Carbon Dioxide Concentration In Air Research Articles

Carbon dioxide concentration in the air of school gyms during classes

BACKGROUND: Elevated levels of carbon dioxide in gym air can diminish the benefits of physical activity and pose health risks for children.. AIM: to access carbon dioxide concentration in the air of school gyms during physical education classes. MATERIAL AND METHODS: A total of 612 measurements were taken to estimate the concentration of carbon dioxide in the air. These measurements were conducted in two separate gymnasiums: in Gym 1, designated for primary classes with an area of 77 m2, and Gym 2, used by middle and high school students with an area of 293 m2. Measurements were taken at 12 different points, both around the perimeter and in the central part of each gym. The height when measuremenmts were taken ranged from 0 to 230 cm. To assess the carbon dioxide concentration in the gym air, the background level was calculated based on GOST 30494-2011 standards (761.5 ppm). Student’s t-tests for independent samples were used to compare the data. Additionally, a regression analysis was utilized to estimate the spatial distribution of carbon dioxide within the gymnasiums. RESULTS: In Gym 1, the initial concentrations ranged from 845 to 1267 ppm, slightly exceeding the expected throughput. Throughout the training session, the carbon dioxide content increased by 1.6 to 2.3 times. By the end of the session, the carbon dioxide content reached 1934 to 1948 ppm at an estimated respiration level of 1.0 to 1.9 m. In Gym 2, the carbon dioxide content increased by 1.1 to 1.2 times by the end of the class. At a height of 0.0 to 1.7 m, the concentration of carbon dioxide was measured at 1016 to 1023 ppm. CONCLUSION: After 20 minutes of training at the expected intensity, carbon dioxide levels in the air exceed not only the background level of 761.5 ppm, but also the permissible level of 1000 ppm. This study highlights the importance of daily monitoring of carbon dioxide levels in school gymnasiums during training sessions and sporting events. Such monitoring is crucial for ensuring the health and safety of students and athletes.

Carbon dioxide absorption in packed bed of lithium orthosilicate pebbles

ABSTRACT Lithium orthosilicate (Li4SiO4) has the highest carbon dioxide (CO2) absorption capacity among the other lithium-based ceramic materials and is also suitable for high-temperature application for CO2 absorption. In this work, lithium orthosilicate pebbles of 1.0 mm size with 20% excess lithium carbonate were synthesized and fabricated by using Solid State Reaction Process (SSRP) and experiments were carried out to study the effect of various process parameters on its adsorption capacity of CO2 from air-CO2 mixture at elevated temperatures. The various process parameters studied were: operating gas flow rate, bed wall temperature and CO2 concentration in air on which very limited works have been reported. Effects of operating temperature, flow rate and inlet concentration of CO2 on absorption capacity have been studied to develop break through curves. The cyclic tests have been carried out with 15% CO2 concentration in air at 400°C and 200 LPH flowrate using the same material and carried out 135 consecutive absorption-desorption experimental runs. It was found that the CO2-absorption capacity of Li4SiO4 pebbles at 400°C and 200 LPH flowrates is about 31% for 30% carbon dioxide concentration in air and 22% for 15% carbon dioxide concentration in air. Moreover, no reduction in CO2-absorption capacity of the material was observed even after 135 consecutive absorption-desorption cycles.

Monitoring photosynthetic activity using in vivo chlorophyll a fluorescence in microalgae and cyanobacteria biofilms in the Nerja Cave (Malaga, Spain)

The characterization of the most common photosynthetic biofilms in the Nerja Cave by the continuous monitoring of the in vivo chlorophyll a (Chl a) fluorescence and the incorporation of the irradiance as a new environmental variable related to previous studies in the cave, have allowed us to improve our knowledge about the photosynthetic pattern of the biofilms of the cave. Effective quantum yield (ΔF/Fm) and relative electron transport rate (rETR) were determined during periods of the light, whereas the maximal quantum yield (Fv /Fm) was determined during dark periods. Increases in the photosynthetic yields and productivity in summer period were found related to the highest values of the environmental variables, such as relative humidity, air carbon dioxide concentration and air temperature. According to the irradiance, the studied biofilms had an optimal growth with cave lighting, considered low in comparison with similar studies, perhaps because they can grow mixotrophically too. Moreover, when the irradiance increased, both the ΔF/Fm′ and the rETR decreased in springtime, suggesting photoinhibition of the photosynthetic yield in the biofilms within the cave, whereas in the summertime, the photosynthetic yield had a positive correlation with the irradiance, suggesting a decreased of the photoinhibition, possibly due to the increase of the environmental variables values which provokes an alleviate on the extent of photoinhibition.

