# Presentation: 107978

## Black Carbon and Organic Carbon Aerosol Mass and Optical Properties: Comparability and Causes of Uncertainties 

- Suzanne Paulson
- Brian Barkey
- Sheldon Friedlander
- Kuo-Nan Liou
- Antonio Miguel
- Departments of Atmospheric & Oceanic Sciences, Chemical Engineering, and Institute of the Environment, UCLA

## EC & OC in Ambient Particles

**EC & OC in Ambient Particles**

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## Many Questions Remain

- Refractive indices of EC and OC aerosols are uncertain.
- Impact of (non-spherical) shape on aerosol scattering.
- Impact of mixing state on optical properties of EC and OC aerosols.
- Impact of mixing state and oxidizers on evolved gas analyzers of EC/OC mass.
- The link between filter-based measurements of EC & OC mass and optical properties.

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**Notes:**
Coating carbon increases its scattering substantially, and also increases its absorption. More quantitative data is needed.
Jacobson & others argue that BC & OC typically exist as an OC coated BC core, however analyses of AERONET data suggest that BC is more commonly externally mixed.

## Goals of this Project

- 1.  Develop an instrument to measure aerosol angular scattering and polarization.

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- Polar Nephelometer

**Notes:**
This is the instrument originally developed at UCLA  to measure the light scattering properties of ice crystals.

A stream of particles is pulled into the center of this scattering chamber. 

Visible laser light scattered off of the particles is routed to detectors via fiber optics.

An onboard embedded CPU is used to acquire and process the measured light intensities.

The instrument is small and lightweight, and ideal for field studies.

We are presently outfitting the instrument for use with aerosols including optimizing the sample tube sizes and suction rates, filtering of the air in the other parts of the scattering volume and determining the instrument sensitivities.
Angular scattering of 670 or 720 nm laser light by particles in the sample volume is monitored with 34 or 44 fiber optic light guides sampled @> 4200 Hz.  Not shown is the extensive array of light absorbers above and below the scattering plane.

## 2. Extract refractive indices from the angular scattering data for OC and BC aerosols, including OC-coated black carbon. 

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**Notes:**
Shown here are the theoretically calculated expectations for the polar nephelometer for particles with identical size distributions, but with different optical properties.
Retrieving the optical properties of small particles is possible because the scattering properties of these particles is highly dependent on the particles properties.
We use a genetic algorithm based directed search routine because: 
There are a high number of possible solutions, and this problem cannot be solved analytically.
There method is computationally efficient
There are ‘off the shelf’ software packages that can be tailored to fit our problem.

## 3. Experimentally verify/reconcile theoretical expectations for the scattering properties of non-spherical aerosols. 

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**Notes:**
This comparison will provide the opportunity to verify the light scattering theory.
These are some results developed via some newly developed theoretical methods.
These plots show how very small spherical and  non-spherical  particles scatter light into the forward (0°) to the reverse (180°) directions.
Note that there are significant differences between the scattering properties of the non-spherical shapes and spheres even at these small sizes.  
These results have significant implications for the remote sensing of aerosols from space and of modeling the radiative effect of aerosols.
We plan to compare our scattering measurements to theoretical results based on the measured microphysical properties of the aerosols.

## Goals of this Project

- 4. Investigate the underlying factors that control differences in EC and OC mass and optical property data from instruments that are in wide use.
- EC/OC mixing state.
- Oxidizing seed.

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**Notes:**
This instrument has already been proven on small ice crystals and preliminary measurements have been made on smoke particles. It will be further developed for application to sub- and super-micron aerosols. 

This comparison will provide the opportunity to verify the light scattering theory.

## Chamber

## Instrumentation: Filter-Based

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**Notes:**
utilizes seven wavelength channels (350 to 950 nm), distinguishes organics (such as PAHs) and minerals that absorb in visible and near UV

This comparison will provide the opportunity to verify the light scattering theory.

## Instrumentation: in-situ Optical 

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## Instrumentation: Physical & Chemical Characterization

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** **

## Goals of this Project

- 4.2. Quantify instrument/method specific responses for the several aerosol types, and differences between methods.
- Focus on fresh & photochemically aged diesel, two stroke gasoline, & secondary organic aerosol, with & without inorganic and oxidizing seed. Internal and external mixtures of these types will be investigated.

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**Notes:**
This instrument has already been proven on small ice crystals and preliminary measurements have been made on smoke particles. It will be further developed for application to sub- and super-micron aerosols. 

This comparison will provide the opportunity to verify the light scattering theory.

## Experiments

**• **** ****Planned for the basic set of runs.**
***C***** Conditional on results of initial experiments.**

**Notes:**
 Indicates an experiment that is planned for the basic set of runs.
C indicates an experiment that will be carried out if related initial experiments indicate that additional insights will be gained.
 1-Pinene, initial concentration less than 50 ppb. Urban VOC/NOx ratio ~8, rural ~40.
3Several types of potentially oxidizing seed will be investigated, as described in section above. Depending on the results, additional experiments will be conducted with the materials with the largest impact.
4Photochemical oxidation will be provided by propene/NOx chemistry, a system that generates negligible aerosol.
5Externally mixed means that diesel/gasoline will be added to the chamber after secondary organic aerosol has already formed. 
6Ammonium sulfate aerosol, generated by nebulizing and drying aqueous ammonium sulfate. This is not expected to be oxidizing.
7Internally mixed means that diesel/gasoline particles will be added to the chamber prior to the initiation of photochemistry, so that the primary BC/OC aerosols will serve as seed aerosols.

## Goals of this Project

- 4.3 The additivity of instrument responses to aerosol components and for external mixtures will be assessed.
- 4.4 The evolution of the fractal structure of ultrafine diesel particles as they are incorporated into the accumulation mode will be investigated.
- 4.5 Establish the relationship between common off-line measurements of EC and OC mass and optical absorption, and* in situ* properties of scattering and absorption.

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**Notes:**
This instrument has already been proven on small ice crystals and preliminary measurements have been made on smoke particles. It will be further developed for application to sub- and super-micron aerosols. 

This comparison will provide the opportunity to verify the light scattering theory.

## Evolved Gas Analyzer Data

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- PM2.5 from Riverside, CA in late summer. Analyzed with a Sunset Labs NIOSH EGA. The solid line indicates the evolved carbon signal. ‘PC’ is material that has been assigned as charred polar OC; it does not volatilize and only leaves the filter under oxidizing conditions.