# Presentation: 632618

## ARM - ACP AEROSOL IOP

**ARM**** - ****ACP** AEROSOL **IOP**
- Chemical - Microphysical - Optical - Radiative Closure Experiments

- Steve Schwartz and Dan Imre

- ACP Annual Meeting
- Orlando FL March 4-5, 2003

- www.tap.bnl.gov/arm_acp_aerosol_iop

## ARM ACP AEROSOL IOP

- Motivation: Aerosols are the greatest source of present uncertainty in radiative forcing of climate change.

## ARM ACP AEROSOL IOP

- Motivation: Radiative flux components in cloud-free air are very sensitive to aerosol loading and properties.

- Particle radius r = 85 nm; surface reflectance R = 0.15;single scatter albedo 0 = 1.

- Global-average AOT 0.1 corresponds to global-average forcing -3.2 W m-2.

## ARM ACP AEROSOL IOP

- Motivation: Aerosol optical depths leading to substantial direct forcing are not uncommon.

- Multiple-year record of aerosol optical depth at ARM SGP site in north-central Oklahoma.

*Michalsky et al., JGR, 2001*

## ARM ACP AEROSOL IOP

- Motivation: There are substantial discrepancies between measured and modeled radiation components.

- Measurements during cloud-free conditions at ARM SGP site in north-central Oklahoma.

## ARM ACP AEROSOL IOP

- Motivation: Aerosol indirect forcing is highly sensitive to number concentration of cloud drops.

- A 30% enhancement in cloud drop concentration in marine stratus clouds results in a global-mean forcing of -1 W m-2.

## ARM ACP AEROSOL IOP

- Motivation: Anthropogenic enhancement of CCN and cloud-drop concentrations by several fold are common.

- Measurements of aerosol and cloud drop concentrations in North Atlantic (ASTEX, 1992)

## AEROSOLS & CLIMATE:THE HOLY GRAIL

- Sources of Aerosols & Precursors
- Aerosol Chemical & Optical Properties
- Chemical Transport Models
- Detailed Aerosol Loading (ƒ(*t*, *X*,*Y*,*Z*))
- Radiation Transfer Models
- Global and Regional Climate Models

## ARM ACP AEROSOL IOP

- An ARM *Intensive Operational Period* to be conducted at the Southern Great Plains site in north central Oklahoma in May 2003.
**IOP Objectives**: Evaluate present understanding of aerosol influences on atmospheric radiation and clouds.
**IOP Requirements**: Detailed characterization of aerosol optical properties and influences on radiation and clouds, at the surface and in the vertical by aircraft and remote sensing.

## ARM Objectives

**ARM Objectives**

- “Closure experiments” will compare measurement of a quantity with modeled quantity based on measured input variables.
- Careful measurement of aerosol optical properties will remove “wiggle room” in modeling aerosol radiative forcing: extinction coefficient, single scattering albedo and asymmetry parameter.
- Measure vertical distributions of aerosol optical properties and radiative flux components. Compare aerosol extinction with *d****/dz*.
- Measurement of CCN spectra and relation to size distribution, composition, and hygroscopic growth will allow development and testing of parametrizations for cloud drop concentration.
- Multiple measurements will constrain uncertainties and identify weaknesses in measurement.

## ARM ACP AEROSOL IOP

**ARM ACP AEROSOL IOP**

- Some Closure Experiments During ARM Aerosol IOP

## ARM ACP AEROSOL IOP

**What is the role of ACP****In this IOP?**

## ARM ALONE

- Sources of Aerosols & Precursors
- Aerosol Chemical & Optical Properties
- Chemical Transport Models
- Detailed Aerosol Loading
- Radiation Transfer Models
- Global and Regional Climate Models

## ACP + ARM

- Sources of Aerosols & Precursors
- Aerosol Chemical & Optical Properties
- Chemical Transport Models
- Detailed Aerosol Loading
- Radiation Transfer Models
- Global and Regional Climate Models

## It is impossible to generalize what will be learned at the ARM site during IOP without the combined knowledge of aerosol chemical, optical, and radiative properties. 

**ARM ACP AEROSOL IOP**

## ACP Objectives

**ACP Objectives**

- 1.	Quantify the relationships between aerosol composition and microphysics and aerosol optical properties on the 1 m3 scale.
- 2.	Quantify the relationships between aerosol composition and microphysics and atmospheric radiation on the 1 to 2 km column scale.

## Aerosol Characterization by ACP

- Rapid size distribution - (120 nm - 3 μm) PCASP and (3 nm - 1 μm) DMA*****
- Particle refractive index - OPC+DMA*****
- Particle hygroscopicity - Humidified Tandem DMA*****
- Single particle size, composition - SPLAT*****
- Single particle size, composition, density, and hygroscopicity - SPLAT-       MS/HTDMA*****
- Aerosol size resolved composition - AMS
- Aerosol total soluble organic carbon - PILS-TOC*****
- Aerosol ion content - PILS-IC*****
- Elemental and Organic Carbon - Light spectrometer and thermal analysis*****
- Soot photometer - SP2 by Droplet Measurement Technology
- Total aerosol mass - TEOM

*******One-of-a-kind system designed and constructed by ACP scientists**

## Scanning Mobility Particle Sizer And Index of Refraction(Jian Wang)

- Scanning Mobility Particle Sizer And Index of Refraction(Jian Wang)

- (1)	Measure particle size distribution with high temporal resolution (60 s), using DMA to cover the 10 nm to 400 nm,  and
- (2) In-situ calibration of OPC and refractive index of particle in the range of 0.1 < Dp < 0.4 μm

## HTDMA – Particle Hygroscopicity (Jian Wang)

- HTDMA – Particle Hygroscopicity (Jian Wang)

- Measure particle water uptake in real-time. The Hydrated Tandem DMA system uses two identical DMAs and a humidity conditioner in-between.

