions, to Scandinavia. [ABSTRACT FROM AUTHOR]

Sensitive diffusive samplers for concentration measurements in ambient air have been used successfully in Sweden for several years. The samplers have the advantage of being stable at room temperature before, as well as after, sampling, easy to handle, and cost-efficient. Furthermore, they do not require electricity or field calibration. In order to test their use in tropical and subtropical environments and toobtain a preliminary set of data to validate atmospheric chemistry transport models in this part of the world, duplicate samples were collected at 11 sites every second month during one year. Eight of the sites were background sites in Asia. It was not possible within the Project to compare the measured concentrations with other measurement techniques. However, the reproducibility of the duplicates was satisfactory over the whole measuring range (almost three orders of magnitude of the concentration for SO 2 ) and reasonable agreementwith model calculations was obtained at least for SO 2 and NH 3. Further testing of the measuring technique in tropical areas is, however, warranted. [ABSTRACT FROM AUTHOR]

Simulations of oxidized nitrogen performed with global transport tracer models systematically underestimate the concentrations of total nitrate at remote marine locations in the Mid-Pacific. Higher emissionrates in the models of nitrogen oxides (NOx = NO + NO2) from continental sources or a larger influx from the stratosphere do not seem to be able to account for the shortfall. We are led to conclude that there has to be a substantial source located in oceanic areas. We speculate that NOx-emission from electrical discharges over the oceans could be the source we are looking for. Airborne observations of atmospheric concentrations of oxidized nitrogen and ozone in the remote atmosphere and observations of nitrate wet deposition in remote sites are used as additional constraints to check the plausibility of this hypothesis. We find that a larger emission of NOx due to lightning activity over the oceans indeedresults in a much improved simulation of total nitrate in the remotePacific, particularly in the Equatorial and Tropical South Pacific and that such a scenario is generally consistent with available observations of nitrate wet deposition and atmospheric concentrations of oxidized nitrogen and ozone. An alternative hypothesis is that there isa hitherto unknown in situ source of NOx over the PacificOcean. [ABSTRACT FROM AUTHOR]