M. de Reus

Transport of biomass burning smoke to the upper troposphere by deep convection in the equatorial region

During LBA-CLAIRE-98, we found atmospheric layers with aged biomass smoke at altitudes >10 km over Suriname. CO, CO2, acetonitrile, methyl chloride, hydrocarbons, NO, O3, and aerosols were strongly enhanced in these layers. We estimate that 80-95% of accumulation mode aerosols had been removed during convective transport. Trajectories show that the plumes originated from large fires near the Brazil/Venezuela border during March 1998. This smoke was entrained into deep convection over the northern Amazon, transported out over the Pacific, and then returned to South America by the circulation around a large upper-level anticyclone. Our observations provide evidence for the importance of deep convection in the equatorial region as a mechanism to transport large amounts of pyrogenic pollutants into the upper troposphere. The entrainment of biomass smoke into tropical convective clouds may have significant effects on cloud microphysics and climate dynamics.

Aerosol production and growth in the upper free troposphere

During the Second Aerosol Characterization Experiment (ACE 2), aircraft measurements of aerosol number concentration and size distribution were performed in the upper free troposphere. Temporal changes in aerosol number concentration and size distribution were studied by repeatedly probing three different altitude levels during one single flight. The observations provide indirect evidence for particle formation and growth. Simulations with a coupled gas-phase chemistry and aerosol dynamical model, including binary homogeneous nucleation of sulfuric acid and water vapor, suggest that the ultrafine particles observed in the early morning were most likely formed when the air mass was lifted over a cold front, one day prior to the measurements. Particle growth was studied using two different aerosol dynamical models assuming particle growth by condensation of sulfuric acid and water vapor. The models were unable to simulate the observed particle growth, which suggests that another process might be important for aerosol growth, or multicomponent condensation involving species not observed and modeled play a key role in the evolution of the aerosol size distribution.

Measurement of aerosol sulfuric acid 2. Pronounced layering in the free troposphere during the second Aerosol Characterization Experiment (ACE 2)

Measurements of aerosol sulfuric acid in the free troposphere were performed in the vicinity of Tenerife, Canary Islands (28degreesN, 16degreesW), in July 1997. These measurements were carried out on board a Dutch Cessna Citation 11 research aircraft within the framework of the second Aerosol Characterization Experiment (ACE 2). We used the Volatile Aerosol Component Analyzer for the detection of sulfuric acid (H2SO4). Vertical profiles between 2 and 13 km altitude were obtained. Typically, H2SO4 mixing ratios ranged between 10 and 120 pptv. Between 4 and 6 km altitude a distinct H2SO4 aerosol layer was observed repeatedly with H2SO4 mixing ratios of up to 550 pptv. The measurements are in agreement with total aerosol mass concentrations inferred from simultaneous measurements of aerosol size distributions using two condensation particle counters, a differential mobility analyzer, and an optical aerosol counter. At altitudes above 4 km the predominant aerosol component was sulfuric acid, frequently correlated with ozone, suggesting photochemical air pollution as a common source. Sulfur dioxide measured by chemical ionization mass spectrometry technique revealed typical mixing ratios between 10 and 60 pptv at altitudes above 6 kin and up to 200 pptv in the lower troposphere.