A.D. Clarke, V.N. Kapustin

School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, USA

AEROSOL SIZE DISTRIBUTIONS, PROPERTIES AND VERTICAL PROFILES OVER THE PACIFIC: TOWARDS AN AEROSOL CLIMATOLOGY

A.D. Clarke, K.G.Moore, V.N. Kapustin

School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, USA

REGIONAL AEROSOL AND LONG RANGE TRANSPORT OVER THE PACIFIC

FOCUS

Contribute to the understanding of the climatology and variability of aerosol over the remote oceans (Pacific) and the processes that establish its characteristics (size, concentration, chemistry, optical properties)

STUDY REGIONS

Various research programs have explored the aerosol fields in the Central Pacific remote marine boundary layer (MBL) and free troposphere (FT) - PEM-Tropics A&B, ACE-1, GLOBE 1&2, CPACE, SAGA 1, 2&3, RITS 88, 93&94 ...

AC E 1 G LO B E 1 & 2

WE HAVE OBSERVED

In regions free of continental influence the marine boundary layer (MBL) aerosol mass and optical properties are dominated by sea-salt (e.g. ACE-1 Tasmania ) with some natural sulfate.

Continental aerosol can influence or dominate (MBL) aerosol and optical properties over extensive regions until depleted by removal processes in MBL.

Lofting of continental aerosol above 2km often creates structured rivers of aerosol (dust, pollution) that is advected over global scales before re-entrainment into the surface boundary layer.

(CONT.)

Deep convection and precipitation removes MBL aerosol mass and number and vents cleaned surface air aloft. Can provide favorable region for natural nucleation with enhanced “new” aerosol number but with little mass.

Cloud venting aloft and larger scale subsidence and entrainment will couple free troposphere (FT) aerosol and MBL aerosol cycles including their evolution and properties.

Column aerosol properties (satellite) will reflect the above processes and a mix of natural and anthropogenically influenced aerosol. In general – surface based in-situ measurements will provide uncertain assessments of column aerosol properties.

Aerosol Size Distributions - Basics and Interpretation

0

1000

2000

3000

4000

Background Marine DOY323.4-323.6

Background Marine DOY327.0-327.2Continental DOY331.7-331.9

dN/d

logD

p (

cm -3

)

0.01 0.1 1 100.1

1

10

100

1000

Dp (m)

dN/d

logD

p (

cm -

3 )

Ultrafine Aitken Accumulation Coarse

0 40 80 120 1600

1

NUCLEATION:HIGH SULF.ACIDHIGH HUMIDITYLOW TEMPERATURELOW SURF.AREA

COAGULATION &CONDENSATION

ULTRAFINE MODE

AITKEN MODEdN/d

logD

Diam, nm

0 40 80 120 160

0.0

0.1

0.2 AITKEN MODE

CCN - CLOUDS - ACCUM. MODE

dN/d

logD

0 40 80 120 1600

1

300C

CLEAN

SOOT "OLD"

SOOT "NEW"

POLLUTION

dN/d

logD

Diam, nm

0 40 80 120 160

0.0

0.1

0.2

0.3

0.4

0.5

MBL AEROSOL

POLLUTION

dN/d

logD

Modal structure of an MBL aerosolMBL processes

FT processes

MBL - polluted and clean case

Volatility and size distributions

0.01 0.1 1 100

10

20

30

40

50

DMAOPC

NOTE: Scale

dA/dlogDp

0.01 0.1 1 100

500

1000

1500

2000

OPCDMA

dN/dlogDp

0.01 0.1 1 100

1

2

3

4

5

DMAOPC

NOTE: Scale

dV/dlogDp

0.01 0.1 1 100

10

20

30

40

50

NOTE: Scale

0.01 0.1 1 100

500

1000

1500

2000

0.01 0.1 1 100

1

2

3

4

5

NOTE: Scale

0.01 0.1 1 100

50

100

150

200

250polluted MBL

clean MBL

clean FT

Dp (m)0.01 0.1 1 10

0

500

1000

1500

2000

DMA 40 DMA 150 DMA 300 OPC 40 OPC 150 OPC 300

Dp (m)0.01 0.1 1 10

0

5

10

15

Dp (m)

