First Year Of Measurements Research Articles

Greenhouse gases in the tall tower of El Arenosillo station in Southwestern Europe: First-year of measurements

Carbon dioxide (CO2), methane (CH4) and carbon monoxide (CO) were measured at 10, 50 and 100 m in a tall tower located at El Arenosillo observatory (Southwestern Europe) from December 2021 to December 2022. Depending on the height, hourly averages varied between 418 ± 5 at 100 m and 422 ± 8 μmol mol−1 at 10 m for CO2, while CH4 varied between 1999 ± 30 nmol mol−1 at 100 m and 1986 ± 25 at 10 m and ∼ 102 ± 19 nmol mol−1 for CO. A monthly variation with a common maximum in January–February was obtained while the minimum was found in June for CH4 and CO, whereas the minimum for CO2 was in August. The seasonal daily patterns showed a maximum between 5:00 and 10:00 UTC while the minimum was observed at 15:00–18:00 UTC. The daily variations are controlled by atmospheric stability, photochemical activity and vegetation influence, among other factors. The CO2 gradient was strongly conditioned by the photosynthesis, plant and soil respiration and vertical mixing with peaks higher than 19 × 10−2 μmol mol−1 m−1 at ∼5:00 UTC in spring and autumn. The CH4 gradient, greater in winter and autumn (12–27 × 10−2 μmol mol−1 m−1) is affected by vertical stability, local emissions and photochemical activity while CO depicted small vertical gradients. A different behavior was found in the CO2 and CH4 gradients, for CO2 the 10–50 m gradient is higher than 50–100 m while CH4 was the opposite; which could reflect a lower CO2 surface layer than CH4. The observations at 100 m registered CO and CH4 peaks that were not recorded at 10 m, which could be associated with the arrival of a forest fire plume and potential CH4 fugitive emissions.

Long-Term Shrinkage Measurements on Large-Scale Specimens Exposed to Real Environmental Conditions

This article presents an experimental testing campaign on large-scale concrete specimens with cross-sectional areas of up to 1 m2 and a specimen length of 3 m. The primary goal of the testing campaign was to study the shrinkage behaviour of large-scale specimens exposed to real environmental conditions. Large-scale prismatic concrete specimens were equipped with vibrating wire strain gauges to monitor the strain evolution inside the specimens. To analyse the shrinkage behaviour of the specimens, the thermal strain had to be deducted from the measured strain. To study the influence of seasonal environmental conditions, different specimen production dates (in summer and winter) were examined. The measured shrinkage strains of the large-scale specimens are compared with the results of shrinkage models developed by two engineering entities (fib (Fédération Internationale du Béton) and RILEM (International Union of Laboratories and Experts in Construction, Materials, Systems and Structures)). The comparison shows a poor agreement of the measurements with the models, even though the results from the model for small specimens tested in the laboratory under constant environmental condition agree well with the experimental results. This leads to the conclusion that the poor agreement between the measurements and the shrinkage models must be due to the seasonally changing environmental conditions. The comparison of the results from specimens with different production dates shows that different shrinkage behaviour occurs, especially in the first year of measurements.

Long-term variability and source signature of gases emitted from oil & natural gas and cattle feedlot operations in the Colorado front range

