Wavelength Dependence of Aerosol Light Absorption in Urban and Biomass Burning Impacted Conditions: An Integrative Perspective. Paper A11E-02. W. Patrick Arnott Madhu Gyawali Kristin Lewis Hans Moosm

1
Wavelength Dependence of Aerosol Light Absorption
in Urban and Biomass Burning Impacted Conditions
An Integrative Perspective. Paper A11E-02.W.
Patrick ArnottMadhu GyawaliKristin LewisHans
Moosmüller
AGU Fall Meeting 2009 San Francisco CA ID
A11E-02
Atmospheric Science Program University of
Nevada Reno, NV
Division of Atmospheric Science Reno, NV
2
Outline

1. Introduction
2. Measurements show that the wavelength dependence
   of aerosol light absorption from biomass burning
   can be quite different than typical urban
   aerosol.
3. Model results suggest that some aspects of our
   conventional wisdom on this subject need
   adjustment.
4. Conclusions

3
Quantify Wavelength Dependence of Light
Absorption by Aerosol

• ??????Ångström Coefficient for Absorption.
• ? 1 for motor vehicle emission generated BC.
• Biomass burning aerosols exhibit ? as high as
  3.5.
• Depends on chemical composition and particle
  size and morphology.
• We use measurements at 405 nm and 870 nm to
  determine ??

4
Optical Model for Light Absorption by Soot
Bottom Line Light absorption by fresh soot has
?1 when m does not depend on wavelength.
5
Photoacoustic Aerosol Optics Instrument
355 nm (new!) 405 nm,870 nm 532 nm 671 nm, 676
nm 1047 nm

• Aerosol Absorption and
• Scattering Coefficients

f0
f0 df
6
Ångström Coefficient Example
7
Example Homogeneous Soot Sphere Calculation
Mie Theory for Homogeneous Spheres
8
Morphology Change Upon Humidification
9
Example of Dry Chamise Particle SEM Image

10
Example of Chamise Particle SEM Image After H20
Vapor Applied at 85

11
Soot Compaction from Sulfuric Acid and Water
Vapors
Soot Compaction Process
12
Lead Experiments on People!
Circa 1975!
13
Particle Collapse Upon Humidification in the
Lungs!
Chamberlain, A. C., W. S. Clough, M. J. Heard, D.
Newton, A. N. B. Stott, and A. C. Wells (1975),
Uptake of lead by inhalation of motor exhaust,
Proceedings of the Royal Society of London.
Series B, Biological Sciences, 192, 77-110.
14
Wildfire Smoke in Northern California During
July 2008

• Around 3000 Individual Fires
• Most of The Fires Were Triggered
• By Lightning
• Burned Area Around 4686 km2

Source NASA California Wild Fires 2008
JULY-10, 2008
SEPT-22, 2008
Reno Days in Photographs Similar Location and
Sun Angle
15
Aerosol Optics of July and August, 2008

• Common Definition of Light Absorbing Organic
  Carbon
• Assumes Inverse Wavelength Dependence for Light
  Absorption

16
Aerosol Optics of July and August, 2008
Single Scattering Albedo (SSA)
Angstrom Exponent of Absorption (AEA)
SmokeUrban
SmokeUrban
Urban
Urban
17
Comparison With Lab Data
Ångström Exponent of Absorption vs Single
Scattering Albedo

• July Dominated
• by pine burning aerosol

• August Dominated
• by vehicle emissions

18
Chemistry of Primary Smoke Emissions
Ponderosa Pine Smoke Electron Microscopy
Ponderosa Pine Smoke Composition
Ponderosa Pine Smoke BC Is Hugely Coated With
Organics
Alexandar Laskin, PNNL, and Aerodyne
Aerosol Mass Spec measurements
19
Urban and Biomass Aerosol
They are fundamentally different!
20
Particle Morphology Strongly Affects the Ångström
Exponent for Absorption Computational Model
L. Liu , Michael I. Mishchenko, W. Patrick
Arnott Journal of Quantitative Spectroscopy
Radiative Transfer 109 (2008) 26562663
21
Simulation of the Ångström Exponent of Absorption
(405 and 870 nm)
Core RI (1.55, 0.8i) Coating RI (1.5, 0.012i)
at 405 nm and (1.5, 0.0i) at 870 nm (Coating
absorbs at 405nm)
Core RI (1.55, 0.8 i) Coating RI (1.5,
0.0i) (Non absorbing coating)
Key Message Coatings need not be absorbing to
cause Ångström coefficients for absorption
considerably different from 1.
22
East Las Vegas NV, Jan-Feb 2003
Linear regression is a blunt tool !
23
Summary

• The organic coating need not be intrinsically
  brown to observe the effects commonly referred
  to as those caused by brown carbon light
  absorption. Ångström coefficients as large as
  1.6 are possible for some wood smoke even though
  the coating doesnt absorb light.
• Aerosol morphology, size, and mixing state are of
  comparable importance with intrinsically brown
  carbon coatings in explaining deviations of
  absorption Ångström coefficients from the
  canonical value of unity.
• Ångström coefficients less than unity are not
  necessarily due to measurement precision and
  accuracy limitations.

24
Thank for your Attention!
Å 1 ???