1. Impacts of Dust Mixing State on Cloud Microphysics
I-Chun Tsai1, Jen-Ping Chen1, Yi-Chiu Lin1, Chein-Jung Shiu2 and Charles Chung Kuang Chou2
Department of Atmospheric Sciences, National Taiwan University
Research Center for Environmental Changes, Academia Sinica

2. sulfate/ nitrate/ ammonium
Aerosol mixtures
sulfate/ nitrate/ ammonium
mineral dust
sea salt
EC OC
aggregate
core with shell RH
Core with Shell
better CCN and IN (?)
stronger absorption
heterogeneous chemistry
mixture state

3. Dust nucleation rate
Immersion freezing rate (haze)
Immersion (haze)

4. Model & simulation setup
MM5 + CMAQ
physics-based multimodal aerosol scheme
3 moments log-normal size distribution
case: 2006/03/14-20
VOC
(Zhang et al., 2009)
Add SOA emission plot (but what species……)._
dust
(Wang et al., 2000)
SO2
(Zhang et al., 2009)
soot
(Zhang et al., 2009)

5. Multi-modal aerosol scheme
hygroscopic aerosol
size
Number density
dust/soot
size
Number density
mixture
size
Number density
dust

6. Impacts on aerosol properties
Mi,mix – Mi,no_mix
Mi : the ith moment
M0: number, M2: surface area, M3: volume %
Dust source
Sulfate source
Open ocean
Taiwan M0
-17.7
-12.8
79.9
-10.6 M2
-24.4
-31.7
52.8
50.9 M3
-39.9
-53.6
-7.7
-22.34

7. Single Scattering Albedo
mix_ex
mix
mix

8. Single Scattering Albedo in Taipei

9. CCN concentration at 0.1% ss.
Inorganic CCN
Increase due to dust mixing
109 m-3
1010 m-3
Increase due to soot mixing
109 m-3
Dust: order of magnitude differences (under strong dust storm activity)
Soot: a factor of 2 to 3 differences
No mix case CCN

10. Internal (dust/sulfate)
Nucleation rate at -20C
External (dust)
Internal (dust/sulfate)
106 m-3 s-1
106 m-3 s-1
Internal - external
106 m-3 s-1
Pure dust
coated dust
Ammonium sulfate
up to 10% differences

11. Summary
Mixing (coagulation) between these two types aerosols greatly affects
Aerosol microphysical processes
Cloud microphysical processes: CCN # (and ice nucleation rate)
Effect of aerosol mixing on cloud initiation
CCN (at 0.1% supersaturation) generally increased due to aerosol mixing
Solute coating may cause a switch of nucleation mode from
deposition nucleation to “immersion freezing”
Solute coating suppress dust nucleation; enhance soot nucleation at above -28C but suppress at lower temperatures
On-line calculation by coupled WRF-CLR-kosa (Lin, 11/06 11:25 AM)

12. Thank You

13. Correction of refractive index
Dust (1.544,-0.025)+ sulfate mixture(1.53,-1e-7)
Toon and Ackerman (1981)

14. Internal (soot/sulfate)
Nucleation rate at -20C
External (soot)
Internal (soot/sulfate)
Internal - external
Pure soot
coated soot
Ammonium sulfate
Mixing enhance soot nucleation at -20C

15. Internal (soot/sulfate)
Nucleation rate at -30C
External (soot)
Internal (soot/sulfate)
Internal - external
Pure soot
coated soot
Ammonium sulfate
Mixing suppress soot nucleation at -30C