Monitors to improve indoor air carbon dioxide concentrations in the hospital: A randomized crossover trial

BackgroundVentilation has emerged as an important strategy to reduce indoor aerosol transmission of coronavirus disease 2019. Indoor air carbon dioxide (CO2) concentrations are a surrogate measure of respiratory pathogen transmission risk. ObjectivesTo determine whether CO2 monitors are necessary and effective to improve ventilation in hospitals. MethodsA randomized, placebo (sham)-controlled, crossover, open label trial. Between February and May 2021, we placed CO2 monitors in twelve double-bed patient rooms across two geriatric wards. Staff were instructed to open windows, increase the air exchange rate and reduce room crowding to maintain indoor air CO2 concentrations ≤800 parts per million (ppm). ResultsCO2 levels increased during morning care and especially in rooms housing couples (rooming-in). The median (interquartile range, IQR) time/day with CO2 concentration > 800 ppm (primary outcome) was 110 min (IQR 47–207) at baseline, 82 min (IQR 12–226.5) during sham periods, 78 min (IQR 20–154) during intervention periods and 140 min (IQR 19.5–612.5) post-intervention. The intervention period only differed significantly from the post-intervention period (P = 0.02), mainly due to an imbalance in rooming-in. Significant but small differences were observed in secondary outcomes of time/day with CO2 concentrations > 1000 ppm and daily peak CO2 concentrations during the intervention vs. baseline and vs. the post-intervention period, but not vs. sham. Staff reported cold discomfort for patients as the main barrier towards increasing ventilation. DiscussionIndoor air CO2 concentrations in hospital rooms commonly peaked above recommended levels, especially during morning care and rooming-in. There are many possible barriers towards implementing CO2 monitors to improve ventilation in a real-world hospital setting. A paradigm shift in hospital infection control towards adequate ventilation is warranted. Trial registrationClinicalTrials.gov Identifier: NCT04770597

Development of Weighting Scheme for Indoor Air Quality Model Using a Multi-Attribute Decision Making Method

When planning the energy demand of ventilation, proper consideration should be given to the possible scenarios of indoor air quality and pollutant concentrations. The purpose of the present research is to create a practical method of prioritising indoor air pollutants, considering technical, economical and health aspects, in the Indoor Air Quality model (IAQ). In order to find the global weights for the combined IAQindex model sub-elements (in practice, air pollutant concentrations), the Multi-Criteria Decision Making (MCDM) approach is used. The authors have approached the problem of a weighting scheme in a model such as the complex model of the IAQ related to making decisions with many criteria and with the Multi-Attribute Decision Making MADM approach (specifically MCDM). The basis of the MADM method is a decision matrix constructed rationally by the authors, which includes six attributes: actual indoor air carbon dioxide concentration, total volatile organic compounds (TVOCs) and formaldehyde HCHO concentration, and their anthropogenic and construction product emissions to the indoor environment. The decision model of IAQindex includes five alternatives (possible situations), and the combination of pollutant concentration attributes with additional emission attributes is related to the indoor environment under specific situation. For defining the weights of criteria, the authors provide objective approaches: (i) entropy-based approach considering measuring the amount of information, and (ii) CRITIC, a statistic-based approach. The value of the presented method, i.e., the determination of global weights for IAQ components, is shown as a practical application to determine IAQ and the Indoor Environmental Quality (IEQ) index for an office building used as a case study.

Variations in leaf growth parameters within the tree structure of adult Coffea arabica in relation to seasonal growth, water availability and air carbon dioxide concentration.

