# Presentation: 228057

## Aerosols in global models: from direct effect to nucleation

- Jean-François Lamarque
- SciDAC Team Member
- Atmospheric Chemistry Division
- National Center for Atmospheric Research, Boulder, CO

- DOE Atmospheric Science Program October 31

## Outline

- Direct effect of aerosols
- OC in the FT model discrepancy
- Nucleation
- CCN activation
- Future direction and needs

## CAM with interactive chemistry and aerosols

- Building the NCAR CCSM with chemistry

## What is in CAM/Chem now?

- Ozone chemistry (including hydrocarbons up to isoprene, toluene and terpenes)
- Bulk aerosols: soot, organic aerosols (primary and secondary), sulfate, ammonium nitrate, sea-salt and dust
- Coupling through radiative fluxes (direct effect only)
- Approximately 100 species

## Response of the chemistry-climate system to changes in aerosols emissions.

- The hydrological cycle (measured here by the global integral of the latent heat flux) slows down with increasing aerosol loading

- 0

- 0.5

- 1

- 1.5

- Response of the chemistry-climate system to changes in aerosols emissions.

## Without any changes to surface emissions of ozone precursors, the global integrals (surface to 300 hPa) of OH, ozone and NOx show a large increase from decreasing aerosols.   This is due to a combination of an increase in water vapor (shown here by the integrated precipitable water) and reduced chemical uptake on aerosols.

## Direct impact of aerosols

- 	The previous figures indicate the importance of the
- direct effect of aerosols
- chemical uptake of aerosols

- How well do we know them?

## AOD at 550 nm

- MOZART

- STEM

- A priori

- Optimized

- From Bates et al., 2005, submitted to ACPD.

## AOD at 550 nm

- From Bates et al., 2005

## Direct effect parameters

- Aerosol extinction
- Single-scattering albedo
- Asymmetry parameter

- But there is the difficulty of accurately representing the effect of humidity

-  subgrid-scale variability
-  aerosol composition

## Chemical uptake

- How do we model particle aging? Do we need to do a better job at representing the conversion from hydrophobic to hydrophilic?
- What is the uptake of ozone and sulfate on dust?
- What is the role of chemical aging in defining the iron solubility in dust?

## ACE-ASIA: OC AEROSOL MEASUREMENTS IN THE FREE TROPOSPHERE

- Mean Observations
- Mean Simulation
- Observations

**High Levels of OC were observed in the FT during ACE-Asia by 2 independent **
**measurement techniques.  We cannot simulate this OC with direct emissions**

**What is the source**
**of this FT organic**
**carbon aerosol?**

**   ****Seinfeld group****	****	****   Huebert group****	****	****   Russell group**** ****   ****  **

- Heald et al., GRL, 2005

- +

## GEOS-CHEM AEROSOL SIMULATION

- Mean Observations
- Mean Simulation

**GEOS-Chem simulates both the magnitude and shape of sulfate and EC**
**concentrations throughout the troposphere ******** what is different about OC?**

- Heald et al., GRL, 2005

## ACE-ASIA: OC AEROSOL MEASUREMENTS IN THE FREE TROPOSPHERE

- Mean Observations
- Mean Simulation
- Observations

**High Levels of OC were observed in the FT during ACE-Asia by 2 independent **
**measurement techniques.  We cannot simulate this OC with direct emissions**

**What is the source**
**of this FT organic**
**carbon aerosol?**

**   ****Seinfeld group****	****	****   Huebert group****	****	****   Russell group**** ****   ****  **

- Heald et al., GRL, 2005

- +

## Future direction

- Resolved-size aerosols are needed for a reasonable treatment of the indirect aerosol effect(s) : modal or bin
- 4-dimensional information can be used in global models

## Nucleation in a pristine environment

- Kulmala et al,        J. Aerosol Science, 2004

- Particle diameter (m)

## Nucleation in polluted environments

- From Laaksonen et al., GRL, 2005

## New particle formation

- For global models, we can use simple formulations for the formation of particles from sulfuric acid above a threshold defined by
- Competition with condensation

- Ccrit = 0.16 exp(0.1 T - 3.5 RH -27.7)   (Wexler et al., 1994)
- Ccrit = f(RH,T)                                 (Vehkamaki et al., 2002)

## Binary nucleation

-  (Vehkamaki et al., 2002)

-  (Berndt et al., 2004)

## CCN Closure in ARM Aerosol IOP Ponca City, OK May 2003; SS = 0.8%

- Observed CCN Concentration (cm–3)

- Predicted CCN Concentration (cm–3)

*Data courtesy of Tracy Rissman, Caltech*

- Discrepancy between observations and predictions is a factor of between 2 and 4!

- Even if we assume that organics are completely insoluble, CCN concentration is still overpredicted!

- From P. Chuang, UCSC

## Equilibrium effects: 
solution interactions
interfacial interactions
Kinetic effects
gas-liquid mass transfer
solid-liquid mass transfer

- solution interactions
- interfacial interactions
- Kinetic effects
- gas-liquid mass transfer
- solid-liquid mass transfer

- CCN activation

-  What is the role of organic films?
-  Are time scales for mass transfer relevant to cloud droplet activation?

- From P. Chuang, UCSC

## Future needs: measurements

- Size and composition dependent measurements
- Time series over diurnal to annual cycle
- Primary emissions that are size-dependent
- Radiative parameters

## Future needs: science questions

- What are the processes driving the nucleation of new particles?
- Where are the missing organic aerosols coming from?  Missing SOA source, underestimate of production rate, ...?