0.01 0.1 1 100

500

1000

1500

2000

0.01 0.1 1 100

5

10

15

polluted FT

0.01 0.1 1 100

50

100

150

200

250

Size Distributions and Volatility as a Tool to Study Particles Composition

= 550 nm

sp=2.6x10-7 (1/m)tot. A =2.71 (m2/cm3)(ref. V)/(unht V) =0.01 sub-m

=(sp+ ap)/sp=0.999

=0.98sp=1.2x10-5 (1/m)tot A =46.2 (m2/cm3)(ref. V)/(unht V) =0.06 sub-m

=0.94 sp=9.51x10-5 (1/m)tot A =123.1 (m2/cm3)(ref. V)/(unht V) =0.12 sub-m

=0.80 sp=2.94x10-5 (1/m)tot A =65.1 (m2/cm3)(ref. V)/(unht V) =0.23 sub-m

PageSize Distributions and Volatility...

• Some selected examples of size distributions (number, surface, volume) for various cases (clean/polluted free troposphere - FT, clean/polluted marine boundary layer -MBL).• Some related properties (single scattering albedo - ω, scattering coefficient, surface area and refractory volume fraction) indicated in panels on the left.

PageRCN Ratio - an Indicator ..

• A lidar image from the NASA DC8 at 8-10km from Darwin to Tokyo.• Variable low level clouds are evident alone with a dramatic Asian dust plume reaching 7km over Japan. • Regions of no backscatter are very clean regions where elevated new particle concentrations can be see over the ITCZ and where refractory surface derived CNs (@300C) are at minimum.

Comments

Zonal Aerosol Features in the Pacific Free Troposphere (FT)

-60 -40 -20 0 20 40 60 800

2

4

6

8

10

NASA GLOBE2 Expt. (1990) Alt. > 3 km only

UFCN

(>3n

m) t

o CN

(>12

nm) R

atio

-60 -40 -20 0 20 40 60 800.0

0.5

1.0

NS

HotC

N(30

0C) t

o Co

ldCN

(40C

) Rat

io

Latitude

0

2

4

6

RefrCN CN (Dp>15nm)

CN(#

/cm

3)*1

000

@ST

P

0

30

60

Altitude ~ 10kmDARWIN TOKYO

UCN (Dp>3nm)

UCN(

#/cm

3)*1

000

@ST

P

0.00

0.05

0.10

0.15

Tota

lVol

(um

3/cm

3)

TotVol@40C RefrVol

-10 0 10 20 300.0

0.5

1.0

Latitude

RefrCN(@300C)/TotCN(@40C))

RefR

atio

0

25

50

75

UCN

/CN

Ratio UCN(>3nm)/CN(>15nm)

• A flight from Darwin to Tokyo revealed zonal variations in aerosol properties. Enhanced nucleation in clean air near the equator changed to continental air aloft above Tokyo with high mass loading and large surface derived refractory aerosol fraction.

• The ratio of total (UCN) to larger CN and ratio of refractory CN (soot, dust, sea salt) to total CN show zonal regions aloft where clean or polluted air is most prevalent.

INDOEX99 - Aerosol Plumes from India.

0.01 0.1 10

500

1000

1500

2000

0.01 0.1 10

500

1000

1500

2000

1750 -- 2000 1500 -- 1750 1250 -- 1500 1000 -- 1250 750.0 -- 1000 500.0 -- 750.0 250.0 -- 500.0 0 -- 250.0

Inversion

"mix" layer

MBL plume

biomass plume

"clean" layer

0

2

4

6

8

10

{

10.0

OPCDMA

Isopleths of dN/dlogDp

0.01 0.10

Dp (m)

Altit

ude

(km

)

40 deg C 300 deg C

dN/d

logD

p

Dp (m)

40 deg C 300 deg C

dN/d

logD

p

Dp (m)

-90 -80 -70 -60 -50 -20

-10

0

800

600

400

200

Pres

sure

(mb)

Latitude (deg)

Longitude (deg)

Structure of Aerosol Plumes over Pacific South America Pollution (PEMT-A)

Regional haze(biomass)

Clean marine air

NASA PEMT-AE. Browell

-40

-30

-20

-100

800

600

400

200

Longitude (deg)-90-1351801359045

Pres

sure

(mb)

Latitude (deg)

Structure of Aerosol Plumes over PacificAfrican Biomass Burning (PEMT-A)

Structure of Aerosol Plumes over Pacific African Biomass Burning (cont.)