Dynamics in branch and leaf growth parameters, such as the phyllochron, duration of leaf expansion, leaf life span and bud mortality, determine tree architecture and canopy foliage distribution. We aimed to estimate leaf growth parameters in adult Arabica coffee plants based on leaf supporter axis order and position along the vertical profile, considering their modifications related to seasonal growth, air [CO2] and water availability. Growth and mortality of leaves and terminal buds of adult Arabica coffee trees were followed in two independent field experiments in two sub-tropical climate regions of Brazil, Londrina-PR (Cfa) and Jaguariúna-SP (Cwa). In the Cwa climate, coffee trees were grown under a FACE (free air CO2 enrichment) facility, where half of those had been irrigated. Plants were observed at a 15-30 d frequency for 1 year. Leaf growth parameters were estimated on five axes orders and expressed as functions of accumulated thermal time (°Cd per leaf). The phyllochron and duration of leaf expansion increased with axis order, from the seond to the fourth. The phyllochron and life span during the reduced vegetative seasonal growth were greater than during active growth. It took more thermal time for leaves from the first- to fourth-order axes to expand their blades under irrigation compared with rainfed conditions. The compensation effects of high [CO2] for low water availability were observed on leaf retention on the second and third axes orders, and duration of leaf expansion on the first- and fourth-order axes. The second-degree polynomials modelled leaf growth parameter distribution in the vertical tree profile, and linear regressions modelled the proportion of terminal bud mortality. Leaf growth parameters in coffee plants were determined by axis order. The duration of leaf expansion contributed to phyllochron determination. Leaf growth parameters varied according the position of the axis supporter along the vertical profile, suggesting an effect of axes age and micro-environmental light modulations.

Implementasi Monitoring Kualitas Udara Menggunakan Peramalan Exponential Smoothing dan NodeMCU Berbasis Mobile Android

Poor air quality threatens the health of all living things from humans to plants. Most people don’t know that the air they are breathing may be polluted. WHO said that 92% population in the world are living in the area with poor air quality that exceed the safe limit from WHO. Carbondioxide is one of many dangerous gas that must be considered by human. It can cause serious problem to human health. Industries are contribute to carbondioxide concentration in air. The purpose of this system is build the tool using NodeMCU microcontroler to measure the air quality in some place. This system can inform the user about air quality in their place by using Android smartphone. The forecast feature can be used to prevent the dangerous air quality.
 Index Terms— Carbondioxide, Air Quality, Android, Forecast

Modeling indoor air carbon dioxide concentration using artificial neural network

Many studies have been conducted on estimating the number of occupants in a building to set the right ventilation rate in order to maintain standard indoor air quality. However, few have focused on predicting carbon dioxide itself based on the room’s available parameters, such as temperature and humidity. This study was aimed at predicting indoor air carbon dioxide concentration in a room using a multilayer perceptron neural network with relative humidity and temperature as inputs. The neural network is a popular data-driven method to provide geometry-independent prediction algorithms. In this study, the neural network was trained in three different ways with the complete, partial, and zero real carbon dioxide concentrations available in the learning process. The sensitivity and specificity analyses were conducted on the output. The most accurate model, based on the calculated mean-square-error method, was five-steps-ahead prediction model with less than 17 PPM difference on average to actual CO2 concentration in the room. Results were also promising for the open-loop model. Carbon dioxide predictions can be used in maintaining indoor air quality by improving ventilation control in buildings.

Evaluation and environmental correction of ambient CO2 measurements from a low-cost NDIR sensor.

Non-dispersive infrared (NDIR) sensors are a low-cost way to observe carbon dioxide concentrations in air, but their specified accuracy and precision are not sufficient for some scientific applications. An initial evaluation of six SenseAir K30 carbon dioxide NDIR sensors in a lab setting showed that without any calibration or correction, the sensors have an individual root mean square error (RMSE) between ~5 and 21 parts per million (ppm) compared to a research-grade greenhouse gas analyzer using cavity enhanced laser absorption spectroscopy. Through further evaluation, after correcting for environmental variables with coefficients determined through a multivariate linear regression analysis, the calculated difference between the each of six individual K30 NDIR sensors and the higher-precision instrument had an RMSE of between 1.7 and 4.3 ppm for 1 min data. The median RMSE improved from 9.6 for off-the-shelf sensors to 1.9 ppm after correction and calibration, demonstrating the potential to provide useful information for ambient air monitoring.