## PILS-IC: Aerosol PM2.5 Ionic Composition(Yin Nan Lee)

- PILS-IC: Aerosol PM2.5 Ionic Composition(Yin Nan Lee)

**PILS-IC: ****(Particle Into Liquid Sampler - Ion Composition)**
- Rapid in-situ determination of aerosol chemical composition
**Ionic Species:**
- NH4+, NO3-, SO42-, K+, Ca2+, Na+, Mg2+, Cl-
**Time response:**
- 3 minutes
**Sensitivity:**
- 0.1 μg m-3

## PILS-TOC: Aerosol Total Organic Carbon Composition(Yin Nan Lee)

- PILS-TOC: Aerosol Total Organic Carbon Composition(Yin Nan Lee)

**PILS-TOC: ****(Particle Into Liquid Sampler Total Organic Carbon)**
- Rapid in-situ determination of aerosol total carbon composition
**Time response:**
- 1 minute
**Sensitivity:**
- 0.2 μg m-3

## SPLAT-MS: Single Particle Size and Composition(Dan Imre and Alla Imre)

- SPLAT-MS: Single Particle Size and Composition(Dan Imre and Alla Imre)

**SPLAT-MS: ****Single Particle Laser Ablation Time of Flight Mass Spectrometer**
- Real-time determination of individual particle size and composition
**Time resolution:**
- ~20 particles s -1
**Size range: **50 nm to 3.5 μm
**Size resolution: **3 nm

## Single Particle Size, Composition, Density, and Hygroscopicity(Dan Imre, Alla Imre, Jian Wang)

- Single Particle Size, Composition, Density, and Hygroscopicity(Dan Imre, Alla Imre, Jian Wang)

**SPLAT-MS/HTDMA:**
- Real-time determination of individual particle size, composition, hygroscopicity, and density
**Time resolution:**
- ~20 particles s -1
**Size range: **100 nm to 1 μm
**Size resolution: **3 nm
**Density resolution: **0.05 g cm-3

## Aerosol Mass Spectrometer(Aerodyne)

- Aerosol Mass Spectrometer(Aerodyne)

**AMS**
- Real-time determination of aerosol size and composition
**Time resolution:**
- ~20 particles s -1
**Size range: **30 nm to 3 μm
**Size resolution: **10 nm

- Aerosol Mass Spectrometer(Aerodyne)

## Aerosol Mass Spectrometer(Aerodyne)

- Single Particle Soot Photometer(Droplet Measurement Tech., Inc.)

-  	Nd:YAG Intracavity laser induced particle incandescence
-  	Size determination by light scattering (soot and non soot particles)
-  	Highly specific for soot
-  	Single particle sensitivity down to 80 nm equivalent diameter
-  	Capable of analyzing 5000 particles cm-3

## Aerosol Mass Spectrometer(Aerodyne)

- Thermal Analysis TC/OC/BC (Tom Kirchstetter and Tica Novakov)

## Aerosol Mass Spectrometer(Aerodyne)

- Thermal Analysis TC/OC/BC (Tom Kirchstetter and Tica Novakov)

## Aerosol Mass Spectrometer(Aerodyne)

- Closure of Aerosol Optical And Microphysical Properties(Bob McGraw)

*APPROACH:*
*Calculate effective refractive index of each particle from its measured composition using mixing rules. *
*    **The difference in optical properties between a homogeneous vs. a core/shell particle is largest for mixtures involving black carbon, but even here differences are typically less than 5% (Chylek, 2002).*
*Compute aerosol optical properties through statistical analysis of ground-based single-particle composition and size measurements.  *
* **Compare results with ground-based and air-to-ground optical measurements under well-mixed boundary layer conditions for closure (taking into account water uptake as a function of RH**).*

## Aerosol Mass Spectrometer(Aerodyne)

- Statistical Methods for Closure of Optical Properties from Measured Composition and Size Distribution(Bob McGraw and Yangang Liu)

- Aerosol optical properties will be calculated from statistical properties of the measured particle size/composition distribution, including its ***multivariate mixed moments***, using advanced statistical methods developed in collaboration with the USB/AMS Dept.).
- Optical properties of ***non-spherical particles*** will be computed at optimal surrogate compositions using *T*-matrix methods.

***Example:  Multivariate classification of a particle distribution  using Principal Components Analysis (PCA). Red points are optimal surrogate compositions obtained by PCA-quadrature methods.***

- Only through the measurements conducted by ACP scientists will it be possible to understand and generalize the observed optical and radiative aerosol properties.
- It will establish a much needed relationship between two arms of OBER in which the sum of the two is much greater than the individual parts alone.

**CONCLUSION**