Variation Of Carbon Dioxide Concentration Research Articles

Environment in stone chamber of an unexcavated tumulus and preservation of buried relics: Part 1. Environmental monitoring for simulated tumulus

Japan has many unexcavated tumuli, most of which were buried along with artifacts of precious cultural heritage. For such a tumulus, it is essential to understand how changes in its exterior environment affect its interior environment, and how those interior changes affect the deterioration of the relics buried in the stone chamber. In this study, an underground space was constructed in the forest of the Katsura Campus of Kyoto University to simulate the environment of an unexcavated tumulus, and long-term monitoring was implemented in the simulated stone chamber, including the temperature, humidity, water potential, wetness, and oxygen and carbon dioxide concentrations, along with metal corrosion tests. This article is focused on environmental monitoring, and the results demonstrate that the simulated tumulus has the general characteristics of the hygrothermal environments of an unexcavated tumulus that has small temperature fluctuation and near-saturation humidity. The ceiling of the simulated chamber condensed significantly from October to April, which is related to the variations of the ceiling and floor temperatures. Also, the wetness of the walls in the simulated chamber was affected by rainfall. The oxygen concentration in the simulated stone chamber varied in the range of 13%–19% in 2015, and the variation of carbon dioxide concentration in the simulated stone chamber was contrary to the oxygen concentration and varied in the range of 3%–9% in 2016. The oxygen concentration in the stone chamber was similar to that in the surrounding soil that decreased at times of rainfall, contrary to the fluctuations in the soil water content.

Temporal and spatial variation of carbon dioxide concentration and its exchange fluxes in Lake Chaohu

为揭示巢湖水体二氧化碳浓度（cCO₂）时空变化特征及其影响因素，2017年2、4、8和11月分别采集巢湖表层水样，测定水样的理化、生物学参数以及cCO₂，并以此计算其水-气界面交换通量.结果表明：巢湖表层水体cCO₂的变化范围为13.31~55.47 μmol/L，年平均值为26.27 μmol/L，在空间上呈现出西高东低的分布趋势；在季节上表现为暖季（夏季）低、冷季（春、秋和冬季）高的规律.巢湖表层水体cCO₂与溶解性有机碳浓度呈显著正相关，与叶绿素a浓度呈显著负相关，说明有机质分解和光合作用在巢湖CO₂生物化学循环过程中占重要作用；同时，南淝河等入湖河流污染严重，输入大量有机和无机碳，对西巢湖水体CO₂贡献较大.总体上，巢湖CO₂排放量相对较低，巢湖部分区域在冷季（2、11月）表现为CO₂的汇.本研究对于明晰富营养化湖泊CO₂排放特征以及准确估算全球内陆湖泊碳通量等都具有参考价值.;In order to understand the temporal and spatial variation of carbon dioxide concentration (cCO₂)and its influencing factors in the surface water of Lake Chaohu, the physicochemical parameters, biological parameters, and cCO₂ of surface (15-30 cm)water samples collected in February, April, August and November in 2017 from Lake Chaohu, representing different seasons, were measured. The surface water-air flux of CO₂ was then calculated based on gradient method as well. The results showed that the cCO₂ ranged from 13.31-55.47 μmol/L. The average annual cCO₂ was 26.27 μmol/L. The cCO₂ was higher in the west lake sub-lake zone than that in the central and east sub-lake zones. The surface water of Lake Chaohu had a lower cCO₂ in the warm season (summer) than in cool and cold seasons (spring, autumn and winter). cCO₂ was positively correlated with dissolved organic carbon (DOC)concentration and negatively correlated with chlorophyll-a concentration, suggesting that photosynthesis and decomposition of organic matter plays an important role in the biochemical cycle of CO₂. Due to the serious pollution of inflowing rivers surrounding Lake Chaohu, DOC input from the watershed supplied substrates for CO₂ production. Lake Chaohu was a relatively small source for atmosphere CO₂ compared to others studies. Lake Chaohu shifted from a CO₂ source to a sink in cold seasons.

