BASIC SCIENCE OF THE ATMOSPHERE Al Sweedler San Diego State University

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BASIC SCIENCE OF THE ATMOSPHEREAl
SweedlerSan Diego State University
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I. Atmosphere

• Structure
• Composition
• Energy balance for earth and atmosphere
• Temperature in lower atmosphere and inversions

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CHARACTERISTICS OF TROPOSPHERE AND STRATOSPHERE

• Troposphere
• Ground level to 15 miles (25 km).
• Temp. normally decreases with altitude.
• Much vertical mixing.
• Pollutants may be washed back to earth.
• All weather and climate take place in the
  troposphere.

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CHARACTERISTICS OF TROPOSPHERE AND STRATOSPHERE

• Stratosphere
• 10 to 50 miles (15-80 km)
• Temp. increases with altitude
• Little vertical mixing, very slow diffusion
  exchange of gases with troposphere
• Pollutants entering remain here unless attacked
  by light or other chemicals
• Isolated from troposphere by tropopause

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Half of air below 5.5 km
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Some Properties of Atmosphere

• Atmosphere is vast weighs about 5.7 x 1015 tons,
  about one millionth of the weight of the earth.
• Density or air at earths surface is 1.3 kg/m3
  pressure is 14.7 lb/in2. At 50,000 ft, pressure
  is only 1.6 lb/in2.
• Temperature decreases with increasing altitude up
  to 10 km from 10 - 50 km, T increases, then
  decreases again.

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AVERAGE COMPOSITION OF THE ATMOSPHERE
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ENERGY INPUTS TO EARTH AND ATMOSPHERE
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Radiation

• Basically all energy reaching the earth comes
  from the sun in the form of electromagnetic
  radiation
• Sun radiates over entire EM spectrum, but most of
  energy is between wavelengths of 0.4 to 0.7 x
  10-6 m, in visible spectrum
• Energy of a photon E hf hc/? h Plancks
  constant 6.63 x 10-34 joule sec, f frequency
  c speed of light (3x108 m/s) ? wavelength
  (m), E in joules

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Electromagnetic Spectrum
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Blackbody Radiation

• A body that absorbs all radiation incident upon
  it is called a blackbody
• A blackbody will reradiate all the absorbed
  energy in characteristic spectrum that depends on
  its temperature
• Planck discovered the mathematical formula for
  this blackbody radiation, and in the process
  introduced the idea of a quantum of energy

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BLACKBODY RADIATION
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PLANCKS RADIATION LAWBlackbody radiation

• E(? , T) 2? c2h? -5(ech/kT? - 1)-1
• E energy radiated per unit time per unit area
  in a wavelength range ? to d? (W/sq.cm angstrom
  )
• Plancks law yields two important characteristics
  of blackbody radiation

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1. WEIN DISPLACEMENT LAW

• Wavelength at which maximum amount of radiation
  occurs is inversely proportional to the absolute
  temperature (differentiate PL wrt to ? and set
  equal to zero)
• ?max (2.897 x 106)/T
• wavelength in nm T in degrees Kelvin

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2. STEFAN-BOLTZMANN LAW

• Total power (energy/time) radiated by a blackbody
  is proportional to the area of the object and the
  fourth power of its absolute temperature.
  (Integrate PL over all wavelengths)
• E ?AT4
• Where E Energy/time (watt/sec) ? 5.673 x
  10-8 watt m-2 K-4 is called the
  Stefan-Boltzmann constant A is surface area (m2)
  and T is the absolute temperature (degrees
  Kelvin 0 degrees Kelvin -273 degrees Celsius)

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BLACKBODY RADIATION
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HEAT BUDGET OF EARTH AND ATMOSPHERE
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TEMPEARTURE IN THE ATMOSPHERE AND THERMAL
INVERSION
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TEMPEARTURE IN THE ATMOSPHERE AND THERMAL
INVERSION

• A parcel of air will rise or fall in surrounding
  atmosphere depending on the temperature profile
  of the atmosphere and the adiabatic lapse rate
  (ALR)
• ALR - rate at which a parcel of air cools as it
  rises in the atmosphere under adiabatic
  conditions. As air parcel rises it expands, due
  to lower atmos. pressure above than below.
• Adiabatic - no heat energy is exchanged between
  air parcel and surrounding air.

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TEMPEARTURE IN THE ATMOSPHERE AND THERMAL
INVERSION

• Consider a parcel of warm air released near
  surface of earth it will tend to rise because it
  has a lower density than surrounding, cooler air.
• If a parcel of warm, polluted air is released
  from a smokestack under normal meteorological
  conditions, it will rise to 10,000 meters, where
  is usually presents no immediate problems

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Atmospheric Temperature Profiles

• When temperature in atmosphere cools faster than
  ALR, unstable conditions exist and good mixing
  occurs. Less pollution at ground level.
• When temperature in atmosphere cools slower than
  ALR, stable conditions exist and little mixing
  occurs. More pollution at ground level.

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stable
Unstable
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THERMAL INVERSION
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Types of Thermal Inversions

• Radiative Earth cools during night by radiating
  thermal energy into space. In morning, air near
  surface will be cooler than air above creating
  thermal inversion. More frequent, but less
  problematic and persistent than -
• High pressure subsidence high pressure mass of
  air moves towards earth. Is compressed and
  heated, causing thermal inversion some distance
  above ground.