Aerosol particles from tropical convective systems: Cloud tops and cirrus anvils

Aerosol particles from the upper troposphere (UT) and lower stratosphere (LS) were collected during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) and studied by transmission electron microscopy (TEM). Samples were classified into three categories: (1) UT in-cloud, (2) UT out-of-cloud, and (3) LS. Sulfate particles, including former H₂SO₄ droplets, are dominant in samples from all categories. The morphology of H₂SO₄ droplets indicates that they had been ammoniated to some extent at the time of collection. They are internally mixed with organic materials, metal sulfates, and solid particles of various compositions. K- and S-bearing organic particles and Si-Al-rich particles are common to the three kinds of samples. In-cloud samples contain abundant Zn-rich particles. Their origin is unclear, but it seems likely that they are contaminants that originated through impact by ice cloud particles on the aircraft or sampling system. Ammoniation and internal mixing of H₂SO₄ in the UT aerosols may result in freezing at higher temperature than in pure H₂SO₄ aerosols. The relatively high extent of ammoniation in the UT in-cloud samples may have resulted from vertical transport of ammonia by strong convection. Abundances of nonsulfate particles decrease with increasing altitudes. The nonsulfate particles originated from the lower troposphere and were transported to the UT and LS.