Multiple tropospheric gases are analyzed in ten years of observations (2010–2019) using a high-resolution ground-based solar absorption Fourier Transform InfraRed (FTIR) instrument in the Colorado Northern Front Range (CNFR). The first year of measurements in 2010 coincides with the start of the remarkable increase of oil and natural (O&NG) extraction in the region. We show seasonal variations and trends of atmospheric gases related to O&NG (C2H6), cattle feedlot activities (NH3), urban emissions (CO, C2H2), biomass burning (HCN), and volatile organic compounds related to photochemistry and ozone production (H2CO, HCOOH). The long-term time series of C2H6 shows clear episodic peak-enhancements related to local O&NG emissions that contribute to a positive trend of 0.9 ± 0.3% ⋅yr−1. NH3 also shows episodic enhancements and has the greatest rate of change for the gases studied here (2.7 ± 0.7% ⋅yr−1). Simulations of all gases are presented using the Community Atmosphere Model with chemistry (CAM-chem) within the Community Earth System Model (CESM) framework. Modeled gases are compared to the observations using different combinations of global emissions in order to determine the best combination for the CNFR. For most gases, using best emissions, the annual rate of change obtained with CAM-chem agrees with the FTIR observations, except for NH3, which is underestimated by a factor of 6. Nevertheless, simulations of NH3 show that the positive trend in NH3 is due to a decrease in its removal via reaction with H2SO4 from a reduction in coal power plant emissions. The seasonal variations of all gases are generally well represented in the model, although magnitudes are often underestimated. The anthropogenic emissions of CO, C2H2, and C2H6 are underestimated by about 20%, 40%, and 65%, respectively, independent of emission inventories. While NH3 summer values are underestimated significantly, other months show low relative mean difference between FTIR observations and CAM-chem simulations. Excellent agreement is found for H2CO, but for HCOOH a factor of 2–3 is needed in the simulations to match observations, pointing to a significant missing source. HCN, a tracer for biomass burning emissions, is well reproduced by the NCAR Fire Inventory (FINN). Furthermore, we show here a simple approach to identify local enhancements of gases related to nearby O&NG and concentrated animal feeding operations. These enhancements above ambient levels are used to estimate emission ratios (ER) of C2H6, H2CO, and HCOOH relative to CO from O&NG air masses. A median ER (and standard deviation) of 0.48 ± 0.41, 0.26 ± 0.15, and 0.13 ± 0.09 [ppb/ppb] are estimated for C2H6, H2CO, and HCOOH, respectively and are representative of the ten years of observations. ER can be used to estimate emission factors (EF), although CO emissions from O&NG need to be well-known. To complement the FTIR observations, we show results derived with airborne observations during The Front Range Air Pollution and Photochemical Experiment (FRAPPE) in 2014. Even though FTIR and FRAPPE observations can not be compared easily they both yield similar median ER. Finally, plumes of fires originated in the western United States in August 2015 were identified and EF are estimated.

Carbon Exchange and Accumulation in an Orinoco High Plains Native Savanna Ecosystem as Measured by Eddy Covariance

Savanna ecosystems cover ∼20% of the total land surface and account for ∼30% of the terrestrial global net primary production. They are also highly sensitive to climate change, since their carbon (C) sink capacity may decline under rising temperatures and irregular rainfall. These responses, which will define the future climate role of the savanna ecosystems, are currently not well understood. The Colombian Orinoco River basin (“Llanos”) natural savannas are being rapidly converted to agriculture. The impact of this transformation on C fluxes and accumulation is not clear. It is thus urgent to understand the Llanos natural savanna ecosystem services, including their C cycle and underlying mechanisms. Here we report and analyze 2 years of measurements of carbon dioxide fluxes from a naturally-restored (secondary) Llanos High Plains savanna ecosystem, using eddy covariance. Meteorological conditions, particularly rainfall, were quite variable during the measurement period. During the first year of measurements, the savanna was a weak carbon source (35 gC m−2), while during the second year, the system was a comparatively strong carbon sink (−273 gC m−2), despite receiving less rainfall than during the first year. As expected, the savanna net ecosystem exchange (NEE) was highly dependent on global solar radiation, soil water content, and ecosystem respiration. We found that after ∼10 days of nominal drought, i.e., with less than ∼5 mm/day of precipitation, the NEE became highly dependent on drought duration. The ecosystem reached a critical condition of low photosynthetic activity after ∼60 days of nominal drought. Based on these findings, we developed and applied a simple standard meteorology-based model that properly reproduced the observations. Our results indicate that a shift to a climate with similar total precipitation but split into extreme dry and wet seasons might eventually suppress the savanna C uptake capacity.

