Introduction to Meteorology Evolution and Composition of the atmosphere

1. Introduction to MeteorologyEvolution and Composition of the atmosphere Leila M. V. Carvalho

2. In the beginning…

5. Earth first atmosphere The original atmosphere was primarily helium (He) and hydrogen (H). Heat from the still-molten crust, the sun, and a probably enhanced solar wind, dissipated this atmosphere. Gravity is important to keep an atmosphere. H, He have low molecular weight and may have achieved the escape velocity (the velocity necessary to escape gravity) Other explanations: gases would have been removed by collision between the growing Earth and other large bodies (failed planets). The tremendous energy released may have ejected the early atmosphere This theory explains the origin of the Moon and the tilting of the Earth axis to 23o (http://www.psrd.hawaii.edu/Dec98/OriginEarthMoon.html)

6. The second atmosphere 4.4 billion years ago… About 4.4 billion years ago, the surface had cooled enough to form a crust. Many volcanoes released steam, carbon dioxide, and ammonia. This led to the early "second atmosphere", which was primarily carbon dioxide and water vapor, with some nitrogen but virtually no oxygen. Additional water was imported by collisions, probably with asteroids ejected from the asteroid belt under the influence of Jupiter's gravity. As it cooled much of the carbon dioxide was dissolved in the seas and precipitated out as carbonates. Simulations run at the University of Waterloo and University of Colorado suggest that it may have had up to 40% hydrogen. It is generally believed that the greenhouse effect, caused by high levels of carbon dioxide and methane, kept the Earth from freezing.

7. Life and the formation of the third atmosphere cyanobacteriaS existed approximately 3.3 billion years ago and were the first oxygen-producing evolving phototropic organisms. They were responsible for the initial conversion of the Earth's atmosphere from an anoxic state to an oxic state (that is, from a state without oxygen to a state with oxygen) during the period 2.7 to 2.2 billion years ago. They were the first to carry out oxygenic photosynthesis, and were able to produce oxygen while sequestering carbon dioxide in organic molecules, playing a major role in oxygenating the atmosphere. This is often referred to as the Oxygen Catastrophe. (oxygen was toxic to the microscopic anaerobic organisms dominant then.) The increase in the concentration of oxygen in the atmosphere required time because iron and other elements in the Earth's crust reacted with oxygen, removing it from the atmosphere.

8. The third atmosphere: Photosynthesizing plants later evolved and continued releasing oxygen and sequestering carbon dioxide. As oxygen was released, it reacted with ammonia to release nitrogen. Bacteria also converted ammonia (NH3) into nitrogen, but most of the nitrogen currently in the atmosphere resulted from sunlight-powered photolysis of ammonia As more plants appeared, the levels of oxygen increased significantly, while carbon dioxide levels dropped. At first the oxygen combined with various elements, but eventually oxygen accumulated in the atmosphere, contributing to Cambrian explosion and further evolution.

14. Steady state and residence time:

16. How to compute the residence time? Divide the mass of the substance in the atmosphere (in kilograms) by the rate at which the substance enters and exits the atmosphere (in kilograms per year).

17. Example The mass of nitrogen in the atmosphere is 4 x 1018 kg, and its sinks from the atmosphere include (i) biological nitrogen fixation by bacteria, 2 x 1011 kg yr-1; (ii) production of NO in thunderstorms, 7 x 1010 yr-1; (iii) chemical synthesis of ammonia, 5 x 1010 kg yr-1 (all data refer to loss of nitrogen). Calculate the residence time of nitrogen in the atmosphere.

18. Water Vapor

19. Water vapor from satellite

20. Water vapor Water vapor is not the same as droplets – it is a gas Main source: evaporation Concentration decreases rapidly with altitude Most atmospheric water vapor: lowest 5km (3mi) of the atmosphere in quantities the vary from 1-4 % Outside tropics it does not exceed 2% It is constantly cycled between the planet and the atmosphere in the so called hydrological cycle. Water evaporates from river, oceans lakes, ice sheets, and underground water (removed from the soil sometimes by vegetation)

21. Question to discuss with your partner: What in your opinion is the most important role of tropical rainforests such as the Amazon forest (justify your answer): A) contribution for the Earth input of O2 B) contribution for input H2O vapor C) (A) and (B) are correct D) Neither (A) or (B) is correct

22. Carbon dioxide CO2 currently accounts for about 0.038% of the atmosphere’s volume. When a gas occupies such a small proportion of the atmosphere, we often express its content as part per million (ppm) - today 380 ppm. Sources: plant, animal respiration, decay of organic material, volcanic eruptions, natural anthropogenic (human produced) combustion. CO2 is removed by photosynthesis by plants CO2 gas a residence time of about 150 yrs.

24. Methane CH4 about 3.5 billion years ago—there was 1,000 times as much methane in the atmosphere as there is now. The earliest methane was released into the atmosphere by volcanic activity. With life and increase in O2 methane decreased (reaction with OH). With industrialization the rate of increase accelerated so that values have more than doubled over the last 200yrs (~ 1.7 ppm in 1999) The residence time for methane is about 10 yrs. The current input of CH4 is approximately equal to its natural removal CH4 is a very efficient greenhouse gas

25. Hum… it seems something else happened these past years that might change the trends observed before and potentially cause a climate shift (if persisted).

26. What is ‘greenhouse’ effect?

27. Ozone O3 Ozone is observed in the stratosphere (above 20km) and in the troposphere (~below 12 km) In the stratosphere ~ 25km at concentration of 15ppm (that is 15 out of every one million molecules is ozone), is essential for life on Earth! In the lower atmosphere occur in highly polluted urban areas and association with forest burning. Can cause irritation to lungs, eyes, and damage to vegetation. Concentration in polluted urban areas up to 0.15 ppm (that is, 15 out of every 100 million molecules are ozone)

29. But… how is ozone formed in the stratosphere ?http://www.ccpo.odu.edu/SEES/ozone/oz_class.htm

31. Discussion

32. But… what is the ozone hole? Why does it occur? Is it caused by natural or is it anthropogenic induced ?

34. Aerosols Definition: small solid particles and liquid droplets in the air (excluding cloud droplets and precipitation). Can be formed by human or natural processes. Normal concentration: 10,000 particles per cubic centimeter over land surface (~ 17,000 particles per cubic inch) Size : below 0.1 µm (Aitken nuclei) 0.1 – 1.0 µm (large particle) > 1 µm = giant particle

35. Effects in the atmosphere and society

36. Did you know?

37. Discussions and conclusions… Earth had three atmospheres: the composition of the third one is completely linked to the existence of life in our planet 21% O2 and 78% N2 The ozone layer formed only recently (~ 7 mi yrs) Green house gases have been important to maintain the temperature of earth above freezing. Human activity has increased the amount of greenhouse gases in the atmosphere The ozone hole is a natural feature of the atmosphere. Its increase over time is due to human activity (input of chlorine and bromine that reacts with free oxigen) Aerosols are important component of the atmosphere (they may be of natural sources or human produced)

38. Training a few concepts…

39. How was the 2010 SH ozone hole compared with previous years?

41. Important concepts