ENVIRON 102 Chapter Notes - Chapter 3: Tropopause, Cold Front, Intertropical Convergence Zone
10 May 2018
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Chapter 3 The Physical Science of the Environment
3. Earth’s Atmosphere
− Atmosphere: layers of gases above planets’ surfaces
− Presence of life is a cause for Earth’s oxygen-rich atmosphere
o 3 billion years ago, Earth’s atmosphere was mostly carbon dioxide
o Photosynthetic microbes used carbon dioxide to create carbohydrates and oxygen
− Earth’s atmosphere – 480 km; mostly nitrogen and oxygen
− Atmospheric pressure: force caused by the pull of gravity on a column of air (mb – millibars)
o Increasing altitude → decrease in amount of air above → decreasing atmospheric pressure
− Four layers of atmosphere (lowest to highest) = troposphere, stratosphere, mesosphere,
thermosphere
− Troposphere provides the air we breathe
o Thermal convection – air at lower altitudes warmed by Earth’s surface → air expands and
rises, cools, then sinks back into surface → air in troposphere is well mixed
▪ Pollutants are quickly dispersed throughout troposphere
o Temperature decreases as you travel up the troposphere
o Tropopause: upper layer of troposphere where temperature will stop decreasing
− Stratosphere: temperature increases as you go up
o Stratopause: upper boundary of stratosphere
o Similar chemical composition as troposphere + large amounts of ozone (O3)
▪ Ozone layer: concentration of ozone is highest in this layer (15-35 km altitude)
▪ Ozone absorbs and scatters UV light that strikes Earth’s upper atmosphere
• UV photons are high energy and can damage organic molecules
o Little thermal convection as compared to the troposphere → chemical pollutants are not
dispersed
− Mesosphere: temperature drops again
− Thermosphere: low-density gas molecules (low atmospheric pressure)
o Heated by direct solar radiation to 2000 degrees Celsius
o Most gases are ions → interact with solar wind and magnetic field → auroras
(northern/southern lights)
− Water vapor – 1% of molecules in atmosphere
− Vapor pressure of water – relative contribution to total atmospheric pressure
o Saturation vapor pressure – amount of water the air can potentially hold – increases as
temperature increases
− Relative humidity: measure of the extent to which air is saturated (percentage)
o Affects rate of evaporation
▪ Low humidity – faster evaporation
− Dew point: temperature at which relative humidity is 100%
− Transformations of water influence variations of rainfall and evaporation and climate
3. Earth’s Energy Budget, Weather, and Climate
− Solar radiation mostly arrives in visible light and UV radiation
− Energy budget: system of accounting that measures all the energy entering and leaving Earth
o On average, energy received from sun = energy reflected back into space (budget is
balanced)
o Incoming solar energy (100%) is reflected (30%) or absorbed and/or radiated to space
(70%)
▪ Absorbed solar energy increases kinetic energy (temperature)
▪ Heat is eventually radiated back to space as infrared radiation
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Document Summary
Chapter 3 the physical science of the environment: photosynthetic microbes used carbon dioxide to create carbohydrates and oxygen, 3 billion years ago, earth"s atmosphere was mostly carbon dioxide. Atmosphere: layers of gases above planets" surfaces. Presence of life is a cause for earth"s oxygen-rich atmosphere. Earth"s atmosphere 480 km; mostly nitrogen and oxygen. Atmospheric pressure: force caused by the pull of gravity on a column of air (mb millibars: thermal convection air at lower altitudes warmed by earth"s surface air expands and. Troposphere provides the air we breathe thermosphere: temperature decreases as you travel up the troposphere, tropopause: upper layer of troposphere where temperature will stop decreasing. Water vapor 1% of molecules in atmosphere. Vapor pressure of water relative contribution to total atmospheric pressure: low humidity faster evaporation. Dew point: temperature at which relative humidity is 100% Transformations of water influence variations of rainfall and evaporation and climate.
