Cloud Condensation Nuclei Concentrations in the Amazon Basin G P Frank, G Roberts, E Swietlicki, P Artaxo, L Rizzo, P Guyon, O L Mayol-Bracero, A Vestin, J Rissler, J Zhou, M O Andreae

CCN measurements (ground-based) ProjectDatesSeason CLAIRE-98March- April 1998 Wet EUSTACH April-May 1999 Transition wet- dry EUSTACH September- October 1999 Transition dry- wet CLAIRE July 2001Dry CLAIRE/ SMOCC-2002 September- November 2002 Transition dry- wet

CCN measurements (aircraft) ProjectDatesSeason CLAIRE July 2001Dry CLAIRE/ SMOCC-2002 September- October 2002 Transition dry- wet

Ground site at Fazenda Nossa Senhora (FNS), Rondônia

SMOCC Aircraft

Experiment/Season/Period (ground-based) Total aerosol particle concentration (CN) (part/cm 3 ) CLAIRE-98 Wet season 450 CLAIRE-2001 Dry season, clean period 640 CLAIRE-2001 Dry season, influence from fresh biomass burning 1300 SMOCC Transition dry-wet, semi-clean period 2000 SMOCC Transition dry-wet, transition period 5500 SMOCC Biomass burning period 11000

Experiment/Period (aircraft) Total aerosol particle concentration (CN) (part/cm 3 ) SMOCC Biomass burning period Regional haze (altitude ~ m) 3600 SMOCC Biomass burning period Cloud-processed smoke (altitude ~ m) 1300

Error bars are ± 1  of the averages

From Reid et al. 1998, JGR, 103, D24, (SCAR-B) 1-2 km Schematic

Error bars are ± 1  of the averages

Size distribution of the SMOCC smoke aerosols

Conclusions CCN efficiencies of the aerosols can partly be explained by the size and partly by the chemical composition 1.The background aerosol (CLAIRE-98) are efficient CCN, although they are small (the number of particles below 100 nm in diameter are relatively high). The higher efficiency can be explained by the fact that they are more hygroscopic (Zhou et al., 2002). 2.The smoke aerosol at the ground during the biomass burning and transition periods are efficient CCN. These particles have a peak in the size distribution above 100 nm, and a relatively low fraction of smaller particles. The particles are not very hygroscopic, but anyway efficient due to their large size.

3.The aerosol particles in the regional haze have a lower CCN efficiency The size is nearly the same as for the particles at ground during the biomass burning period, although the concentration of particles below 100 nm are slightly higher relative to the larger particles. Possible explanations of the low efficiency: –Gas-to-particle conversion can change the hygroscopic properties. The gas-to-particle conversion might not be so important at the ground, but more in the regional haze. –The number of nucleation mode particles might be relatively higher (not measured). 4.The cloud-processed smoke particles are effective CCN This smoke consists mainly of large particles (relatively few particles below 100 nm). The cloud-processing might also change the chemical composition.

5.The aerosol at the ground during the semi-clean period are less efficient CCN This aerosol contains most likely of a mix between some biomass burning smoke, natural aerosol and local pollution, such as traffic, industry (e.g. char-coal factories) and energy production. Most particles are below 100 nm in diameter and not very hygroscopic, which can explain the low efficiency. They also probably contain residual particles after washout, which are poor CCN.