Assessment of seasonal variations of carbon dioxide concentration in Iran using GOSAT data

Global warming and climate change have been identified as the most important challenges of the 21st century. Greenhouse Gases Observation Satellite (GOSAT) measures the concentrations of carbon dioxide (CO 2) and methane (CH 4) in the atmosphere column from the earth's surface to the upper atmosphere. In this research, GOSAT Thermal And Near Infrared Sensor for Carbon Observation – Fourier Transform Spectrometer (TANSO‐FTS) level 2 data and meteorological parameters were used in the assessment of changes in CO 2 concentration (XCO 2) from 2009 to 2015. We investigated the relationship between XCO 2 and meteorological parameters (temperature and precipitation) obtained from weather stations and the Normalized Difference Vegetation Index (NDVI) in the year 2013 in Iran. The results reveal a steady increase in the mean atmospheric CO 2 concentration, from 384.89 to 400.39 ppm. It was observed that the XCO 2 varied significantly depending on the month, with the highest concentration of CO 2 in April/May and the lowest concentration in August/September. The correlation between XCO 2 and average monthly air temperature is negative, which means that a reduction in XCO 2 with an increase in temperature is dependent on photosynthetic activities in the growing seasons. The highest and lowest correlation coefficient between the NDVI and XCO 2 was obtained in the spring and in the fall, respectively. These findings are useful for recognizing factors that affect CO 2 concentration in different seasons in arid and semi‐arid regions, and as an initial step toward sustainable management.

A study of different‑scale relationship between changes of the surface air temperature and the СО2 concentration in the atmosphere

A concept of the anthropogenic origin of the current global climate warming assumes that growth of concentration of the atmospheric carbon dioxide and other greenhouse gases is of great concern in this process. However, all earlier performed analyses of the Antarctic ice cores, covering the time interval of several glacial cycles for about 1 000 000 years, have demonstrated that the carbon dioxide concentration changes had a certain lag relative to the air temperature changes by several hundred years during every beginning of the glacial terminations as well as at endings of interglacials. In contrast to these findings, a recently published careful analysis of Antarctic ice cores (Parrenin et al., 2013) had shown that both, the carbon dioxide concentration and global temperature, varied almost synchronously during the transition from the last glacial maximum to the Holocene. To resolve this dilemma, a special technique for analysis of the paleoclimatic time series, based on the wavelets, had been developed and applied to the same carbon dioxide concentration and temperature time series which were used in the above paper of Parrenin et al., 2013. Specifically, a stack of the Antarctic δ18O time series (designated as ATS) and the deuterium Dome C – EPICA ones (dD) were compared to one another in order to: firstly, to quantitatively estimate differences between time scales of these series; and, secondly, to clear up the lead–lag relationships between different scales variations within these time series. It was found that accuracy of the mutual ATS and dD time series dating lay within the range of 80–160 years. Perhaps, the mutual dating of the temperature and carbon dioxide concentration series was even worse due to the assumed displacement of air bubbles within the ice. It made us to limit our analysis by the time scales of approximately from 800 to 6000 years. But it should be taken into account that any air bubble movement changes the time scale of the carbon dioxide series as a whole. Therefore, if a difference between variations in any temperature and the carbon dioxide time series is found to be longer than 80–160 years, and if these variations are timescale‑dependent, it means that the bubble displacements are not essential, and so these advancing and delays are characteristic of the time series being compared. Our wavelet‑based comparative and different‑scale analysis confirms that the relationships between the carbon dioxide concentration and temperature variations were essentially timescale‑dependent during the transition from the last glacial maximum to the Holocene. The carbon dioxide concentration variations were ahead of the temperature ones during transition from the glacial maximum to the Boelling – Alleroud warming as well as from the Young Drias cooling to the Holocene optimum. However, the temperature variations were ahead during the transition from the Boelling – Alleroud warming to the Young Drias cooling and during the transition from the Holocene optimum to the present‑day climate.

Effect of Environmental Tax on Carbon Dioxide Emission: A Mathematical Model

The objective of this work is to study effect of environmental tax on emitters to attain a pollution free environment. In this paper, an attempt has been made to study the effect of environmental tax to control carbon dioxide (a global warming gas) concentration in the atmosphere using a nonlinear mathematical model. It is assumed that the environmental tax is levied only when the concentration of carbon dioxide crosses a threshold level over which it is harmful to our environment. Analytically, it is shown that the concentration of carbon dioxide decreases as the rate of environmental tax increases. The variation of carbon dioxide concentration (with and without environmental tax) has also been shown in a plot to confirm analytical results. Further, carbon dioxide concentration can also be reduced by greenbelt (leafy trees) plantation. It is shown, analytically and numerically, that carbon dioxide concentration decreases as its rate of interaction (absorption) with leafy trees increases.

