Illumination Independent Aerosol Optical Properties

Extinction• Scattering• Absorption

Volume scattering function (phase) Transmittance

The extinction coefficient is made up of

particle and gas scattering and absorption:

where s, a, g, and p refer to scattering, absorption, gases, and particles, respectively.

ext sg ag sp apb = b +b +b +b

Extinction =

Components of Scattering and Extinction

Animations of scattering and absorption

One Approximation for Estimating bext

].[10

]SO

]SO

344

344

lacclacf)[SOIL](e +(RH)[OMC]f)(e +

]NO(RH)[NH)f(e +iated(RH)[Ammon)f(e

)[SOIL](e +(RH)[OMC]f)(e +

]NO(RH)[NH)f(e +iated(RH)[Ammon)f(e = b

soilcocmocmc

nncssc

soilfocmocmf

nnfssfext

(D)d(D)n),m(QD4

=B iie2

o

iext,

(x)dx)x,,( fmE=B iie

-

iext,

where Ee is mass extinction efficiency, f i(x) is the aerosol mass distribution dm/dx of the ith species, x=ln[D/Do], and λ is the wavelength.

Extinction as Function of Size

m =B iiiext,

(x)dx)x,,( fmE=iie

o

i

where

m =B i i

iext

and for multiple species

Externally Mixed Model

Scattering Efficiency (Q)

Single Particle Efficiency

Particle Size Distribution

Scattering Efficiency as Function of Size

Carbon Extinction Efficiency

Phase Function for Soil and Sulfate

Phase Function for Carbon

Forward and Backward Scattering

Pollutant Species

Primary vs. Secondary Particles and Gases (Pollutants)

Primary particles and gases are those emitted into the atmosphere directly from some source.

Secondary particles and gases are formed in the atmosphere by chemical reactions, by condensation growth, and/or by coagulation.

Particle Size Distribution

Sources of Primary Particles

Anthropogenic Wind Blown Dust

Roads, Over Grazing, Farming practices, Mining

Biomass BurningLand Clearing Practices

Emissions from fossil fuel combustionFly Ash Condensation of Hot Vapors

Naturally Occurring Wind Blown Dust

Deserts

Volcanoes Fires Plant Particles

(pollen)

Sea Salt Spray(NaCl)

Sources of Primary Gases Important to Secondary Particle Formation

Compound Anthropogenic Naturally Occurring

SO2 Fossil-FuelSmelters

Oil Refining

Volcanoes 

NOxFossil-Fuel Combustion

Mobil SourcesSoil Release (Fertilizer)

Soil ReleaseLightning

NH3 Farm Animals Wild AnimalsVegetation

Ocean Volatile

OrganicsMobile Sources Vegetation

Hygroscopic Aerosols

Water uptake by particles in the atmosphere Aerosol particles grow and scatter more light Deliquescence - the RH value at which the

crystal begins to absorb water and becomes a solution droplet

Hysteresis - water is retained on the particle at RH values lower than predicted by equilibrium

Growth of Sulfate

Hygroscopic Growth of Particles

Ammonium Sulfate D/Do Curves

Two Measured f(RH) Curves and Theoretical Estimated

F(rh) for Grand Canyon

Estimated f(rh) for Sulfate and Organics

] [ ...... ] [ ] [ ) (2 1 ,Species Other a OMC a SULFATE a a RH bn o water scat

Internally Mixed Aerosol

m B

m FM

i i

iext

i

i

however,

Mass Removal Issues

From previous equations, it is apparent that changes in visibility that correspond to changes in aerosol species concentrations can be expressed by forming the derivative τr/Ci, where Ci refers to the concentration of

particulate species i, and that this derivative will have terms containing the derivative bext/Ci. Therefore, define partial scattering

efficiency as:

Partial Scattering Efficiency

)C/b(=e etc ,ciextp j

Extinction for External and Internal Mixture

D/Do Curves for Partial Scattering Calculation

Partial Scattering Efficiency for External and Internally Mixed Aerosols