Propagation Experiment at <italic>Ka</italic>-Band in French Guiana: First Year of Measurements

ONERA, the French Aerospace Lab, and CNES, the French Space Agency, are currently running a Ka -band propagation experiment at the Guiana Space Centre (CSG) in Kourou (French Guiana). A rain gauge and a beacon receiver able to record the 20.2 GHz beacon signal of the Amazonas 3 satellite have been deployed. The equipment is operational since January 1, 2017, and the duration of the experiment has been set to three years. This letter addresses some results of the first year of measurements (from January 2017 to December 2017). The annual and monthly complementary cumulative distribution functions of rainfall rate and rain attenuation are presented as well as a comparison with the rain attenuation prediction method recommended in ITU-R P.618-13.

Understanding Traffic-Related Air Pollution Exposures through Mobile Monitoring

Human exposures to air pollution can vary sharply in space and time. Carefully designed mobile sampling campaigns are now able to reveal patterns of long-term ambient air pollution concentrations at fine scales (<< 100 m). Here, we report on a campaign where two specially equipped Google Street View cars mapped spatial patterns of air quality in the San Francisco Bay Area between May 2015 and December 2017. Cars were outfitted with reference-grade instruments to measure NO, NO2, black carbon (BC) and ultrafine particle number count at ~ 1 Hz. During a 30-month campaign, measurements occured on most weekdays during daytime hours, resulting in a large dataset: ~10M samples collected during > 4000 h, encompassing 100k km of driving. First, we sampled every road 20-50× within three neighborhoods (~30 km2) in Oakland, CA, during the first year of measurements. We found persistent fine-scale variability in pollution exists within many neighborhoods. In some neighborhoods, prominent ~50-200 m sized hotspots of elevated primary pollutants were ubiquitous, with pollutant levels varying by 5-8× within many city blocks. Next, during 1.5 years of follow-up measurements, we mapped pollutant concentrations in rural, suburban, and dense urban neighborhoods throughout the SF Bay Area. These measurements reveal how within-neighborhood pollution structure is overlaid on top of regional spatial gradients in air quality. Repeated measurements over the 2.5-year period demonstrate persistent spatial variability over time. Patterns of NO, NO2 and BC in Oakland had high correlation (r2 > 0.85) between the first and second years of measurement. Short-term measurement periods (~1-2 months) were sufficient to reproduce overall spatial patterns, albeit with ±30% bias in mean concentrations relative to annual-average conditions. This presentation summarizes how routine mobile air pollution monitoring reveals new information about spatial variability in population exposure to air pollution.

The Raam regional soil moisture monitoring network in the Netherlands

Abstract. We have established a soil moisture profile monitoring network in the Raam region in the Netherlands. This region faces water shortages during summers and excess of water during winters and after extreme precipitation events. Water management can benefit from reliable information on the soil water availability and water storing capacity in the unsaturated zone. In situ measurements provide a direct source of information on which water managers can base their decisions. Moreover, these measurements are commonly used as a reference for the calibration and validation of soil moisture content products derived from earth observations or obtained by model simulations. Distributed over the Raam region, we have equipped 14 agricultural fields and 1 natural grass field with soil moisture and soil temperature monitoring instrumentation, consisting of Decagon 5TM sensors installed at depths of 5, 10, 20, 40 and 80 cm. In total, 12 stations are located within the Raam catchment (catchment area of 223 km2), and 5 of these stations are located within the closed sub-catchment Hooge Raam (catchment area of 41 km2). Soil-specific calibration functions that have been developed for the 5TM sensors under laboratory conditions lead to an accuracy of 0.02 m3 m−3. The first set of measurements has been retrieved for the period 5 April 2016–4 April 2017. In this paper, we describe the Raam monitoring network and instrumentation, the soil-specific calibration of the sensors, the first year of measurements, and additional measurements (soil temperature, phreatic groundwater levels and meteorological data) and information (elevation, soil physical characteristics, land cover and a geohydrological model) available for performing scientific research. The data are available at https://doi.org/10.4121/uuid:dc364e97-d44a-403f-82a7-121902deeb56.

