Concentrations Of CO2 In Air Research Articles

Interpreting natural climate signals in ice cores

Polar ice caps preserve information about atmospheric composition over the past tens of thousands to hundreds of thousands of years. They contain a rich history of the Earth's volcanic activity, terrestrial dust sources, sea ice location, terrestrial and marine biological activity, pollution, and atmospheric oxidation capacity. Differences in concentrations of CO2 and CH4 in air extracted from ice of various ages, changes in temperature inferred from d18O in ice, and differences in the dust or acid loading of ice are all used to deduce major changes in the global environment [Oeschger and Langway, 1989]. These temporal patterns of physical properties and chemical species that are recorded in ice offer an opportunity to study the cause and effect relationships of environmental change.

CO2 Stimulation of the Cornea: A Comparison Between Human Sensation and Nerve Activity in Polymodal Nociceptive Afferents of the Cat

Excitation of nociceptors by low pH has been proposed as a cause of pain following tissue injury. Here we have studied the effect of pH reductions caused by application of CO2 pulses to the cornea on the activity of corneal afferent nerves of the cat and on the magnitude of pain sensations in humans. Single-unit activity was recorded from corneal afferent fibres in anaesthetized cats. The corneal receptive field of A-delta or C polymodal nociceptive units was exposed for 30 s to a gas mixture with different concentrations of CO2 in air (0, 35, 50, 65, 80 and 98.5%). Responses to CO2 were evoked at a mean threshold concentration of 40 +/- 3% CO2. They consisted of a discharge of impulses that decayed gradually to a tonic level. In 15% of the units the initial burst was absent. The CO2 concentration and firing frequency data could be fitted to a power function with an exponent of 1.12. Pulses of CO2 were also applied to the cornea of 16 human volunteers. Sensations experienced were measured by means of a visual analogue scale and a verbal descriptor scale. Flow was adjusted below the mechanical stimulation threshold (2.8 +/- 0.5 mg). When mixtures containing 10-90% CO2 in 5% steps were applied as 3 s pulses, threshold sensation, described as a mild stinging pain, was evoked at 33.5 +/- 4.0% CO2. This sensation became overtly painful with higher CO2 concentrations (47.5 +/- 3.6% CO2). For the same subject the sensory threshold was remarkably constant, though it changed with longer exposure times. The relationship between CO2 concentration and magnitude of pain could be adjusted to a power function with a power exponent of 1.12. Curves of CO2 concentration versus neural discharges in the cat and versus psychophysical sensation in humans were very similar. These results show that corneal polymodal nociceptors respond to protons, and encode changes in CO2 concentration presumably reflecting pH changes. The same stimulus evokes corneal pain sensations in humans, thus opening the possibility of using CO2 as an effective stimulus for corneal aesthesiometry.

Carbon-dioxide exchange in lichens: determination of transport and carboxylation characteristics

Measurements were made of net rates of CO2 assimilation in lichens at various ambient concentrations of CO2 in air and in helox (79% He, 21% O2). Because of the faster rate of CO2 diffusion in the pores of lichen thalli when filled with helox than when filled with air, a given net rate of assimilation was achieved at a lower ambient concentration of CO2 in helox. The differences were used to estimate resistances to diffusion through the gas-filled pore systems in lichens. The technique was first tested with five lichen species, and then applied in a detailed study with Ramalina maciformis, in which gas-phase resistances were determined in samples at four different states of hydration and with two irradiances. By assuming, on the basis of previous evidence, that the phycobiont in R. maciformis is fully turgid and photosynthetically competent at the smallest hydration imposed (equilibration with vapour at 97% relative humidity), and that, with this state of hydration, diffusion of CO2 to the phycobiont takes place through continuously gas-filled pores, it was possible also to determine both the dependence of net rate of assimilation in the phycobiont on local concentration of CO2 in the algal layer, and, with the wetter samples, the extents to which diffusion of CO2 to the phycobiont was impeded by water films. In equilibrium with air of 97% relative humidity, the thallus water content being 0.5 g per g dry weight, the resistance to CO2 diffusion through the thallus was about twice as large as the resistance to CO2 uptake within the phycobiont. Total resistance to diffusion increased rapidly with increase in hydration. At a water content of 2 g per g it was about 50 times as great as the resistance to uptake within the phycobiont and more than two-thirds of it was attributable to impedance of transfer by water. The influences of water content on rate of assimilation at various irradiances are discussed. The analysis shows that the local CO2 compensation concentration of the phycobiont in R. maciformis is close to zero, indicating that photorespiratory release of CO2 does not take place in the alga, Trebouxia sp., under the conditions of these experiments.

Considerable change in DC breakdown characteristics of positive-point-plane gaps due to varying concentrations of NOx, CO2 and H2O in air and intensity of irradiation

The sparking potential of DC positive-point-plane gaps in air for the centimetre gap range shows an abrupt change at a critical gap length dc. The value of dc is affected markedly by the intensity of irradiation and by concentrations of CO2, H2O and NOx produced by the discharges in air. The change in dc leads to a pronounced change in breakdown characteristics. This effect becomes more striking as the degree of non-uniformity of the gap is reduced and can be demonstrated clearly by using a flow system to avoid the accumulation effect of the decomposition products produced by successive discharges.

EFFECTS OF CARBON DIOXIDE ON THE GROWTH AND MORPHOGENESIS OF MARSILEA

Increased concentrations of CO2 in air (1–50%) cause young plants of Marsilea vestita to exhibit many characteristics of the water form when they are grown on a solid substrate under sterile conditions. Thus these plants have longer internodes, shorter petioles, more rectangular‐shaped epidermal cells and fewer stomata on the lower leaf epidermis than controls grown in 0.03% CO2. Over a 2‐week period, dry weight increase is considerably greater in 12.5% and 25% CO2 than in 0.03% CO2. Fifty percent CO2 is inhibitory to growth. CO2‐enriched air has the same morphogenetic effect when supplied in the light or the dark. Possible explanations for this effect are discussed.

Heart activity during experimental diving of snakes.

Diving bradycardia has been demonstrated in snakes, ( Tropidonotus natrix). The bradycardia was developed rapidly and amounted to a reduction in heart rate of about 85%. The electrocardiographic findings revealed the slowing of the heart rate as effected mainly through a prolongation of the diastole, amounting to 30 times the prediving value. Duration of the electrical systole showed a prolongation of the P-R interval by 15% and the Q-T interval by 130%. A rapid and pronounced shift in the T-wave amplitude occurred upon submersion. The results suggest that the described T-wave shifts are due to changes in concentration of CO2 in the organism. Increased concentrations of CO2 in the respiratory air induced bradycardia and had a depressant effect on respiration.