Measurement of aerosol and VOC turbulent fluxes

and in-canopy particle characterization at a pristine forest in Amazonia

Luciana Rizzo

The Amazon forestThe Amazon forest

• Greatest tropical forest in extension (~6 millions km2)

• Biosphere-atmosphere interaction: fluxes of momentum, heat, water vapor, aerosol particles and trace gases

• Natural source of biogenic particles and trace gases like VOC, CO2, H2O etc

• Intense convective activity: transport over large distances, in a way that the forest acts as a natural global source

The Brazilian Amazon

(IPAM, 2004)

Biosphere-atmosphere interactions

Biogenic aerosols in Biogenic aerosols in Amazonia Amazonia • Mass: 10-15 g/m3, Number: 300-500 cm-3

• 70% of the mass on the coarse mode• Organic matter = 60-70% FPM and 70-85% of CPM

LBA/ZF2-2004 LBA/ZF2-2004 ExperimentExperiment

• Cuieiras forest reserve (100 km North of Manaus), Central Amazonia

• Particle and VOC flux measurements

• Conducted during the dry season between August and October

Soil (2m)

Canopy (28m)

Top (40m)

Anemometer (54m)

10

Canopy level: SFU, scattering, number

Top level: SFU, scattering, mass, number, BC, size distribution

Anemometer level: Particle, VOC, CO2 fluxes

oil level: SFU, scatt

oil level: SFU, scatte

oil level: SFU, scatter

oil level: SFU, scatteri

oil level: SFU, scatterin

oil level: SFU, scattering

Hei

ght a

bove

gro

und

[m]

20

30

40

50

60

Soil level: SFU, scattering, mass, number, BC

Measurement of aerosol properties

CPC Datalogger

1,5 m

Sonic Anemometer

Analog output

Counting electrical pulses

at 10 Hz

Particle flux measurement

''''11 1

0

cwcwN

ccwwN

N

iiic

Particle counter (Dp < 1 m)

Measured aerosol FluxesMeasured aerosol Fluxes• Net flux of fine particles close to zero (under optimal sampling conditions)

•Predominance of emission (asc.) during the day and deposition (desc.) during the night

• Consequence of equilibrium between the biosphere and the atmosphere?

• Or most of exchanges occur on the coarse mode?

0.05 106 particles/m2/s

Measured VOC fluxesMeasured VOC fluxes

• Strong diurnal variability: temperature and light dependence

• Comparison with boreal forest (max diurnal flux): 40 g/m2/h for isoprene and 150 g/m2/h for monoterpenes

Fluxo de COVs

-4

-2

0

2

4

6

8

10

12

14

16-Sep 18-Sep 20-Sep 22-Sep 24-Sep 26-Sep 28-Sep

[mg

C/m

2/h

]

isopreno

monoterpenos

.

g

/m2/h

]

Do these VOC emissions Do these VOC emissions lead to the formation of lead to the formation of

new particles?new particles?• No significant correlation between VOC

fluxes and aerosol fluxes• Aerosol size distributions (10-350nm): no

clear nucleation events were observedIsopreno X Partículas Finas

0.00

0.10

0.20

0.30

0.40

0.50

0 60 120 180 240 300 360 420 480 540tempo de atraso [min]

corr

elaç

ão n

orm

aliz

ada

Isoprene X particle conc (30<Dp<350nm)

Nor

mal

ized

co

rrel

atio

n

Delay time [min]

The only clue:

• 7 hour delay

• suggests the influence of isoprene over nucleation and/or growth of particles

Interesting and recurrent Interesting and recurrent nocturnal eventsnocturnal events

• Nocturnal bursts (observed in 15 of 34 days)• Observed in clean days and under the influence of regional fires• No systematic relationship with aerosol and VOC fluxes

0

5

10

15

20

0:00 6:00 12:00 18:00 0:00

Co

nc

. 1

m [

cm

-3]

topodossel

23-set-04

-30

-20

-10

0

10

20

30

0:00 6:00 12:00 18:00 0:00

Flu

xo d

e C

O2

[mm

ol/m

2/s

]

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Ve

loc.

Atr

ito u

* [m

/s]

Fluxo de CO2

u*

Coeficiente de espalhamento - 23 set

102030405060708090

100110

0:00 6:00 12:00 18:00 0:00

Esp

alh

am

en

to 5

50

nm

[1/M

m]

topo

dossel

solo

• Burst of particles with Dp > 0,5 m

• Emission?

• In-canopy CCN activation?

• CO2 emission: biological activity

• u* peak: indicates turbulent activity at night

• Increased scattering

coefficient at the Canopy level

• Strong gradient of coarse mode P at night• Recurrent observation in Amazonia• Emission of nutrients at coarse mode at night: cycle

only locally, avoiding losses outside the ecosystem via turbulent transportation.

Coarse mode P - Cuieiras forest

0 10 20 30

Soil

Canopy

Top

Average concentration [ng/m3]

Night

Day

SummarySummary

• Net fine particle flux close to zero• Traces of in-canopy particle emissions

were observed, specially at night → the biophysical mechanisms controlling those emissions remain unknown

• No nucleation events • Not significant relationships between VOC

and particle fluxes• Results can not be extrapolated, because

of the heterogeneity of the Amazon region

Remaining questions Remaining questions 1. Net fine particle flux close to zero (Amazonia

and Finland)• Equilibrium between biosphere-atmosphere?• Is this a matter of improving measurement

techniques?• Does that also apply for the coarse particle mode?

Range of particle flux measurements Develop new

techniques to measure size segregated fluxes and coarse mode fluxes

2. No nucleation events observed in the pristine Amazon forest

– What are the limiting factors?– What is the role of VOC on particle growth?– What is the influence of SOA over the physical

properties of aerosol population?

Amazonia Finland

Max isoprene flux [mg/m2/h]

10 2

Max monoterp flux [mg/m2/h]

2 15

SO2 [ppt] 30 400

O3 [ppb] 0.05 30

RH >80% 40-80%

To begin with:

Chamber experiments reproducing typical

Amazonian atmospheric conditions

Amazonia - Annual deforestation rate

0

5000

10000

15000

20000

25000

30000

35000

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01

20

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20

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20

05

km2

/ye

ar

Cumulative deforestation percentual (raw calculations)

0.0%

1.0%

2.0%

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6.0%

7.0%

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