Global Electric Circuit research at Graciosa Island (ENA-ARM facility): First year of measurements and ENSO influences

Around 100 years after Carnegie expeditions discovered the Global Electric Circuit, a measuring campaign started at ARM, Eastern North Atlantic facility (Graciosa Island, Azores), meant for the first time to resemble the conditions in which those took place. Here, the first year of measurements (starting April 2015) are analysed and initial results are discussed. The Potential Gradient findings show a deviation from the Carnegie Curves towards inland measurements as a consequence of local aerosol and ion load. The Potential Gradient maxima evolves from 18 UTC (spring/autumn) to 20 UTC (summer), being consistent with the strong 2015 El Niño.

Effects of agricultural management on measurements, prediction, and partitioning of evapotranspiration in irrigated grasslands

Irrigation is an important component of the hydrologic cycle in agricultural ecosystems, affecting both quantity and quality of surface and ground water. Well-managed irrigation involves balancing irrigation with water consumption by evaporation and transpiration (collectively evapotranspiration), maximizing ecosystem water-use efficiency and minimizing drainage. Here we compare rates of actual crop evapotranspiration (ETC) measured by eddy covariance with reference evapotranspiration (ET0) calculated from meteorological variables for two irrigated ryegrass systems in central South Island, New Zealand between June 2011 and March 2013. The sites were similar in climate, but contrasted in management: one grazed by dairy cattle and the other harvested annually for seed. Over the first year of measurements, cumulative ETC was very similar at the two sites, totalling 791 and 819mm for the dairy pasture and seed crop respectively, although temporal patterns of partitioning of ETC amongst evaporation and transpiration differed as a result of management activities. Responses of ETC to global radiation, temperature and vapour pressure deficit were all similar during active growing season periods. Differences between the two sites were observed at the end of the second measurement season, when irrigation was ceased in the seed crop prior to final harvest and ETC was reduced compared to ET0. As a result, cumulative ETC was 13% greater for the dairy pasture at the end of the study period.

Analysis of non-methane hydrocarbon data from a monitoring station affected by oil and gas development in the Eagle Ford shale, Texas

Abstract Within the last decade, unconventional oil and gas exploration in the US has become a new source of atmospheric hydrocarbons. Although a geographically dispersed source, field measurements in and downwind of a number of shale basins demonstrate the impact exploration activities have on ambient levels of hydrocarbons. Due to concerns related to ozone production, regulatory agencies are adding monitoring stations to better understand the potential influence of emissions from areas with increased oil and gas related activities. The Eagle Ford shale in south Texas is a rapidly developing shale play producing both oil and natural gas, providing 10% and 5% of US domestic oil and gas production, respectively, in 2013. We analyzed the first year of measurements from a newly established monitoring site at its central north edge. The data reveal median ethane mixing ratios—used as a marker for oil and gas exploration related emissions—at five times its typical clean air background. Ethane mixing ratios above ten times the background occurred regularly. Saturated hydrocarbons with likely origin in oil and gas exploration explain half of the data set’s variability. They dominate OH radical reactivity at levels both similar to other shale areas and similar to Houston’s ship channel area a decade ago. Air advecting slowly across the shale area from east-southeast and southwest directions shows the most elevated hydrocarbon concentrations, and evidence is presented linking elevated alkene abundances to flaring in the shale area. A case study is presented linking high emissions from an upwind facility to hydrocarbon plumes observed at the monitor.

Development and first year of results from the Heliometer of Observatório Nacional

AbstractRecent research on global climate changes points to three distinct sources of climate disturbance: anthropogenic; natural changes in the oceans and atmosphere; and irregularities in the solar cycles. One of the most direct ways to survey an exogenous component of the climatic variability is through the measurement of variations in the diameter and shape of the solar disk. At Observatório Nacional/MCTI, Rio de Janeiro, after several years of diameter observation using a CCD Solar Astrolabe, these measurements are now performed by a state-of-the-art Solar Heliometer. The heliometric method is one of the most successful techniques to measure small variations of angles. Its principle has been used for the latest space borne astrometric missions, aiming to milli-arcsecond precision. The success of this method relies in the fact that it minimizes the dependence of angular measurements to the thermal and mechanical stability of the instrument. However in the classic heliometer the objective is split into two halves to which is applied a linear displacement along the cut, thus still leaving room for a residual dependence with the focus, due to non-concentricity of the beams of the two images. The focus variation, as well as the effects brought by the large temperature variations during solar observations, was tackled in the Solar Heliometer by having all optical elements and their niches made on CCZ, and the telescope tube on carbon fiber, both materials of negligible thermal coefficient. Additionally, the measures are made perpendicular to the separation direction and the plate scale can be known at every time from the solar motion itself. We present the results from the first year of measurements, in special exploring the upheaval of solar activity on late 2011.