Golden age of gas and its impact on the world energy, the global carbon cycle and climate

Global and regional resource and environmental problems of production and use of unconventional gas (UG) are studied. Estimations for world and national reserves of various kinds of UG are presented. The dynamics of the gas share in total energy consumption and thermal power generation around the world is analyzed. Projections of the world production of conventional gas and UG are proposed. Variations in carbon dioxide concentration in the atmosphere and the corresponding changes in average global air temperature are calculated for various scenarios suggesting unconventional gas substitution of different energy sources. The possible consequences of expected climate changes for Russia’s power industry are analyzed. It is shown that, despite the uncertainty in the estimates of the economic and environmental consequences of shale gas (SG) production, its use, according to the available resource estimates, can make it possible to solve global and regional problems associated with energy (import substitution) and environment protection (replacing the less clean coal fuel). However, the development of the huge global resources of this type of fuel can have a significant effect on the chemical and thermal radiative balance of the Earth’s atmosphere, and it must be noted that the climatic effect of carbon dioxide emissions from the UG combustion greatly exceeds the consequences of methane leakage during its production. In order to sustain the stability of the global climate system, the development of the world’s large UG resources must be accompanied by an equivalent reduction in the use of coal. This is the only way for UG to become a safe energy bridge to the future, able to keep the climate system at the threshold of critical values. Direct effects of possible climatic changes on the territory of Russia for the domestic energy complex are estimated as more positive than adverse, mainly due to lower energy costs for space heating.

갯벌에서 여름철 일몰 전후 이산화탄소 농도 변동 분석

Abstract In this study, before and after sunset carbon dioxide concentration and air temperature were observed in two points of atmosphere (lower observation point of the GL + 0.1 m, the upper observation point of GL + 1.0 m) on the foreshore at located in Suncheon Bay and their variations were analyzed. Observation was performed on the foreshore on 2~4 August 2010. Instrument (VAISALA, GMP343) was set two hours before sunset and then observation was made continuously for six hours. In three days, observed carbon dioxide concentration was 375~419 ppm, and the air temperature was in the range of 28.7~32.5 . The average concentration of carbon dioxide was 388~399 ppm in the upper observation point and 386~396 ppm in the lower observation point. It was higher in the upper observation point and its fluctuations were similar in two observation points. Correlation coefficients between carbon dioxide concentration and air temperature in the upper observation point were in the range of 0.64~ 0.88, and were calculated 0.65 to -0.90 in the lower observation point. For the carbon dioxide concentration, correlation coefficients between the upper part and the lower part were very high as 0.98 in three times. For th e air temperature, correlation coefficients between the upper part and the lower part were very high as 0.97 and 0.99. In the sam e observation time, the slope of the linear regression function as carbon dioxide concentration in the lower observation point fo r the upper observation point was in the range of 0.97~1.01. Carbon dioxide concentration Gwas slightly higher in the upper observation point. Because carbon dioxide in the lower observation point was closer on the surface of the foreshore and absorbed from atmosphere to the foreshore. In this study, it was showed that the vertical variation of carbon dioxide concentration was insignificant in the several meter scale of atmosphere on the surface of the foreshore.Key words : Foreshore, Sunset, Carbon dioxide, Air temperature

Determination of diffusion coefficients of carbon dioxide in water between 268 and 473 K in a high-pressure capillary optical cell with in situ Raman spectroscopic measurements

Accurate values of diffusion coefficients for carbon dioxide in water and brine at reservoir conditions are essential to our understanding of transport behavior of carbon dioxide in subsurface pore space. However, the experimental data are limited to conditions at low temperatures and pressures. In this study, diffusive transfer of carbon dioxide in water at pressures up to 45MPa and temperatures from 268 to 473K was observed within an optical capillary cell via time-dependent Raman spectroscopy. Diffusion coefficients were estimated by the least-squares method for the measured variations in carbon dioxide concentration in the cell at various sample positions and time. At the constant pressure of 20MPa, the measured diffusion coefficients of carbon dioxide in water increase with increasing temperature from 268 to 473K. The relationship between diffusion coefficient of carbon dioxide in water [D(CO2) in m2/s] and temperature (T in K) was derived with Speedy–Angell power-law approach as:D(CO2)=D0[T/Ts-1]mwhere D0=13.942×10−9m2/s, Ts=227.0K, and m=1.7094. At constant temperature, diffusion coefficients of carbon dioxide in water decrease with pressure increase. However, this pressure effect is rather small (within a few percent).

