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Major topics of Atmospheric Chemistry course are Acid Rain, Aerosol, Aerosols Optics, Geochemical Cycles, Global Models, Trop Ozone Pollution and many others. These lecture slides contain following keywords: Aerosols Optics, Condensed-Phase Particles, Atmospheric Aerosol, Air Pollution, Particulate Matter, Ozone, Aerosol Optical Depths, Annual Mean Concentrations, U.S. Wilderness Areas, Raoult’S Law
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numberarea volume
Aerosols are the visible part of the atmosphere:
Pollution off U.S. east coast
Dust off West Africa
California fire plumes
Soil dustSea salt
Size range: 0.
m (molecular cluster) to 100
m (small raindrop)
75 ppb (8-h average)
g m
-3^ (1-y av.)
http://epa.gov/airtrends/2010/
Ozone
By scatteringsolar radiation,aerosolsdecreasevisibility andincrease theEarth’s albedo
Scattering efficiency ismaximum whenparticle radius =
particles in 0.1-
m
size range are efficientscatterers of solarradiation
2 (diffractionlimit)
green light( λ^ = 0.5 μm)
Pollution off U.S. east coast
Dust off West Africa
Relatively easy to do qualitatively for thick plumes over dark ocean…California fire plumes
)exp[-AOD]
…but difficult quantitatively! Fundamental quantity is aerosol optical depth (AOD)
aerosolscattering,absorption
Measured top-of-atmosphere reflectance= f (AOD, aerosol properties,surface reflectance, air scattering,gas absorption, Sun-satellite geometry)
m
m
m
m (transparent atmosphere) to derive surface reflectance2. Assume fixed 0.47/2.13 and 0.65/2.13surface reflectance ratios to deriveatmospheric reflectances at 0.47 and 0.
m
by subtraction3. Assume generic aerosol optical propertiesto convert atmospheric reflectance to AOD
TOAreflectance
2.^
VISIBILITY IN U.S. WILDERNESS AREAS
Statistics for 20% worst visibility days
Deciviews
2001 observations
Natural
Background; includestransboundary pollution
Visual range (km)
EPA Regional Haze Rule requires that natural visibility be achieved in allUS wilderness areas by 2064 Park et al. [2006]
Consider an aqueous sea salt (NaCl) particle: it must satisfy
Na^
Cl^
s
Na^
Cl
Na^
Cl^
H^ O
^
^
^
This requires:
1 2
s
At lower RH, the particle is dry.
Deliquescence RH;depends on particlecomposition
NaCl/H
