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    Topic: Lower atmosphere. Advanced.
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    • Tropospheric processes

      Tropospheric processes

      When we talk about chemical reactions most of us think about processes occurring in large industrial plants and in laboratories.  However, thousands of chemical reactions also occur every second in the air we breathe.  Most of these chemical reactions are oxidation processes or are started with the help of sunlight.

      1. Chemical and physical processes occur everywhere in the air and in the clouds.   We can think about the atmosphere, both over the cities and the countryside, as a big chemical plant which continuously produces new molecules and destroys old ones.   Photomontage: Elmar Uherek.

      In this unit we will learn about the most important oxidising compounds in the atmosphere - ozone and the hydroxyl and nitrate radicals.  We will look at the importance of sunlight and how energy is transported through the atmosphere.  We will also explain in more detail how greenhouse gases affect our climate.  Finally, we will discuss the special reactions of ozone in the troposphere and how human activity has altered the chemistry of the lower atmosphere.

      • 1. The main oxidants in the troposphere and how we observe them

        1. The main oxidants in the troposphere and how we observe them

        The troposphere is the most chemically reactive part of the atmosphere.

        Most chemical reactions which occur in the troposphere involve oxidation.  In this unit we look at the major oxidising species during the day and during the night and how we go about measuring them.

        1. We will discuss only basic atmospheric chemistry in this unit.  However the chemistry which goes on can be really complicated.  Just have a look at the atmospheric chemistry of a simple organic molecule such as butane (which is used, for example, in camping stoves).  From: lecture by Jim Smith at NCAR.

      • 2. Radiation, greenhouse gases and the Greenhouse Effect

        2. Radiation, greenhouse gases and the Greenhouse Effect

        Almost all the energy on Earth comes originally from the Sun.  In this unit we look at what happens to solar energy in the atmosphere and what proportion of it actually reaches the surface of the Earth.  We also look at the energy emitted back into space from the Earth.

        So in this unit we look at the radiation budget of the Earth - how much energy enters and leaves the system.  We then study how increasing greenhouse gas concentrations have altered the radiation budget.  We focus on carbon dioxide and methane, levels of which have increased dramatically as a result of human activity.  We also look in detail at the role of water vapour.  We know that water vapour is the most important natural greenhouse gas but we are very unsure how it will affect global warming in the future.

        Over the past few decades, the average temperature of the Earth has been increasing dramatically.  Greenhouse gases are responsible for this.  © NASA GISS.

      • 3. More on ozone and fire

        3. More on ozone and fire

        Ozone is a rather aggressive gas. In this unit we look at how it attacks other molecules and what impact it has on human health.

        High ozone concentrations affect the alveoli in our lungs. Do you know why?  © US national library of medicine.

        Atmospheric concentrations of ozone are difficult to predict because they depend strongly on the local conditions at a particular time and on the chemical composition of the air.  We look at the factors which control the atmospheric concentration of ozone here. 

        Fires are an important source of carbon dioxide, nitrogen oxides and ozone.  In the final text of this unit, we look at the chemistry of fires and fire events worldwide.

        About this page:

        author: Elmar Uherek - Max Planck Institute for Chemistry, Mainz, Germany
        last published: 2004-04-06

      • 4. Gases in our atmosphere

        4. Gases in our atmosphere

        There are thousands of gases in the troposphere.  In this unit we look in more detail at the most important components of the lower atmosphere.

        Some of the gases are evenly spread all over the world, whereas the concentrations of others depends strongly on sources, local conditions and on the time of day. In this unit we give a short overview on how gases in our atmosphere can be characterised.

        Animation: © Michael Weigend - University of Hagen

        About this page:

        author: Elmar Uherek - Max Planck Institute for Chemistry, Mainz
        Scientific reviewer: Dr. Rolf Sander - Max Planck Institute for Chemistry, Mainz - 2004-05-18
        last published: 2004-04-06