Comparison of Seasonal Variations in Carbon Dioxide Concentrations between a Natural Hardwood Stand and a Fir Plantation at the Guandaushi Subtropical Forest, Taiwan

The purpose of this study was to understand variations in carbon dioxide concentrations at different canopy heights in a natural hardwood stand and a China-fir (Cunninghamia lanceolata) plantation at the Guandaushi subtropical forest. The measurements began in September 2004 and continued to the end of June 2005. There were 4 sampling heights, including 0.5, 4, and 12 m above ground level (agl) and 3~4 m above the canopy at the 2 stands. Results showed that the highest concentration of carbon dioxide was near the forest floor, and the lowest ones were at 12 m agl and 3~4 m above the canopy for both the natural hardwood stand and fir plantation. Seasonal and yearly variations of sampling heights between 12 m agl and 3~4 m above the canopy were not significant. The carbon dioxide concentrations of the 4 sampling heights were higher in spring and summer than in winter. Variations in carbon dioxide concentrations of the sampling height at 12 m in the natural hardwood forest were influenced by light intensity, regardless of daily or yearly variations. We concluded that the forest floor soil of the natural hardwood stand had a higher respiration rate, and there was a lower photosynthetic rate at the 12m level of the canopy. Therefore, at all sampling points, the concentrations of carbon dioxide were higher than these in the China-fir plantation. This concentration gradient was more significant in the higher-temperature season (June) than in the lower-temperature season (December to January).

Role of changing environmental parameters in leaf gas exchange of Arbutus unedo L. assessed by field and laboratory measurements

In the frame of the foreseen climate global changes we analysed the physiological responses of Arbutus unedo L. to the variations of carbon dioxide concentration, leaf temperature, and irradiance by measurements of leaf gas exchange and leaf water potential performed both in field and in the laboratory. Stomatal conductance was not affected by increase of leaf temperature. The growth conditions of potted plants likely made stomata more sensitive to the variation of external parameters than naturally growing plants. The interaction between high CO2 concentration and temperature involved important down-regulation mechanisms in the metabolic pathway of the carbon fixation. From an ecological point of view, the ability of A. unedo to adapt to the field stress makes it highly competitive in the Mediterranean plant community.

Stalagmite growth and palaeo-climate: an inverse approach

The growth of stalagmites is controlled by climatic conditions such as temperature, soil activity, and precipitation. Hence, a stalagmite stratigraphy reflects fluctuations of palaeo-climate conditions on various time scales, from annual variations to ice-age cycles. However, no attempt has been made to infer palaeo-climate fluctuations from the stratigraphy itself. We describe the complicated growth of a stalagmite with a simple mathematical model, in which both the growth rate and the equilibrium diameter of stalagmites are functions of palaeo-climate variables. Hence, inverting a given stalagmite stratigraphy in terms of growth rate and equilibrium diameter can in principle recover the palaeo-climate signal. The strongly nonlinear dependence of these two geometrical parameters, however, limits the success of a formal inversion of stratigraphical data. In this paper, we explore the resolving power of both growth rate and equilibrium diameter data for the palaeo-climate signals temperature, carbon-dioxide concentration, and precipitation. We use numerically generated stalagmite stratigraphies as observational data, thus we know beforehand the palaeo-climate signal contained in the stratigraphic record. Our results indicate that both variations in carbon-dioxide concentrations (as a proxy of soil cover) and drip interval (as a proxy of precipitation) can be recovered from the stratigraphy. However, temperature variations are poorly resolved.

