Measurement of aerosol and VOC turbulent fluxes and in-canopy particle characterization at a pristine forest in Amazonia Luciana Rizzo

The Amazon forest Greatest tropical forest in extension (~6 millions km 2 ) Biosphere-atmosphere interaction: fluxes of momentum, heat, water vapor, aerosol particles and trace gases Natural source of biogenic particles and trace gases like VOC, CO 2, H 2 O 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 Amazonia Mass:  g/m 3, Number: cm -3 70% of the mass on the coarse mode Organic matter = 60-70% FPM and 70-85% of CPM

LBA/ZF Experiment 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)

Measurement of aerosol properties

CPC Datalogger 1,5 m Sonic Anemometer Analog output Counting electrical pulses at 10 Hz Particle flux measurement Particle counter (D p < 1  m)

Measured 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? particles/m 2 /s

Measured VOC fluxes Strong diurnal variability: temperature and light dependence Comparison with boreal forest (max diurnal flux): 40  g/m 2 /h for isoprene and 150  g/m 2 /h for monoterpenes.  g/m 2 /h]

Do these VOC emissions lead to the formation of new particles? No significant correlation between VOC fluxes and aerosol fluxes Aerosol size distributions (10-350nm): no clear nucleation events were observed Isoprene X particle conc (30<Dp<350nm) Normalized correlation Delay time [min] The only clue: 7 hour delay suggests the influence of isoprene over nucleation and/or growth of particles

Interesting and recurrent nocturnal 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

Burst of particles with D p > 0,5  m Emission? In-canopy CCN activation? CO 2 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.

Summary 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 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? AmazoniaFinland Max isoprene flux [mg/m 2 /h] 102 Max monoterp flux [mg/m 2 /h] 215 SO 2 [ppt]30400 O 3 [ppb] RH>80%40-80% To begin with: Chamber experiments reproducing typical Amazonian atmospheric conditions