Comparison of Aerosol Particles Collected From Cloud Bases and Cirrus Anvils

Deep convection in tropical regions can vertically transport aerosol particles that potentially affect formation of cirrus clouds. In order to better understand the processes occurring in the convective clouds, we studied aerosol particles from cloud bases (altitudes:1-3 km ) and cirrus anvils (altitudes: 13-15 km) and compared their morphologies and compositions. Aerosol sampling was performed during the July 2002 CRYSTAL-FACE mission. Particles between 0.07 and 3 \micron were collected directly onto TEM grids. Cloud-base samples consist of ammonium sulfate (50-90 % by number), sea salt (5-35 %), Na- and Ca-sulfates (2-25 %), soil particles (2-15 %), and anthropogenic materials such as soot and flyash (< 3 %). These particles are similar in morphology to those from marine boundary layers (Posfai et al., 1995; Li et al., 2002). In contrast, cirrus samples have different particle types. They contain abundant (35-80 %) tiny round particles (0.05-0.5 \micron) that appear to have been solution droplets. The particles are rich in S and O and contain elements such as Na, Mg, Cl, K, Ca, and Fe. Droplets of sulfuric acid (10-25 %) and Zn-rich particles (5-40 %) are also abundant in cirrus samples. Direct links between aerosol particles from cloud bases and cirrus anvils are not evident. Hygroscopic ammonium sulfate and sea salt particles tend to develop into aqueous droplets that rapidly grow and are removed from convecting air mass by precipitation. The remaining particles experience mixing, coagulation, and break-up in the clouds. The round S- and O-rich particles in the cirrus samples presumably formed through such complex processes.