Optimization of environmental factors affecting tertiary treatment of municipal wastewater by Chlorella protothecoides in a lab scale photobioreactor

In the present study, a lab scale externally illuminated photobioreactor was used to study the potential of a freshwater microalga Chlorella protothecoides (SAG-211-10C) in tertiary treatment of municipal wastewater. The effect of parameters such as: light intensity, photoperiod, pH, concentration of carbon dioxide in air, temperature and aeration rate on nutrient removal efficiencies of wastewater was analyzed. Low irradiance and low photoperiods (2 klux and 8h:12h) resulted in poor treatment efficiency (17.97% Chemical oxygen demand,29.44% total nitrogen, 23.91% total phosphorous). Alkaline pH (8,9 and 10) reduced the COD and TN removal efficiency, but improved total phosphorous removal rates. Higher carbon dioxide concentration in air adversely affected COD removal rates (27.97% at 8% CO2 v/s 69.95% at 2% CO2). The nutrient removal efficiencies could not be increased by operating the PBR under a non-optimum lower temperature(20°C) or higher temperature (30°C). Under optimum conditions (Light intensity-6 klux, photoperiod–16h:8h, pH-6.8, concentration of carbon dioxide in air −6%, temperature–25°C and aeration rate-3 lpm), highest removal of COD (78.03% on 10th day), 100% removal of TN (on 7th day) and 100% removal of TP (on 6th day) was observed. The highest biomass concentration under optimum conditions was 1.96g/L.

Linnebjer—A South Swedish Oak Forest and Meadow Area—Revisited after Half a Century

An oak forest and three wet meadows/fens were reinvestigated after 50 years concerning tree vitality, biomass and productivity, and soil chemistry. Sulphur and nitrogen deposition has changed dramatically during these years, and the aim was to analyse the differences in both the oak forest and the open field ecosystems. Trees were re-measured and soil profiles were resampled. Important visible changes in the oak forest were stated concerning the vitality of oaks. Aboveground there was a decrease in tree biomass, production and litter fall, but a huge increase in standing dead logs. During the years, the deposition of sulphur had decreased drastically, but nitrogen deposition was still high. Soil acidification in the forest had decreased, reflected in an increased base saturation in the forest, in spite of slightly lowered pH-values. Strongly increased amounts of exchangeable Ca and Mg now appeared in the forest soil, and a substantial transport of calcium and magnesium had obviously taken place from the forest soil to the meadow and fens during the years. However, the most important soil change was the accumulation of organic matter. The increased accumulation of organic matter in turn meant increased amounts of colloid particles and microsites for ion exchange in the soil. This favoured 2-valence base cations, and especially Ca and Mg that increased very much in all the studied ecosystems. Carbon as well as nitrogen had strongly increased in the forest, meadow and fen soils. This was interpreted as a natural result of increased vegetation growth due to high nitrogen deposition, increased global annual temperature and increased carbon dioxide concentration in air. It was concluded that the decreased deposition of sulphur had had a positive effect on soil chemistry, and that the deposition of nitrogen probably had stimulated vegetation growth in general, and contributed to increased amount of organic matter in the soils. However, in this studied oak forest, the decreased vitality and many killed trees were also suspected to be a result of high nitrogen deposition. Obviously increased tree growth was counteracted by decreased stress resistance, and increased appearance of pathogens in the oak trees.

Experimental investigations on carbonation of sodium aerosol generated from sodium fire in the context of fast reactor safety