0

2

4

6

8

10

0 500 1000 1500 20000

2

4

6

8

10

20 40 60 80 100

CN conc.

CN concentration (#/cm3)

Palt

(km

)

0.0 0.2 0.4 0.6 0.8 1.0RCN ratio

RCNratio

0.0 5.0x10 -6 1.0x10 -5 1.5x10 -5

sp (1/m)

sp @ 550 nm

O3

O3 concentration (ppbv)

40 60 80 100

CO concentration (ppbv)

CO

0.01 0.1 1 100

200

400

600

800

1000

Inversion

875.0 -- 1000 750.0 - - 875.0 625.0 - - 750.0 500.0 - - 625.0 375.0 - - 500.0 250.0 - - 375.0 125.0 - - 250.0 0 - - 125.0

0

2

4

6

8

10

Elevated sp region

Biomass plume (Africa?)

Nucleation region

High altitude plume

Tahitian Plume-No OPC data

10.00.100.01

OPCDMA

Dp (m)

Altit

ude

(km

)

Isopleths of dN/dlogDp

DMA 40 deg OPC 40 deg

dN/d

logD

p

Dp (m)

0.01

0.1Hawaii

ITCZ

Diverg.Easterlies

SPCZTahiti

PEM Tropics, Flt10

1000

600

• A PEMT flight over the ITCZ and the SPCZ separated by a zone of subsidence. • Marked changes in aerosol size reveal regions of nucleation aloft above the ITCZ and SPCZ, with larger aerosol at intermediate altitudes. • Size distributions in the MBL are even larger and show a cloud processed mode with intermodal minimum near 0.09 um.

Variability of Aerosol Size Distributions

A 3D latitude-longitude distributions of small differential condensation nuclei - DCN (3nm<Dp<12nm) are highest aloft (above 3km) near ITCZ and SPCZ and almost no DCN particles are present in the MBL (observations from all PEM Tropics flights).

20 10 0 -10 -20 -30-160

-150

-140

-130-120-110

0

500

1000

1500

2000

2500

SPCZITCZ

Above 3 km

Lon

gitu

de

DCN

(3nm

<Dp<

12nm

), cm

-3

Latitude20 10 0 -10 -20 -30

-160

-150

-140

-130-120-110

0

500

1000

1500

2000

2500

Below 3 km

Lon

gitu

de

DCN

(3nm

<Dp<

12nm

), cm

-3

Latitude

Number Concentration is Enhanced in FT as the Result of New Particles Production.

The modulations in MBL aerosol number distributions in passing through the key Pacific meteorological zones.

Covert et al.

The data suggest some predictable features of the size distributions associated with key meteorological zones in the Pacific. Each zone has characteristic aerosol sources (natural and anthropogenic) and mean processes associated with FT/MBL exchange, removal mechanisms, wind and cloud fields.

Zonal Structure of MBL Aerosol Size Distributions

Cloud processed bimodal structure is the most obvious signature of the MBL aerosol in equatorial regions. Exchange with FT also plays a major role in shaping size distribution (note the same size of the particles below and just

above inversion).

An example of a sharp transition to aged MBL equatorial region aerosol upon passing through SPCZ region with strong convection.

-12

-9

-6

-3

0.550.1350.030.005

800 -- 1000 400 -- 800 200 -- 400 100 -- 200 0 -- 100

A

Transition

Dp, Diam,

dN/dlogDp, cm-1

Divergent Easterlies

SPCZLatit

ude

0.01 0.10

200

400

600

800 C

SPCZ

ITCZ

SPCZ and ITCZ

dN/d

logD

p, c

m

-3

0.01 0.10

200

400

600

800 B

dN/d

logD

p, c

m -3

Divergent Easterlies

Inversion

MBL

FTInversion

MBL

Vert.Profile

ITCZ

800.0 -- 1000 600.0 -- 800.0 400.0 -- 600.0 200.0 -- 400.0 0 -- 200.0

dN/dLogDp, cm-3

1205010

Dp, nm

3

6

9

12

Lat

itude

42

Altitude, km

FT / MBL exchange and size distributionsin the equatorial Pacific

FT/MBL exchange affects shape the size distributions: UFCN (Dp<20nm) appeared in the MBL after the frontal passage (a) and as the result of cumulus clouds mixing( b). No UFCN (<20nm) during the stratus clouds period (c).

