# Presentation: 200360

## The Effects of Cloud Processes on the Optical Properties of Aerosols

*Carl M. Berkowitz, Larry K. Berg, Rahul A. Zaveri*
*Pacific Northwest National Laboratory*
*Richland, WA*
*Atmospheric Sciences Program *
*First Annual Science Team Meeting*
*Charleston, South Carolina*
*January 25-27,2005*

## Scientific Objectives

***“...******to quantify and explain mechanisms by which the optical properties of fresh aerosols change with passage from the boundary layer into the free atmosphere through cumuliform clouds*****. “**
***A) What do we see?***
**what is the vertical and horizontal variability in aerosol absorption and scattering over regions occupied primarily by cumuliform clouds? What are the differences in these properties below and above cumulus clouds? **
***B) Why do we see it?***
**Can we reproduce the statistical properties of outflow aerosols using detailed process models?**
***C) How do we parameterize it for use in regional-scale models?***
**How can we describe these processes in a computationally efficient manner?**

## Basis for this Work

***No particulate mass (PM) = no PM scattering or absorption***
**PM mass is the single most important factor in determining the amount of scattered and absorbed radiation under clear sky conditions **
***PM lifetime is greater aloft than within the boundary layer***
**Clouds can move optically active aerosols from within the boundary layer to the free atmosphere greatly enhancing the particle lifetime and hence PM mass loading in areas downwind of the source region. **
***Chemistry within cloud droplets can enhance PM***
**Is there more than just basic sulfur oxidation processes occurring...might there be SOA formation within cloud droplets? Morphology changes associated with activation? All could affect (+/-) mass scattering coefficients following droplet evaporation. **
***Cloud scavenging is a function of aerosol composition ***
**Some types of PM will more readily pass through cloudy systems without activating (e.g. fresh soot) than others (e.g., sulfate) leading to different size and composition of aerosols after cloud processing.**

## What do we see? Measure changes to the composition, size and optical properties as PM pass through clouds with known LWC, Ndrop and w.        Task Leader = Carl Berkowitz

Why do we see it? Test hypotheses with a detailed Lagrangian gas/aerosol/cloud chemistry model using trajectories from Mikhail Ovtchinnikov’s cloud resolving model. Task Leader = Rahul Zaveri

How do we parameterize it? Parameterize aerosol processes within an existing cumulus parameterization scheme, with an evaluation of the resulting scheme against the detailed cloud/aerosol model to be used in Task B.                                                                     Task Leader = Larry Berg

**What do we see? **Measure changes to the composition, size and optical properties as PM pass through clouds with known LWC, Ndrop and w.        *Task Leader = Carl Berkowitz*
**Why do we see it? **Test hypotheses with a detailed Lagrangian gas/aerosol/cloud chemistry model using trajectories from Mikhail Ovtchinnikov’s cloud resolving model. *Task Leader = Rahul Zaveri*
**How do we parameterize it? **Parameterize aerosol processes within an existing cumulus parameterization scheme, with an evaluation of the resulting scheme against the detailed cloud/aerosol model to be used in Task B. *                                                                    Task Leader = Larry Berg*

- Approach

## 2005 Pt. Reyes Campaigntest concepts and models on stratiform clouds system

****** ****= 5.1 m****2**** g****-1**

****** ****= 4.3 m****2**** g****-1**

****** ****= 4.6 m****2**** g****-1**

*z *(km)

- 1

- 0.5

- 0.0

*x*

- ?

- CCJ

- North

- South

- CCJ

## 2007 Aerosol Outflow Campaign

*x*

*z *(km)

- 1

- 0.5

- 0.0

## Gas-Aerosol-Cloud Chemistry ModelingTask Leader: Rahul Zaveri

**Development and improvements planned for the next 3 years**
**Gas ****(CBM-Z: Zaveri and Peters, JGR, 1999)**
- Extend gas chemistry to include important secondary organic aerosol precursors (SOAp) based on Master Chemical Mechanism work to be performed in collaboration with S. Madronich.
**Aerosol ****(MOSAIC: Zaveri et al., 3 papers to appear in JGR, 2005)**
- Implement size, composition, and processing history resolved chemistry (i.e., get rid of internal mixing assumption and represent unprocessed and cloud-processed aerosols as two separate aerosol populations).
- Develop detailed SOA formation modules (in collaboration with S. Madronich)
**Cloud ****(MTCRM: Zaveri, PhD Dissertation, 1997. Based on Pandis and Seinfeld, 1989)**
- Extend aqueous chemistry to include dissolved hydrocarbon chemistry.
- Implement size and composition resolved cloud chemistry (as opposed to bulk cloud-phase approach).
- Implement the new gas-aerosol-cloud model in a Lagrangian box model which will be driven by output from Mikhail Ovtchinnikov’s cloud resolving model **(Ovtchinnikov and Kogan, JAS, 2000)** developed to investigate ice production in small cumuliform clouds and evaluated against observations of summertime cumulus clouds observed over New Mexico  **(Ovtchinnikov et al., JAS, 2000)**.

## Slide 8

## Cumulus Parameterization: Development and TestingTask Leader: Larry Berg

**Berg LK and RB Stull. 2004a. JAS (submitted).**
**Berg LK and RB Stull. 2004b. JAS 61:813-828.**
**Berg LK and RB Stull. 2004c. JAS (submitted)**

## Coupling Aerosol Processing Model with Cumulus Parameterization

**Unprocessed and cloud-processed aerosols will be represented as two separate populations in the model for a more realistic representation of size-resolved aerosol composition, hygroscopic, and optical properties.**
**The resulting system will be initialized and evaluated using ASP field measurements.**

- Coupling Aerosol Processing Model with Cumulus Parameterization

## What We Will Provide

**Meteorological Observations**
**vertical sounding of winds (u,v), temperature, humidity**
**vertical velocity at cloud base and within cloud**
**Aerosol/Gas Phase Observations in inflow and outflow regions and within cloud, before and after cloud processing**
**CCN activation spectrum**
**size distributions of number, composition, humidification**
**aerosol optical properties**
**aerosol morphology**
**interstitial and cloud-phase aerosol mass and composition**
**precursor and oxidant gases (SO2, H2O2, O3, VOCs) **
**clouds droplet and rain/drizzle size distribution**
**Computationally efficient gas/cloud/aerosol modules coupled with a cumulus parameterization, all of which have been evaluated using ASP field measurements for cloud cases**

**Field measurements that characterize cloud processing (transport and transformation) of aerosols and trace gases, and the clouds themselves**

## Time Line

|  | Task 1: 
Field Studies | Task 2:
Aerosol Model | Task 3:
Cumulus Parameterization |
| --- | --- | --- | --- |
| 2005 | *Pt.  Reyes
(Aerosol processing by coastal stratus) | Development and improvement of existing process models.
Use cloud resolving model (CRM) for Pt. Reyes fields.
Incorporate process modules into CRMs. | Develop parameterization for converting aerosol size distribution to cloud droplet size distribution. Start work on coupled aerosol/cloud parameterization for regional scale models |
| 2006 | Support for Mexico City and Houston | Continued development of process models.
Testing new model with Pt. Reyes data | Continue development of coupled parameterization. Start tests of the new parameterizations with Pt. Reyes data |
| 2007 | * Aerosol Outflow Campaign | Use process models for both planning and analysis of observations from Aerosol Outflow Campaign. | Continue development of coupled parameterization. Start testing new parameterization with data from the aerosol outflow campaign.  |