Carbonation of sodium aerosols is the most important aspects to be considered for the evaluation of chemical hazards as a part of fast reactor safety studies. The sodium oxide, immediately formed as the combustion product due to sodium fire, undergoes chemical changes to NaOH, Na2CO3 and NaHCO3 upon reactions with moisture and CO2 prevailed in the atmosphere. Of which, hydroxide aerosols are highly corrosive and harmful, and it has stringent concentration limit for human exposure. Hence, in order to assess the condition for human intervention in the event of sodium fire, chemical composition of aerosols resulting from controlled sodium fires in a closed Aerosol Test Facility was investigated. The real time chemical species of aerosols generated from sodium fire and the effect of relative humidity (RH) and carbon dioxide concentration in air on carbonation have been studied. The experiments were carried out with the initial mass concentration of ∼4gm−3, RH between 20% and 90% and the CO2 concentration in surrounding environment at 390 and 280ppm. It is observed from the experimental study that aerosols are enriched with NaOH (0.8mol fraction) in the beginning stage (samples collected during first few minutes after sodium fire) when surrounding atmosphere contains any of the following compositions – (i) ∼90% RH and 390ppm CO2, (ii) ∼90% RH and 280ppm CO2 or (iii) 50% RH and 280ppm CO2 whereas they are almost equally distributed between NaOH and Na2CO3 in the beginning stage when the atmosphere has any of the compositions (i) 50% RH, 390ppm CO2, (ii) 20% RH, 390ppm CO2 or (iii) 20% RH, 280ppm CO2. Carbonation of aerosols is completed between 20min and 1h just after sodium fire depending upon the prevailing atmosphere. The present study shows that highly humid condition promotes carbonation process. Faster the carbonation process the lesser would be the chemical hazard.

The thermodynamics of direct air capture of carbon dioxide

An analysis of thermodynamic constraints shows that the low concentration of carbon dioxide in ambient air does not pose stringent limits on air capture economics. The thermodynamic energy requirement is small even using an irreversible sorbent-based process. A comparison to flue gas scrubbing suggests that the additional energy requirement is small and can be supplied with low-cost energy. In general, the free energy expended in the regeneration of a sorbent will exceed the free energy of mixing, as absorption is usually not reversible. The irreversibility, which grows with the depth of scrubbing, tends to affect flue gas scrubbing more than air capture which can successfully operate while extracting only a small fraction of the carbon dioxide available in air. This is reflected in a significantly lower theoretical thermodynamic efficiency for a single stage flue gas scrubber than for an air capture device, but low carbon dioxide concentration in air still results in a larger energy demand for air capture. The energy required for capturing carbon dioxide from air could be delivered in various ways. I analyze a thermal swing and also a previously described moisture swing which is driven by the evaporation of water. While the total amount of heat supplied for sorbent regeneration in a thermal swing, in accordance with Carnot's principle, exceeds the total free energy requirement, the additional free energy required as one moves from flue gas scrubbing to air capture can be paid with an amount of additional low grade heat that equals the additional free energy requirement. Carnot's principle remains satisfied because the entire heat supplied, not just the additional amount, must be delivered at a slightly higher temperature. Whether the system is driven by water evaporation or by low grade heat, the cost of the thermodynamically-required energy can be as small as $1 to $2 per metric ton of carbon dioxide. Thermodynamics does not pose a practical constraint on the implementation of air capture but leaves quite some leeway for unavoidable inefficiencies in practical systems.

Elevated air carbon dioxide concentrations increase dissolved carbon leaching from a cropland soil

Increasing leaching losses of carbon from soils due to accelerated weathering and increasing concentrations of dissolved carbon as a result of intensified soil respiration are suspected to provide a negative feedback on rising atmospheric CO2 concentrations. We tested this hypothesis by studying concentrations of dissolved carbon and groundwater recharge at the Braunschweig free air carbon dioxide enrichment (FACE) experiment under winter wheat and winter barley. Dissolved carbon concentrations under elevated atmospheric CO2 and ambient conditions were rather similar and not consistently higher under FACE. An analysis of δ13C signatures suggested that dissolved organic and inorganic carbon contained 9–29% (DOC) and 26–49% (DIC) of “new” carbon originating from CO2 added to the FACE rings. Dissolved inorganic carbon additionally contained 15–42% of carbonate-derived C. A 15% reduction in evapotranspiration under elevated CO2 increased groundwater recharge by 60 mm or 55%, which was the main driver for an observed 81% increase in dissolved carbon leaching from 2.7 to 4.9 g C m−2 year−1 at 90 cm depth. Our results suggest that future changes of dissolved carbon leaching losses will be mainly governed by changes in climate and groundwater recharge and to a lesser extent by increasing dissolved carbon concentrations.