Carbon dioxide variability during cold front passages and fair weather days at a forested mountaintop site

Abstract This study describes temporal carbon dioxide (CO2) changes at a new meteorological site on a mountaintop in the Virginia Blue Ridge Mountains during the first year of measurements. Continental mountaintop locations are increasingly being used for CO2 monitoring, and investigations are needed to better understand measurements made at these locations. We focus on CO2 mixing ratio changes on days with cold front passages and on fair weather days. Changes in CO2 mixing ratios are largest during cold front passages outside the growing season and on clear, fair weather days in the growing season. 67% (60%) of the frontal passages during the non-growing (growing) season have larger postfrontal than prefrontal CO2 mixing ratios. The increase in CO2 mixing ratio around the frontal passage is short-lived and coincides with changes in CO and O3. The CO2 increase can therefore be used as an additional criterion to determine the timing of frontal passages at the mountaintop station. The CO2 increase can be explained by an accumulation of trace gases along frontal boundaries. The magnitude and duration of the CO2 increase is affected by the wind speed and direction that determine the source region of the postfrontal air. Southward-moving fronts result in the largest prolonged period of elevated CO2, consistent with the postfrontal advection of air from the Northeastern United States where anthropogenic contributions are relatively large compared to other areas in the footprint of the mountaintop station. These anthropogenic contributions to the CO2 changes are confirmed through concurrent CO measurements and output from NOAA’s CarbonTracker model.

Pre and post fire carbon dynamics in a Florida Scrub oak

AbstractScrub oak is a xeromorphic shrub ecosystem discontinuously distributed in coastal and inland Florida. It supports a high biodiversity which includes a large number of endangered and threatened species. Its structural features are maintained by a fire return cycle of 7 to 10 years which maintains the biodiversity. Management of fire prone ecosystems such as this raises the question of whether the management strategy contributes to the system being a carbon sink or carbon source over the long-term. We used eddy covariance and biometric approaches to measure carbon dynamics in a Florida scrub oak ecosystem located at Kennedy Space Center in east Central Florida from April 2004 to December 2007. The study site was controlled burned in February 2006. Two years previous to fire, the site experienced average precipitation but drought conditions during the two years after fire. Net ecosystem production (NEP) was 419 g C m-2 yr-1 during the first year of measurements, and the ecosystem incorporated 823 g C m-2 during the 22 months before the fire. Aboveground net primary production (NPP) represented 50% of annual NEP. Carbon released by fire reached 316 g C m-2. Ecosystem respiration (Re) dominated the carbon balance during the first six months after fire, and the ecosystem released an extra 119 g C m-2. However, gross ecosystem production (GEP) increased with leaf area index (LAI) after fire, dominating the carbon balance during the following six months. The ecosystem was a carbon sink of 88 g C m-2 yr-1 during the first year after the fire. Leaf area index (LAI) reached 1.54 m2 m-2 by October 2007 (80% of pre-burn value for the same time period). The scrub oak ecosystem was a continuous carbon sink six months after the fire despite the dominant drought conditions during 2006 – 2007. The ecosystem offset 80% (251 g C m-2) of the carbon released in the fire during the following twenty two months after the fire. Considering the fire return cycle of 7 to 10 years and the fact that the study site and a similar site nearby incorporated more than 400 g C m-2 yr-1 during the two years before fire, this scrub oak is a net carbon sink in the landscape under current management strategies.