On the prediction of concentration variations in a dispersing heavy-duty truck exhaust plume using k– ε turbulent closure

This work presents the computational fluid dynamic modeling of an exhaust plume dispersed from the exhaust pipe of a class-8 tractor truck powered by 330 hp Cummins M11 electronically controlled diesel engine. This effort utilizes an advanced CFD technique to accurately predict the variation of carbon dioxide concentration inside a turbulent plume using a k– ε eddy dissipation model. The simulation includes the “real-world” operation of a truck and its exhaust plume in a NASA, Langley aircraft testing wind tunnel, that had an effective volume of 226, 535 m 3 (8,000,000 ft 3). The predicted results show an excellent agreement with the experimentally measured values of CO 2 concentrations, dilution ratios, and the temperature variations inside the plume. A specific goal of this effort was to study the effect of recirculation region near the truck walls on dispersion of the plume. For this purpose, growth of the plume from the center of the exhaust pipe is also presented and discussed. This work also shows the benefits of CFD modeling in applications where dispersion correlations are not required a priori, instead the dispersion coefficients are calculated precisely by solving the turbulent kinetic energy and dissipation equations.

Factors Affecting the Diurnal Variation of Carbon Dioxide Concentration in Standing Water in a Rice Field.

The carbon dioxide concentration (pCO2) in irrigation water in a rice field was measured from August 9 to 11, 1996. The pCO2 showed low values of a few μatm in the daytime, and high values over 2, 500μatm (=253.3Pa) in the early morning. This large diel change of pCO2 is associated with three factors; water temperature change, gas exchange across air-water interface, and biological consumption of carbon dioxide in water through photosynthesis. The effect of water temperature change results in the modification by 60μatm in pCO2 (2% of the diurnal change) taking into account the diurnal change of water temperature (ca. 6°C). The carbon dioxide exchange across the air-water interface varied from -2.7 to 28.4μgm-2s-1, with a daily mean of 5.5μgm-2s-1, causing a variation of about 609μatm per day (24% of the diurnal change). Dissolved carbon dioxide [CO2] and oxygen [O2] data showed the photosynthetic (respiration) relationship: [CO2]/[O2]=-106/138. This suggests the possibility that the photosynthetic (respiration) activity of algae is responsible for the residual fraction (ca. 73%) of the diurnal change of pCO2. It is also noted that there was a measurable increase in the downward carbon dioxide flux (ca. 0.3mgm-2s-1) from the atmosphere when the paddy field was flooded compared to when it was drained. The increment of the downward carbon dioxide flux was compatible with the carbon dioxide emission rates at the soil surface. The carbon dioxide exchange rates at the water surface were smaller by a factor of 1, 000 compared with fluxes over a rice stand and smaller by a factor of 100 than the carbon dioxide emission rates at the soil surface.

Physical variation of water vapor, and the relation with carbon dioxide

Analysis of the long term NOAA carbon dioxide flask sample records to examine the exchange among the continental Antarctic air mass and other air masses shows a meteorological variation of carbon dioxide concentration. There is an inverse relation between the seasonal variation of carbon dioxide concentration and water vapor at all stations examined. Well established diffusion coefficients indicate an interaction of water and carbon dioxide vapor on the molecular scale. Laboratory experiments using a Fourier transform spectrometer show carbon dioxide to be removed from an airstream in proportion to water vapor precipitated. We propose that interaction of carbon dioxide and water vapor in the atmosphere provides temporary sinks that can influence the balance of the carbon dioxide budget.

Variations of atmospheric carbon dioxide concentration and greenhouse effect at Syowa Station (69°00′S, 39°35′E), Antarctica

On the basis of the analysis of atmospheric carbon dioxide concentration variations and the annual mean air temperature at Syowa Station, Antarctica in the period of 1984–1988, the following results are easily obtained: (1) The annual mean values of the atmospheric carbon dioxide concentration are gradually increased and equal to 342.59, 343.80, 345.15, 346.83 and 348.82 ppmv for 1984, 1985, 1986, 1987 and 1988, respectively. Its annual increase rates are 1.21, 1.35, 1.68 and 1.99 ppmv/yr. For 1984–1985, 1985–1986, 1986–1987 and 1987–1988, respectively and are raised year by year. The seasonal variations are observed and the maximum concentration is in spring and the minimum one is in late-summer or early-autumn. (2) The increasing tendency of the concentration of the atmospheric carbon dioxide is consistent with that of the air temperature.

