Title: BASIC SCIENCE OF THE ATMOSPHERE Al Sweedler San Diego State University
1BASIC SCIENCE OF THE ATMOSPHEREAl
SweedlerSan Diego State University
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3I. Atmosphere
- Structure
- Composition
- Energy balance for earth and atmosphere
- Temperature in lower atmosphere and inversions
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5CHARACTERISTICS 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.
6CHARACTERISTICS 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
7 Half of air below 5.5 km
8Some 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.
9AVERAGE COMPOSITION OF THE ATMOSPHERE
10ENERGY INPUTS TO EARTH AND ATMOSPHERE
11Radiation
- 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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13Electromagnetic Spectrum
14Blackbody 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
15BLACKBODY RADIATION
16PLANCKS 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
171. 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
182. 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)
19BLACKBODY RADIATION
20HEAT BUDGET OF EARTH AND ATMOSPHERE
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22TEMPEARTURE IN THE ATMOSPHERE AND THERMAL
INVERSION
23TEMPEARTURE 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.
24TEMPEARTURE 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
25Atmospheric 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.
26stable
Unstable
27THERMAL INVERSION
28Types 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.