The composition of atmospheric air

Atmospheric air is breathed in during inspiration. This inspired air mixes with the gas already in the respiratory tree and some is drawn into the alveoli where gas comes into intimate relation with the blood circulating in the pulmonary capillaries. The gas here is called alveolar gas. Blood entering the lungs from the pulmonary artery has a partial pressure of oxygen which is lower than that in the alveolar gas. Oxygen diffuses from the alveolar gas into the pulmonary blood. For carbon dioxide, the partial pressure gradient is from blood to alveolar gas and so this is the direction in which carbon dioxide diffuses. 

At the end of inspiration, the conducting airways (trachea, bronchi etc.) are full of gas similar in composition to air, except that the gas is saturated with water vapour. Since this gas does not take part in gaseous exchange with the blood, it is called the dead space. During expiration, gas is forced out of the lungs. The first gas to leave via nose and mouth is this dead space gas and it is followed by alveolar gas. This gas mixture can be collected and is known as mixed expired gas. Its composition is between that of air and alveolar gas, since it is a mixture of the two. 

The total pressure of gases in alveolar gas is equal to the barometric pressure. Since 47 mmHg is contributed by water vapour, the sum of the partial pressures of all other gases equals barometric pressure minus 47 mmHg. 

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Note In the composition of atmospheric air the relative humidity (RH) is indicated separately along with the temperature. ... 

Gay-Lussac and Humboldt used Volta s method (see Vol. Ill, p. 327) of explosion with hydrogen in a eudiometer to determine the composition of atmospheric air. In a number of experiments they found as a mean that 100 vols. of oxygen combined with 199-89 vols. of hydrogen, or in round munbers, that 100 of oxygen require for saturation 200 of hydrogen . The whole-... 

His most Important work was on the composition of atmospheric air and the preparation of oxygen, which he achieved before Priestley. Scheele prepared a number of highly toxic compounds, and his early death may have been due to his experiments with substances such as hydrogen cyanide. 

The pressure of atmospheric air falls with rising altitude above the earth s surface (see Fig. 9.3 in Chapter 9). High vacuum prevails at an altitude of about 100 km and ultrahigh vacuum above 400 km. The composition of the air also changes with the distance to the surface of the earth (see Fig. 9.4 in Chapter 9). 

POLLUTION (Air). Prior to the Industrial Revolution (circa 1840s). the composition of pure air making up Earth s surrounding atmospheres essentially remained constant for several thousand years. True, certain natural phenomena, such as volcanic eruptions, may have altered the atmospheric composition over relatively short lime spans. 

Troposphere A layer of the atmosphere closest to the Earth which contains about 75% of the mass of the atmosphere. The composition of dry air is relatively constant in this layer of the atmosphere. 

The composition of dry air at sea level is primarily composed of N2 (78%) and O2, (21%). Temporal and spatial variability in concentrations of atmospheric gases will largely depend on gas stability, source and sink processes, source strength, and residence time. 

Whereas diffusion of gas at depth is widespread, mass flow is often localised (near the ground surface, in faults) or intermittent (volcanic emptions). Mass flow is an important consideration in the application of gas geochemistry to mineral because of its significant role in the interchange of atmospheric air and soil air, and therefore its influence on gas composition in the shallow subsurface from where most samples and measurements are taken. Lovell (1979) reviewed soil aeration in this context. 

Table 17.1 shows the composition of dry air at sea level. The total mass of the atmosphere is about 5.3 X 10 kg. Water is excluded from this table because its concentration in air can vary drastically from location to location. 

Rayleigh s view seemed more attractive. The composition of atmosphere had been thoroughly studied for more than a hundred years and it was hardly possible that some components of the air could have remained undetected. It is just the time to remember Cavendish s experiment and for Ramsay s hidden memory to work. On April 29, Ramsay sent a letter to his wife in which he wrote that nitrogen. 

Aerosol Dynamics. Inclusion of a description of aerosol dynamics within air quaUty models is of primary importance because of the health effects associated with fine particles in the atmosphere, visibiUty deterioration, and the acid deposition problem. Aerosol dynamics differ markedly from gaseous pollutant dynamics in that particles come in a continuous distribution of sizes and can coagulate, evaporate, grow in size by condensation, be formed by nucleation, or be deposited by sedimentation. Furthermore, the species mass concentration alone does not fliUy characterize the aerosol. The particle size distribution, which changes as a function of time, and size-dependent composition determine the fate of particulate air pollutants and their... 

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