On the Cause of the Relative Greenhouse Strength of Gases such as the Halocarbons

This note examines some of the factors important in determining the large radiative impact, relative to carbon dioxide, of increased concentrations of gases in the optically thin limit (such as the halocarbons at their present day concentrations). A narrow-band radiative transfer model is used to show that an absorber with the same integrated band strength as CFC-12, but with almost the same spectral variation of tropopause net flux change as occurs for small variations in carbon dioxide concentration, is 400 times more effective than carbon dioxide, on a molecule-per-molecule basis; this can be compared with the relative strength of 20,000 for CFC-12. This illustrates that the dominant reason for the relative strength of such gases is not their position in the 8-13 [mu]m window. It is not possible to unambiguously separate the possible reasons (spectral position, preexisting amounts and spectroscopic strength) for the variations in relative strength, as they are all related. 9 refs., 6 figs.

EFFECT OF HYPOCARBIA AND HYPERCARBIA ON THE ANTAGONISM OF PANCURONIUM-INDUCED NEUROMUSCULAR BLOCKADE WITH NEOSTIGMINE IN MAN

The effects of variations in carbon dioxide concentration on the antagonism of pancuronium-induced neuromuscular block by neostigmine were studied in 21 patients: normocarbia (PE'CO2 5.4%, PaCO2 4.93 kPa, n = 7), hypocarbia (PE'CO2 3.6%, PaCO2 3.30 kPa, n = 7) and hypercarbia (PE'CO2 7.5%, PaCO2 7.13 kPa, n = 7). Mechanical and electromyographic responses to ulnar nerve stimulation (0.1 Hz and 2 Hz) were recorded. A 90% block during nitrous oxide in oxygen anaesthesia was maintained by incremental single injections of pancuronium and reversed with neostigmine 0.35 mg kg-1 with atropine 0.0175 mg kg-1. The recovery of twitch tension up to 50% was similar in all groups but thereafter slower in the hypercarbia group. The recovery times from 25% to 75% twitch tension correlated with PaCO2 (r = 0.55, P less than 0.05). A residual block of about 10% was seen in hypercarbic patients. However, the recovery of e.m.g. amplitude and train-of-four ratios was similar in all groups. Thus, the impaired recovery of twitch tension seems to be the result of depressed contractility rather than failure of neuromuscular transmission.

Spatial and Temporal Variations in Carbon Dioxide Concentrations in an Oak-Hickory Forest Ravine

Spatial and Temporal Variations in Carbon Dioxide Concentrations in an Oak-Hickory Forest Ravine

In situ measurements of carbon dioxide gradients in a soil-plant-atmosphere system.

In order to more fully understand carbon dioxide dynamics in a soil-plant-atmosphere system, an in situ sampling technique has been developed to measure carbon dioxide concentration within the soil profile as well as in the atmosphere. Gas samples are automatically pumped in sequence from six porous collectors within the soil profile and five aboveground inlets through an infrared gas analyzer. Field measurements in a first year field, indicated that carbon dioxide concentrations reached a maximum value (∼1800 ppm) in the deepest soil sampling site (-180 cm). Temporal and spatial variations of carbon dioxide concentration were related to the development of root and vegetation structure as well as the position of the groundwater table.

Variations in carbon dioxide concentration over an agricultural field

Carbon dioxide concentration of the air over an agricultural field was monitored from July to December 1962 and from January to June 1964 using an infrared CO 2 analyzer. Supporting micrometeorological data, including windspeed, incident shortwave radiation (0.30-3.0 μm), net radiation, air temperature, and soil temperature were taken during part of the monitoring program. The CO 2 concentration showed much larger amplitudes of annual cycles than have been observed over oceans, polar regions, or at high altitudes. The computed average annual daytime CO 2 concentration near the earth's surface was 312 p.p.m. Diurnal cycles in concentration during the summer months usually showed ranges in excess of 100 p.p.m. During July, August, and September 1962, the daytime average CO 2 concentration at the top of the vegetation ( Zea mays L.) was about 291 p.p.m. In the diurnal cycle of CO 2 concentration the daytime average CO 2 concentration was very steady over an individual day, usually with little or no change during the day after the nocturnal build-up had been dispersed or consumed. Incident shortwave radiation flux density had a relatively small effect on CO 2 concentration during daylight hours. Nighttime CO 2 build-up was directly proportional to mean temperature and to soil-air temperature difference, and was inversely proportional to wind speed. After harvest of the 1962 crop, the diurnal cycle was altered, with gradual draw-down of CO 2 occurring throughout the daylight period. After snow cover, diurnal variations became small, the typical maximum range being 22 p.p.m.