Atmosphere: Composition, Origin, Evolution and Climate
This Chapter will show you that (a) our atmosphere changed over geological time scales drastically, (b) the chemical composition of the atmosphere is mainly a result of life processes, (c) the chemical composition has been about constant over the last 10000 years despite of cyclic variations, and (d) climate is being described as the long-term physico-chemical status (including its statistics) of our earth’s system.
3.1 3.1.1 3.1.2 3.2 3.2.1 3.2.2 3.2.3 3.3 3.3.1 3.3.2 3.3.3 3.4 3.4.1 3.4.2 Appendix 1 Appendix 2 Literature Chemical composition of air Concentration measures Residence time Evolution of the earth system Origin of the solar system Degassing the earth Evolution of the atmosphere Biosphere-atmosphere relationship Origin of life The budget of carbon and oxygen Water budget Climate The climate conception Past climate (paleoclimate) The photosynthesis (history) The GAIA hypothesis 2 2 5 8 8 10 14 16 16 20 23 25 25 29 31 34 35
Note: This version will be processed from time to time – look on the following date of edition: May 2004 (2nd edition, 1st in October 2003)
Chair for Atmospheric Chemistry and Air Quality, Brandenburg Technical University Cottbus
Detlev Möller: Atmospheric Chemistry and Air Pollution - Atmosphere: Origin, Evolution and Climate
Chemical composition of air
3.1.1 Concentration measures
As mentioned in the introduction of this script series (part 1), natural air, i.e. air uninfluenced by humans, consists of a large number of chemicals. The main constituents of natural air are shown in Table 3.1. A lot of components not listed there, escaped from natural sources into air, are within very small concentrations (below 1 ppb). Table 3.2 shows the ranges of magnitude between different groups of constituents, which we now distinguish in major, minor and trace species as well as condensed phases (liquid and solid). The range of concentration makes it clear how sensitive analytical methods need to work for air chemical monitoring. Also, this is the reason that many trace gases have been found in the recent past, e.g. CS2 and COS in 1976. Table 3.1 Present chemical composition of drya remote air species concentration nitrogen 78.084 % oxygen 20.946 % argon 0.934 % carbon dioxide 360 ppm (variable and increasing) neon 18.18 ppm helium 5.24 ppm methane 1.6 ppm (increasing) krypton 1.14 ppm hydrogen 0.5 ppm nitrogen dioxide 0.3 ppm (increasing) xenon 0.087 ppm a Note: water vapour may be in the range up to 3 % and must be included in the chemical composition of (wet) air
Table 3.2 Ranges of concentration of air constituents (in Vol-% if not otherwise marked, based on dry air; presence of water vapor will change the numbers slightly); number concentration in cm–3 constituent main components by-components cloud water rainwater trace gases atmospheric aerosol (r < 1 µm) radicals species/phase nitrogen oxygen noble gases water vapor carbon dioxide liquid water dissolved species dissolved species methane SO2, NOx VOC (NMHC) continental maritime OH, HO2, NO3 concentration 78 % 21 % 0.09 % 0.001-0.02 % based on humid air 0.035 % 10–4 % (n ≈ 300) ≥10–4 mass-% related to cloud water (≤10–4 mass-% related to rainwater 1,6 10–4 % 10–9 - 10–5 % 10–8 - 10–6 % 10–8 % (50 µg m–3) (n ≥ 500) 10–10 % (< 10 µg m–3) (n ≥ 100) (n ≤ 107) ≤ 10–13 %
You see that the range of concentrations covers more than 15 orders of magnitude. In Tables 3.1 and 3.2 different measures for concentrations have been used. According to the SI units (Système International d'unités), the modern metric system of measurements, physical quantities should espressed only by these base units; for the purpose of concentration we need the quantities mass, amount of substance and length with the units kilogramm (kg), mole (mol) and meter (m). Area (m2)...