Optical Properties of Aerosol Particles
Based on Size-Resolved Chemical Composition:
Data Analysis Algorithm Development
Mariya Petrenko, Derek Montague, Peter Liu, and Terry Deshler
Department of Atmospheric Science, University of Wyoming, Laramie, Wyoming 82071, USA
Introduction
Atmospheric aerosol particles play a significant role in determining Earth's climate, through their interactions
with solar radiation (the direct effect), and through their action as cloud condensation nuclei (the indirect effect).
Our current ability to predict the aerosol direct effect on the atmospheric radiation balance on both global and
local scales is restricted by a number of factors, among which are the high variability of aerosol properties in
space and time, and instrumentation limitations for the production of quantitative size-dependent particle
chemical composition and optical properties data with high time resolution. Comprehensive studies of the
relationship of aerosol optical properties to particle composition as a function of size are therefore needed to
improve our ability to compute radiative scattering by the aerosol on all size scales.
Laramie, WY
One goal of this study is the development of a data analysis algorithm to calculate aerosol scattering extinction, and hence overall optical properties, using the sizedependent chemical composition of the particles. The algorithm is being tested with data from comprehensive measurements obtained at the UW Keck Aerosol
Laboratory in Laramie, WY during the Elk Mountain/Laramie Aerosol Characterization Experiment (EMLACE) in the summer of 2005. A partial data set from August
3, 2005 is shown below.
Experimental Setup and Instrumentation
Aerodyne Aerosol Mass
Spectrometer (AMS)
Roof Inlet
Size-resolved chemical
composition data (SO4, NO3,
NH4, Organics) from AMS
0.5 lpm
Measures total mass loading
(μg/m3) of volatile aerosol
species and their size-resolved
mass loading (20-1000 nm
vacuum aerodynamic
diameter range)
Heat
Coil
Data Analysis
Scanning Mobility Particle Sizer (SMPS)
Measures particle size distribution in 15-770
nm mobility diameter range. (resolution 64
chan/decade, averaging time interval: 303 sec)
Total mass loadings from filterpacks (sulphates, nitrates, organics,
black carbon, refractory material)
To pump
1.Simple/complicated chemical
Size-resolved
composition
chemical
model
composition
(dM/dlogD or
dM/dD)
RH Sensor
TSI 3-wavelength Integrating
Nephelometer
Measures total- and back-scattering
coefficients at 3 wavelengths: 700 nm
(red), 550 nm (green), and 450 nm (blue)
Aethalometer
Measures mass loading of
black carbon (μg/m3)
4 lpm
Ultrafine Condensation Particle
Counter (UCPC)
Counts number concentration (up to
105 cm-3) of particles of the size 3 nm
and higher
5. Mie
Total scattering
coefficient calculated calculations
from the sampled
aerosol
1 lpm
Aerodynamic Particle Sizer
(APS) (5.0 lpm)
Measures particle size distribution
in 0.5-20 μm aerodynamic diameter
range (resolution 32 chan/decade,
averaging time – 1 min)
Passive Cavity Aerosol Spectrometer
Probe (PCASP) (0.5 lpm)
Measures particle size distribution in 0.13 μm optical diameter range (resolution
30 chan total, averaging time – 1sec)
Surface Aerosol Properties, Laramie, WY
Comparison/
optical closure
Size-resolved
Refractive index (n)
2. Partial Molar
of comprehensive
Refraction (PMR)
size distribution
method for n calc.
(Stelson, 1982)
Total scattering coefficient
measurements from Nephelometer
Data Processing Algorithm Development
Alignment of size distributions
for generated aerosols
2. Partial Molar
Refraction (PMR)
method for n calc.
(Stelson, 1982)
3.Volumeweighted density
in each particle
size range
Mass Closure
Size-resolved
Refractive index (n)
and density (ρ)
Comprehensive
size distribution
over 15 nm – 20
μm size range
4. Diameter
conversion and
distributions
alignment method
Size-distribution measurements
from SMPS, PCASP, and APS
Preliminary Results and
Conclusions
•The general data analysis
algorithm has been tested using
lab-generated aerosols (sodium
nitrate, ammonium nitrate, and
ammonium sulphate).
•Size
distributions
of
labgenerated poly- and monodisperse
aerosols measured by the APS and
SMPS are in excellent agreement.
Comparison
of
PCASP
distributions with those from the
APS and SMPS show some
variability, but are nevertheless
reasonable.
Optical closure (total scattering coefficient)
References
•
Bohren, C. F. and Huffman, D. R.: Absorption and scattering by small particles, John Wiley and
Sons, Inc., 1983
•
DeCarlo, P., Slowik, J. G., Worsnop, D. R., Davidovits, P., and Jimenez, J. L.: Particle morphology
and density characterization by combined mobility and aerodynamic diameter measurements. Part I:
Theory. Aerosol Science and Technology, 38: 1185–1205, 2004. DOI: 10.1080/027868290903907
•
•
Calc-Blue TotS Cf-B % diff
1.5E-05 1.6E-05
8.25
2.1E-05 2.3E-05
6.82
2E-05 2.2E-05 11.75
1.6E-05 1.8E-05 11.01
1.5E-05 1.6E-05
9.06
1.4E-05 1.5E-05
6.99
Calc -Green TotS Cf-G % diff Calc-Red TotS Cf-R % diff
8.264E-06 8.49E-06
2.70 3.73E-06 3.9E-06 4.47
1.2776E-05 1.33E-05
3.94 6.48E-06 6.5E-06 0.19
0.00001156 1.25E-05
7.31 5.74E-06 6.1E-06 5.80
9.7097E-06 1.13E-05 13.84 5.26E-06
6E-06 11.84
1.0886E-05 1.15E-05
4.99 5.86E-06
6E-06 1.62
1.0511E-05 1.09E-05
3.73 5.54E-06 5.7E-06 2.82
Total extinction coefficient for ammonium sulphate ((NH4)2SO4)
polydisperse aerosol calculated using Mie theory for TSI
Hand, J. L. and Kreidenweis, S. M.: Size corrections based on refractive index for Particle Measuring Nephelometer wavelengths: red (700 nm), green (550 nm) and blue
Systems Active Scattering Aerosol Spectrometer Probe, CIRA report 0373-5352-31, Colorado State (450 nm) over 7-170 degrees (determined by instrument optics),
University, Fort Collins, CO, 1996
compared with the total scattering coefficient measured by the TSI
Nephelometer.
Stelson, A. W.: Urban aerosol refractive index prediction by partial molar refraction approach,
Environ. Sci. Technol., 24, 1676–1679, 1990
•Comparison
of
measured
scattering extinctions at three
wavelengths for dried polydisperse (NH4)2SO4 aerosol with
values calculated by Mie theory
using measured size distributions
are in very good agreement (≤
14%).
•The analytical tools developed in
this study are now being applied
to the ambient aerosol data
acquired during EMLACE. These
analyses account for variability in
the
size-dependent
chemical
composition of the particles.