A vertical profile near the ITCZ shows recent nucleation near 4 km with monomodal aerosol size increasing as particles subside toward the inversion near 1km. Below the inversion the particles entrained into MBL become bimodal as a result of MBL cloud processing.

FT / MBL exchange and size distributionsin the equatorial Pacific (cont.)

40 8010

MBL

Dp, nm

1600 -- 2400 800.0 -- 1600 400.0 -- 800.0 400.0 -- 400.0 0 -- 400.0 0 -- 0

0

2

4

6

-10 0 10 20

Alti

tude

, km

T, deg

AmbTemp

0 30 60 90 RH, %

RH

b.346

344

Day

of Y

ear

Aerosol size distribution,dN/dlogD

10 24 50 108 261

c.

Dp, nm

325

323

a.333

332

Some Aerosol Optical and Microphysical Properties of Aerosol Plumes over South

Pacific

0 1 2 3 4 50.0

1.0x10-5

2.0x10-5

3.0x10-5

4.0x10-5

y-int.=-5.67x10-7 (1/m)slope=7.51x106 (1/m)R2=0.998

F18 F17 F12

sub-m

sp

(1/m

)

sub-m unheated V (m3/cm3)0.0 1.0x10-5 2.0x10-5 3.0x10-5 4.0x10-5 5.0x10-5

0.0

2.0x10-6

4.0x10-6

6.0x10-6

8.0x10-6

1.0x10-5

=sp/(sp+ap)=1/(1+slope) =0.81

F18 F17 F12

ap (

1/m

)

sp (1/m)

0 1 2 3 4 50.0

0.5

1.0

1.5

NOTE: sp =550 nm & ap =565 nm

y-int.=-0.03 (m3/cm3)slope=0.26R2=0.980

y-int.=-3.54x10-7 (1/m)slope=0.242R2=0.890

F18 F17 F12

sub-m

ref.

V (

m3 /c

m3 )

sub-m unheated V (m3/cm3)

0.0 0.5 1.0 1.50.0

2.0x10-6

4.0x10-6

6.0x10-6

8.0x10-6

1.0x10-5

y-int.=-3.34x10-7 (1/m)slope=7.33x106 (1/m)R2=0.910

F18 F17 F12

ap (

1/m

)

sub-m ref. V (m3/cm3)

Scattering vs. absorption coefficients suggest a typical single scattering albedo of 0.81

Submicrometer total and refractory (soot) volume are related for these plumes indicating similar refractory fraction in aerosol

Submicrometer scattering and volume are strongly linear indicating a similar particle size independent of concentrationLight absorption and refractory volume are related with values indicative of a soot carbon core

CONCLUSIONS

The relative simplicity of an unperturbed marine aerosol system makes it possible to identify links of FT and MBL size distributions to regional meteorological regimes and processes

The evaporating regions of ITCZ cloud outflow layers [4 to >12km] are sources of new particles (nucleation) that could populate extensive regions of the tropical free troposphere.

Nucleation is linked to elevated sulfuric acid derived from oceanic DMS for these near-cloud environments and appeared consistent with classical binary nucleation theory.

CONCLUSIONS (cont.)

Exchange (entrainment/subsidence) with the free troposphere (FT) plays a major role in shaping the particle size distribution in the remote MBL.

Cloud processing of the aerosols have an important effect on aerosol size distributions in the MBL and the bimodal structure is the most obvious signature of the MBL aerosol in equatorial regions.

The relative simplicity of an unperturbed marine aerosol system makes it possible to identify links of FT and MBL size distributions to regional meteorological regimes and processes