ハーブの香気成分の代謝・放出に及ぼす空気中二酸化炭素濃度の影響

ハーブの香気成分の代謝・放出に及ぼす空気中二酸化炭素濃度の影響

Carbon dioxide concentration in air within the Nerja Cave (Malaga, Andalusia, Spain)

From 2001 to 2005 the CO2 concentration of the air in the interior and exterior of the Nerja Cave was studied and its relation with the air temperature and visitor number. The average annual CO2 concentration outside of the cave is 320 ppmv, whilst inside, the mean concentration increases to 525 ppmv during autumn and winter, and in the order of 750 ppmv during spring and summer. The temporal variation of CO2 content in the air of the cave is strongly influenced by its degree of natural ventilation which is, in turn, determined by the difference between external and internal air temperatures. During autumn, winter and spring, a positive correlation between the CO2 content of the air inside the cave and the temperature difference between the external and internal air was observed, such that when this difference increased, there was a higher level of CO2 within the cave. Then, the ventilation is high and CO2 levels are mainly of human origin. During summer, there was a negative correlation between CO2 and the temperature difference between the air outside and that inside the cave: when the temperature difference increases, the CO2 content within the cave is lower. At this time of the year, the renovation of the air is much slower due to the lower ventilation. A positive correlation between CO2 concentration of the air in the cave and the visitor number can only be observed during August, the month that receives the most visits throughout the year averaging 100,000.

On the conservative behavior of biomass water productivity

The ever-increasing demand and competition for the finite water resource worldwide call for more efficient use of water in all sectors, including firstly agricultural food production. One important consideration is the existence of a limit to the amount of biomass a crop can produce per unit of water consumed. This article analyzes the theoretical background and the experimental evidence for the conservative behavior of the efficiency in water use by crops to produce biomass, i.e., biomass water productivity (WPb), under variable environmental conditions. Particularly, WPb is approximately constant for a given crop species after normalization for evaporative demand of the atmosphere and air carbon dioxide concentration. A stepwise scaling up approach, from leaf to canopy, is undertaken to underline the processes involved at the different hierarchical levels of biological organization that lead to the conservative behavior of WPb. Starting at the leaf level, the basic gas exchange equations are outlined to demonstrate that the normalized photosynthetic WPb at the leaf scale is proportional to the ambient CO2 concentration. New experimental evidence in support of that conclusion is presented for several C3 and a C4 crops. Additional factors are introduced to assess photosynthetic WPb at the canopy scale, including the extent of radiation capture and the role of respiration. The composition of biomass was then considered in the analysis of WPb over a season. The paper highlights the need to normalize WPb for differences in climate, specifically, in evaporative demand of the atmosphere to extrapolate WPb values between climatic zones, and in atmospheric CO2 concentration to account for changes in CO2 with time, when looking at the past and into the future. Two procedures for normalization for differences in evaporative demand are presented, and a procedure for normalization for changes in CO2 concentration is derived for the leaf scale and shown to be applicable to canopy scale. Some knowledge gaps and research needs are pointed out and the potential offered by the near constancy of normalized WPb in crop simulation modeling is emphasized.

Effect of carbon isotopic variations on measured CO2 abundances in reference gas mixtures

