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Engineering LibreTexts

11: Atmospheric Chemistry and Air Pollution

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    • 11.1: Atmospheric Composition
      Key features of the gases include their compressibility, their transparency in the visible, their momentum, and their heat capacity. Water vapor has the additional important feature of existing in the vapor, liquid, and solid phases in the atmosphere and on Earth’s surface. The most important properties of small particles include their ability to dissolve in water in order to be Cloud Condensation Nuclei or to maintain a lattice structure similar to ice to be Ice Nuclei.
    • 11.2: Changes in Atmospheric Composition
      Since the rise of oxygen, 2 billion years ago, the nitrogen and oxygen fractions in the atmosphere have been stable. Water vapor is highly variable but, on average, appears to also have been fairly stable. Recent data from satellites and sondes indicate that perceptible water (the total amount of water that is in a column from the surface to space) has increased 1.3 ± 0.3% per decade over the oceans in the past 25 years (Trenberth et al., Climate Dynamics, 2005).
    • 11.3: Other Trace Gases
      Hundreds of different trace gases have been measured in the atmosphere and perhaps thousands more have yet to be measured. Many of these are volatile organic compounds (VOCs). Volatile means that the compound may exist in the liquid or solid phase but that it easily evaporates. Organic means that the compound contains carbon but is not carbon dioxide, carbon monoxide, or carbides and carbonates found in rocks.
    • 11.4: Stratospheric Ozone Formation
      Ozone is ozone no matter where it is in the atmosphere. Good ozone is good only because it is in the stratosphere where we cannot breathe it. Bad ozone also absorbs solar ultraviolet light, but it is down near Earth's surface where we can breathe it. For UV protection, we are interested in the total number of ozone molecules between us and the Sun. 90% of ozone molecules are in the stratosphere and 10% are in the troposphere - some down near Earth's surface where we can breathe them.
    • 11.5: The Story of the Atmosphere's PAC-MAN
      The atmosphere's oxidation capacity is its ability to clean itself of all of the gases that are emitted into it. What does stratospheric ozone have to do with the atmosphere’s oxidation capacity, which mostly occurs in the troposphere and mostly by the atmosphere's PAC-MAN, hydroxyl (OH)? It turns out that natural dynamic processes actually pull air down from the stratosphere and mix it into the troposphere, eventually mixing some of this ozone to Earth’s surface.