One year of tropospheri clidar measurements of aerosol extinction and backscatter

The aerosol lidar system operational at IMAA-CNR in Tito Scalo (PZ) (Southern Italy, 40°36'N, 15°44'E, 820 m above sea level) is part of the EARLINET project. Systematic lidar measurements of aerosol backscatter and extinction in the troposphere have been performed since May 2000. Aerosol backscatter measurements were performed at both 355 nm and 532 nm, while aerosol extinction coeffi cient were retrieved from simultaneous N2 Raman backscatter signals at 386.6 nm. The observations were performed on a regular schedule of two night time measurements per week (around sunset) and one daytime measurement per week (around 13:00 UTC). Furthermore, special observations concerning Saharan dust outbreaks have been carried out. Starting in May 2000 the lidar measurements performed in Tito Scalo have been collected and analysed. Preliminary results regarding the fi rst year of measurements are reported. In particular, the evolution of the aerosol integrated backscatter and extinction as well as of the mean value of the lidar ratio in the whole aerosol layer is reported. Results show clear evidence of seasonal variation of the observed parameters, with higher values and greater variability during summertime.

The next chapter in radiocarbon dating at the Australian National University: Status report on the single stage AMS

In February 2007, a single stage AMS from the National Electrostatics Corporation (NEC) was installed at the Research School of Earth Sciences at the Australian National University. This instrument is equipped with a gas/graphite hybrid ion source allowing direct analysis of CO2 as well as traditional graphite targets. The instrument was funded by an Australian Research Council grant and by a consortium of eight universities plus the CSIRO Division of Land and Water. Its purpose is to support integrated environmental and archaeological research and access is open to the wider research community. In the first year ∼1500 samples have been analysed. A precision of ∼3‰ is routinely observed. The background for processed graphite (coal, calcite, Carrera marble) is better than 45,000 years. This paper summarizes the first year of measurements.

A national survey on radon concentration in underground inspection rooms and in buildings of a telephone company: methods and first results

A national survey has been carried out to measure radon concentration in a large sample of Telecom-Italia small underground inspection rooms, which form a particularly dense net in urban areas. Measuring radon in such underground places is interesting both for a possible contribution to radon mapping activities and to evaluate workers exposures. Radon concentration was also measured in Telecom buildings (i.e. buildings housing plant equipment, including telephone switches, often also offices, etc.) close and partially connected to the selected inspection rooms. The methodology and the first results of the survey related to the first year of measurements, for a total of 1438 inspection rooms and 1414 Telecom buildings, are reported. Radon concentration was measured with passive devices containing CR-39 detectors for about 12 consecutive months, in order to average seasonal variations. In underground inspection rooms, measured radon concentration reached values up to about 44,000 Bq/m 3, with a regional median ranging from about 90 Bq/m 3 up to about 1600 Bq/m 3. In Telecom buildings, the regional median concentration ranged from 13 Bq/m 3 to 174 Bq/m 3. These results show that radon concentration in underground inspection rooms can reach very high values, whereas medians in monitored buildings are generally lower than those measured in dwellings in a representative national survey.

European scale application of atmospheric reactive nitrogen measurements in a low-cost approach to infer dry deposition fluxes

A European scale network was established in 2006 as part of the NitroEurope Integrated Project to infer reactive nitrogen (Nr) dry deposition fluxes, based on low-cost sampling of gaseous and aerosol species and inferential modelling. The network provides monthly measurements of NH 3, NH 4 +, HNO 3 and NO 3 −, as well as SO 2, SO 4 2−, HCl, Cl − and base cations at 58 sites. Measurements are made with an established low-cost denuder methodology (DELTA) as a basis to: (1) examine temporal trends and spatial patterns across Europe, (2) improve and calibrate inferential modelling techniques to estimate exchange of Nr species, (3) provide best estimates of atmospheric dry N deposition, and (4) permit an analysis of net GHG exchange in relation to atmospheric and agricultural N inputs at the European scale. Responsibility for measurements is shared among seven European laboratories. An inter-comparison of the DELTA implementation by 6 laboratories at 4 test sites (Montelibretti, Italy; Braunschweig, Germany; Paterna, Spain and Auchencorth, UK) from July to October 2006 provided training for the laboratories and showed that good agreement was achieved in different climatic conditions (87% of laboratory site-means within 20% of the inter-laboratory median). Results obtained from the first year of measurements show substantial spatial variability in atmospheric Nr concentrations, illustrating the major local (NH 3) and regional (HNO 3, NO 3 −, and NH 4 +) differences in Nr concentrations. These results provide the basis to develop future estimates of site-based Nr dry deposition fluxes across Europe, and highlight the role of NH 3, largely of agricultural origin, which was the largest single constituent and will dominate dry Nr fluxes at most sites.