Changes in the Earth's climate caused by global warming are a looming problem that poses serious challenges not only for our generation but for future generations. An accurate determination of CO2 gas plays a critical role in this field of research. The measurement of greenhouse gases is pivotal to understanding the changes in Earth's climate and needs to be carried out with a high degree of accuracy. Precision measurements on a 0.1 μmol/mol scale may provide research data for precisely monitoring the continuing changes that the planet is undergoing. The World Meteorological Organization (WMO) has recommended that carbon dioxide concentrations in air can be measured by comparing these with national reference gases using a nondispersive infrared (NDIR) analyzer to standardize international data. The CO2 molecules absorb the distinctive resonant frequencies in IR spectrometers. The NDIR analyzers usually use narrow band path filter to determine 12CO2 in all carbon dioxide molecules, which can possibly ignore the measurement of 13CO2 partially or totally. However, if the carbon isotopic abundances of CO2 samples deviate from those in standard CO2 gas, the NDIR measurement will not be exact. For accurate measurements, producers of reference gas mixtures either must use gas with natural isotopic abundances, or report the isotopic abundances of CO2. In order to document shifts based on isotopic variability, we prepared artificial air as CO2 reference gas mixtures gravimetrically with CO2 having different carbon isotopic signatures to study the resulting isotopic variations. We used different δ13C values of two CO2 source gases, A and B, corresponding to −41.97‰ and −14.88‰, respectively, which were measured using an isotope ratio mass spectrometer. One set of reference gas mixtures (A1 to A5) was prepared from the CO2 source of δ13C = −41.97‰, and the other set of reference gas mixtures (B1, B2) was prepared from that of δ13C = −14.88‰. The CO2 abundances of the two sets of mixtures were compared by using NDIR. The reproducibility test for the set A showed that the data are consistent within uncertainty (calibration line was obtained by the best secondary polynomial least squares fit). The uncertainty of CO2 concentration in the reference gas mixtures are 0.06 μmol/mol with a 95% confidence level. The reproducibility of the NDIR measurement is 0.012 μmol/mol (standard deviation). The difference between the set A (A1 to A5) and set B (B1, B2) was found to be 0.17 ± 0.01 μmol/mol, which is in excellent agreement with the theoretically predicted value of 0.17 μmol/mol.

Climate change as a confounding factor in reversibility of acidification: RAIN and CLIMEX projects

Abstract. The RAIN and CLIMEX experiments at Risdalsheia, southernmost Norway, together cover 17 years (1984-2000) of whole-catchment manipulation of acid deposition and climate. A 1200 m2 roof placed over the forest canopy at KIM catchment excluded about 80% of ambient acid deposition; clean rain was sprinkled under the roof. A climate change treatment (3.7°C increase in air temperature and increase in air carbon dioxide concentrations to 560 ppmv) was superimposed on the clean rain treatment for four years (1995-1998). Sea-salt inputs and temperature are climate-related factors that influence water chemistry and can confound long-term trends caused by changes in deposition of sulphur and nitrogen. The RAIN and CLIMEX experiments at Risdalsheia provided direct experimental data that allow quantitative assessment of these factors. Run-off chemistry responded rapidly to the decreased acid deposition. Sulphate concentrations decreased by 50% within three years; nitrate and ammonium concentrations decreased to new steady-state levels within the first year. Acid neutralising capacity increased and hydrogen ion and inorganic aluminium decreased. Similar recovery from acidification was also observed at the reference catchment, ROLF, in response to the general 50% reduction in sulphate deposition over southern Norway in the late 1980s and 1990s. Variations in sea-salt deposition caused large variations in run-off chemistry at the reference catchment ROLF and the year-to-year noise in acid neutralising capacity was as large as the overall trend over the period. These variations were absent at KIM catchment because the sea-salt inputs were held constant over the entire 17 years of the clean rain treatment. The climate change experiment at KIM catchment resulted in increased leaching of inorganic nitrogen, probably due to increased mineralisation and nitrification rates in the soils. Keywords: acid deposition, global change, water, soil, catchment, experiment, Norway.

Effect of ambient and evolved CO 2 on an equilibrium reaction in YBa 2CU 3O 6 + X synthesis

The formation of YBa 2Cu 3O 6 + x in air involves two main reactions. The first is between BaCO 3 and CuO to form BaCuO 2 and CO 2. Increasing the partial pressure of carbon dioxide in air shifts the endothermic BaCO 3 reaction to higher temperatures. At a fixed carbon-dioxide concentration in air, the reaction onset-temperature of a thick sample (2 mm) determined by TG/DTA exceeds by approximately 200 °C that of a thin film (10 mm) determined by in situ HT-XRD. Evolved CO 2 in thick samples disguises the dependence of the intrinsic reaction onset-temperature and reaction rate on the ambient CO 2 concentrations. The intrinsic equilibrium constant and associated thermodynamic parameters for this reaction should be determined by experiments in which the impact of transport limitations is eliminated, i.e., use of a thin film and high gas-velocity next to the sample surface.