Climate and Chemical Composition of the Atmosphere

Just as in the case for the hydrosphere, the atmosphere participates in all of the major biogeochemical cycles (except for phosphorus). In turn, the chemical composition of the atmosphere dictates its physical and optical properties, the latter being of great importance for the heat balance of Earth and its climate. Both major constituents (O2, H2O) and minor ones (CO2, sulfur, nitrogen, and other carbon compounds) are involved in mediating the amounts and characteristics of both incoming solar and outgoing infrared radiation. 

IPCC (Intergovernmental Panel on Climate Change), Aviation and the Global Atmosphere, 1999, J.E.Penner, D. H. Lister, D. 1. Griggs, D.J. Dokken, M. McFarland (Eds), Chapter 4 Modelling the Chemical Composition of the Atmosphere, I.S.A. Isaksen and C. Jackman, Cambridge University Press. 

As such, it is absolutely clear that the chemical composition of the atmosphere as well as the physical characteristics of condensed phase trace species are of leading importance as determinants of climate. A well-known example is the increase in the temperature of the Earth s surface due to the absorption of infrared radiation from the Earth s surface by CO2 in the air (see box). Without CO2, the Earth s surface would be several degrees cooler than at present, depending on cloud cover, water vapor, and other controlling factors. Of course, there is substantial concern over the secular increase of CO2, which will double from its pre-industrial level by the early to mid-twenty-first century. 

The Earth s climate depends among other parameters (see later) on the chemical composition of the atmosphere. Thus, any variation in the composition raises the possibility of climatic change. First of all, the chemical composition regulates the radiation balance of the Earth-atmosphere system. However, since differences in radiation balance in various geographical regions control the atmospheric circulation, there is also a relationship between composition and dynamic processes. In this chapter we shall deal mainly with the effects of compositional variations on the radiation balance. Moreover, the significance of so-called feedback mechanisms will also be stressed. 

The Earth-atmosphere system consists of the ensemble of the atmosphere, ocean, continents and ice cover. The climate of this system is controlled by the orbit and rotation of the Earth, the physical state and chemical composition of the surface (including liquid water and ice), and by the density and composition of the atmosphere. This last parameter participates mainly in the control of the radiation balance. For this reason our knowledge of the radiation balance of the Earth-atmosphere system will be summarized briefly in this section. The interested reader is referred to Paltridge and Platt (1976) for further details. 

The possible modification of the chemical composition of the atmosphere, and the attendant climatic effects, is a problem which attracts the attention of the international scientific community, decision makers, and the public. Some of the processes which may produce these modifications will be briefly identified in this section. A more detailed analysis will be presented in Chapter 6. 

Changes in solar irradiance can modify the physical structure, dynamics, and chemical composition of the middle atmosphere. The question of effects of solar activity on the troposphere, particularly the surface climate, has been a subject of scientific and public fascination for many decades. However, it has been stressed that despite a massive literature on the subject, there is at present little or no evidence of... 

The Paul trap is housed in a central climate chamber which can be cooled down to the temperature of liquid nitrogen. The pressure and composition of the background gas in this chamber can be controlled by a gas mixing and inlet system and is usually adapted to stratospheric conditions. This chamber is suspended inside an insulation chamber which is kept at high vacuum. This chamber is equipped with a quadrupole mass spectrometer to analyze the chemical composition of the atmosphere, which leaks from the central chamber through a small pinhole. This system of vacuum chambers is connected to a standard time-of-flight mass spectrometer by means of a droplet translator. This is a cold finger which can be used to... 

Without discussing in any detail the biological and physical processes within the climate system in this book, the chemical composition of the atmosphere and its variation in time and space, as well as its trends, is essential for an understanding of climate change. Atmospheric substances with their physical and chemical properties will have many effects in the climate system we list the most important among them here together with impacts (there are many more impacts, parallel and synergistic effects) ... 

The isotope compositions of oxygen and hydrogen in the ice record the temperature at the time and place of deposition. The relationship between isotope composition and the average annnal temperature has been used to reveal the history of climate change in the accumulation areas from the present to 800,000 years in the past. In addition, the ice contains samples of air that was trapped between snow flakes at the time of deposition. Therefore, the climate history has been augmented by a history of the chemical composition of the atmosphere. 

Figure 1 shows the mean annual distribution of the fractional area covered by clouds whose tops are above the 440 mb pressure level. All these clouds are likely to contain ice. The total atmospheric burden of ice is not known, but very crude estimates suggest it is around 10 to 10 kg. This mass is small compared with that (over 10 kg [5]) in surface ice and snow. Despite its relatively small abundance, atmospheric ice has considerable impact on global climate, the chemical composition of the atmosphere and of precipitation, and on thunderstorm electrification. Figure 2 represents the ice-related tropospheric processes to be discussed in this paper, and we will refer to this figure in succeeding sections. 

Atmospheric aerosols have a direct impact on earth s radiation balance, fog formation and cloud physics, and visibility degradation as well as human health effect[l]. Both natural and anthropogenic sources contribute to the formation of ambient aerosol, which are composed mostly of sulfates, nitrates and ammoniums in either pure or mixed forms[2]. These inorganic salt aerosols are hygroscopic by nature and exhibit the properties of deliquescence and efflorescence in humid air. That is, relative humidity(RH) history and chemical composition determine whether atmospheric aerosols are liquid or solid. Aerosol physical state affects climate and environmental phenomena such as radiative transfer, visibility, and heterogeneous chemistry. Here we present a mathematical model that considers the relative humidity history and chemical composition dependence of deliquescence and efflorescence for describing the dynamic and transport behavior of ambient aerosols[3]. 

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