Spectral analysis of the Galactic e+e- annihilation emission

We present a spectral analysis of the e+e- annihilation emission from the Galactic Centre region based on the first year of measurements made with the spectrometer SPI of the INTEGRAL mission. We have found that the annihilation spectrum can be modelled by the sum of a narrow and a broad 511 keV line plus an ortho-positronium continuum. The broad line is detected (significance 3.2σ) with a flux of () 10-3 photons s-1 cm-2. The measured width of keV FWHM is in agreement with the expected broadening of 511 keV photons emitted in the annihilation of positroniums that are formed by the charge exchange process of slowing down positrons with hydrogen atoms. The flux of the narrow line is () 10-3 photons s-1 cm-2 and its width is keV FWHM. The measured ortho-positronium continuum flux yields a fraction of positronium of ()%. To derive in what phase of the interstellar medium positrons annihilate, we have fitted annihilation models calculated for each phase to the data. We have found that 49% of the annihilation emission comes from the warm neutral phase and 51% from the warm ionized phase. While we may not exclude that less than 23% of the emission might come from cold gas, we have constrained the fraction of annihilation emission from molecular clouds and hot gas to be less than 8% and 0.5%, respectively. We have compared our knowledge of the interstellar medium in the bulge (size, density, and filling factor of each phase) and the propagation of positrons with our results and found that they are in good agreement if the sources are diffusively distributed and if the initial kinetic energy of positrons is lower than a few MeV. Despite its large filling factor, the lack of annihilation emission from the hot gas is due to its low density, which allows positrons to escape this phase.

Full-scale testing to determine the wind loads on free-standing walls

Recent developments in the wind loading codes for the UK, Australia and Europe have introduced new, more onerous, pressure coefficient data for the design of free-standing walls. These data, derived from wind-tunnel studies conducted in the mid 1980s in the UK and Australia, have been called into question by various interested parties. In the summer of 1993, a 3 yr research programme was initiated to undertake an independent, full-scale study of the wind pressures on free-standing walls in order to critically appraise the new data and to determine; reliable design data. The full-scale, variable-geometry experimental facility which includes automatic, rapid, data-logging instrumentation is described. Results obtained in the first year of measurements are presented which reveal the significance of wall length, position along the wall, wind direction and the presence of return corners. Priorities for the future are also outlined.

Indoor radon concentrations in Greek apartment dwellings.

Radon concentrations indoors were determined in 24 typical occupied apartments in the city of Thessaloniki, North Greece (40 degrees 38'N, 22 degrees 58'E), by means of 12 surveys, each 2 mo long, over a 2-y period starting October 1989. The ratio of the winter and summer averages for the first year of measurements was 1.8 +/- 0.78, and for the second year of measurements was 1.6 +/- 0.61. The indoor radon concentration in the summer (1990) period ranged between 8 and 81 Bq m-3, while in the winter (1989-1990) it ranged between 20 and 143 Bq m-3 for the first year of measurements or between 8 and 92 Bq m-3 in the summer (1991) period and between 12 and 119 Bq m-3 in the winter (1990-1991) for the second year of measurements. These results were obtained by type CN-85 alpha track detectors. Some parameters that influenced the concentrations, such as precipitation rates and use of fly ash in building materials, are discussed.